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Book: Anatomy and Physiology II (Lumen) - Biology

Book: Anatomy and Physiology II (Lumen) - Biology


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Book: Anatomy and Physiology II (Lumen)

27.2 Anatomy and Physiology of the Female Reproductive System

The female reproductive system functions to produce gametes and reproductive hormones, just like the male reproductive system however, it also has the additional task of supporting the developing fetus and delivering it to the outside world. Unlike its male counterpart, the female reproductive system is located primarily inside the pelvic cavity (Figure 27.9). Recall that the ovaries are the female gonads. The gamete they produce is called an oocyte . We’ll discuss the production of oocytes in detail shortly. First, let’s look at some of the structures of the female reproductive system.

External Female Genitals

The external female reproductive structures are referred to collectively as the vulva (Figure 27.10). The mons pubis is a pad of fat that is located at the anterior, over the pubic bone. After puberty, it becomes covered in pubic hair. The labia majora (labia = “lips” majora = “larger”) are folds of hair-covered skin that begin just posterior to the mons pubis. The thinner and more pigmented labia minora (labia = “lips” minora = “smaller”) extend medial to the labia majora. Although they naturally vary in shape and size from woman to woman, the labia minora serve to protect the female urethra and the entrance to the female reproductive tract.

The superior, anterior portions of the labia minora come together to encircle the clitoris (or glans clitoris), an organ that originates from the same cells as the glans penis and has abundant nerves that make it important in sexual sensation and orgasm. The hymen is a thin membrane that sometimes partially covers the entrance to the vagina. An intact hymen cannot be used as an indication of “virginity” even at birth, this is only a partial membrane, as menstrual fluid and other secretions must be able to exit the body, regardless of penile–vaginal intercourse. The vaginal opening is located between the opening of the urethra and the anus. It is flanked by outlets to the Bartholin’s glands (or greater vestibular glands).

Vagina

The vagina , shown at the bottom of Figure 27.9 and Figure 27.9, is a muscular canal (approximately 10 cm long) that serves as the entrance to the reproductive tract. It also serves as the exit from the uterus during menses and childbirth. The outer walls of the anterior and posterior vagina are formed into longitudinal columns, or ridges, and the superior portion of the vagina—called the fornix—meets the protruding uterine cervix. The walls of the vagina are lined with an outer, fibrous adventitia a middle layer of smooth muscle and an inner mucous membrane with transverse folds called rugae . Together, the middle and inner layers allow the expansion of the vagina to accommodate intercourse and childbirth. The thin, perforated hymen can partially surround the opening to the vaginal orifice. The hymen can be ruptured with strenuous physical exercise, penile–vaginal intercourse, and childbirth. The Bartholin’s glands and the lesser vestibular glands (located near the clitoris) secrete mucus, which keeps the vestibular area moist.

The vagina is home to a normal population of microorganisms that help to protect against infection by pathogenic bacteria, yeast, or other organisms that can enter the vagina. In a healthy woman, the most predominant type of vaginal bacteria is from the genus Lactobacillus. This family of beneficial bacterial flora secretes lactic acid, and thus protects the vagina by maintaining an acidic pH (below 4.5). Potential pathogens are less likely to survive in these acidic conditions. Lactic acid, in combination with other vaginal secretions, makes the vagina a self-cleansing organ. However, douching—or washing out the vagina with fluid—can disrupt the normal balance of healthy microorganisms, and actually increase a woman’s risk for infections and irritation. Indeed, the American College of Obstetricians and Gynecologists recommend that women do not douche, and that they allow the vagina to maintain its normal healthy population of protective microbial flora.

Ovaries

The ovaries are the female gonads (see Figure 27.9). Paired ovals, they are each about 2 to 3 cm in length, about the size of an almond. The ovaries are located within the pelvic cavity, and are supported by the mesovarium, an extension of the peritoneum that connects the ovaries to the broad ligament . Extending from the mesovarium itself is the suspensory ligament that contains the ovarian blood and lymph vessels. Finally, the ovary itself is attached to the uterus via the ovarian ligament.

The ovary comprises an outer covering of cuboidal epithelium called the ovarian surface epithelium that is superficial to a dense connective tissue covering called the tunica albuginea. Beneath the tunica albuginea is the cortex, or outer portion, of the organ. The cortex is composed of a tissue framework called the ovarian stroma that forms the bulk of the adult ovary. Oocytes develop within the outer layer of this stroma, each surrounded by supporting cells. This grouping of an oocyte and its supporting cells is called a follicle . The growth and development of ovarian follicles will be described shortly. Beneath the cortex lies the inner ovarian medulla, the site of blood vessels, lymph vessels, and the nerves of the ovary. You will learn more about the overall anatomy of the female reproductive system at the end of this section.

The Ovarian Cycle

The ovarian cycle is a set of predictable changes in a female’s oocytes and ovarian follicles. During a woman’s reproductive years, it is a roughly 28-day cycle that can be correlated with, but is not the same as, the menstrual cycle (discussed shortly). The cycle includes two interrelated processes: oogenesis (the production of female gametes) and folliculogenesis (the growth and development of ovarian follicles).

Oogenesis

Gametogenesis in females is called oogenesis . The process begins with the ovarian stem cells, or oogonia (Figure 27.11). Oogonia are formed during fetal development, and divide via mitosis, much like spermatogonia in the testis. Unlike spermatogonia, however, oogonia form primary oocytes in the fetal ovary prior to birth. These primary oocytes are then arrested in this stage of meiosis I, only to resume it years later, beginning at puberty and continuing until the woman is near menopause (the cessation of a woman’s reproductive functions). The number of primary oocytes present in the ovaries declines from one to two million in an infant, to approximately 400,000 at puberty, to zero by the end of menopause.

The initiation of ovulation —the release of an oocyte from the ovary—marks the transition from puberty into reproductive maturity for women. From then on, throughout a woman’s reproductive years, ovulation occurs approximately once every 28 days. Just prior to ovulation, a surge of luteinizing hormone triggers the resumption of meiosis in a primary oocyte. This initiates the transition from primary to secondary oocyte. However, as you can see in Figure 27.11, this cell division does not result in two identical cells. Instead, the cytoplasm is divided unequally, and one daughter cell is much larger than the other. This larger cell, the secondary oocyte, eventually leaves the ovary during ovulation. The smaller cell, called the first polar body , may or may not complete meiosis and produce second polar bodies in either case, it eventually disintegrates. Therefore, even though oogenesis produces up to four cells, only one survives.

How does the diploid secondary oocyte become an ovum —the haploid female gamete? Meiosis of a secondary oocyte is completed only if a sperm succeeds in penetrating its barriers. Meiosis II then resumes, producing one haploid ovum that, at the instant of fertilization by a (haploid) sperm, becomes the first diploid cell of the new offspring (a zygote). Thus, the ovum can be thought of as a brief, transitional, haploid stage between the diploid oocyte and diploid zygote.

The larger amount of cytoplasm contained in the female gamete is used to supply the developing zygote with nutrients during the period between fertilization and implantation into the uterus. Interestingly, sperm contribute only DNA at fertilization —not cytoplasm. Therefore, the cytoplasm and all of the cytoplasmic organelles in the developing embryo are of maternal origin. This includes mitochondria, which contain their own DNA. Scientific research in the 1980s determined that mitochondrial DNA was maternally inherited, meaning that you can trace your mitochondrial DNA directly to your mother, her mother, and so on back through your female ancestors.

Everyday Connection

Mapping Human History with Mitochondrial DNA

When we talk about human DNA, we’re usually referring to nuclear DNA that is, the DNA coiled into chromosomal bundles in the nucleus of our cells. We inherit half of our nuclear DNA from our father, and half from our mother. However, mitochondrial DNA (mtDNA) comes only from the mitochondria in the cytoplasm of the fat ovum we inherit from our mother. She received her mtDNA from her mother, who got it from her mother, and so on. Each of our cells contains approximately 1700 mitochondria, with each mitochondrion packed with mtDNA containing approximately 37 genes.

Mutations (changes) in mtDNA occur spontaneously in a somewhat organized pattern at regular intervals in human history. By analyzing these mutational relationships, researchers have been able to determine that we can all trace our ancestry back to one woman who lived in Africa about 200,000 years ago. Scientists have given this woman the biblical name Eve, although she is not, of course, the first Homo sapiens female. More precisely, she is our most recent common ancestor through matrilineal descent.

This doesn’t mean that everyone’s mtDNA today looks exactly like that of our ancestral Eve. Because of the spontaneous mutations in mtDNA that have occurred over the centuries, researchers can map different “branches” off of the “main trunk” of our mtDNA family tree. Your mtDNA might have a pattern of mutations that aligns more closely with one branch, and your neighbor’s may align with another branch. Still, all branches eventually lead back to Eve.

But what happened to the mtDNA of all of the other Homo sapiens females who were living at the time of Eve? Researchers explain that, over the centuries, their female descendants died childless or with only male children, and thus, their maternal line—and its mtDNA—ended.

Folliculogenesis

Again, ovarian follicles are oocytes and their supporting cells. They grow and develop in a process called folliculogenesis , which typically leads to ovulation of one follicle approximately every 28 days, along with death to multiple other follicles. The death of ovarian follicles is called atresia, and can occur at any point during follicular development. Recall that, a female infant at birth will have one to two million oocytes within her ovarian follicles, and that this number declines throughout life until menopause, when no follicles remain. As you’ll see next, follicles progress from primordial, to primary, to secondary and tertiary stages prior to ovulation—with the oocyte inside the follicle remaining as a primary oocyte until right before ovulation.

Folliculogenesis begins with follicles in a resting state. These small primordial follicles are present in newborn females and are the prevailing follicle type in the adult ovary (Figure 27.12). Primordial follicles have only a single flat layer of support cells, called granulosa cells , that surround the oocyte, and they can stay in this resting state for years—some until right before menopause.

After puberty, a few primordial follicles will respond to a recruitment signal each day, and will join a pool of immature growing follicles called primary follicles . Primary follicles start with a single layer of granulosa cells, but the granulosa cells then become active and transition from a flat or squamous shape to a rounded, cuboidal shape as they increase in size and proliferate. As the granulosa cells divide, the follicles—now called secondary follicles (see Figure 27.12)—increase in diameter, adding a new outer layer of connective tissue, blood vessels, and theca cells —cells that work with the granulosa cells to produce estrogens.

Within the growing secondary follicle, the primary oocyte now secretes a thin acellular membrane called the zona pellucida that will play a critical role in fertilization. A thick fluid, called follicular fluid, that has formed between the granulosa cells also begins to collect into one large pool, or antrum . Follicles in which the antrum has become large and fully formed are considered tertiary follicles (or antral follicles). Several follicles reach the tertiary stage at the same time, and most of these will undergo atresia. The one that does not die will continue to grow and develop until ovulation, when it will expel its secondary oocyte surrounded by several layers of granulosa cells from the ovary. Keep in mind that most follicles don’t make it to this point. In fact, roughly 99 percent of the follicles in the ovary will undergo atresia, which can occur at any stage of folliculogenesis.

Hormonal Control of the Ovarian Cycle

The process of development that we have just described, from primordial follicle to early tertiary follicle, takes approximately two months in humans. The final stages of development of a small cohort of tertiary follicles, ending with ovulation of a secondary oocyte, occur over a course of approximately 28 days. These changes are regulated by many of the same hormones that regulate the male reproductive system, including GnRH, LH, and FSH.

As in men, the hypothalamus produces GnRH, a hormone that signals the anterior pituitary gland to produce the gonadotropins FSH and LH (Figure 27.13). These gonadotropins leave the pituitary and travel through the bloodstream to the ovaries, where they bind to receptors on the granulosa and theca cells of the follicles. FSH stimulates the follicles to grow (hence its name of follicle-stimulating hormone), and the five or six tertiary follicles expand in diameter. The release of LH also stimulates the granulosa and theca cells of the follicles to produce the sex steroid hormone estradiol, a type of estrogen. This phase of the ovarian cycle, when the tertiary follicles are growing and secreting estrogen, is known as the follicular phase.

The more granulosa and theca cells a follicle has (that is, the larger and more developed it is), the more estrogen it will produce in response to LH stimulation. As a result of these large follicles producing large amounts of estrogen, systemic plasma estrogen concentrations increase. Following a classic negative feedback loop, the high concentrations of estrogen will stimulate the hypothalamus and pituitary to reduce the production of GnRH, LH, and FSH. Because the large tertiary follicles require FSH to grow and survive at this point, this decline in FSH caused by negative feedback leads most of them to die (atresia). Typically only one follicle, now called the dominant follicle, will survive this reduction in FSH, and this follicle will be the one that releases an oocyte. Scientists have studied many factors that lead to a particular follicle becoming dominant: size, the number of granulosa cells, and the number of FSH receptors on those granulosa cells all contribute to a follicle becoming the one surviving dominant follicle.

When only the one dominant follicle remains in the ovary, it again begins to secrete estrogen. It produces more estrogen than all of the developing follicles did together before the negative feedback occurred. It produces so much estrogen that the normal negative feedback doesn’t occur. Instead, these extremely high concentrations of systemic plasma estrogen trigger a regulatory switch in the anterior pituitary that responds by secreting large amounts of LH and FSH into the bloodstream (see Figure 27.13). The positive feedback loop by which more estrogen triggers release of more LH and FSH only occurs at this point in the cycle.

It is this large burst of LH (called the LH surge) that leads to ovulation of the dominant follicle. The LH surge induces many changes in the dominant follicle, including stimulating the resumption of meiosis of the primary oocyte to a secondary oocyte. As noted earlier, the polar body that results from unequal cell division simply degrades. The LH surge also triggers proteases (enzymes that cleave proteins) to break down structural proteins in the ovary wall on the surface of the bulging dominant follicle. This degradation of the wall, combined with pressure from the large, fluid-filled antrum, results in the expulsion of the oocyte surrounded by granulosa cells into the peritoneal cavity. This release is ovulation.

In the next section, you will follow the ovulated oocyte as it travels toward the uterus, but there is one more important event that occurs in the ovarian cycle. The surge of LH also stimulates a change in the granulosa and theca cells that remain in the follicle after the oocyte has been ovulated. This change is called luteinization (recall that the full name of LH is luteinizing hormone), and it transforms the collapsed follicle into a new endocrine structure called the corpus luteum , a term meaning “yellowish body” (see Figure 27.12). Instead of estrogen, the luteinized granulosa and theca cells of the corpus luteum begin to produce large amounts of the sex steroid hormone progesterone, a hormone that is critical for the establishment and maintenance of pregnancy. Progesterone triggers negative feedback at the hypothalamus and pituitary, which keeps GnRH, LH, and FSH secretions low, so no new dominant follicles develop at this time.

The post-ovulatory phase of progesterone secretion is known as the luteal phase of the ovarian cycle. If pregnancy does not occur within 10 to 12 days, the corpus luteum will stop secreting progesterone and degrade into the corpus albicans , a nonfunctional “whitish body” that will disintegrate in the ovary over a period of several months. During this time of reduced progesterone secretion, FSH and LH are once again stimulated, and the follicular phase begins again with a new cohort of early tertiary follicles beginning to grow and secrete estrogen.

The Uterine Tubes

The uterine tubes (also called fallopian tubes or oviducts) serve as the conduit of the oocyte from the ovary to the uterus (Figure 27.14). Each of the two uterine tubes is close to, but not directly connected to, the ovary and divided into sections. The isthmus is the narrow medial end of each uterine tube that is connected to the uterus. The wide distal infundibulum flares out with slender, finger-like projections called fimbriae . The middle region of the tube, called the ampulla , is where fertilization often occurs. The uterine tubes also have three layers: an outer serosa, a middle smooth muscle layer, and an inner mucosal layer. In addition to its mucus-secreting cells, the inner mucosa contains ciliated cells that beat in the direction of the uterus, producing a current that will be critical to move the oocyte.

Following ovulation, the secondary oocyte surrounded by a few granulosa cells is released into the peritoneal cavity. The nearby uterine tube, either left or right, receives the oocyte. Unlike sperm, oocytes lack flagella, and therefore cannot move on their own. So how do they travel into the uterine tube and toward the uterus? High concentrations of estrogen that occur around the time of ovulation induce contractions of the smooth muscle along the length of the uterine tube. These contractions occur every 4 to 8 seconds, and the result is a coordinated movement that sweeps the surface of the ovary and the pelvic cavity. Current flowing toward the uterus is generated by coordinated beating of the cilia that line the outside and lumen of the length of the uterine tube. These cilia beat more strongly in response to the high estrogen concentrations that occur around the time of ovulation. As a result of these mechanisms, the oocyte–granulosa cell complex is pulled into the interior of the tube. Once inside, the muscular contractions and beating cilia move the oocyte slowly toward the uterus. When fertilization does occur, sperm typically meet the egg while it is still moving through the ampulla.

Interactive Link

Watch this video to observe ovulation and its initiation in response to the release of FSH and LH from the pituitary gland. What specialized structures help guide the oocyte from the ovary into the uterine tube?

If the oocyte is successfully fertilized, the resulting zygote will begin to divide into two cells, then four, and so on, as it makes its way through the uterine tube and into the uterus. There, it will implant and continue to grow. If the egg is not fertilized, it will simply degrade—either in the uterine tube or in the uterus, where it may be shed with the next menstrual period.

The open-ended structure of the uterine tubes can have significant health consequences if bacteria or other contagions enter through the vagina and move through the uterus, into the tubes, and then into the pelvic cavity. If this is left unchecked, a bacterial infection (sepsis) could quickly become life-threatening. The spread of an infection in this manner is of special concern when unskilled practitioners perform abortions in non-sterile conditions. Sepsis is also associated with sexually transmitted bacterial infections, especially gonorrhea and chlamydia. These increase a woman’s risk for pelvic inflammatory disease (PID), infection of the uterine tubes or other reproductive organs. Even when resolved, PID can leave scar tissue in the tubes, leading to infertility.

Interactive Link

Watch this series of videos to look at the movement of the oocyte through the ovary. The cilia in the uterine tube promote movement of the oocyte. What would likely occur if the cilia were paralyzed at the time of ovulation?

The Uterus and Cervix

The uterus is the muscular organ that nourishes and supports the growing embryo (see Figure 27.14). Its average size is approximately 5 cm wide by 7 cm long (approximately 2 in by 3 in) when a female is not pregnant. It has three sections. The portion of the uterus superior to the opening of the uterine tubes is called the fundus . The middle section of the uterus is called the body of uterus (or corpus). The cervix is the narrow inferior portion of the uterus that projects into the vagina. The cervix produces mucus secretions that become thin and stringy under the influence of high systemic plasma estrogen concentrations, and these secretions can facilitate sperm movement through the reproductive tract.

Several ligaments maintain the position of the uterus within the abdominopelvic cavity. The broad ligament is a fold of peritoneum that serves as a primary support for the uterus, extending laterally from both sides of the uterus and attaching it to the pelvic wall. The round ligament attaches to the uterus near the uterine tubes, and extends to the labia majora. Finally, the uterosacral ligament stabilizes the uterus posteriorly by its connection from the cervix to the pelvic wall.

The wall of the uterus is made up of three layers. The most superficial layer is the serous membrane, or perimetrium , which consists of epithelial tissue that covers the exterior portion of the uterus. The middle layer, or myometrium , is a thick layer of smooth muscle responsible for uterine contractions. Most of the uterus is myometrial tissue, and the muscle fibers run horizontally, vertically, and diagonally, allowing the powerful contractions that occur during labor and the less powerful contractions (or cramps) that help to expel menstrual blood during a woman’s period. Anteriorly directed myometrial contractions also occur near the time of ovulation, and are thought to possibly facilitate the transport of sperm through the female reproductive tract.

The innermost layer of the uterus is called the endometrium . The endometrium contains a connective tissue lining, the lamina propria, which is covered by epithelial tissue that lines the lumen. Structurally, the endometrium consists of two layers: the stratum basalis and the stratum functionalis (the basal and functional layers). The stratum basalis layer is part of the lamina propria and is adjacent to the myometrium this layer does not shed during menses. In contrast, the thicker stratum functionalis layer contains the glandular portion of the lamina propria and the endothelial tissue that lines the uterine lumen. It is the stratum functionalis that grows and thickens in response to increased levels of estrogen and progesterone. In the luteal phase of the menstrual cycle, special branches off of the uterine artery called spiral arteries supply the thickened stratum functionalis. This inner functional layer provides the proper site of implantation for the fertilized egg, and—should fertilization not occur—it is only the stratum functionalis layer of the endometrium that sheds during menstruation.

Recall that during the follicular phase of the ovarian cycle, the tertiary follicles are growing and secreting estrogen. At the same time, the stratum functionalis of the endometrium is thickening to prepare for a potential implantation. The post-ovulatory increase in progesterone, which characterizes the luteal phase, is key for maintaining a thick stratum functionalis. As long as a functional corpus luteum is present in the ovary, the endometrial lining is prepared for implantation. Indeed, if an embryo implants, signals are sent to the corpus luteum to continue secreting progesterone to maintain the endometrium, and thus maintain the pregnancy. If an embryo does not implant, no signal is sent to the corpus luteum and it degrades, ceasing progesterone production and ending the luteal phase. Without progesterone, the endometrium thins and, under the influence of prostaglandins, the spiral arteries of the endometrium constrict and rupture, preventing oxygenated blood from reaching the endometrial tissue. As a result, endometrial tissue dies and blood, pieces of the endometrial tissue, and white blood cells are shed through the vagina during menstruation, or the menses . The first menses after puberty, called menarche , can occur either before or after the first ovulation.

The Menstrual Cycle

Now that we have discussed the maturation of the cohort of tertiary follicles in the ovary, the build-up and then shedding of the endometrial lining in the uterus, and the function of the uterine tubes and vagina, we can put everything together to talk about the three phases of the menstrual cycle —the series of changes in which the uterine lining is shed, rebuilds, and prepares for implantation.

The timing of the menstrual cycle starts with the first day of menses, referred to as day one of a woman’s period. Cycle length is determined by counting the days between the onset of bleeding in two subsequent cycles. Because the average length of a woman’s menstrual cycle is 28 days, this is the time period used to identify the timing of events in the cycle. However, the length of the menstrual cycle varies among women, and even in the same woman from one cycle to the next, typically from 21 to 32 days.

Just as the hormones produced by the granulosa and theca cells of the ovary “drive” the follicular and luteal phases of the ovarian cycle, they also control the three distinct phases of the menstrual cycle. These are the menses phase, the proliferative phase, and the secretory phase.

Menses Phase

The menses phase of the menstrual cycle is the phase during which the lining is shed that is, the days that the woman menstruates. Although it averages approximately five days, the menses phase can last from 2 to 7 days, or longer. As shown in Figure 27.15, the menses phase occurs during the early days of the follicular phase of the ovarian cycle, when progesterone, FSH, and LH levels are low. Recall that progesterone concentrations decline as a result of the degradation of the corpus luteum, marking the end of the luteal phase. This decline in progesterone triggers the shedding of the stratum functionalis of the endometrium.

Proliferative Phase

Once menstrual flow ceases, the endometrium begins to proliferate again, marking the beginning of the proliferative phase of the menstrual cycle (see Figure 27.15). It occurs when the granulosa and theca cells of the tertiary follicles begin to produce increased amounts of estrogen. These rising estrogen concentrations stimulate the endometrial lining to rebuild.

Recall that the high estrogen concentrations will eventually lead to a decrease in FSH as a result of negative feedback, resulting in atresia of all but one of the developing tertiary follicles. The switch to positive feedback—which occurs with the elevated estrogen production from the dominant follicle—then stimulates the LH surge that will trigger ovulation. In a typical 28-day menstrual cycle, ovulation occurs on day 14. Ovulation marks the end of the proliferative phase as well as the end of the follicular phase.

Secretory Phase

In addition to prompting the LH surge, high estrogen levels increase the uterine tube contractions that facilitate the pick-up and transfer of the ovulated oocyte. High estrogen levels also slightly decrease the acidity of the vagina, making it more hospitable to sperm. In the ovary, the luteinization of the granulosa cells of the collapsed follicle forms the progesterone-producing corpus luteum, marking the beginning of the luteal phase of the ovarian cycle. In the uterus, progesterone from the corpus luteum begins the secretory phase of the menstrual cycle, in which the endometrial lining prepares for implantation (see Figure 27.15). Over the next 10 to 12 days, the endometrial glands secrete a fluid rich in glycogen. If fertilization has occurred, this fluid will nourish the ball of cells now developing from the zygote. At the same time, the spiral arteries develop to provide blood to the thickened stratum functionalis.

If no pregnancy occurs within approximately 10 to 12 days, the corpus luteum will degrade into the corpus albicans. Levels of both estrogen and progesterone will fall, and the endometrium will grow thinner. Prostaglandins will be secreted that cause constriction of the spiral arteries, reducing oxygen supply. The endometrial tissue will die, resulting in menses—or the first day of the next cycle.

Disorders of the.

Female Reproductive System

Research over many years has confirmed that cervical cancer is most often caused by a sexually transmitted infection with human papillomavirus (HPV). There are over 100 related viruses in the HPV family, and the characteristics of each strain determine the outcome of the infection. In all cases, the virus enters body cells and uses its own genetic material to take over the host cell’s metabolic machinery and produce more virus particles.

HPV infections are common in both men and women. Indeed, a recent study determined that 42.5 percent of females had HPV at the time of testing. These women ranged in age from 14 to 59 years and differed in race, ethnicity, and number of sexual partners. Of note, the prevalence of HPV infection was 53.8 percent among women aged 20 to 24 years, the age group with the highest infection rate.

HPV strains are classified as high or low risk according to their potential to cause cancer. Though most HPV infections do not cause disease, the disruption of normal cellular functions in the low-risk forms of HPV can cause the male or female human host to develop genital warts. Often, the body is able to clear an HPV infection by normal immune responses within 2 years. However, the more serious, high-risk infection by certain types of HPV can result in cancer of the cervix (Figure 27.16). Infection with either of the cancer-causing variants HPV 16 or HPV 18 has been linked to more than 70 percent of all cervical cancer diagnoses. Although even these high-risk HPV strains can be cleared from the body over time, infections persist in some individuals. If this happens, the HPV infection can influence the cells of the cervix to develop precancerous changes.

Risk factors for cervical cancer include having unprotected sex having multiple sexual partners a first sexual experience at a younger age, when the cells of the cervix are not fully mature failure to receive the HPV vaccine a compromised immune system and smoking. The risk of developing cervical cancer is doubled with cigarette smoking.

When the high-risk types of HPV enter a cell, two viral proteins are used to neutralize proteins that the host cells use as checkpoints in the cell cycle. The best studied of these proteins is p53. In a normal cell, p53 detects DNA damage in the cell’s genome and either halts the progression of the cell cycle—allowing time for DNA repair to occur—or initiates apoptosis. Both of these processes prevent the accumulation of mutations in a cell’s genome. High-risk HPV can neutralize p53, keeping the cell in a state in which fast growth is possible and impairing apoptosis, allowing mutations to accumulate in the cellular DNA.

The prevalence of cervical cancer in the United States is very low because of regular screening exams called pap smears. Pap smears sample cells of the cervix, allowing the detection of abnormal cells. If pre-cancerous cells are detected, there are several highly effective techniques that are currently in use to remove them before they pose a danger. However, women in developing countries often do not have access to regular pap smears. As a result, these women account for as many as 80 percent of the cases of cervical cancer worldwide.

In 2006, the first vaccine against the high-risk types of HPV was approved. There are now two HPV vaccines available: Gardasil ® and Cervarix ® . Whereas these vaccines were initially only targeted for women, because HPV is sexually transmitted, both men and women require vaccination for this approach to achieve its maximum efficacy. A recent study suggests that the HPV vaccine has cut the rates of HPV infection by the four targeted strains at least in half. Unfortunately, the high cost of manufacturing the vaccine is currently limiting access to many women worldwide.

The Breasts

Whereas the breasts are located far from the other female reproductive organs, they are considered accessory organs of the female reproductive system. The function of the breasts is to supply milk to an infant in a process called lactation. The external features of the breast include a nipple surrounded by a pigmented areola (Figure 27.17), whose coloration may deepen during pregnancy. The areola is typically circular and can vary in size from 25 to 100 mm in diameter. The areolar region is characterized by small, raised areolar glands that secrete lubricating fluid during lactation to protect the nipple from chafing. When a baby nurses, or draws milk from the breast, the entire areolar region is taken into the mouth.

Breast milk is produced by the mammary glands , which are modified sweat glands. The milk itself exits the breast through the nipple via 15 to 20 lactiferous ducts that open on the surface of the nipple. These lactiferous ducts each extend to a lactiferous sinus that connects to a glandular lobe within the breast itself that contains groups of milk-secreting cells in clusters called alveoli (see Figure 27.17). The clusters can change in size depending on the amount of milk in the alveolar lumen. Once milk is made in the alveoli, stimulated myoepithelial cells that surround the alveoli contract to push the milk to the lactiferous sinuses. From here, the baby can draw milk through the lactiferous ducts by suckling. The lobes themselves are surrounded by fat tissue, which determines the size of the breast breast size differs between individuals and does not affect the amount of milk produced. Supporting the breasts are multiple bands of connective tissue called suspensory ligaments that connect the breast tissue to the dermis of the overlying skin.

During the normal hormonal fluctuations in the menstrual cycle, breast tissue responds to changing levels of estrogen and progesterone, which can lead to swelling and breast tenderness in some individuals, especially during the secretory phase. If pregnancy occurs, the increase in hormones leads to further development of the mammary tissue and enlargement of the breasts.

Hormonal Birth Control

Birth control pills take advantage of the negative feedback system that regulates the ovarian and menstrual cycles to stop ovulation and prevent pregnancy. Typically they work by providing a constant level of both estrogen and progesterone, which negatively feeds back onto the hypothalamus and pituitary, thus preventing the release of FSH and LH. Without FSH, the follicles do not mature, and without the LH surge, ovulation does not occur. Although the estrogen in birth control pills does stimulate some thickening of the endometrial wall, it is reduced compared with a normal cycle and is less likely to support implantation.

Some birth control pills contain 21 active pills containing hormones, and 7 inactive pills (placebos). The decline in hormones during the week that the woman takes the placebo pills triggers menses, although it is typically lighter than a normal menstrual flow because of the reduced endometrial thickening. Newer types of birth control pills have been developed that deliver low-dose estrogens and progesterone for the entire cycle (these are meant to be taken 365 days a year), and menses never occurs. While some women prefer to have the proof of a lack of pregnancy that a monthly period provides, menstruation every 28 days is not required for health reasons, and there are no reported adverse effects of not having a menstrual period in an otherwise healthy individual.

Because birth control pills function by providing constant estrogen and progesterone levels and disrupting negative feedback, skipping even just one or two pills at certain points of the cycle (or even being several hours late taking the pill) can lead to an increase in FSH and LH and result in ovulation. It is important, therefore, that the woman follow the directions on the birth control pill package to successfully prevent pregnancy.

Aging and the.

Female Reproductive System

Female fertility (the ability to conceive) peaks when women are in their twenties, and is slowly reduced until a women reaches 35 years of age. After that time, fertility declines more rapidly, until it ends completely at the end of menopause. Menopause is the cessation of the menstrual cycle that occurs as a result of the loss of ovarian follicles and the hormones that they produce. A woman is considered to have completed menopause if she has not menstruated in a full year. After that point, she is considered postmenopausal. The average age for this change is consistent worldwide at between 50 and 52 years of age, but it can normally occur in a woman’s forties, or later in her fifties. Poor health, including smoking, can lead to earlier loss of fertility and earlier menopause.

As a woman reaches the age of menopause, depletion of the number of viable follicles in the ovaries due to atresia affects the hormonal regulation of the menstrual cycle. During the years leading up to menopause, there is a decrease in the levels of the hormone inhibin, which normally participates in a negative feedback loop to the pituitary to control the production of FSH. The menopausal decrease in inhibin leads to an increase in FSH. The presence of FSH stimulates more follicles to grow and secrete estrogen. Because small, secondary follicles also respond to increases in FSH levels, larger numbers of follicles are stimulated to grow however, most undergo atresia and die. Eventually, this process leads to the depletion of all follicles in the ovaries, and the production of estrogen falls off dramatically. It is primarily the lack of estrogens that leads to the symptoms of menopause.

The earliest changes occur during the menopausal transition, often referred to as peri-menopause, when a women’s cycle becomes irregular but does not stop entirely. Although the levels of estrogen are still nearly the same as before the transition, the level of progesterone produced by the corpus luteum is reduced. This decline in progesterone can lead to abnormal growth, or hyperplasia, of the endometrium. This condition is a concern because it increases the risk of developing endometrial cancer. Two harmless conditions that can develop during the transition are uterine fibroids, which are benign masses of cells, and irregular bleeding. As estrogen levels change, other symptoms that occur are hot flashes and night sweats, trouble sleeping, vaginal dryness, mood swings, difficulty focusing, and thinning of hair on the head along with the growth of more hair on the face. Depending on the individual, these symptoms can be entirely absent, moderate, or severe.

After menopause, lower amounts of estrogens can lead to other changes. Cardiovascular disease becomes as prevalent in women as in men, possibly because estrogens reduce the amount of cholesterol in the blood vessels. When estrogen is lacking, many women find that they suddenly have problems with high cholesterol and the cardiovascular issues that accompany it. Osteoporosis is another problem because bone density decreases rapidly in the first years after menopause. The reduction in bone density leads to a higher incidence of fractures.

Hormone therapy (HT), which employs medication (synthetic estrogens and progestins) to increase estrogen and progestin levels, can alleviate some of the symptoms of menopause. In 2002, the Women’s Health Initiative began a study to observe women for the long-term outcomes of hormone replacement therapy over 8.5 years. However, the study was prematurely terminated after 5.2 years because of evidence of a higher than normal risk of breast cancer in patients taking estrogen-only HT. The potential positive effects on cardiovascular disease were also not realized in the estrogen-only patients. The results of other hormone replacement studies over the last 50 years, including a 2012 study that followed over 1,000 menopausal women for 10 years, have shown cardiovascular benefits from estrogen and no increased risk for cancer. Some researchers believe that the age group tested in the 2002 trial may have been too old to benefit from the therapy, thus skewing the results. In the meantime, intense debate and study of the benefits and risks of replacement therapy is ongoing. Current guidelines approve HT for the reduction of hot flashes or flushes, but this treatment is generally only considered when women first start showing signs of menopausal changes, is used in the lowest dose possible for the shortest time possible (5 years or less), and it is suggested that women on HT have regular pelvic and breast exams.


Book: Anatomy and Physiology II (Lumen) - Biology


Required Text (used both semesters):
Shier, Butler, and Lewis. 2015. Hole's Human Anatomy and Physiology, 14th ed. McGraw-Hill Book Co. ISBN 9780078024290 . Also acceptable: Shier, Butler, and Lewis. 2013. 12th ed. ISBN 9780073378275 ] [ Amazon] . Companion website for 13th ed. (Connect)

Required Lab Manual (used both semesters):

Marieb, Mitchell, and Smith. 2015. Human Anatomy and Physiology Laboratory Manual: Cat Version. 12th e d. ISBN 9780321980878 (Sp iral bound) (Optional: with new copies, access to the “Mastering A&P” website with online PhysioEx 9.0 and online PAL Practice Anatomy Lab 3.0.) Also acceptable: 11th ed. ISBN 9780321821843 11th edition with online MasteringA&P Access

Recommended (used both semesters): Interactive Physiology 10-System CD (ISBN-13: 978-0321506825). [Used from Amazon about $5.00] [ Access most of this material here IPWeb (requires Adobe Flash, so use IE browser) ]

Optional (recommended) (used both semesters): Morton, David A. 2016. Van De Graaff's Photographic Atlas for the Anatomy & Physiology Laboratory, 8th ed. Loose Leaf ISBN-13: 978-1617312779 [Amazon] Earlier editions are also acceptable

Required Supplement (for spring semester) : Ross, Anna E. 2017 . Biology 218 A&P II Lecture and Lab Course Supplement. Purchase from CBU Print Shop in St. Joseph Hall

  • Companion website for Hole's 13th ed. (Connect) (FREE "Online Learning Center" with practice quizzes, etc.) Includes answer keys to "Student Study Outline" and much more.
  • GetBodySmart Interactive image tutorials
  • A&P Study Resources: Anatomy drill, cadaver practicals (Allen & Harper Lab Manual)
  • A&P Lab resources (Univ. Wisconsin-L) Images, etc.
  • A&P Essential Study Partner (tutorials, etc.) McGraw Hill
  • Dr. Arnold's Glossary of Anatomy anatomical word search engine
  • Medical Term Pronunciation (Merck)
  • Medical Terminology tutorial (Des Moines Univ.) Free online
  • Medical Terminology Course (free online) material from U.S. Army manual, Basic Medical Terminology
  • Maricopa A&P tutorials, practice quizzes, etc.
  • Cyber Anatomy Tutorials (Univ. of Newcastle)
  • UNM A&P Resources
  • Histology by A&P topic (WebAnatomy)
  • Cat Dissection Videos
  • Net Anatomy: Radiographic, Cross Sectional, and Gross Anatomy (Excellent!)
  • Interactive A&P Exams (Link Publishing)
  • Interactive Tutorials by Dr. Bowne at Alverno
  • Links to sites on A&P II topics (NHC)
  • Models and Photomicrographs, unlabeled (Angelo Sate)
  • Models (Interactive labels) Palomar
  • PDR Health (info on drugs and diseases)
  • Lab Tests (Family Medicine Resource)
  • Anatomy Word of the Day
  • Acland Atlas of Human Anatomy Cadaver dissection DVD series (video online)

A&P II Laboratory Schedule -- Spring 2017

  • Hematocrit
  • Frequencies of ABO and Rh Blood Types in the U.S.
  • Modern Human Variation: Distribution of Blood Types
  • Immunology and Blood Typing
  • Blood Banking Tutorial
  • BloodBook
  • Hemostasis
  • Unopette illustrated procedure (total RBC or total WBC count)
  • Blood pressure training guide: a review of how to take blood pressure blood pressure simulator assessment guides for adults and children practice drills for the assessment of hypertension in children and a series of case studies on hypertension and hypotension blood pressure.
  • Blood Pressure AnimationAnother site with this animation
  • Blood Pressure measurement: Instructional clip on how to take BP using an aneroid sphygmomanometer.
  • Which Is More Important: Systolic Hypertension or Diastolic Hypertension? There is now considerable evidence to support the concept that systolic hypertension is a good predictor of future cardiovascular disease. Medscape Cardiology 7(1) 2003


  • Dr. Ross's Web page for the A&P heart lab(includes information on next week's lab Quiz)
  • Cadaver dissection of Heart (U Mich)
    • Smaller version
    • Thoracic Wall, Pleura, Pericardium, external heart
    • The Cardiac Exam: Auscultation (Case Western University)
    • A History of Electrocardiography
    • Play the ECG game! Examine ECG's in some virtual patients and see if you can correctly diagnose their conditions.
    • More about ECG and Willem Einthoven from the Nobel web site.
    • University of Utah's ECG learner provides excellent tutorials (12 lessons) as well as self-quizzes.
    • Cardiac Exam and heart sounds tutorial
    • Learn CPR
    • CPR Procedure (from the Merck Manual of Diagnosis and Therapy) Pediatric CPR
    • American Heart Association CPR
    • CPR from eMedicine
    • Adult, child and infant CPR from Medline
    • Choking from Medline
    • Cardiovacular Sys Web Anatomy Tutorial
    • Cardiovascular Physiology Concepts (Dr. Klabunde)
    • Cat Circulatory System Interactive with photos (Penn State)
    • Human vessels Cadaver Practical (Wiley)
    • Edible Vaccines (article from Sept 2000 Sci. Amer.)
    • Lymphatic System Web Anatomy Tutorial
    • Lymph and Immunity (Biology Text from Maricopa) Includes excellent illustrations.
    • Atherosclerosis
    • Role of blood vessel growth in chronic disorders (Sci Amer)
    • Human Anatomy (cadaver dissection, etc.) Gold Standard Integrated Medical Curriculum.
    • Cardiovacular Sys Web Anatomy Tutorial
    • Cardiovascular Embryology (Animations) U. Indiana A&P students need to complete the section on "prenatal vs. postnatal circulation"
    • Human Anatomy Dissector online (cadaver photos)
    • Renin-Angiotensin-Aldosterone Pathway Interactive Tutorial from Alverno
    • Human vessels Cadaver Practical (Wiley)
    • Acland Atlas of Human Anatomy Cadaver dissection DVD series (video online)
    • Edible Vaccines (article from Sept 2000 Sci. Amer.)
    • Lymphatic System Web Anatomy Tutorial
    • Lymphatic organs Cadaver Practical (Wiley)
    • What is tissue typing (using Human Leucocyte Antigen)
    • Immunology Chapters
    • Crawling Neutrophil (video)Video with description (BioChemWeb)
    • Lymphatic Filariasis (Elephantiasis)VOA video on elephantiais
    • Lymphedema
    • Lymphatic System (with illustrations including an animation of flow at a lymph capillary)
    • T-cell subsets: How do they do their work? (Succinct description of T-cell functions.)
    • Allergy shots: Immunotherapy is used to stimulate production of IgG, IgG is used in allergy desentizations to cover the allergen so no IgE can attach to the allergen to cause a reaction.
    • Rx for Survival pbs online video on vaccines, discovery of antibodies, etc.
    • Dendritic Cells: The Sentry Cells of the Immune System (tutorial)
    • Cytokine network diagram
    • Toll-like Receptors and Innate Immunity
    • Hygiene Hypothesis Questioned Previous exposure to influenza A virus increases predisposition to asthma (The Scientist Feb. 2004) "A new study by a team at Stanford questions the controversial hygiene hypothesis, which states that raising children in an overly clean environment leads to the development of asthma."
    • Histology of the Digestive Sys. (Univ. Wisconsin)
    • Anatomy of the Digestive Sys. (Univ. Wisconsin)
    • Digestive System Web Anatomy Tutorial
    • Animation: stem cells in the intestinal crypts (of Lieberkuhn) produce daughter cells that move up and out of the crypt to replace cells lost at the apices of the intestinal villi (from The Scientist)
    • Acland Atlas of Human Anatomy Cadaver dissection DVD series (video online) Volume 6 includes abdominal organs. Vol. 4 includes oral cavity and salivary glands.
    • Human Anatomy Dissector online (cadaver photos)
    • Cadaver Practical (Wiley)
    • Cadaver dissection video: Stomach (U Mich)
      • Dissection of Duodenum, Pancreas, Liver, & Gallbladder
      • Peritoneal Cavity & Intestine
      • The average human liver is more than five times the weight of the human heart. The liver stretches across almost the width of the body, occupying a space about the size of a football. It weighs more than 3 pounds.
      • If 80 percent of your liver were to be removed, the remaining part would continue to function. Within a few months, the liver would have reconstituted itself to its original size.

      S = Suprarenal (adrenal) glands
      A = Aorta/Inferior Vena Cava
      D = Duodenum (second and third segments)

      P = Pancreas
      U = Ureters
      C = Colon (ascending and descending only)
      K = Kidneys
      E = Esophagus
      R = Rectum

      Or instead,
      Ursula Uses Kids to Deliver All Lemon Pies except Sue’s Tasty Crust
      Ureters
      Urinary bladder
      Kidneys
      Duodenum
      Adrenal glands
      Large intestine
      Pancreas
      except (not retroperitoneal) Sigmoid and Transverse Colon

      • Tests for sugars, starch, etc. (NHC)
      • Tests for Carbohydrates (A&P lab uses Benedict's)
      • Team assignments and review sheets are on winfile2iology.
      • Lab Midterm Exam format & coverage
      • Autopsy DVD (Autopsy)
      • View streaming videos of surgical procedures (Discovery Health)
      • Respiratory System (Image tutorials and quizzes from GetBodySmart)
      • Anatomy of the Larynx Tutorialhttp://anatome.ncl.ac.uk/tutorials/larynx/text/index.html
      • Respiratory System Web Anatomy Tutorial
      • Cadaver dissection: Superior mediatinum and Lungs (U Mich)
        • Dissection video: Upper respiratory tract
        • The Interactive Curve
        • Understanding Oxyhemoglobin
        • Partial Pressures of O2 and CO2

        Acid Base
        Tutorial
        Tulane University
        School of
        Medicine

        LAB QUIZ 7 on the previous lab will be administered at the start of lab.

        Online Calculator to determine predicted Vital Capacity from sex, age and height. http://keisan.casio.com/exec/system/1341376925

        Lung function values are influenced by height, age, and sex. Consequently, to compare pulmonary function among different individuals, percent predicted values can be determined from the following equations (A = age in yr, and H = height in cm): Forced vital capacity = FVC.
        FVC males: 0.0844(H) - 0.0298(A) - 8.782
        FVC females: 0.0427(H) - 0.0174(A) - 2.900

        Forced expiratory volume in the first second (FEV1)
        FEV1 males: 0.067(H) - 0.0292(A) - 6.515
        FEV1 females: 0.0309(H) - 0.0201(A) - 1.405
        [Source]

        • Outlline of Biopac Lesson 12 (Pulmonary Function I) Calibration Video Demo
        • Outline of Biopac Lesson 13 (Pulmonary Function II)
        • Respiratory System Web Anatomy Tutorial
        • Respiratory Sounds: http://www.RALE.ca/Repository.htm
        • Lung Sounds: Chest Auscultation
        • Respiratory Volumes and Capacities
        • Practice problems: calculating respiratory volumes (interactive)
        • Why do we yawn?
        • Respiratory System (Includes O2-Hb dissociatin curves from GetBodySmart)
        • Partial Pressures of O2 and CO2
        • Acid Base Tutorial Tulane University School of Medicine
        • Carbon Dioxide Tutorial
        • Urinary System Web Anatomy Tutorial
        • Cadaver Dissection video: Kidney and retroperitoneum (U Mich)
        • Urinary Sys Cadaver Practical (Wiley)
        • Acland Atlas of Human Anatomy Cadaver dissection DVD series (video online). Vol. 6 includes kidneys and bladder.
        • Kidney function
        • Physiology of Kidney Function (Illustrated tutorial by Dr. Jacobs)
        • Atlas of Diseases of the Kidney (full text and illustrations)
        • The Kidney at a Glance (with self assessments)
        • An Interactive Tutorial on Kidney Function (by Dr. Bowne at Alverno)
        • WebCast of Kidney Transplant Surgery, Live Donor
        • Histology of the kidney and urinary bladder (paired labeled and unlabeled photomicrographs)
        • Reabsorption from the nephron

        LAB QUIZ 8 on the previous lab will be administered at the start of lab.

        • Atlas of Urinary sediment: See images on facstaffiology.
        • Color chart for urine test strips: See images on facstaffiology.
        • Urinalysis This site gives information on normal and abnormal urine chemistry, urine sediment exam, etc.
        • Urinalysis Tutorial
          " Specific gravity (which is directly proportional to urine osmolality which measures solute concentration) measures urine density, or the ability of the kidney to concentrate or dilute the urine over that of plasma. Dipsticks are available that also measure specific gravity in approximations. Most laboratories measure specific gravity with a refractometer.
          Specific gravity between 1.002 and 1.035 on a random sample should be considered normal if kidney function is normal. Since the sp gr of the glomerular filtrate in Bowman's space ranges from 1.007 to 1.010, any measurement below this range indicates hydration and any measurement above it indicates relative dehydration."
          "Less than 0.1% of glucose normally filtered by the glomerulus appears in urine (< 130 mg/24 hr). Glycosuria (excess sugar in urine) generally means diabetes mellitus. Dipsticks employing the glucose oxidase reaction for screening are specific for glucos glucose but can miss other reducing sugars such as galactose and fructose. For this reason, most newborn and infant urines are routinely screened for reducing sugars by methods other than glucose oxidase (such as the Clinitest, a modified Benedict's copper reduction test)."
        • Blood Urea Nitrogen (BUN)
        • Fluid and Electrolyte Balance Tutorial
        • Renin-Angiotensin-Aldosterone Pathway Interactive Tutorial from Alverno

        Clinical correlates
        of pH levels
        (The Biology Project )
        These Tutorials
        are highly
        recommended.

        • Reproductive System Web Anatomy Tutorial
        • Pelvic Anatomy Tutorialhttp://anatome.ncl.ac.uk/tutorials/pelvis/text/index.html
        • Ovarian and Uterine cycles (with animations)
        • Prepuce (non-circumcised male)
        • Structure and function of the prepuce (Video) Highly recommended.
        • Clitoris
        • Acland Atlas of Human Anatomy Cadaver dissection DVD series (video online). Vol. 6 includes reproductive system.
        • Why so many sperm?http://www.gbhap.com/Science_Spectra/16-article.htm
        • Sperm Smarts: Optimizing Fertility (Mayo Clinic Health Center)
        • We don't know exactly how the two ovaries coordinate to release only one egg per cycle
        • An Interactive Tutorial on the Ovarian Cycle (by Dr. Bowne at Alverno)
        • Positive and Negative Feedback of Estrogen, Progesterone, and LH
        • Human Anatomy (cadaver dissection, etc.) Gold Standard Integrated Medical Curriculum.
        • Mitosis/Meiosis video online
        • Nondisjunction and Meiosis
        • Ultrasound: Procedures and Images
        • Life's Greatest Miracle (NOVA episode, you can view it on line)
          • Follow human fertilization and embryonic development to birth.
          • Fetal development

          Human
          Development -- 23
          Biology of
          Human Aging


          Human Anatomy and Physiology

          Why is it so important that the outer portion of the cerebral hemisphere (cortex) is convoluted?

          Hydrocephalus Causes in Adults and Kids

          What causes hydrocephalus and why is it more serious in adults than kids?

          Neuron Transmission

          Hi-Please explain. A neuron with several hundred axon terminals synapsing on it and the majority are firing. The neuron in question though is not transmitting an impulse-why and when would this occur?

          Dehydration and the Brain

          What part of the brain - where - would be affected if a combative and confused Alzheimer's patient was hospitalized with dehydration? Please explain where the brain may be affected to lead to dehydration.

          Overcoming Limits Placed on Body by Cellular Respiration

          We live in an age which has seen great scandal involving athletes and performance enhancing substances. Describe one method by which an athlete may enhance his or her performance and overcome the limits placed on the body by cellular respiration.

          Biological Radioactivity Test - Theoretical

          Remember the nuclear accident at Chernobyl (former Soviet Union - now the territory of Ukraine) in 1986? A scientist suspects that the food in a nearby ecosystem may have been contaminated with radioactive nitrogen over a period of months. Which substances in plants and animals could be examined for radioactivity to test

          OSMORECEPTORS AND MICTURITION AND DEFECATION

          Using the negative feedback system, explain how osmoreceptors and CO2 receptors maintain water balance and respiratory rates. Include a diagram. How are micturation and defecation reflexes different? NOTE: Moved from Physiology to Biology to expose question to different Online TAs.

          What is responsible for hyperpolarization?

          What is responsible for hyperpolarization in an action potential. Why is it more difficult to initiate an action potential when the membrane is hyperpolarized?

          Diagram amino acid adsorption in the small intestinal lumen.

          i need help diagraming the process of the following instructions. please help me. On a single page, diagram removal of an amino acid from protein by a peptidase in the intestinal lumen, followed by absorption of the amino acid. This process will include an epithelial cell actively transporting the an amino acid from the lumen

          Twitch contraction

          Hi-Please explain what the refractory period is and when it happens-before or after relaxation? Thanks.

          This job compares cerebral cortexes.

          I understand that a mammal brain with a relatively smooth cerebral cortex would have a smaller surface area compared to a mammal brain with many sulci. This job examines the effect on the habits of these mammals in respect of feeding, breeding etc.

          Body Metabolism

          Sports scientists distinguish between aerobic fitness (as achieved, for example, by long distance running) and anaerobic fitness (as achieved by sprinting exercise). ----------------------------------------------------------------------------------------------- Why have they chosen these particular terms to describe these two

          The body Metabolism

          Involving the glycolysis, what is the net gain of ATP? What does "net" mean? For each turn of the Kreb's cycle, how much ATP is produced? How many molecules of CO2 are produced? What is the significance of stripping off high-energy electrons from the pyruvate?

          The Digestion System

          How is the villus the functional unit of the small intestine? What is the structure and function and the enzymes found there. What is the importance of the surface area to the functioning villi? What an approiate way to counsel a friend who is overweight and blames herself for a lack of self-control?

          Biology

          #1 How did the theory of biogenesis lead the way for the germ theory of disease? (1pt.) #2 In 1864, Lister observed that patients recovered completely from simple fractures, but compound fractures had "disastrous consequences." He knew that the application of phenol (carbolic acid) to fields in the town of Carlisle prevent

          Infection & Immunity

          The interactions and origins of the different types of T cells and B cells and the role of "recognition." Description of their connection in a specific immune response.

          Immunity & Infectious Diseases

          Why are the symptoms of a cold similar every time? What is the role of the mast cells? How is it that a person becomes immune to a particular infection once she or he has recovered?

          Mechanisms of an Action Potential

          Why is the term "action potential" used to describe a nerve impulse? What is the role of sodium ions (Na+) and potassium ions (K+) in generating an action potential. What is a "threshold"?

          Construct a flow diagram to show the effect of drinking a solution containing water

          Construct a flow diagram to show the effect of drinking a solution containing water, Na+ Cl- and glucose (Sports drink) upon the transport of water across intestinal cells and into the blood (absorption).

          The menstrual cycle

          What is the intricate and coordinated interplay of the hypothalamus, pituitary, ovary, and uterus.

          Need help answering questions below

          T cell response to T-cell-dependent antigen reqiures: a) typically a protein antigen b) binding of T cell to a Class II MHC receptor on a macrphage c) binding of T cell to a site on the antigen d) interleukin-1 activating the T helper cell e) all of the choices are correct Antitoxins: a) contain modified bacterial e

          BROWN AND WHITE ADIPOSE TISSUE

          What are the main differences between brown and white adipose tissue?

          Case Study: Analysis of Cause of Death

          So I am studying my micro book, and came across a case study. I am hoping a T.A may be able to assist me in answering the 4 questions. The case study is as follows: In the summer of 1999 you are working as a triage nurse in the Emergency department of a hospital. A young-athletic man in his early 20's is helped into the

          Characteristics All Organisms Share

          Understanding characteristics that humans share with all organisms understanding anatomy and physiology List 10 characteristics that humans share with all organisms.

          How are Chemistry, Anatomy, and Physiology Connected?

          How does chemistry relate to Anatomy and Physiology? Please give a detailed explanation.

          Blood values and acids and bases are included.

          Using the following sets of blood values, I name the acid-base imbalance (acidosis or alkalosis), determine its cause (metabolic or respiratory), decide whether the condition is being compensated for, and cite at least one possible cause for the imbalance: pH = 7.2, PCO2 = 47 mmHg, HCO3- = 33 mEq/L.

          A case of respiratory alkalosis

          Using the following sets of blood values, name the acid-base imbalance (acidosis or alkalosis), this job determines its cause (metabolic or respiratory), decides whether the condition is being compensated for and cites at least one possible cause for the imbalance: pH=7.3, PCO2 = 30 mm Hg, HCO3- = 18 mEq/L.

          The kidney and blood loss

          You have just been in an accident and experienced substantial blood loss. What autoregulatory mechanisms in the kidney will be initiated to maintain filtration pressure? If blood loss occurs, what further mechanisms are used to maintain pressure? Please be detailed and do not copy and paste from a website.

          Kidney Filtration

          Describe the three pressures involved in the process of filtration. Give a brief description of what would occur if a kidney stone was present. Which of the three pressures would increase? How would this effect filtration? Please do not copy and paste from a website. Be detailed.

          Diarrhea

          While visiting a foreign country, you inadvertently drink the water, even though you have been advised not to. You contact an intestinal disease that causes severe diarrhea. How would you expect your condition to affect your blood pH, urine pH and pattern of ventilation?


          Colleges

          Focus on courses and programs offered by specific colleges. Search for, and browse, specific courses and programs at the college you are interested in.

          The courses listed on this VCCS website are updated on a term by term basis and reflect only those courses approved for offering during the most current term. All VCCS colleges must use, as a minimum, the standard course prefix, course number, credit value(s), and descriptions contained in this listing.

          When scheduling courses, colleges may use the local rule to assign pre- or co-requisites that are not listed in the Master Course File.

          Questions, additional information, and corrections regarding the Master Course File should be addressed here.


          Requirements

          Prerequisites:

          There are no prerequisites to take this course.

          Requirements:

          • PC: Windows 8 or later.
          • Mac: OS X Snow Leopard 10.6 or later.
          • Browser: The latest version of Google Chrome or Mozilla Firefox are preferred. Microsoft Edge and Safari are also compatible.
          • Adobe Acrobat Reader. Click here to download the Acrobat Reader.
          • Software must be installed and fully operational before the course begins.

          The instructional materials required for this course are included in enrollment and will be available online.

          Instructor-Led: A new session of each course begins each month. Please refer to the session start dates for scheduling.

          Self-Paced: You can start this course at any time your schedule permits.

          Instructor-Led: Once a session starts, two lessons will be released each week, for the 6 week duration of your course. You will have access to all previously released lessons until the course ends.

          Self-Paced: You have three-month access to the course. After enrolling, you can learn and complete the course at your own pace, within the allotted access period.

          Instructor-Led: The interactive discussion area for each lesson automatically closes 2 weeks after each lesson is released, so you're encouraged to complete each lesson within two weeks of its release.

          Self-Paced: There is no time limit to complete each lesson, other than completing all lessons before your three-month access expires.

          Instructor-Led: The Final Exam will be released on the same day as the last lesson. Once the Final Exam has been released, you will have 2 weeks plus 10 days to complete the Final and finish any remaining lessons in your course. No further extensions can be provided beyond these 10 days.

          Self-Paced: Because this course is self-paced, no extensions will be granted after the start of your enrollment.


          Cathy Whiting’s Human Anatomy & Physiology Lab Manual

          The Amerman package includes a companion lab manual by Cathy Whiting. An award-winning teacher, Whiting takes an active-learning approach that uses a rich variety of hands-on activities along with guided questions to get students engaged in lab and asking questions. The Whiting Lab Manual includes extensive pre-lab assignments and uses the same art and terminology as the Amerman textbook.

          Also Available! Mastering A&P with eText + Amerman's Human Anatomy & Physiology + Whiting's Laboratory Manual (Cat Version) + Hebert's Photographic Atlas (ISBN 9780134115603)


          Anatomy Drill & Practice

          Anatomy Drill & Practice: This site covers the human body, the chemical, cellular, and tissue levels of organization, the integumentary system, skeletal system, muscular system, nervous system, cardiovascular system, respiratory system, digestive system, excretory system , and reproductive system.

          This site not only includes images of and information on the above listed systems, but it also includes interactive drills and practice questions for students. NOTE: Flash required for the quizzes/practice questions.


          27.1 Anatomy and Physiology of the Male Reproductive System

          Unique for its role in human reproduction, a gamete is a specialized sex cell carrying 23 chromosomes—one half the number in body cells. At fertilization, the chromosomes in one male gamete, called a sperm (or spermatozoon), combine with the chromosomes in one female gamete, called an oocyte. The function of the male reproductive system (Figure 27.2) is to produce sperm and transfer them to the female reproductive tract. The paired testes are a crucial component in this process, as they produce both sperm and androgens, the hormones that support male reproductive physiology. In humans, the most important male androgen is testosterone. Several accessory organs and ducts aid the process of sperm maturation and transport the sperm and other seminal components to the penis, which delivers sperm to the female reproductive tract. In this section, we examine each of these different structures, and discuss the process of sperm production and transport.

          Scrotum

          The testes are located in a skin-covered, highly pigmented, muscular sack called the scrotum that extends from the body behind the penis (see Figure 27.2). This location is important in sperm production, which occurs within the testes, and proceeds more efficiently when the testes are kept 2 to 4°C below core body temperature.

          The dartos muscle makes up the subcutaneous muscle layer of the scrotum (Figure 27.3). It continues internally to make up the scrotal septum, a wall that divides the scrotum into two compartments, each housing one testis. Descending from the internal oblique muscle of the abdominal wall are the two cremaster muscles, which cover each testis like a muscular net. By contracting simultaneously, the dartos and cremaster muscles can elevate the testes in cold weather (or water), moving the testes closer to the body and decreasing the surface area of the scrotum to retain heat. Alternatively, as the environmental temperature increases, the scrotum relaxes, moving the testes farther from the body core and increasing scrotal surface area, which promotes heat loss. Externally, the scrotum has a raised medial thickening on the surface called the raphae.

          Testes

          The testes (singular = testis) are the male gonads —that is, the male reproductive organs. They produce both sperm and androgens, such as testosterone, and are active throughout the reproductive lifespan of the male.

          Paired ovals, the testes are each approximately 4 to 5 cm in length and are housed within the scrotum (see Figure 27.3). They are surrounded by two distinct layers of protective connective tissue (Figure 27.4). The outer tunica vaginalis is a serous membrane that has both a parietal and a thin visceral layer. Beneath the tunica vaginalis is the tunica albuginea, a tough, white, dense connective tissue layer covering the testis itself. Not only does the tunica albuginea cover the outside of the testis, it also invaginates to form septa that divide the testis into 300 to 400 structures called lobules. Within the lobules, sperm develop in structures called seminiferous tubules. During the seventh month of the developmental period of a male fetus, each testis moves through the abdominal musculature to descend into the scrotal cavity. This is called the “descent of the testis.” Cryptorchidism is the clinical term used when one or both of the testes fail to descend into the scrotum prior to birth.

          The tightly coiled seminiferous tubules form the bulk of each testis. They are composed of developing sperm cells surrounding a lumen, the hollow center of the tubule, where formed sperm are released into the duct system of the testis. Specifically, from the lumens of the seminiferous tubules, sperm move into the straight tubules (or tubuli recti), and from there into a fine meshwork of tubules called the rete testes. Sperm leave the rete testes, and the testis itself, through the 15 to 20 efferent ductules that cross the tunica albuginea.

          Inside the seminiferous tubules are six different cell types. These include supporting cells called sustentacular cells, as well as five types of developing sperm cells called germ cells. Germ cell development progresses from the basement membrane—at the perimeter of the tubule—toward the lumen. Let’s look more closely at these cell types.

          Sertoli Cells

          Surrounding all stages of the developing sperm cells are elongate, branching Sertoli cells . Sertoli cells are a type of supporting cell called a sustentacular cell, or sustentocyte, that are typically found in epithelial tissue. Sertoli cells secrete signaling molecules that promote sperm production and can control whether germ cells live or die. They extend physically around the germ cells from the peripheral basement membrane of the seminiferous tubules to the lumen. Tight junctions between these sustentacular cells create the blood–testis barrier , which keeps bloodborne substances from reaching the germ cells and, at the same time, keeps surface antigens on developing germ cells from escaping into the bloodstream and prompting an autoimmune response.

          Germ Cells

          The least mature cells, the spermatogonia (singular = spermatogonium), line the basement membrane inside the tubule. Spermatogonia are the stem cells of the testis, which means that they are still able to differentiate into a variety of different cell types throughout adulthood. Spermatogonia divide to produce primary and secondary spermatocytes, then spermatids, which finally produce formed sperm. The process that begins with spermatogonia and concludes with the production of sperm is called spermatogenesis .

          Spermatogenesis

          As just noted, spermatogenesis occurs in the seminiferous tubules that form the bulk of each testis (see Figure 27.4). The process begins at puberty, after which time sperm are produced constantly throughout a man’s life. One production cycle, from spermatogonia through formed sperm, takes approximately 64 days. A new cycle starts approximately every 16 days, although this timing is not synchronous across the seminiferous tubules. Sperm counts—the total number of sperm a man produces—slowly decline after age 35, and some studies suggest that smoking can lower sperm counts irrespective of age.

          The process of spermatogenesis begins with mitosis of the diploid spermatogonia (Figure 27.5). Because these cells are diploid (2n), they each have a complete copy of the father’s genetic material, or 46 chromosomes. However, mature gametes are haploid (1n), containing 23 chromosomes—meaning that daughter cells of spermatogonia must undergo a second cellular division through the process of meiosis.

          Two identical diploid cells result from spermatogonia mitosis. One of these cells remains a spermatogonium, and the other becomes a primary spermatocyte , the next stage in the process of spermatogenesis. As in mitosis, DNA is replicated in a primary spermatocyte, before it undergoes a cell division called meiosis I. During meiosis I each of the 23 pairs of chromosomes separates. This results in two cells, called secondary spermatocytes, each with only half the number of chromosomes. Now a second round of cell division (meiosis II) occurs in both of the secondary spermatocytes. During meiosis II each of the 23 replicated chromosomes divides, similar to what happens during mitosis. Thus, meiosis results in separating the chromosome pairs. This second meiotic division results in a total of four cells with only half of the number of chromosomes. Each of these new cells is a spermatid . Although haploid, early spermatids look very similar to cells in the earlier stages of spermatogenesis, with a round shape, central nucleus, and large amount of cytoplasm. A process called spermiogenesis transforms these early spermatids, reducing the cytoplasm, and beginning the formation of the parts of a true sperm. The fifth stage of germ cell formation—spermatozoa, or formed sperm—is the end result of this process, which occurs in the portion of the tubule nearest the lumen. Eventually, the sperm are released into the lumen and are moved along a series of ducts in the testis toward a structure called the epididymis for the next step of sperm maturation.

          Structure of Formed Sperm

          Sperm are smaller than most cells in the body in fact, the volume of a sperm cell is 85,000 times less than that of the female gamete. Approximately 100 to 300 million sperm are produced each day, whereas women typically ovulate only one oocyte per month. As is true for most cells in the body, the structure of sperm cells speaks to their function. Sperm have a distinctive head, mid-piece, and tail region (Figure 27.6). The head of the sperm contains the extremely compact haploid nucleus with very little cytoplasm. These qualities contribute to the overall small size of the sperm (the head is only 5 μm long). A structure called the acrosome covers most of the head of the sperm cell as a “cap” that is filled with lysosomal enzymes important for preparing sperm to participate in fertilization. Tightly packed mitochondria fill the mid-piece of the sperm. ATP produced by these mitochondria will power the flagellum, which extends from the neck and the mid-piece through the tail of the sperm, enabling it to move the entire sperm cell. The central strand of the flagellum, the axial filament, is formed from one centriole inside the maturing sperm cell during the final stages of spermatogenesis.

          Sperm Transport

          To fertilize an egg, sperm must be moved from the seminiferous tubules in the testes, through the epididymis, and—later during ejaculation—along the length of the penis and out into the female reproductive tract.

          Role of the Epididymis

          From the lumen of the seminiferous tubules, the immotile sperm are surrounded by testicular fluid and moved to the epididymis (plural = epididymides), a coiled tube attached to the testis where newly formed sperm continue to mature (see Figure 27.4). Though the epididymis does not take up much room in its tightly coiled state, it would be approximately 6 m (20 feet) long if straightened. It takes an average of 12 days for sperm to move through the coils of the epididymis, with the shortest recorded transit time in humans being one day. Sperm enter the head of the epididymis and are moved along predominantly by the contraction of smooth muscles lining the epididymal tubes. As they are moved along the length of the epididymis, the sperm further mature and acquire the ability to move under their own power. Once inside the female reproductive tract, they will use this ability to move independently toward the unfertilized egg. The more mature sperm are then stored in the tail of the epididymis (the final section) until ejaculation occurs.

          Duct System

          During ejaculation, sperm exit the tail of the epididymis and are pushed by smooth muscle contraction to the ductus deferens (also called the vas deferens). The ductus deferens is a thick, muscular tube that is bundled together inside the scrotum with connective tissue, blood vessels, and nerves into a structure called the spermatic cord (see Figure 27.2 and Figure 27.3). Because the ductus deferens is physically accessible within the scrotum, surgical sterilization to interrupt sperm delivery can be performed by cutting and sealing a small section of the ductus (vas) deferens. This procedure is called a vasectomy, and it is an effective form of male birth control. Although it may be possible to reverse a vasectomy, clinicians consider the procedure permanent, and advise men to undergo it only if they are certain they no longer wish to father children.

          Interactive Link

          Watch this video to learn about a vasectomy. As described in this video, a vasectomy is a procedure in which a small section of the ductus (vas) deferens is removed from the scrotum. This interrupts the path taken by sperm through the ductus deferens. If sperm do not exit through the vas, either because the man has had a vasectomy or has not ejaculated, in what region of the testis do they remain?

          From each epididymis, each ductus deferens extends superiorly into the abdominal cavity through the inguinal canal in the abdominal wall. From here, the ductus deferens continues posteriorly to the pelvic cavity, ending posterior to the bladder where it dilates in a region called the ampulla (meaning “flask”).

          Sperm make up only 5 percent of the final volume of semen , the thick, milky fluid that the male ejaculates. The bulk of semen is produced by three critical accessory glands of the male reproductive system: the seminal vesicles, the prostate, and the bulbourethral glands.

          Seminal Vesicles

          As sperm pass through the ampulla of the ductus deferens at ejaculation, they mix with fluid from the associated seminal vesicle (see Figure 27.2). The paired seminal vesicles are glands that contribute approximately 60 percent of the semen volume. Seminal vesicle fluid contains large amounts of fructose, which is used by the sperm mitochondria to generate ATP to allow movement through the female reproductive tract.

          The fluid, now containing both sperm and seminal vesicle secretions, next moves into the associated ejaculatory duct , a short structure formed from the ampulla of the ductus deferens and the duct of the seminal vesicle. The paired ejaculatory ducts transport the seminal fluid into the next structure, the prostate gland.

          Prostate Gland

          As shown in Figure 27.2, the centrally located prostate gland sits anterior to the rectum at the base of the bladder surrounding the prostatic urethra (the portion of the urethra that runs within the prostate). About the size of a walnut, the prostate is formed of both muscular and glandular tissues. It excretes an alkaline, milky fluid to the passing seminal fluid—now called semen—that is critical to first coagulate and then decoagulate the semen following ejaculation. The temporary thickening of semen helps retain it within the female reproductive tract, providing time for sperm to utilize the fructose provided by seminal vesicle secretions. When the semen regains its fluid state, sperm can then pass farther into the female reproductive tract.

          The prostate normally doubles in size during puberty. At approximately age 25, it gradually begins to enlarge again. This enlargement does not usually cause problems however, abnormal growth of the prostate, or benign prostatic hyperplasia (BPH), can cause constriction of the urethra as it passes through the middle of the prostate gland, leading to a number of lower urinary tract symptoms, such as a frequent and intense urge to urinate, a weak stream, and a sensation that the bladder has not emptied completely. By age 60, approximately 40 percent of men have some degree of BPH. By age 80, the number of affected individuals has jumped to as many as 80 percent. Treatments for BPH attempt to relieve the pressure on the urethra so that urine can flow more normally. Mild to moderate symptoms are treated with medication, whereas severe enlargement of the prostate is treated by surgery in which a portion of the prostate tissue is removed.

          Another common disorder involving the prostate is prostate cancer. According to the Centers for Disease Control and Prevention (CDC), prostate cancer is the second most common cancer in men. However, some forms of prostate cancer grow very slowly and thus may not ever require treatment. Aggressive forms of prostate cancer, in contrast, involve metastasis to vulnerable organs like the lungs and brain. There is no link between BPH and prostate cancer, but the symptoms are similar. Prostate cancer is detected by a medical history, a blood test, and a rectal exam that allows physicians to palpate the prostate and check for unusual masses. If a mass is detected, the cancer diagnosis is confirmed by biopsy of the cells.

          Bulbourethral Glands

          The final addition to semen is made by two bulbourethral glands (or Cowper’s glands) that release a thick, salty fluid that lubricates the end of the urethra and the vagina, and helps to clean urine residues from the penile urethra. The fluid from these accessory glands is released after the male becomes sexually aroused, and shortly before the release of the semen. It is therefore sometimes called pre-ejaculate. It is important to note that, in addition to the lubricating proteins, it is possible for bulbourethral fluid to pick up sperm already present in the urethra, and therefore it may be able to cause pregnancy.

          Interactive Link

          Watch this video to explore the structures of the male reproductive system and the path of sperm, which starts in the testes and ends as the sperm leave the penis through the urethra. Where are sperm deposited after they leave the ejaculatory duct?

          The Penis

          The penis is the male organ of copulation (sexual intercourse). It is flaccid for non-sexual actions, such as urination, and turgid and rod-like with sexual arousal. When erect, the stiffness of the organ allows it to penetrate into the vagina and deposit semen into the female reproductive tract.

          The shaft of the penis surrounds the urethra (Figure 27.7). The shaft is composed of three column-like chambers of erectile tissue that span the length of the shaft. Each of the two larger lateral chambers is called a corpus cavernosum (plural = corpora cavernosa). Together, these make up the bulk of the penis. The corpus spongiosum , which can be felt as a raised ridge on the erect penis, is a smaller chamber that surrounds the spongy, or penile, urethra. The end of the penis, called the glans penis , has a high concentration of nerve endings, resulting in very sensitive skin that influences the likelihood of ejaculation (see Figure 27.2). The skin from the shaft extends down over the glans and forms a collar called the prepuce (or foreskin). The foreskin also contains a dense concentration of nerve endings, and both lubricate and protect the sensitive skin of the glans penis. A surgical procedure called circumcision, often performed for religious or social reasons, removes the prepuce, typically within days of birth.

          Both sexual arousal and REM sleep (during which dreaming occurs) can induce an erection. Penile erections are the result of vasocongestion, or engorgement of the tissues because of more arterial blood flowing into the penis than is leaving in the veins. During sexual arousal, nitric oxide (NO) is released from nerve endings near blood vessels within the corpora cavernosa and spongiosum. Release of NO activates a signaling pathway that results in relaxation of the smooth muscles that surround the penile arteries, causing them to dilate. This dilation increases the amount of blood that can enter the penis and induces the endothelial cells in the penile arterial walls to also secrete NO and perpetuate the vasodilation. The rapid increase in blood volume fills the erectile chambers, and the increased pressure of the filled chambers compresses the thin-walled penile venules, preventing venous drainage of the penis. The result of this increased blood flow to the penis and reduced blood return from the penis is erection. Depending on the flaccid dimensions of a penis, it can increase in size slightly or greatly during erection, with the average length of an erect penis measuring approximately 15 cm.

          Disorders of the.

          Male Reproductive System

          Erectile dysfunction (ED) is a condition in which a man has difficulty either initiating or maintaining an erection. The combined prevalence of minimal, moderate, and complete ED is approximately 40 percent in men at age 40, and reaches nearly 70 percent by 70 years of age. In addition to aging, ED is associated with diabetes, vascular disease, psychiatric disorders, prostate disorders, the use of some drugs such as certain antidepressants, and problems with the testes resulting in low testosterone concentrations. These physical and emotional conditions can lead to interruptions in the vasodilation pathway and result in an inability to achieve an erection.

          Recall that the release of NO induces relaxation of the smooth muscles that surround the penile arteries, leading to the vasodilation necessary to achieve an erection. To reverse the process of vasodilation, an enzyme called phosphodiesterase (PDE) degrades a key component of the NO signaling pathway called cGMP. There are several different forms of this enzyme, and PDE type 5 is the type of PDE found in the tissues of the penis. Scientists discovered that inhibiting PDE5 increases blood flow, and allows vasodilation of the penis to occur.

          PDEs and the vasodilation signaling pathway are found in the vasculature in other parts of the body. In the 1990s, clinical trials of a PDE5 inhibitor called sildenafil were initiated to treat hypertension and angina pectoris (chest pain caused by poor blood flow through the heart). The trial showed that the drug was not effective at treating heart conditions, but many men experienced erection and priapism (erection lasting longer than 4 hours). Because of this, a clinical trial was started to investigate the ability of sildenafil to promote erections in men suffering from ED. In 1998, the FDA approved the drug, marketed as Viagra ® . Since approval of the drug, sildenafil and similar PDE inhibitors now generate over a billion dollars a year in sales, and are reported to be effective in treating approximately 70 to 85 percent of cases of ED. Importantly, men with health problems—especially those with cardiac disease taking nitrates—should avoid Viagra or talk to their physician to find out if they are a candidate for the use of this drug, as deaths have been reported for at-risk users.

          Testosterone

          Testosterone, an androgen, is a steroid hormone produced by Leydig cells . The alternate term for Leydig cells, interstitial cells, reflects their location between the seminiferous tubules in the testes. In male embryos, testosterone is secreted by Leydig cells by the seventh week of development, with peak concentrations reached in the second trimester. This early release of testosterone results in the anatomical differentiation of the male sexual organs. In childhood, testosterone concentrations are low. They increase during puberty, activating characteristic physical changes and initiating spermatogenesis.

          Functions of Testosterone

          The continued presence of testosterone is necessary to keep the male reproductive system working properly, and Leydig cells produce approximately 6 to 7 mg of testosterone per day. Testicular steroidogenesis (the manufacture of androgens, including testosterone) results in testosterone concentrations that are 100 times higher in the testes than in the circulation. Maintaining these normal concentrations of testosterone promotes spermatogenesis, whereas low levels of testosterone can lead to infertility. In addition to intratesticular secretion, testosterone is also released into the systemic circulation and plays an important role in muscle development, bone growth, the development of secondary sex characteristics, and maintaining libido (sex drive) in both males and females. In females, the ovaries secrete small amounts of testosterone, although most is converted to estradiol. A small amount of testosterone is also secreted by the adrenal glands in both sexes.

          Control of Testosterone

          The regulation of testosterone concentrations throughout the body is critical for male reproductive function. The intricate interplay between the endocrine system and the reproductive system is shown in Figure 27.8.

          The regulation of Leydig cell production of testosterone begins outside of the testes. The hypothalamus and the pituitary gland in the brain integrate external and internal signals to control testosterone synthesis and secretion. The regulation begins in the hypothalamus. Pulsatile release of a hormone called gonadotropin-releasing hormone (GnRH) from the hypothalamus stimulates the endocrine release of hormones from the pituitary gland. Binding of GnRH to its receptors on the anterior pituitary gland stimulates release of the two gonadotropins: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These two hormones are critical for reproductive function in both men and women. In men, FSH binds predominantly to the Sertoli cells within the seminiferous tubules to promote spermatogenesis. FSH also stimulates the Sertoli cells to produce hormones called inhibins, which function to inhibit FSH release from the pituitary, thus reducing testosterone secretion. These polypeptide hormones correlate directly with Sertoli cell function and sperm number inhibin B can be used as a marker of spermatogenic activity. In men, LH binds to receptors on Leydig cells in the testes and upregulates the production of testosterone.

          A negative feedback loop predominantly controls the synthesis and secretion of both FSH and LH. Low blood concentrations of testosterone stimulate the hypothalamic release of GnRH. GnRH then stimulates the anterior pituitary to secrete LH into the bloodstream. In the testis, LH binds to LH receptors on Leydig cells and stimulates the release of testosterone. When concentrations of testosterone in the blood reach a critical threshold, testosterone itself will bind to androgen receptors on both the hypothalamus and the anterior pituitary, inhibiting the synthesis and secretion of GnRH and LH, respectively. When the blood concentrations of testosterone once again decline, testosterone no longer interacts with the receptors to the same degree and GnRH and LH are once again secreted, stimulating more testosterone production. This same process occurs with FSH and inhibin to control spermatogenesis.

          Aging and the.

          Male Reproductive System

          Declines in Leydig cell activity can occur in men beginning at 40 to 50 years of age. The resulting reduction in circulating testosterone concentrations can lead to symptoms of andropause, also known as male menopause. While the reduction in sex steroids in men is akin to female menopause, there is no clear sign—such as a lack of a menstrual period—to denote the initiation of andropause. Instead, men report feelings of fatigue, reduced muscle mass, depression, anxiety, irritability, loss of libido, and insomnia. A reduction in spermatogenesis resulting in lowered fertility is also reported, and sexual dysfunction can also be associated with andropausal symptoms.

          Whereas some researchers believe that certain aspects of andropause are difficult to tease apart from aging in general, testosterone replacement is sometimes prescribed to alleviate some symptoms. Recent studies have shown a benefit from androgen replacement therapy on the new onset of depression in elderly men however, other studies caution against testosterone replacement for long-term treatment of andropause symptoms, showing that high doses can sharply increase the risk of both heart disease and prostate cancer.


          Readings

          Please see the complete syllabus below for additional information.

          Required Course Materials:

          (1) Anatomy and Physiology: An Integrative Approach, 2nd edition, by McKinley, O&rsquoLoughlin and Bidle. McGraw Hill Education, 2016. Bring to every class. You will be using the McGraw Hill Connect access to complete homework and other assignments. You can also purchase Connect access for 1 year this comes with an e-book. (If you used Amerman text for A&P 1, you can use that textbook. You will need to purchase Connect access.)

          (2) A Photographic Atlas for the Anatomy and Physiology Laboratory, 8th edition by Van de Graff & Crawley. Morton Publishing, Englewood, CO. Bring to every lab. If you have an earlier edition of the photo atlas, that will be fine.

          (3) Safety glasses or safety goggles (highly recommended for people who wear contacts) that meet Z87.1 standards. You are required to bring these to labs involving dissection or chemicals or biohazards or you will not be able to attend the lab on those days. Due to safety issues, safety goggles cannot be loaned or shared.

          (4) Closed shoes are required footwear for all labs in this course.

          Recommended Materials:

          Many students have found The Anatomy Coloring Book (Kapit and Elson) useful.


          Watch the video: Human Anatomy Lecture- Ch 2 Cells (May 2022).


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