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A number of reproductive structures are exterior to the female’s body. The clitoris is a structure with erectile tissue that contains a large number of sensory nerves and serves as a source of stimulation during intercourse. The labia majora are a pair of elongated folds of tissue that run posterior from the mons pubis and enclose the other components of the vulva. The labia minora are thin folds of tissue centrally located within the labia majora. The greater vestibular glands are found at the sides of the vaginal opening and provide lubrication during intercourse.
|Table 1. Female Reproductive Anatomy|
|Mons pubis||External||Fatty area overlying pubic bone|
|Labia majora||External||Covers labia minora|
|Labia minora||External||Covers vestibule|
|Greater vestibular glands||External||Secrete mucus; lubricate vagina|
|Breast||External||Produce and deliver milk|
|Ovaries||Internal||Carry and develop eggs|
|Oviducts (Fallopian tubes)||Internal||Transport egg to uterus|
|Uterus||Internal||Support developing embryo|
|Vagina||Internal||Common tube for intercourse, birth canal, passing menstrual flow|
The breasts consist of mammary glands and fat. The size of the breast is determined by the amount of fat deposited behind the gland. Each gland consists of 15 to 25 lobes that have ducts that empty at the nipple and that supply the nursing child with nutrient- and antibody-rich milk to aid development and protect the child.
Internal female reproductive structures include ovaries, oviducts, the uterus, and the vagina, shown in Figure 1. The pair of ovaries is held in place in the abdominal cavity by a system of ligaments. Ovaries consist of a medulla and cortex: the medulla contains nerves and blood vessels to supply the cortex with nutrients and remove waste. The outer layers of cells of the cortex are the functional parts of the ovaries. The cortex is made up of follicular cells that surround eggs that develop during fetal development in utero. During the menstrual period, a batch of follicular cells develops and prepares the eggs for release. At ovulation, one follicle ruptures and one egg is released, as illustrated in Figure 2a.
The oviducts, or fallopian tubes, extend from the uterus in the lower abdominal cavity to the ovaries, but they are not in contact with the ovaries. The lateral ends of the oviducts flare out into a trumpet-like structure and have a fringe of finger-like projections called fimbriae, illustrated in Figure 2b. When an egg is released at ovulation, the fimbrae help the non-motile egg enter into the tube and passage to the uterus. The walls of the oviducts are ciliated and are made up mostly of smooth muscle. The cilia beat toward the middle, and the smooth muscle contracts in the same direction, moving the egg toward the uterus. Fertilization usually takes place within the oviducts and the developing embryo is moved toward the uterus for development. It usually takes the egg or embryo a week to travel through the oviduct. Sterilization in women is called a tubal ligation; it is analogous to a vasectomy in males in that the oviducts are severed and sealed.
The uterus is a structure about the size of a woman’s fist. This is lined with an endometrium rich in blood vessels and mucus glands. The uterus supports the developing embryo and fetus during gestation. The thickest portion of the wall of the uterus is made of smooth muscle. Contractions of the smooth muscle in the uterus aid in passing the baby through the vagina during labor. A portion of the lining of the uterus sloughs off during each menstrual period, and then builds up again in preparation for an implantation. Part of the uterus, called the cervix, protrudes into the top of the vagina. The cervix functions as the birth canal.
The vagina is a muscular tube that serves several purposes. It allows menstrual flow to leave the body. It is the receptacle for the penis during intercourse and the vessel for the delivery of offspring. It is lined by stratified squamous epithelial cells to protect the underlying tissue.
Human Reproductive Anatomy
In general, the reproductive structures in humans can be divided into three main categories: gonads, internal genitalia and external genitalia. The gonads are the organs in which gametes, the cells that fuse in fertilization to form new individuals, develop and mature. All other reproductive structures are called genitalia, or genitals. Internal genitalia are found inside of the body, while external genitalia are visible from the outside. The structures seen in adult males and females actually come from the same precursors in embryos, so there are many similarities in both structure and function between males and females. There is also a wide spectrum of structures present in any one individual many people have structures that resemble a combination of male and female structures, or that resemble neither. In this textbook, we will define “male” and “female” based on individuals who have the most typical structures characteristic of those two sexes other types of structures are also normal and common. We will describe the functions of these structures during vaginal sexual intercourse, since that is the sexual act used in reproduction keep in mind that other types of sexual activity are also common and normal.
Male Reproductive Anatomy
Figure 1. The reproductive structures of the human male are shown.
In the male reproductive system, the scrotum houses the testicles or testes (singular: testis), including providing passage for blood vessels, nerves, and muscles related to testicular function. The testes are a pair of male reproductive organs that produce sperm and some reproductive hormones. Each testis is approximately 2.5 by 3.8 cm (1.5 by 1 in) in size and divided into wedge-shaped lobules by connective tissue called septa. Coiled in each wedge are seminiferous tubules that produce sperm.
Sperm are immobile at body temperature therefore, the scrotum and penis are external to the body, as illustrated in Figure 1 so that a proper temperature is maintained for motility. In land mammals, the pair of testes must be suspended outside the body at about 2 ° C lower than body temperature to produce viable sperm. Infertility can occur in land mammals when the testes do not descend through the abdominal cavity during fetal development.
Which of the following statements about the male reproductive system is false?
- The vas deferens carries sperm from the testes to the penis.
- Sperm mature in seminiferous tubules in the testes.
- Both the prostate and the bulbourethral glands produce components of the semen.
- The prostate gland is located in the testes.
Sperm mature in seminiferous tubules that are coiled inside the testes, as illustrated in Figure 1. The walls of the seminiferous tubules are made up of the developing sperm cells, with the least developed sperm at the periphery of the tubule and the fully developed sperm in the lumen. The sperm cells are mixed with “nursemaid” cells called Sertoli cells which protect the germ cells and promote their development. Other cells mixed in the wall of the tubules are the interstitial cells of Leydig. These cells produce high levels of testosterone once the male reaches adolescence.
When the sperm have developed flagella and are nearly mature, they leave the testicles and enter the epididymis, shown in Figure 1. This structure resembles a comma and lies along the top and posterior portion of the testes it is the site of sperm maturation. The sperm leave the epididymis and enter the vas deferens (or ductus deferens), which carries the sperm, behind the bladder, and forms the ejaculatory duct with the duct from the seminal vesicles. During a vasectomy, a section of the vas deferens is removed, preventing sperm from being passed out of the body during ejaculation and preventing fertilization.
Semen is a mixture of sperm and spermatic duct secretions (about 10 percent of the total) and fluids from accessory glands that contribute most of the semen’s volume. Sperm are haploid cells, consisting of a flagellum as a tail, a neck that contains the cell’s energy-producing mitochondria, and a head that contains the genetic material. Figure 2 shows a micrograph of human sperm as well as a diagram of the parts of the sperm. An acrosome is found at the top of the head of the sperm. This structure contains lysosomal enzymes that can digest the protective coverings that surround the egg to help the sperm penetrate and fertilize the egg. An ejaculate will contain from two to five milliliters of fluid with from 50–120 million sperm per milliliter.
Figure 2. Human sperm, visualized using scanning electron microscopy, have a flagellum, neck, and head. (credit b: modification of work by Mariana Ruiz Villareal scale-bar data from Matt Russell)
The bulk of the semen comes from the accessory glands associated with the male reproductive system. These are the seminal vesicles, the prostate gland, and the bulbourethral gland, all of which are illustrated in Figure 1. The seminal vesicles are a pair of glands that lie along the posterior border of the urinary bladder. The glands make a solution that is thick, yellowish, and alkaline. As sperm are only motile in an alkaline environment, a basic pH is important to reverse the acidity of the vaginal environment. The solution also contains mucus, fructose (a sperm mitochondrial nutrient), a coagulating enzyme, ascorbic acid, and local-acting hormones called prostaglandins. The seminal vesicle glands account for 60 percent of the bulk of semen.
The penis, illustrated in Figure 1, is an organ that drains urine from the renal bladder and functions as a copulatory organ during intercourse. The penis contains three tubes of erectile tissue running through the length of the organ. These consist of a pair of tubes on the dorsal side, called the corpus cavernosum, and a single tube of tissue on the ventral side, called the corpus spongiosum. This tissue will become engorged with blood, becoming erect and hard, in preparation for intercourse. The organ is inserted into the vagina culminating with an ejaculation. During intercourse, the smooth muscle sphincters at the opening to the renal bladder close and prevent urine from entering the penis. An orgasm is a two-stage process: first, glands and accessory organs connected to the testes contract, then semen (containing sperm) is expelled through the urethra during ejaculation. After intercourse, the blood drains from the erectile tissue and the penis becomes flaccid.
The walnut-shaped prostate gland surrounds the urethra, the connection to the urinary bladder. It has a series of short ducts that directly connect to the urethra. The gland is a mixture of smooth muscle and glandular tissue. The muscle provides much of the force needed for ejaculation to occur. The glandular tissue makes a thin, milky fluid that contains citrate (a nutrient), enzymes, and prostate specific antigen (PSA). PSA is a proteolytic enzyme that helps to liquefy the ejaculate several minutes after release from the male. Prostate gland secretions account for about 30 percent of the bulk of semen.
The bulbourethral gland, or Cowper’s gland, releases its secretion prior to the release of the bulk of the semen. It neutralizes any acid residue in the urethra left over from urine. This usually accounts for a couple of drops of fluid in the total ejaculate and may contain a few sperm. Withdrawal of the penis from the vagina before ejaculation to prevent pregnancy may not work if sperm are present in the bulbourethral gland secretions. The location and functions of the male reproductive organs are summarized in Table 1.
|Table 1. Male Reproductive Anatomy|
|Scrotum||External||Carry and support testes|
|Penis||External||Deliver urine, copulating organ|
|Testes||Internal||Produce sperm and male hormones|
|Seminal Vesicles||Internal||Contribute to semen production|
|Prostate Gland||Internal||Contribute to semen production|
|Bulbourethral Glands||Internal||Clean urethra at ejaculation|
BIO 140 - Human Biology I - Textbook
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Anatomy and Physiology of the Female Reproductive System
- Describe the structure and function of the organs of the female reproductive system
- List the steps of oogenesis
- Describe the hormonal changes that occur during the ovarian and menstrual cycles
- Trace the path of an oocyte from ovary to fertilization
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 1). Recall that the ovaries are the female gonads. The gamete they produce is called an oocyte . We&rsquoll discuss the production of oocytes in detail shortly. First, let&rsquos look at some of the structures of the female reproductive system.
Figure 1: The major organs of the female reproductive system are located inside the pelvic cavity.
External Female Genitals
The external female reproductive structures are referred to collectively as the vulva (Figure 2). 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 = &ldquolips&rdquo majora = &ldquolarger&rdquo) are folds of hair-covered skin that begin just posterior to the mons pubis. The thinner and more pigmented labia minora (labia = &ldquolips&rdquo minora = &ldquosmaller&rdquo) 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 &ldquovirginity&rdquo 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&ndashvaginal intercourse. The vaginal opening is located between the opening of the urethra and the anus. It is flanked by outlets to the Bartholin&rsquos glands (or greater vestibular glands).
Figure 2: The external female genitalia are referred to collectively as the vulva.
The vagina , shown at the bottom of Figure 1a and Figure 1b, 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&mdashcalled the fornix&mdashmeets 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&ndashvaginal intercourse, and childbirth. The Bartholin&rsquos 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&mdashor washing out the vagina with fluid&mdashcan disrupt the normal balance of healthy microorganisms, and actually increase a woman&rsquos 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.
The ovaries are the female gonads (see Figure 1). 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&rsquos oocytes and ovarian follicles. During a woman&rsquos 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).
Gametogenesis in females is called oogenesis . The process begins with the ovarian stem cells, or oogonia (Figure 3). 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&rsquos 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 &mdashthe release of an oocyte from the ovary&mdashmarks the transition from puberty into reproductive maturity for women. From then on, throughout a woman&rsquos 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 3, 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.
Figure 3: The unequal cell division of oogenesis produces one to three polar bodies that later degrade, as well as a single haploid ovum, which is produced only if there is penetration of the secondary oocyte by a sperm cell.
How does the diploid secondary oocyte become an ovum &mdashthe 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 &mdashnot 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.
Mapping Human History with Mitochondrial DNA
When we talk about human DNA, we&rsquore 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&rsquot mean that everyone&rsquos 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 &ldquobranches&rdquo off of the &ldquomain trunk&rdquo of our mtDNA family tree. Your mtDNA might have a pattern of mutations that aligns more closely with one branch, and your neighbor&rsquos 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&mdashand its mtDNA&mdashended.
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&rsquoll see next, follicles progress from primordial, to primary, to secondary and tertiary stages prior to ovulation&mdashwith 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 4). 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&mdashsome 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&mdashnow called secondary follicles (see Figure 4b)&mdashincrease in diameter, adding a new outer layer of connective tissue, blood vessels, and theca cells &mdashcells 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&rsquot 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.
Figure 4: (a) The maturation of a follicle is shown in a clockwise direction proceeding from the primordial follicles. FSH stimulates the growth of a tertiary follicle, and LH stimulates the production of estrogen by granulosa and theca cells. Once the follicle is mature, it ruptures and releases the oocyte. Cells remaining in the follicle then develop into the corpus luteum. (b) In this electron micrograph of a secondary follicle, the oocyte, theca cells (thecae folliculi), and developing antrum are clearly visible. EM × 1100. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)
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 5). 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.
Figure 5: The hypothalamus and pituitary gland regulate the ovarian cycle and ovulation. GnRH activates the anterior pituitary to produce LH and FSH, which stimulate the production of estrogen and progesterone by the ovaries.
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&rsquot 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 5). 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 &ldquoyellowish body&rdquo (see Figure 5). 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 &ldquowhitish body&rdquo 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 ). 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&ndashgranulosa 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.
Watch the video linked to below 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&mdasheither in the uterine tube or in the uterus, where it may be shed with the next menstrual period.
Figure 6: This anterior view shows the relationship of the ovaries, uterine tubes (oviducts), and uterus. Sperm enter through the vagina, and fertilization of an ovulated oocyte usually occurs in the distal uterine tube. From left to right, LM × 400, LM × 20. (Micrographs provided by the Regents of University of Michigan Medical School © 2012)
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&rsquos 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.
The Uterus and Cervix
The uterus is the muscular organ that nourishes and supports the growing embryo (see Figure 6). 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&rsquos 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&mdashshould fertilization not occur&mdashit 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 &mdashthe 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&rsquos 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&rsquos 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 &ldquodrive&rdquo 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.
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 , 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.
Figure 7: The correlation of the hormone levels and their effects on the female reproductive system is shown in this timeline of the ovarian and menstrual cycles. The menstrual cycle begins at day one with the start of menses. Ovulation occurs around day 14 of a 28-day cycle, triggered by the LH surge.
Once menstrual flow ceases, the endometrium begins to proliferate again, marking the beginning of the proliferative phase of the menstrual cycle (see Figure 7). 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&mdashwhich occurs with the elevated estrogen production from the dominant follicle&mdashthen 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.
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 7). 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&mdashor 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&rsquos 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 8). 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.
Figure 8: In most cases, cells infected with the HPV virus heal on their own. In some cases, however, the virus continues to spread and becomes an invasive cancer.
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&rsquos genome and either halts the progression of the cell cycle&mdashallowing time for DNA repair to occur&mdashor initiates apoptosis. Both of these processes prevent the accumulation of mutations in a cell&rsquos 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.
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 9), 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 9). 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.
Figure 9: During lactation, milk moves from the alveoli through the lactiferous ducts to the nipple.
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&rsquos 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&rsquos 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&rsquos 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.
The external female genitalia are collectively called the vulva. The vagina is the pathway into and out of the uterus. The man&rsquos penis is inserted into the vagina to deliver sperm, and the baby exits the uterus through the vagina during childbirth.
The ovaries produce oocytes, the female gametes, in a process called oogenesis. As with spermatogenesis, meiosis produces the haploid gamete (in this case, an ovum) however, it is completed only in an oocyte that has been penetrated by a sperm. In the ovary, an oocyte surrounded by supporting cells is called a follicle. In folliculogenesis, primordial follicles develop into primary, secondary, and tertiary follicles. Early tertiary follicles with their fluid-filled antrum will be stimulated by an increase in FSH, a gonadotropin produced by the anterior pituitary, to grow in the 28-day ovarian cycle. Supporting granulosa and theca cells in the growing follicles produce estrogens, until the level of estrogen in the bloodstream is high enough that it triggers negative feedback at the hypothalamus and pituitary. This results in a reduction of FSH and LH, and most tertiary follicles in the ovary undergo atresia (they die). One follicle, usually the one with the most FSH receptors, survives this period and is now called the dominant follicle. The dominant follicle produces more estrogen, triggering positive feedback and the LH surge that will induce ovulation. Following ovulation, the granulosa cells of the empty follicle luteinize and transform into the progesterone-producing corpus luteum. The ovulated oocyte with its surrounding granulosa cells is picked up by the infundibulum of the uterine tube, and beating cilia help to transport it through the tube toward the uterus. Fertilization occurs within the uterine tube, and the final stage of meiosis is completed.
The uterus has three regions: the fundus, the body, and the cervix. It has three layers: the outer perimetrium, the muscular myometrium, and the inner endometrium. The endometrium responds to estrogen released by the follicles during the menstrual cycle and grows thicker with an increase in blood vessels in preparation for pregnancy. If the egg is not fertilized, no signal is sent to extend the life of the corpus luteum, and it degrades, stopping progesterone production. This decline in progesterone results in the sloughing of the inner portion of the endometrium in a process called menses, or menstruation.
The breasts are accessory sexual organs that are utilized after the birth of a child to produce milk in a process called lactation. Birth control pills provide constant levels of estrogen and progesterone to negatively feed back on the hypothalamus and pituitary, and suppress the release of FSH and LH, which inhibits ovulation and prevents pregnancy.
Introduction to Reproduction
Do you have questions about sex hormones or menstrual cycles? This is a crash-course in human reproductive health through fact and biology-based information on a variety of topics. "Sex 101" will cover reproductive anatomy, key biological changes during puberty, sexual biology and contraceptive methods, reproductive disorders, and a special introduction to the exciting field of Oncofertility. Specific lecture titles are as follows: 1) Reproductive Anatomy & Hormones, 2) Menstrual Cycle, Oocyte Maturation, & Sperm Activation, 3) Sexual Biology, Fertilization, & Contraception, and 4) Reproductive Health & Disorders. The objective of this course is to ensure you understand reproductive health and not confuse reproduction with sex (or having sex). This course was designed with you in mind, and is aimed at providing you with quality information that is meaningful to you and that may be hard to find otherwise. Reproductive health is an area of knowledge that needs to be demystified. We have designed this course for you to examine reproduction through a biological and scientific lens addressing these issues in a comfortable and interactive format that will lead to a better understanding of holistic health, long-term.
Thank you for giving me excellent information on reproduction. It is very helpful course for me. Thank you Northwestern University and coursera.
This course is perfect, everything we need to know is there in this course, the videos and the readings are exceptional <3
This module focuses on learning, identifying, and labeling all parts of male and female reproductive anatomy and the function of hormones on development. COURSE GOAL 1: Students will be able to label and analyze the basic functionality of all parts of male and female reproductive anatomy, conceptualize the role of hormones in the interactions between the brain, pituitary, and reproductive tract, and examine the basic functionality of the hormones involved during development and puberty.
Teresa K. Woodruff, Ph.D.
[MUSIC] Female reproductive anatomy begins with the ovary. Women have two ovaries, and together they house the most important tissue of reproduction, the follicle. The follicle has two functions. It houses the female gamete, the egg, and it produces the hormones, estrogen and progesterone. Women are born with about one million follicles. By puberty, that number is reduced to 300 to 400 thousand. And by menopause, the end of the reproductive years, there are no follicles remaining in the ovary. The ovary sits adjacent to a large tube called the Fallopian tube. The Fallopian tube is open to the peritoneal cavity, and a series of fingers, or Fimbriae, reach out and cover the ovary at the time of ovulation. And literally catch and transport the newly released egg into the Fallopian tube. If sperm are available, fertilization takes place in the Fallopian tube. If not, the egg disintegrates. The Fallopian tube has muscles that contract, and cilia gently transport the disintegrated egg or the newly fertilized embryo to the uterus. The uterus has a muscular layer called the myometrium, and two layers of tissue that make up the endometrium. The endometrium is under the control of ovarian hormones, and we'll discuss the hormones in a later section. For now, I want you to remember two things. First, that this tissue has a basal layer which includes cells that proliferate each month. And that the cycling endometrium is the site where neovascularization, or new blood vessels, develop each month. If an embryo arrives in the uterus, it will implant in this receptive tissue. If a degenerating egg arrives in the uterus, the lining of the endometrium is shed. The myometrium, which sits just under the endometrium, contracts once a month under the influence of ovarian hormones. When this happens, the newly formed blood vessels are pinched off, and the secretory endometrial cells die. The blood vessels and the endometrial cells slough off. Which then results in the monthly mense. The cervix is the slender neck at the base of the uterus. The endocervix faces the uterus and the ectocervix is the tissue that faces the vagina. The cervix is a barrier between the outside world and the uterus. It produces mucous throughout the reproductive cycle, which changes in consistency and can block or aid sperm function. The cervix is connected to the vagina, which is a muscular tissue that can stretch to receive the penis, or permit the exit of a fetus during birth. A hymen blocks the opening of the vagina, and is permanently disrupted during sexual intercourse or by physical action. The external genitalia in females is called the vulva. The labia, or folds of skin that encircle and form a foreskin for the clitoris. The clitoris is an erectile tissue, like the penis, and has sensory receptors that make it the sensory center of the female reproductive system. The urinary and reproductive tracts are separate in the female. Recall that the urethra in the male transports both urine and sperm. Additional minor tissues, and further explanations about reproductive anatomy, can be found in the Repropedia. [MUSIC]
Function of the Uterus
Perhaps the principal, albeit lofty function of the uterus is to preserve life. It is the site of nourishment for the growing baby, making it one of the most important reproductive organs in the female body. This all begins when an egg, or ovum, is fertilized by a sperm and will make its downward trek in search of a better home. The tight fallopian tubes will not provide enough space to house the growing embryo! This is where the uterus meets all of these requirements, and more! The uterus’s thick, muscular nature will allow it to contract and expand to make room for the developing baby. The uterus is also rich in vasculature. There are many blood vessels supplying the muscle layers at any given time. This especially applies to the endometrium which is highly vascular and will come to nourish the embryo. In fact, many of the endometrial vessels that will come to supply the embryo will form just for this purpose. All of this explains why the fertilized ovum will choose to implant itself in the uterine lining – coined, the “site of implantation.” Thus, the uterus is the site that allows ours, and many species, to continue reproducing!
Male Reproductive System
To understand the male reproductive system, one must know the external and internal structures, and the process of spermatogenesis (sperm production) including the physiologic pathway of the sperm cell.
The male external structures are the penis and the scrotum (a pouch which protects the testes). The penis consists of the glans (the head), and the shaft (the body). The glans is covered by a fold of skin called the foreskin (circumcision removes the foreskin). The scrotum surrounds and protects the two testes, internal structures also referred to as testicles.
The testes are the male gonads and contain hundreds of tiny seminiferous tubules where sperm cells are produced. The epididymis is a small oblong body which rests on the surface of the testes where sperm mature and are stored. The epididymis leads into the vas deferens (narrow tubes which carry sperm away from the testes). The vas deferens extends to join with the ducts of the two seminal vesicles (located on side of the prostate gland) to form the ejaculatory ducts which extend through the body of the prostate gland and empty into the urethra. The prostate gland surrounds the neck of the bladder (the structure that stores urine) and the urethra, (a thin tube which extends through the penis and carries semen and urine outside of the body, although not simultaneously). The Cowper's glands (also called the bulbourethral glands) are found on each side of the urethra, just below the prostate gland.
Process of Spermatogenesis
Spermatogenesis begins in the seminiferous tubules of the testes. Sperm pass into the epididymis where they mature and become motile so they are able to move through the vas deferens and into the seminal vesicles where they mix with seminal fluids, rich in fructose and other nutrients. The prostate gland and the Cowper's glands secrete fluids which also help to nourish and transport the sperm. This mixture of fluids and sperm is called semen, the fluid which is expelled from a man's penis during ejaculation. Sexual arousal can cause fluid from the Cowper's glands to be released prior to ejaculation. This fluid is called pre-ejaculatory fluid and does not contain sperm unless it is leftover from a previous ejaculation. Contrary to popular belief, there is little evidence to support that pre-ejaculatory fluid contains enough sperm to cause pregnancy.
Although men continue to produce sperm throughout their lives, testosterone production decreases at about 45-65 years of age.
A Basic Introduction to Female Anatomy
The human body is composed of chemical elements. These elements perform vital functions in various cells and organ systems. The human body functions is a ordered system of layers. The smallest unit is composed of atoms and molecules. These particles form cells. The cells are the building blocks of organ systems. Chemistry reveals how structurally matter is assembled together. The human body is literally the product of star matter. Hydrogen and helium are the most abundant elements in the known universe. When atoms make bonds they form molecules and billions of years ago the elements were brought into existence contributing the emergence of life. The elements that form the human body include oxygen, hydrogen carbon, nitrogen, sulfur, potassium, magnesium, sodium, and chlorine. The body also contains a small amount of iron. Anatomy is a scientific discipline which studies the structure of the human body. This should not be confused with physiology which concentrates on function of the organs. The understanding of anatomy and physiology allowed for the advancement in medicine. The problem with this progress in science was that the female body was highly misunderstood. The male body was considered a normal default and only recently sex differences have been examined in relation to health science. Female anatomy differs from males. The reproductive system is the most obvious difference. The are also attributes in morphology related to sexual dimorphism. Women tend to have a higher body fat ratio compared to muscle mass. Biacromial , and billiac width are of different sizes. The female body also contains breasts. Women also produce higher amounts of oestrogen, which serves other physiological functions. The female body just like a male one is composed of various structures that perform a certain function.
The human body has a basic structure. External appearance varies among individuals, however there are features present on everyone. The head contains the nose, ears, eyes, and mouth. The neck is connected to the thorax ( chest). The body has an abdomen holding the stomach and intestines. The body has an umbilicus (navel), which was at one point host to a cord that would provide nourishment prior to birth. Humans have hips connected to legs. The feet are connected to the legs along with five tones on each. Hands are connected to the arms by the wrists. Five fingers are present on both hands. Somatotype varies among people which include three classifications known as endomorphs, mesomorphs, and ectomorphs. Women’s bodies no matter what body type contain a higher fat percentage. Externally, women’s bodies have breasts and a pudenda. Women’s shoulders are more narrow and their bodies have wider hips.
The external anatomy of the female body show a specific sexual dimorphism. The body has more fat and on average there is a size difference among the sexes. The major organ systems of the human body include the circulatory, nervous, respiratory, reproductive, digestive, integumentary, muscular, urinary and immune system. The majority of the human body is made of carbon and oxygen. Calcium is critical for bone strength, blood clotting, and the functioning of nerves as well as muscles.
Female faces differ in relations to chin and nose size. Women have smaller noses and less angular shaped chins. Women hands are also smaller. These are a few of external differences other than reproductive anatomy. Primary sex characteristics refer to the reproductive anatomy of men and women. Secondary sex characteristics emerge during puberty, which are related to phenotypic traits. The production of oestrogen increases during puberty which alters women’s body composition and metabolism. Girls start growth earlier than boys. When girls reach adulthood their bodies will have the distinctive female shape.
The most different anatomical system between males and females is the reproductive system. Both are designed for producing offspring. Women are the only ones that can get pregnant. The female reproductive tract emerges from the lack of testosterone and mullerian-inhibiting factor. During the first 8 to 10 weeks of fetal development the two sexes are indistinguishable from one another. The reproductive tract develops from a paramesonephric duct. Women’s bodies contain both internal and external genitalia. The internal genitals include the uterus, uterine tubes, and vagina. The external genitalia includes the clitoris, labia minora, and labia majora. The vagina is a tube like structure 8 to 10 cm long. This structure allows for discharge of mensural fluid, birth of offspring, an entry point for the penis during copulation. The vaginal wall contains the outer aventitia, a middle muscularis, and an inner muscosa. Through transudation the vagina is lubricated by serous fluid. Mucus is also produced by the cervical glands. The hymen is the membrane that goes across the vaginal opening. The hymen has multiple openings. This structure can be ruptured through intercourse, The clitoris is the major center of sexual stimulation. It is made of corpora cavernosa encased in a network of connective tissue.
The female gonads are referred to as the ovaries. The ovaries produce egg cells called ova including sex hormones. Located in the ovarian fossa it has other parts. The interior of the ovary contains the central medulla and outer cortex. The cortex has huge significance, because it is that area has follicles. Ovulation happens when the follicles burst. Eggs have to be released one at a time . Due to the complexity of the female reproductive system, it runs on a particular cycle. The female sexual cycle describes all of these physiological functions. The ovarian cycle and the menstrual cycle are related to egg production as well as preparing the uterus for gestation. The endometrium must build up tissue and discharge it. Menses occurs to remove eggs that so not have chances for fertilization. The average woman could expel 40 ml of blood and 35 ml serous fluid from menses. The reason blood clots do not occur is due to fibrinolysin. Both ovarian and menstrual cycle function concurrently. Endocrine function, the structure of the uterous, and egg production enable women to reproduce.
The breasts and mammary glands are another feature of the female body. Breasts are mounds of tissue that cover the pectoralis major muscle. The mammary gland develops during pregnancy. This is for the purpose of lactation. When a woman ends nursing a baby they reduce in size. The two regions of the breasts are the conical and pendulous body. Both breasts contain nipples with an axillary tail toward the axilla (arm pit). What surrounds the nipple is the areola. This region is darker than the rest of the breast. Dermal blood capillaries and nerves are closer to the surface. What this does is make the areola’s color more pronounced and sensitive. The sensory nerve fibers enable milk ejection reflex. This essential for successfully nursing an infant.
Breasts internally are a collection of adipose and collagenous tissue ( in non-lactating state). The suspensory ligaments connect the breast to the dermis and the fascia of the pectoralis major. The mammary gland can have up to 20 lobes arranged around the nipple. The lobes are separated from one another by stroma. Each of these lobes are inside a lactiferous duct. This duct has the ability to dilates and forms lactiferous sinus. The duct branches end with sac shaped structures called acini. Clustered into lobules they are present in both the breasts. The acinus are encased in myoepithelial cells. These contractile cells aid in milk release and other aspects of lactating .
What also be understood is anatomy’s basic definition. This scientific field is the study of structures of an organism. Anatomy is not to be confused with physiology. That branch of science examines the function of organ systems . Both are connected and are the foundation of health science. Biomedical science would not exist without it. Methods of study have been employed to comprehend the form and function of the human body. The earliest form of examination involved palpitation. That technique involved feeling with a person with hands alone or feeling for a pulse. Auscultation required listening to the sounds the body made. Anatomists eventually understood that dissection was the only means to understand body stricture. The dissection of cadavers is part of training in schools of anatomy and surgery. Comparative anatomy becomes important to the study of human evolution and zoology. This reveals which organisms might have common genetic ancestors and the change in animals overtime.Multiple biological processes are happening in the human body. Our bodies can be changed through diet and exercise.
Gross anatomy refers to the study of organs that can be detected by human sight. It can also include examining the human body at the microscopic level. Medical imaging has reduced the need to do exploratory surgery. Prior to this, a person would have to be opened up to see what medical issue was going on in the human body. The risk was enormous especially in a time before antibiotics and anesthesia. Histology refers to the study of tissues. This can also be called microscopic anatomy when studying organ tissue. The cells are part of an ultrastructure. Cytology refers to the examination of individual cells of organs. The rapid advance of technology has enabled humanity to know more about the body than ever before. There is more to know about the human body. The interstitium was first detected only in 2018. The organ is fluid filled spaces in the connective tissues inside the body. The reason it was not detected was because it did not appear on microscope slides. That technique was not used for the investigation into the interstitium. Some medical professional debate whether or not it can be considered an organ. Anatomy is an ever evolving science just like physics, biology, and mathematics.
Saladin, Kenneth. Anatomy Physiology The Unity of Form and Function . New York : The McGraw Hill Companies, 2012.
Gray ,Theodore . The Elements A Visual Exploration of Every Know Atom in the Universe . New York : Black Dog and Leventhal
What is Anatomy? (with pictures)
Anatomy is the area of biology that deals with the structure of plants and animals, usually on the scale of whole organisms and their major systems. Major divisions falling under the umbrella of anatomy include the visible structures and organs, the comparative study of related organisms, and growth and development. Bodily systems and their functions and anatomical disease states are also a part of anatomy. Sometimes included is histology, which is the study of the different types of tissues and their special cells. In animals, the field is also concerned with major systems such as the circulatory, digestive, and nervous systems.
Most commonly, the science of anatomy refers to the study of gross anatomy, which is the study of visible structures without the use of aids such as the microscope. This allows for the examination of the various body structures in terms of their entire size and shape, as well as their relationship to other structures. Less commonly, the term also refer to the anatomical study of smaller units like the cell. The study of various types of tissues often requires microscopic analysis to make meaningful comparisons between them. The more inclusive term morphology covers both macroscopic, or large-scale, as well as microscopic structures.
Anatomy has a number of subdivisions that deal with more specific aspects of bodily structures. One of these is the study of the development of organisms, which in animals can include the embryonic stage through maturity. Functional anatomy is the study of organs, their roles in the body, and their place in the body's major systems. Comparative anatomy deals with the anatomical relationship between animals that share similar structures, such as mammals.
Other subdivisions include pathological anatomy, which is the study of diseased organs and how they are changed in form or function. Sometimes the microscopic structures of the smallest unit of biology, the cell, are also included. Broader divisions having a longer scientific history include the animal, plant, and human branches of the field.
In anatomy, the visible structures of the body are related to their places in larger systems. For instance, the circulatory system includes the heart, blood vessels, and arteries. Male and female reproductive anatomy includes sexual organs such as the testes, penis, and vagina. Other systems are the muscular, skeletal, and respiratory systems. Anatomical studies are often paired with the related field of physiology, which deals more specifically with the function of organisms. Physiology also extends the study of anatomical structures to their biological processes.
Compare spermatogenesis and oogenesis as to timing of the processes, and the number and type of cells finally produced.
Stem cells are laid down in the male during gestation and lie dormant until adolescence. Stem cells in the female increase to one to two million and enter the first meiotic division and are arrested in prophase. At adolescence, spermatogenesis begins and continues until death, producing the maximum number of sperm with each meiotic division. Oogenesis continues again at adolescence in batches of eggs with each menstrual cycle. These primary oocytes finish the first meiotic division, producing a viable egg with most of the cytoplasm and its contents, and a second cell called a polar body containing 23 chromosomes. The second meiotic division is initiated and arrested in metaphase. At ovulation, one egg is released. If this egg is fertilized, it finishes the second meiotic division. This is a diploid, fertilized egg.
Describe the events in the ovarian cycle leading up to ovulation.
Low levels of progesterone allow the hypothalamus to send GnRH to the anterior pituitary and cause the release of FSH and LH. FSH stimulates follicles on the ovary to grow and prepare the eggs for ovulation. As the follicles increase in size, they begin to release estrogen and a low level of progesterone into the blood. The level of estrogen rises to a peak, causing a spike in the concentration of LH. This causes the most mature follicle to rupture and ovulation occurs.
Describe the stages of labor.
Stage one of labor results in uterine contractions, which thin the cervix and dilate the cervical opening. Stage two delivers the baby, and stage three delivers the placenta.