Are all endocrine glands associated with common human feelings?

Are all endocrine glands associated with common human feelings?

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I was looking at endocrine glands and found it interesting that a few of them have some very understandable feelings/mentalities associated with them. In particular:

  • Gonads: arousal/romance
  • Pancreas: hunger (glucose)
  • Adrenal glands: fight or flight
  • Pineal gland: sleepiness (melatonin)

Of course, there is a lot more complexity to how these glands work and what they do, but I find the notion of being able to empathize with a part of the body interesting.

As a counter-example, if something is wrong with my spleen, there may be feelings associated with that (ie pain), but they aren't so profound as things like hunger, fear, and arousal.

Anyways, my curiosity here is: do all endocrine glands have a feeling associated with them?

Here's the list of all glands:

  • Pituitary gland
  • Thyroid gland
  • Parathyroid glands
  • Adrenal glands
  • Pancreas
  • Gonads
  • Pineal gland

Also, I know this is a silly question, but please bear with me here. It's piqued my interest, and I just want to fulfil some curiosity.

You may not be able to feel or be aware of the actions of all endocrine glands at the time they occur.

The parathyroid gland secretes parathormone, which affects calcium absorption in the intestine, kidneys and bones, phosphate excretion in the kidneys and vitamin D production in the kidneys. I'm not sure if one can feel these actions or its consequences.

The adrenal cortex secretes aldosterone, which maintains sodium and potassium blood levels, which is related to blood pressure and urine excretion. It also secretes cortisol, which affects glucose utilization, fat breakdown and inflammation and affects the actions of some other hormones, but within normal physiological range, you don't feel these effects. Cortisol is also known as a stress hormone, but its actions are much more subtle (on the level of metabolism) than those of adrenaline (heart rate, excitement). Saying that, cortisol secretion can be related to sleep and appetite. There is a lot of speculation how it might affect mood or "energy levels" (adrenal fatigue).

There are many gastrointestinal hormones (gastrin, secretin, cholecystokinin, ghrelin), some of which affect digestion, some peristalsis and some appetite and you may not be consciously aware of all of that.

Some pituitary gland hormones (ACTH, TSH, FSH, LH) stimulate the secretion of hormones from other glands (adrenal, thyroid, gonades) and some (growth hormone, ADH, oxytocin) act directly on organs - I don't think you can say that you can feel these effects.

Some hormones have effects on other hormones (cortisol > adrenaline ; thyroxine > growth hormone, etc.), so it may not always be possible to pinpoint which feeling is directly related to which hormone.

Common human feelings related to hormone secretion:

  • Excitement or stress response, including fast heart rate and breathing and anxiety: short term response: adrenaline; long-term response: cortisol
  • Appetite: ghrelin, leptin, adiponectin, cholecystokinin, insulin, glucagon-like peptide, gastrointestinal peptide
  • Sexual drive: sex hormones, mainly testosterone and estradiol
  • Sleepiness: melatonin, cortisol
  • Depression: cortisol, sex hormones (mainly in women)

The point of this answer is to show that some of your feelings can be simply affected by hormones, which are note some ultimate forces, and that being aware of that can help you to control them to some extent.

Are all endocrine glands associated with common human feelings? - Biology

In this section, you’ll learn about the basics of the central nervous system, which consists of the brain and spinal cord, as well as the peripheral nervous system. The peripheral nervous system is comprised of the somatic and autonomic nervous systems. The somatic nervous system transmits sensory and motor signals to and from the central nervous system. The autonomic nervous system controls the function of our organs and glands, and can be divided into the sympathetic and parasympathetic divisions. Sympathetic activation prepares us for fight or flight, while parasympathetic activation is associated with normal functioning under relaxed conditions. The endocrine system consists of a series of glands that produce chemical substances known as hormones, which produce widespread effects on the body. Got all that? We’ll review each of these systems in the coming pages.

Learning Objectives

  • Describe the difference between the central and peripheral nervous systems and the somatic and autonomic nervous systems
  • Differentiate between the sympathetic and parasympathetic divisions of the autonomic nervous system
  • Describe the endocrine system and explain its primary responsibilities within the body

Glands of the Endocrine System

Each gland of the endocrine system releases specific hormones into your bloodstream. These hormones travel through your blood to other cells and help control or coordinate many body processes.

  • Adrenal glands: Two glands that sit on top of the kidneys that release the hormone cortisol.
  • Hypothalamus: A part of the lower middle brain that tells the pituitary gland when to release hormones.
  • Ovaries: The female reproductive organs that release eggs and produce sex hormones.
  • Islet cells in the pancreas: Cells in the pancreas control the release of the hormones insulin and glucagon.
  • Parathyroid: Four tiny glands in the neck that play a role in bone development.
  • Pineal gland: A gland found near the center of the brain that may be linked to sleep patterns.
  • Pituitary gland: A gland found at the base of brain behind the sinuses. It is often called the "master gland" because it influences many other glands, especially the thyroid. Problems with the pituitary gland can affect bone growth, a woman's menstrual cycles, and the release of breast milk.
  • Testes: The male reproductive glands that produce sperm and sex hormones.
  • Thymus: A gland in the upper chest that helps develop the body's immune system early in life. : A butterfly-shaped gland in the front of the neck that controls metabolism.

Even the slightest hiccup with the function of one or more of these glands can throw off the delicate balance of hormones in your body and lead to an endocrine disorder, or endocrine disease.

Are all endocrine glands associated with common human feelings? - Biology

Everyone's body undergoes changes, some natural and some not, that can affect the way the endocrine system works. Some of the factors that affect endocrine organs include puberty, aging, pregnancy, the environment, genetics and certain diseases and medications, including naturopathic medicine, herbal supplements, and prescription medicines such as opioids or steroids.


Despite age-related changes, the endocrine system functions well in most older people. However, some changes occur because of either damage to cells during the aging process or medical issues that the aging body accumulates, or genetically programmed cellular changes. These changes may alter the following:

  • hormone production and secretion
  • hormone metabolism (how quickly hormones are broken down and leave the body)
  • hormone levels circulating in blood
  • target cell or target tissue response to hormones
  • rhythms in the body, such as the menstrual cycle

For example, increasing age is thought to be related to the development of type 2 diabetes, especially in people who might be at risk for this disorder. The aging process affects nearly every gland. With increasing age, the pituitary gland (located in the brain) can become smaller and may not work as well, although may provide sufficient hormonal signaling for continuity of life. For example, production of growth hormone might decrease, which is likely not a priority in an aging individual this is also an example of genetic programming that we have evolved as species to adapt to. Decreased growth hormone levels in older people might lead to problems such as decreased lean muscle, decreased heart function, and osteoporosis. Aging affects a woman's ovaries and results in menopause, usually between 50 and 55 years of age. In menopause, the ovaries stop making estrogen and progesterone and no longer have a store of eggs. When this happens, menstrual periods stop.

Diseases and Conditions

Chronic diseases and other conditions may affect endocrine system function in several ways. After hormones produce their effects at their target organs, they are broken down (metabolized) into inactive molecules. The liver and kidneys are the main organs that break down hormones. The ability of the body to break down hormones may be decreased in people who have chronic heart, liver, or kidney disease.

Abnormal endocrine function can result from:

  • congenital (birth) or genetic defects (see section on Genetics below)
  • surgery, radiation, or some cancer treatments
  • traumatic injuries
  • cancerous and non-cancerous tumors
  • infection
  • autoimmune destruction (when the immune system turns against the body's own organs and causes damage)
  • medications or supplements

In general, abnormal endocrine function creates a hormone imbalance typified by too much or too little of a hormone. The underlying problem might be due to an endocrine gland making too much or too little of the hormone, or to a problem breaking down the hormone.


Physical or mental stressors can trigger a stress response. The stress response is complex and can influence heart, kidney, liver, and endocrine system function. Many factors can start the stress response, but physical stressors are most important. For the body to respond to, and cope with physical stress, the adrenal glands make more cortisol. If the adrenal glands do not respond, this can be a life-threatening problem. Some medically important factors causing a stress response are:

  • trauma (severe injury) of any type
  • severe illness or infection
  • intense heat or cold
  • surgical procedures
  • serious diseases
  • allergic reactions

Other types of stress include emotional, social, or economic, but these usually do not require the body to produce high levels of cortisol to survive the stress.

Environmental Factors

An environmental endocrine disrupting chemical (EDC) is a substance outside of the body that may interfere with the normal function of the endocrine system. Some EDCs mimic natural hormone binding at the target cell receptor. (Binding occurs when a hormone attaches to a cell receptor, a part of the cell designed to respond to that particular hormone.) EDCs can start the same processes that the natural hormone would start. Other EDCs block normal hormone binding and thereby prevent the effects of the natural hormones. Still other EDCs can directly interfere with the production, storage, release, transport, or elimination of natural hormones in the body. This can greatly affect the function of certain body systems.

EDCs can affect people in many ways:

  • disrupted sexual development
  • decreased fertility
  • birth defects
  • reduced immune response
  • neurological and behavioral changes, including reduced ability to handle stress


Your endocrine system can be affected by genes. Genes are units of hereditary information passed from parent to child. Genes are contained in chromosomes. The normal number of chromosomes is 46 (23 pairs). Sometimes extra, missing, or damaged chromosomes can result in diseases or conditions that affect hormone production or function. The 23rd pair, for example, is the sex chromosome pair. A mother and father each contribute a sex chromosome to the child. Girls usually have two X chromosomes while boys have one X and one Y chromosome. Sometimes, however, a chromosome or piece of a chromosome may be missing. In Turner syndrome, only one normal X chromosome is present and this can cause poor growth and a problem with how the ovaries function. In another example, a child with Prader-Willi syndrome may be missing all or part of chromosome 15, which affects growth, metabolism, and puberty. Your genes also may place you at increased risk for certain diseases, such as breast cancer. Women who have inherited mutations in the BRCA1 or BRCA2 gene face a much higher risk of developing breast cancer and ovarian cancer compared with the general population.

If you suspect hormone or endocrine-related problems get help from an endocrinologist near you.

Endocrine Glands and Functions

One of the most important components required by the human body for its daily functioning is the endocrine system. This article provides some information about the different endocrine glands and its functions.

One of the most important components required by the human body for its daily functioning is the endocrine system. This article provides some information about the different endocrine glands and its functions.

The endocrine system is responsible to help the body carry out many of its functions. The endocrine glands secrete hormones directly into the blood stream, rather than through a duct. That is the reason these glands are also known as ductless glands. Processes which are associated with growth, development, body metabolism, and reproduction, are all fueled by hormones secreted by these glands.

Functions of the Endocrine Glands

Pituitary Gland
This gland has its location at the base of the brain. It is known as the master gland, because it is responsible to control the function of other glands to put forth their hormones. Growth, body metabolism, sexual development, and reproduction happen to be the elements which come under the domain of the pituitary gland.

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Thyroid Gland
Just below the Adam’s apple, is located what is known as the thyroid gland. The thyroid gland functions by releasing two main hormones, thyroxine and triiodothyronine. These hormones play vital roles in regulating metabolism and organ function.

Pancreas, as most of us must be knowing, are the endocrine glands that are situated in the abdominal region, behind the stomach. The hormones which get secreted into the blood stream by these glands, serve to control proper digestion and blood sugar regulation. Insulin and glucagons are known to be the important hormones produced by the glands. One of the major function of the pancreas is maintaining appropriate levels of sugar throughout the body.

Adrenal Glands
On the upper side of the kidneys, are located these endocrine glands. In hormone production, there are two parts of these adrenal glands which comes into play. One is known as the adrenal cortex. It is known to steroid hormones, which are essential for digestion and sexual maturity. The other is what is known as the adrenal medulla. Now the hormones that this part secretes, are although not essential to sustain life, but help the body to manage stress and improve the quality of life.

The hypothalamus gland is actually a part of the pituitary gland. The hormones that it secretes do the work of inducing the master gland, so that it can go on with its normal function. Growth-hormone-releasing hormone (GHRH), somatostatin, and dopamine, are the hormones which are released by this gland, which we discussed.

Parathyroid Glands
These are located behind the thyroid gland, and that may be the reason they are known as parathyroid glands. They are there with the work of regulating the amount of calcium in the blood stream.

Pineal Gland
The function of this endocrine gland is to secrete melatonin. It is at the base of the brain, and is responsible for alertness or consciousness of one’s self.

Male gonads are known as the testes, and ovaries in case of females. These glands produce hormones and cells that are vital to reproduction, in males and females.

Hormones Produced by Endocrine Glands

Pituitary gland

  • Antidiuretic hormone (vasopressin) – Its primary function is to help the kidneys to retain water in the body.
  • Corticotropin (ACTH) – These hormones are there for regulating the hormones of the adrenal glands.
  • Human growth hormone – As the name suggests, it is associated with the growth and development of the body. It is also known to encourage the production of protein.
  • Luteinizing hormone and follicle-stimulating hormone – Important functions like the production of sperm and semen, and menstruation, are looked after by this particular hormone. Secondary sexual characteristics such as hair growth pattern, muscles, texture and thickness of the skin, nature of the voice, etc.
  • Oxytocin – Helps contraction of the uterus muscles and mammary ducts in the breast.
  • Prolactin – The process of milk production in the mammary glands is carried out by this hormone.
  • Thyroid-stimulating hormone – Again, as the name suggests, this hormone is responsible for the functions of the hormones of the thyroid gland.

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  • Thyroid hormone – The body’s metabolic rate is controlled by this hormone.
  • Calcitonin – It regulates calcium balance in species other than humans. Studies are still in progress to find its function in the human species.
  • Glucagon – The blood sugar level raises with its help.
  • Insulin – It helps in lowering the blood sugar level. Apart from this, metabolism of sugar, protein, and fat are also carried out with its help.
  • Aldosterone – Responsible for maintaining the salt and water balance in the body.
  • Cortisol – The functions which regulate the blood sugar level, blood pressure, and muscle strength in the body is controlled by the cortisol.
  • Dehydroepiandrosterone (DHEA) – It is related to the immune system, bones growth, and also to the mood of an individual.
  • Epinephrine and norepinephrine – The nervous system is associated with it.
  • Hormone-releasing hormone (GHRH) – It is known as the growth hormone.
  • Somatostatin – It works by regulating the endocrine system.
  • Dopamine – It inhibits the release of prolactin from the anterior lobe of the pituitary gland.
  • Parathyroid hormone – Calcium and phosphorus are eliminated from the body with the help of this hormone, which is also responsible for bone formation.
  • Melatonin – Maintains the body’s circadian rhythm, apart from what has been mentioned in the earlier segment.
  • Estrogen – The female sexual characteristics and the function of the reproductive system are influenced by the secretion of this hormone.
  • Progesterone – It plays vital roles in pregnancy. For instance, it helps in preparing the lining of the uterus for the fertilized egg to get implanted.
  • Testosterone – Men’s sexual characteristics and the nature of the reproductive system, involve the secretion of this hormone.

The endocrine system helps in keeping the body working optimally. Any malfunction in this system triggers the occurrence of bouts of medical condition and various unpleasant, mild to severe symptoms.

Study the Endocrine System, its Organs and its Functions

Endocrine glands are glands whose secretions (called hormones) are collected by the blood and reach tissues through circulation. The hypophysis (pituitary gland) and the adrenal glands are examples of endocrine glands. Exocrine glands are a glands whose secretions are released externally through ducts (into the skin, the intestinal lumen, the mouth, etc.). The sebaceous glands and the salivary glands are examples of exocrine glands.

Endocrine Glands and Hormones

More Bite-Sized Q&As Below

2. What are the components of the endocrine system?

The endocrine system is composed of the endocrine glands and the hormones they secrete.

3. What is the histological nature of glands? How are they formed?

Glands are epithelial tissue. They are made of epithelium that during the embryonic development invaginated into other tissues during embryonic development..

In exocrine glands, the invagination contains preserved secretion ducts. In endocrine glands, the invagination is complete and there are no secretion ducts.

4. Why is the endocrine system considered one of the integrative systems of the body? What other physiological system also has this function?

The endocrine system is considered to be of an integrative nature, since the hormones produced by endocrine glands are substances that act at a distance and many of them act in different organs of the body. therefore, endocrine glands receive information from certain regions of the body and can produce effects in other regions, providing functional integration for the body.

In addition to the endocrine system, the other physiological system that also has integrative function is the nervous system. The nervous system integrates the body through a network of nerves connected to central and peripheral neurons. The endocrine system integrates the body through hormones that travel through circulation.

5. What are hormones?

Hormones are substances secreted by endocrine glands and collected by circulation. They produce effects on specific organs and tissues.

Hormones are the effectors of the endocrine system.

6. What are the target organs of hormones?

Target organs, target tissues and target cells are the specific organs, tissues and cells on which each hormone acts and produces its effects. Hormones selectively act on their targets due to the specific receptor proteins present in these targets.

7. How does the circulatory system participate in the function of the endocrine system?

The circulatory system is fundamental for the functioning of the endocrine system. Blood collects hormones produced by endocrine glands and these hormones reach their targets through circulation. Without the circulatory system, the "action at distance" feature of the endocrine system would not be possible.

8. Are hormones only proteins?

Some hormones are proteins, such as insulin, glucagon and ADH, others are derived from proteins (modified amino acids), such as adrenaline and noradrenaline.  Others are steroids, such as corticosteroids and estrogen.

9. What are the main endocrine glands of the human body?

The main endocrine glands of the human body are the pineal gland (or pineal body), the hypophysis (or pituitary gland), the thyroid, the parathyroids, the endocrine part of the pancreas, the adrenal glands and the gonads (the testicles or ovaries).

Other organs such as the kidneys, the heart and the placenta also play a role in the endocrine system.

The Pineal Gland

10. What is the pineal gland?

The pineal gland, also known as the pineal body or epiphysis, is located in the center of the head. It secretes the hormone melatonin, a hormone produced at night and related to the regulation of circadian rhythm (or the circadian cycle, the wakefulness-sleep cycle). Melatonin may also regulate many body functions related to the night-day cycle.

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The Hypophysis

11. In which bone cavity is the pituitary gland located?

The pituitary gland, or hypophysis, is located in the sella turcica of the sphenoid bone (one of the bones at the base of the skull). Therefore, this gland is located within the head.

12. What are the main divisions of the hypophysis? What are their functions?

The hypophysis is divided into two portions: the adenohypophysis, or anterior hypophysis, and the neurohypophysis, or posterior hypophysis.

The adenohypophysis produces two hormones that act directly, growth hormone (GH) and prolactin. It also produces four tropic hormones, that is, hormones that regulate other endocrine glands: adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

The neurohypophysis stores and releases two hormones produced in the hypothalamus, oxytocin and antidiuretic hormone (ADH, or vasopressin).

13. What is the relationship between the hypothalamus and the hypophysis?

The hypothalamus is a part of the brain located just above the hypophysis. The hypothalamus receives peripheral and central neural impulses that trigger the response of its neurosecretory cells. The axons of these cells descend into the adenohypophysis to regulate hypophyseal secretions by means of negative feedback. When the levels of adenohypophyseal hormones in the plasma are too high, the hypothalamus detects this information and commands the stoppage of the production of the hormone. When the blood level of an adenohypophyseal hormone is low, the hypothalamus stimulates the secretion of the hormone.

Hypothalamic cells produce the hormones released by the neurohypophysis. These hormones are transported by their axons to the hypophysis and are then released into the circulation.

The Adenohypophysis

14. What hormones are secreted by the adenohypophysis? What are their respective functions?

The adenohypophysis secretes GH (growth hormone), prolactin, ACTH (adrenocorticotropic hormone), TSH (thyroid-stimulating hormone), FSH (follicle-stimulating hormone) and LH (luteinizing hormone).

GH, also known as somatotropic hormone (STH), acts on bones, cartilage and muscles to promote the growth of these tissues. Prolactin is the hormone that stimulates the production and secretion of milk by the mammary glands in women. ACTH is the hormone that stimulates the cortical portion of the adrenal gland to produce and secrete cortical hormones (glucocorticoids). TSH is the hormone that stimulates the activity of the thyroid gland, increasing the production and secretion of its hormones T3 and T4. FSH is a gonadotropic hormone, meaning that it stimulates the gonads and, in women, it acts on the ovaries to induce the growth of follicles and, in men, it stimulates spermatogenesis. LH is also a gonadotropic hormone it acts upon the ovaries of women to stimulate ovulation and the formation of the corpus luteum (which secretes estrogen) in men, it acts on the testicles to stimulate the production of testosterone.

15. What is the relationship between the thyroid and the hypophysis?

The hypophysis secretes TSH, thyroid-stimulating hormone. This hormone stimulates the secretion of thyroid hormones (triiodothyronine and thyroxine, or T3 and T4).

When the plasma concentration of thyroid hormones is high, this information is detected by the hypothalamus and the hypophysis, and the latter reduces the TSH secretion. When thyroid hormone levels are low, TSH secretion increases. This is therefore an example of negative feedback.

Injuries to the hypophysis that cause TSH hyposecretion (for example, in the case of tissue destruction) or hypersecretion (for example, excessive cell proliferation or cancer) can change the functioning of the thyroid gland completely.

16. What are some diseases caused by abnormal GH secretion by the hypophysis?

During childhood, GH secretion deficiencies may lead to delayed growth and in severe cases to nanism (dwarfism). Excessive production of GH in children may cause exaggerated bone growth and gigantism. In adults, excess GH (for example, in hypophyseal cancer or in people that wrongly mistakenly ingest GH as a nutritional supplement) may lead to acromegaly, which is excessive and disproportional growth of bone extremities, such as the skull, the maxillaries, the hands and the feet.

17. What are the target tissues and target organs of each adenohypophyseal hormone?

GH: bones, cartilage and muscles. Prolactin: the mammary glands. ACTH: the cortical portion of the adrenal glands. TSH: the thyroid gland. FSH and LH: the ovaries and testicles.


18. What hormones are secreted by the neurohypophysis? What are their respective functions?

The neurohypophysis secretes oxytocin and antidiuretic hormone (ADH).

Oxytocin is secreted in women during delivery to increase the strength and frequency of uterine contractions and therefore to help the baby’s birth. During the lactation period, the infant’s sucking action on the mother’s nipples stimulates the production of oxytocin, which then increases the secretion of milk by the mammary glands.

Vasopressin, or ADH, participates in the regulation of water in the body and therefore in the control of blood pressure, since it allows the reabsorption of free water through the renal tubules. As water goes back into circulation, the volume of blood increases.

19. What is the difference between diabetes mellitus and diabetes insipidus? What are the characteristic signs of diabetes insipidus?

Diabetes mellitus is the disease caused by deficient insulin secretion by the pancreas or by the impaired capture of this hormone by cells. Diabetes insipidus is the disease caused by deficient ADH secretion by the pituitary gland (hypophysis) or also by an impaired sensitivity to this hormone in the kidneys.

In diabetes insipidus, blood lacks ADH and, as a result, the reabsorption of water by the tubules in the kidneys is reduced, and a large volume of urine is produced. The patient urinates in large volumes and many times a day, a symptom which is also accompanied by polydipsia (increased thirst and an exaggerated ingestion of water) and sometimes by dehydration.

20. Why does the volume of urine increase when alcoholic beverages are ingested?

Alcohol inhibits ADH (antidiuretic hormone) secretion by the hypophysis. Low ADH reduces the tubular reabsorption of water in the kidneys and therefore urinary volume increases.

21. What are the target organs and target tissues of the neurohypophysis?

The target organs of oxytocin are the uterus and the mammary glands. The target organs of ADH are the kidneys.

The Thyroid Gland

22. Where in the body is the thyroid gland located?

The thyroid is located in the anterior cervical region (frontal neck), in front of the trachea and just below the larynx. It is a਋ilobed mass below the Adam’sਊpple.

23. What hormones are secreted by the thyroid gland? What are their functions?

The thyroid secretes the hormones thyroxine (T4), triiodothyronine (T3) and calcitonin.

T3 and T4 are iodinated substances derived from the amino acid tyrosine. They act to increase the cellular metabolic rate of the body (cellular respiration, metabolism of proteins and lipids, etc.). Calcitonin inhibits the release of calcium cations by bones, thus controlling the level of calcium in the blood.

24. Why is the ingestion of dietary iodine so important for thyroid function?

Obtaining iodine from your diet is important for the thyroid because this chemical element is necessary for the synthesis of the thyroid hormones T3 and T4. Iodine supply often comes from the diet.

25. What is goiter? What is endemic goiter? How is this problem socially solved?

Goiter is the abnormal enlargement of the thyroid gland. Goiter appears as a tumor in the anterior neck. It may or may not be visible but is often palpable. Goiter can occur as a result of hypothyroidism or hyperthyroidism.

Endemic goiter is goiter caused by a deficiency in iodine consumption (a deficiency of iodine in the diet). The endemic character of the disease is explained because dietary iodine is often a social or cultural condition affecting many people in certain geographical regions. The hypothyroidism caused by deficient iodine ingestion is more frequent in regions far from the coast (since sea food is rich in iodine).

Nowadays, the problem is often solved by the obligatory addition of iodine to table salt. As table salt is a widely used condiment, the supply of iodine in the diet is almost always assured by this method.

26. What happens to the level of TSH (thyroid-stimulating hormone) in the blood during hypothyroidism? Why is the thyroid enlarged in the endemic goiter?

When there is a low level of T3 and T4 secretion by the thyroid, TSH secretion by the hypophysis is very stimulated and the level of TSH in the blood level. The increase in the availability of TSH promotes the enlargement of the thyroid gland.

Thyroid enlargement is the reaction of a tissue that tries to compensate for the functional deficiency by making the gland increase in size.

27. What are some signs and symptoms found in patients with hyperthyroidism?

The hormones made by the thyroid gland stimulate the basal metabolism of the body. In hyperthyroidism, there is an abnormally high production and secretion of T3 and T4 and, as a result, the basal metabolic rate is increased. The signs of this condition may be tachycardia (an abnormally high heart rate), weight loss, excessive heat sensation, excessive sweating, anxiety, etc. One of the typical signs of hyperthyroidism is exophthalmos (protrusion of the eyeballs). Generally the patient also presents goiter.

28. What are some signs and symptoms found in patients with hypothyroidism?

In hypothyroidism, the production and secretion of T3 and T4 are impaired. Since these thyroid hormones stimulate the basal metabolism of the body (cellular respiration, fatty acid and protein metabolism, etc.), a patient with hypothyroidism may present bradycardia (a low heart rate), a low respiratory rate, excessive tiredness, depression, cold intolerance and weight gain. Hypothyroidism is normally accompanied by goiter (the enlargement of the thyroid in the neck).

29. What is the physiological cause of the syndrome known as cretinism?

Cretinism is caused by a chronic deficiency of thyroid hormones (T3 and T4) during childhood. Chronic hypothyroidism during childhood may cause retardation and a low stature due to the low basal metabolic rate during a period of life when growth and the development of mental faculty occur.


30. What are the parathyroids? Where are they located and what hormones are secreted by these glands?

The parathyroids are four small glands, two of which are embedded in each posterior face of one lobe of the thyroid. The parathyroids secrete parathormone, a hormone that, along with calcitonin and vitamin D, regulates calcium levels in the blood.

31. What is the relationship between the secretion of parathormone and the level of calcium in the blood?

Parathormone increases the level of calcium in the blood, since it stimulates the reabsorption (remodeling) of the bone tissue. When osteoclasts remodel bones, calcium is released in the circulation.

Parathormone is also involved in increasing calcium absorption in the intestines via vitamin D activation. It also plays a role in the kidneys, promoting the tubular reabsorption of calcium.

The Pancreas

32. What is a mixed gland? Why is the pancreas considered a mixed gland?

A mixed gland is a gland that produces endocrine and exocrine secretions.

The pancreas is an example of a mixed gland because it secretes hormones into circulation, such as insulin and glucagon, while also releasing an exocrine secretion, pancreatic juice.

33. What pancreatic tissues are involved in exocrine and endocrine secretions? What are their respective hormones and enzymes?

Exocrine secretions of the pancreas are produced in the pancreatic acini, aggregates of secretory cells that surround small exocrine ducts. The exocrine pancreas secretes the digestive enzymes of pancreatic juice: amylase, lipase, trypsin, chymotrypsin, carboxypeptidase, ribonuclease, deoxyribonuclease, elastase and gelatinase.

Endocrine secretions of the pancreas are produced and secreted by small groups of cells dispersed throughout the organ called islets of Langerhans. The pancreatic islets make insulin, glucagon and somatostatin.

Hormonal Glucose Regulation

34. What is the importance of blood glucose levels for human health?

Blood glucose levels (glycemia) must be maintained normal. If they are abnormally low, there will not be enough glucose to supply the energy metabolism of cells. If they are abnormally and chronically high, it causes severe harm to peripheral nerves, the skin, the retina, the kidneys and other important organs, and may predispose the person to cardiovascular diseases (acute myocardial infarction, strokes, thrombosis, etc). If they are acutely in excess, medical emergencies such as diabetic ketoacidosis and a hyperglycemic hyperosmolar state may occur.

35. How are insulin and glucagon involved in blood glucose control?

Glucagon increases glycemia and insulin reduces it. They are antagonistic pancreatic hormones. Glucagon stimulates glycogenolysis, thus forming glucose from the breakdown of glycogen. Insulin is the hormone responsible for the entrance of glucose from blood into cells.

When glycemia is low, for example, during fasting, glucagon is secreted and insulin is inhibited. When glycemia is high, like after meals, glucagon is inhibited and insulin secretion is increased.

36. What are the target organs of insulin and glucagon?

Glucagon mainly acts on the liver. In general, insulin acts on all cells. Both also act on the adipose tissue, stimulating (glucagon) and inhibiting (insulin) the use of fatty acids by the energy metabolism (an alternate path of energy metabolism is activated when there is a shortage of glucose).

37. What are the effects of somatostatin on pancreatic hormonal secretions?

Somatostatin inhibits both insulin and glucagon secretions.

Diabetes Mellitus Explained

38. What is diabetes mellitus?

Diabetes mellitus is the disease caused by the deficient production or action of insulin and, as a result, characterized by a low glucose uptake by cells and a high blood glucose level.

39. What are the three main signs of diabetes?

The three main signs of diabetes mellitus are known as the diabetic triad: polyuria, polydipsia and polyphagia.

Polyuria is the excessive elimination of urine in diabetes, it is caused by reduced water reabsorption in the renal tubules due to the increased osmolarity of glomerular filtrate (caused by excessive glucose). Polydipsia is the exaggerated ingestion of water the thirst is due to excessive water loss in the urine. Polyphagia is the exaggerated ingestion of food caused by a deficiency in energy generation by glucose-deficient cells.

40. Why do diabetic patients often undergo dietary sugar restriction? What are the main complications of diabetes mellitus?

Diabetic patients are often advised to ingest less carbohydrates since these substances are broken down into glucose and this molecule is absorbed in the intestines. The goal of dietary sugar restriction is to control glycemia and to maintain it at normal levels.

The main complications of diabetes are tissue injuries that occur in various organs caused by chronic high blood osmolarity: in the peripheral nerves (diabetic neuropathy), resulting in sensitivity loss, increased wounds (the person does not feel that the tissue is being wounded and the wound expands) and muscle fatigue in the kidneys (diabetic nephropathy), causing glomerular lesions that may lead to renal failure in the retina (diabetic retinopathy), leading to vision impairment and blindness and in the skin, as a consequence of the neuropathy. Diabetes mellitus is also one of the major risk factors for cardiovascular diseases such as embolism, myocardial infarction and stroke.

41. What is the difference between type I diabetes mellitus and type II diabetes mellitus?

Type I diabetes, also known as juvenile diabetes, or insulin-dependent diabetes (this name is not adequate, since type II diabetes may become insulin-dependent), is the impaired production of insulin by the pancreas, and is believed to be caused by the destruction of the cells of the islets of Langerhans by autoantibodies (autoimmunity).

Type II diabetes occurs adults and it is often diagnosed in older people. In type II diabetes, the pancreas secretes normal or low levels of insulin,਋ut the main cause of the high glycemia is the peripheral resistance of the cells to the action of the hormone.

42. In ancient Greece, the father of Medicine, Hippocrates, described a method of diagnosing diabetes mellitus by tasting the patient's urine. What is the physiological explanation for this archaic method?

Under normal conditions, the glucose filtered by renal glomeruli is almost entirely reabsorbed in the nephron tubules and is not excreted in urine. With elevated blood glucose levels, the renal tubules cannot reabsorb all the filtered glucose and a certain amount of the substance appears in the urine. This amount is enough to provide the sweet taste that helped Hippocrates diagnose diabetes and differentiate it from other diseases򠫌ompanied by polyuria. Nowadays,  this method is not used due to the danger of contaminating the tester with disease agents possibly present in the patient's urine.

43. What are the main treatments for diabetes mellitus?

The general goal of diabetes treatment is to maintain normal glycemic levels.

Type I diabetes is treated with the parenteral administration of insulin. Insulin must be administered intravenously or intramuscularly because, as a protein, it will be digested if ingested orally. In type II diabetes, treatment is done with oral drugs that regulate glucose metabolism or, in more severe cases, with parenteral insulin administration. The moderation of carbohydrate ingestion is an important aid in diabetes treatment.

Diabetes treatment with the use of hypoglycemic agents, such as insulin or oral medicines, must be carefully and medically supervised, since if wrongly used, these drugs may abruptly decrease the blood glucose levels, causing hypoglycemia and even death.

Many other forms of diabetes treatment are being researched worldwide.

44. How can bacteria produce human insulin on an industrial scale? What are other forms of insulin are made available by the pharmaceutical industry?

Bacteria do not naturally synthesize insulin. However, it is possible to implant human genetic material containing the insulin gene into bacterial DNA. The mutant bacteria then multiply and produce human insulin. The insulin is isolated and purified for subsequent sale. This biotechnology is known as recombinant DNA technology.

In addition to human insulin, the pharmaceutical industry also produces insulin to be used by humans made from the pancreas of pigs and cows.

The Adrenal Glands

45. Where are the adrenal glands located? How many are there and into which parts are they divided?

Each adrenal gland is located on the top of each kidney (forming a hat-like structure on the top of the kidneys) therefore, there are two glands. The adrenal parenchymal structure is divided into two parts: the most outlying part is the cortical portion, or the adrenal cortex, and the central part is the medullary portion, or the adrenal medulla.

The Endocrine System Review - Image Diversity: the adrenal glands

46. What hormones are secreted by the adrenal medulla? What are their respective functions?

The medullary portion of the adrenal glands secretes hormones of the catecholamine group: adrenaline (also known as epinephrine) and noradrenaline (also known as norepinephrine). Besides their hormonal function, adrenaline and noradrenaline also act as neurotransmitters. The neurons that use them as neurotransmitters are called adrenergic neurons.

Adrenaline increases the breakdown of glycogen into glucose (glycogenolysis), thus increasing glycemia and the basal metabolic rate of the body. Adrenaline and noradrenaline are released during situations of danger (fight or flight response) and they intensify the strength and rate of the heartbeat and selectively modulate blood irrigation in some tissues via selective vasodilation and vasoconstriction. Through vasodilation, they increase the supply of blood to the brain, the muscles and the heart and, through vasoconstriction, they reduce the supply of blood to the kidneys, the skin and the gastrointestinal tract.

Substances that promote vasodilation or vasoconstriction, such as adrenaline and noradrenaline, are called vasoactive substances.

47. What hormones are secreted by the adrenal cortex? What are their respective functions?

The cortical portion of the adrenal glands secretes hormones of the corticoid (or corticosteroid) group, which are derived from cholesterol: glucocorticoids, mineralocorticoids and cortical sex hormones.

The glucocorticoids secreted are cortisol and cortisone. Glucocorticoids stimulate the formation of glucose from the degradation of proteins of muscle tissue (gluconeogenesis) and, as a result, help to increase glycemia. These hormones play an important immunosuppressive role, meaning that they reduce the action of the immune system and for this reason are used as medicine to treat inflammatory and autoimmune diseases and the rejection of transplanted organs.

The mineralocorticoids aldosterone and deoxycorticosterone regulate the concentration of sodium and potassium in the blood and, as a result, control the water level in the extracellular space. Aldosterone increases sodium reabsorption and therefore water reabsorption in the renal tubules, and also stimulates the renal excretion of potassium and hydrogen.

The adrenal cortical sex hormones are androgens, male sex hormones present in both men and women. In men, their main site of production is the testicle and they promote the appearance of secondary male sex characteristics, such as body hair and a beard, a deep voice, the male pattern of fat distribution and the maturation of the genitalia. If abnormally high in women, they cause an inhibited maturation of the female genitalia and disturbances in the menstrual cycle.

48. Why are glucocorticoids used in transplant patients?

Patients with transplanted organs are prone to host versus graft rejection, since their own immune system tends to attack the grafted organ because it recognizes the grafted tissue as foreign material. In the prevention and treatment of this common problem, patients are given glucocorticoids or other immunosuppressants. Glucocorticoids have an immunosuppressant�t and, as a result, reduce the aggression of the immune system against the graft.

However, immune action is also very important for the individual. The immune system defends the body against invasion and infection by pathogenic agents (viruses, bacteria, toxins) in addition to being necessary for the elimination of modified cells that may proliferate and cause cancer. Patients receiving immunosuppressants such as glucocorticoids therefore have an increased risk of infectious and neoplastic diseases.

Reproductive Hormones

49. What hormones are produced by the testicles and the ovaries?

The testicles produce androgenic hormones, the main hormone of which is testosterone. The ovaries produce estrogen and progesterone.

50. What is the endocrine function of the placenta?

The placenta is not a permanent gland of the endocrine system but it nonetheless has an endocrine function. The placenta produces estrogen and progesterone. It also secretes human chorionic gonadotropin (HCG, which has a function similar to that of hypophyseal LH), human placental lactogen, similar to prolactin and a mammary gland stimulant, and a series of hormonal peptides similar to the hormones of the hypothalamus-hypophysis axis.

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Lymphatic System

The lymphatic system is sometimes considered part of the immune system. It consists of a network of lymph vessels and ducts that collect excess fluid (called lymph) from extracellular spaces in tissues and transport the fluid to the bloodstream. The lymphatic system also includes many small collections of tissue, (called lymph nodes) and an organ called the spleen, both of which remove pathogens and cellular debris from the lymph or blood. In addition, the thymus gland in the lymphatic system produces some types of white blood cells (lymphocytes) that fight infections.

The Body’s Chemicals Help Control Behavior: The Endocrine System

The nervous system is designed to protect us from danger through its interpretation of and reactions to stimuli. But a primary function of the sympathetic and parasympathetic nervous systems is to interact with the endocrine system to elicit chemicals that provide another system for influencing our feelings and behaviors.

A gland in the endocrine system is made up of groups of cells that function to secrete hormones. A hormone is a chemical that moves throughout the body to help regulate emotions and behaviors. When the hormones released by one gland arrive at receptor tissues or other glands, these receiving receptors may trigger the release of other hormones, resulting in a series of complex chemical chain reactions. The endocrine system works together with the nervous system to influence many aspects of human behavior, including growth, reproduction, and metabolism. And the endocrine system plays a vital role in emotions. Because the glands in men and women differ, hormones also help explain some of the observed behavioral differences between men and women. The major glands in the endocrine system are shown in Figure 3.20 “The Major Glands of the Endocrine System”.

Figure 3.20 The Major Glands of the Endocrine System

The male is shown on the left and the female on the right.

The pituitary gland , a small pea-sized gland located near the center of the brain, is responsible for controlling the body’s growth, but it also has many other influences that make it of primary importance to regulating behavior. The pituitary secretes hormones that influence our responses to pain as well as hormones that signal the ovaries and testes to make sex hormones. The pituitary gland also controls ovulation and the menstrual cycle in women. Because the pituitary has such an important influence on other glands, it is sometimes known as the “master gland.”

Other glands in the endocrine system include the pancreas, which secretes hormones designed to keep the body supplied with fuel to produce and maintain stores of energy the pineal gland, located in the middle of the brain, which secretes melatonin, a hormone that helps regulate the wake-sleep cycle and the thyroid and parathyroid glands, which are responsible for determining how quickly the body uses energy and hormones, and controlling the amount of calcium in the blood and bones.

The body has two triangular adrenal glands, one atop each kidney. The adrenal glands produce hormones that regulate salt and water balance in the body, and they are involved in metabolism, the immune system, and sexual development and function. The most important function of the adrenal glands is to secrete the hormones epinephrine (also known as adrenaline) and norepinephrine (also known as noradrenaline) when we are excited, threatened, or stressed. Epinephrine and norepinephrine stimulate the sympathetic division of the ANS, causing increased heart and lung activity, dilation of the pupils, and increases in blood sugar, which give the body a surge of energy to respond to a threat. The activity and role of the adrenal glands in response to stress provides an excellent example of the close relationship and interdependency of the nervous and endocrine systems. A quick-acting nervous system is essential for immediate activation of the adrenal glands, while the endocrine system mobilizes the body for action.

The male sex glands, known as the testes , secrete a number of hormones, the most important of which is testosterone , the male sex hormone. Testosterone regulates body changes associated with sexual development, including enlargement of the penis, deepening of the voice, growth of facial and pubic hair, and the increase in muscle growth and strength. The ovaries , the female sex glands, are located in the pelvis. They produce eggs and secrete the female hormones estrogen and progesterone. Estrogen is involved in the development of female sexual features, including breast growth, the accumulation of body fat around the hips and thighs, and the growth spurt that occurs during puberty. Both estrogen and progesterone are also involved in pregnancy and the regulation of the menstrual cycle.

Recent research has pinpointed some of the important roles of the sex hormones in social behavior. Dabbs, Hargrove, and Heusel (1996) measured the testosterone levels of 240 men who were members of 12 fraternities at two universities. They also obtained descriptions of the fraternities from university officials, fraternity officers, yearbook and chapter house photographs, and researcher field notes. The researchers correlated the testosterone levels and the descriptions of each fraternity. They found that the fraternities with the highest average testosterone levels were also more wild and unruly, and one of these fraternities was known across campus for the crudeness of its behavior. On the other hand, the fraternities with the lowest average testosterone levels were more well behaved, friendly and pleasant, academically successful, and socially responsible. Banks and Dabbs (1996) found that juvenile delinquents and prisoners who had high levels of testosterone also acted more violently, and Tremblay et al. (1998) found that testosterone was related to toughness and leadership behaviors in adolescent boys. Although testosterone levels are higher in men than in women, the relationship between testosterone and aggression is not limited to males. Studies have also shown a positive relationship between testosterone and aggression and related behaviors (such as competitiveness) in women (Cashdan, 2003).

It must be kept in mind that the observed relationships between testosterone levels and aggressive behavior that have been found in these studies do not prove that testosterone causes aggression—the relationships are only correlational. In fact, there is evidence that the relationship between violence and testosterone also goes in the other direction: Playing an aggressive game, such as tennis or even chess, increases the testosterone levels of the winners and decreases the testosterone levels of losers (Gladue, Boechler, & McCaul, 1989 Mazur, Booth, & Dabbs, 1992), and perhaps this is why excited soccer fans sometimes riot when their team wins.

Recent research has also begun to document the role that female sex hormones may play in reactions to others. A study about hormonal influences on social-cognitive functioning (Macrae, Alnwick, Milne, & Schloerscheidt, 2002) found that women were more easily able to perceive and categorize male faces during the more fertile phases of their menstrual cycles. Although researchers did not directly measure the presence of hormones, it is likely that phase-specific hormonal differences influenced the women’s perceptions.

At this point you can begin to see the important role the hormones play in behavior. But the hormones we have reviewed in this section represent only a subset of the many influences that hormones have on our behaviors. In the chapters to come we will consider the important roles that hormones play in many other behaviors, including sleeping, sexual activity, and helping and harming others.

Key Takeaways

  • The body uses both electrical and chemical systems to create homeostasis.
  • The CNS is made up of bundles of nerves that carry messages to and from the PNS
  • The peripheral nervous system is composed of the autonomic nervous system (ANS) and the peripheral nervous system (PNS). The ANS is further divided into the sympathetic (activating) and parasympathetic (calming) nervous systems. These divisions are activated by glands and organs in the endocrine system.
  • Specific nerves, including sensory neurons, motor neurons, and interneurons, each have specific functions.
  • The spinal cord may bypass the brain by responding rapidly using reflexes.
  • The pituitary gland is a master gland, affecting many other glands.
  • Hormones produced by the pituitary and adrenal glands regulate growth, stress, sexual functions, and chemical balance in the body.
  • The adrenal glands produce epinephrine and norepinephrine, the hormones responsible for our reactions to stress.
  • The sex hormones, testosterone, estrogen, and progesterone, play an important role in sex differences.

Exercises and Critical Thinking

  1. Recall a time when you were threatened or stressed. What physiological reactions did you experience in the situation, and what aspects of the endocrine system do you think created those reactions?
  2. Consider the emotions that you have experienced over the past several weeks. What hormones do you think might have been involved in creating those emotions?

Human Organs

An organ is a collection of tissues joined in a structural unit to serve a common function. Organs exist in most multicellular organisms, including not only humans and other animals but also plants. In single-celled organisms such as bacteria, the functional equivalent of an organ is an organelle.

Tissues in Organs

Although organs consist of multiple tissue types, many organs are composed of the main tissue that is associated with the organ&rsquos major function and other tissues that play supporting roles. The main tissue may be unique to that specific organ. For example, the main tissue of the heart is the cardiac muscle, which performs the heart&rsquos major function of pumping blood and is found only in the heart. The heart also includes nervous and connective tissues that are required for it to perform its major function. For example, nervous tissues control the beating of the heart, and connective tissues make up heart valves that keep blood flowing in just one direction through the heart.

Vital Organs

The human body contains five organs that are considered vital for survival. They are the heart, brain, kidneys, liver, and lungs. The locations of these five organs and several other internal organs are shown in Figure (PageIndex<2>). If any of the five vital organs stops functioning, the death of the organism is imminent without medical intervention.

  1. The heart is located in the center of the chest, and its function is to keep blood flowing through the body. Blood carries substances to cells that they need and also carries away wastes from cells.
  2. The brain is located in the head and functions as the body&rsquos control center. It is the seat of all thoughts, memories, perceptions, and feelings.
  3. The two kidneys are located in the back of the abdomen on either side of the body. Their function is to filter blood and form urine, which is excreted from the body.
  4. The liver is located on the right side of the abdomen. It has many functions, including filtering blood, secreting bile that is needed for digestion, and producing proteins necessary for blood clotting.
  5. The two lungs are located on either side of the upper chest. Their main function is exchanging oxygen and carbon dioxide with the blood.

Critical Thinking Questions

Describe several main differences in the communication methods used by the endocrine system and the nervous system.

Compare and contrast endocrine and exocrine glands.

True or false: Neurotransmitters are a special class of paracrines. Explain your answer.

Compare and contrast the signaling events involved with the second messengers cAMP and IP3.

Describe the mechanism of hormone response resulting from the binding of a hormone with an intracellular receptor.

Compare and contrast the anatomical relationship of the anterior and posterior lobes of the pituitary gland to the hypothalamus.

Name the target tissues for prolactin.

Explain why maternal iodine deficiency might lead to neurological impairment in the fetus.

Define hyperthyroidism and explain why one of its symptoms is weight loss.

Describe the role of negative feedback in the function of the parathyroid gland.

Explain why someone with a parathyroid gland tumor might develop kidney stones.

What are the three regions of the adrenal cortex and what hormones do they produce?

If innervation to the adrenal medulla were disrupted, what would be the physiological outcome?

Compare and contrast the short-term and long-term stress response.

Seasonal affective disorder (SAD) is a mood disorder characterized by, among other symptoms, increased appetite, sluggishness, and increased sleepiness. It occurs most commonly during the winter months, especially in regions with long winter nights. Propose a role for melatonin in SAD and a possible non-drug therapy.

Retinitis pigmentosa (RP) is a disease that causes deterioration of the retinas of the eyes. Describe the impact RP would have on melatonin levels.

Compare and contrast the role of estrogens and progesterone.

Describe the role of placental secretion of relaxin in preparation for childbirth.

What would be the physiological consequence of a disease that destroyed the beta cells of the pancreas?

Why is foot care extremely important for people with diabetes mellitus?

Summarize the role of GI tract hormones following a meal.

Compare and contrast the thymus gland in infancy and adulthood.

Distinguish between the effects of menopause and andropause on fertility.