Endocrine System

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Environmental Signals: Redefinition of Hormone. Between same species at distance: pheromonesBetween body parts, some distance: hormonesBetween cells: neurotransmitters, prostaglandins, histamine. A hormone is any chemical that acts as a messenger between individual organisms, between organs wit

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Endocrine System

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1. Endocrine System

2. Environmental Signals: Redefinition of Hormone Between same species at distance: pheromones Between body parts, some distance: hormones Between cells: neurotransmitters, prostaglandins, histamine Hormones subject of most of the lecture. Neurotransmitters in nervous system, histamine was in immune system, prostaglandins. Prostaglandins act locally, are very powerful. They act locally and have many functions, too numerous and complicated for this course—but interesting!Hormones subject of most of the lecture. Neurotransmitters in nervous system, histamine was in immune system, prostaglandins. Prostaglandins act locally, are very powerful. They act locally and have many functions, too numerous and complicated for this course—but interesting!

3. Endocrine System Homeostatic functions Whole body processes Associated organs Hypothalamus, Pituitary, Pineal gland, Thyroid, Thymus, Heart, Stomach, Pancreas, Adrenal glands, Kidneys, Intestines, Gonads The endocrine system acts along with the nervous system to coordinate the various activities of the body. It uses the cardiovascular system for transport. Both the endocrine and nervous systems use chemical messengers to coordinate body actions, the nervous system uses neurotransmitters and the endocrine system uses hormones The endocrine system acts along with the nervous system to coordinate the various activities of the body. It uses the cardiovascular system for transport. Both the endocrine and nervous systems use chemical messengers to coordinate body actions, the nervous system uses neurotransmitters and the endocrine system uses hormones

4. Characteristics Access through blood stream to almost all cells A particular hormone will act only on certain cells

5. Hormones: Signals Pheromones, hormones, paracrine hormones Chemical messenger produced in one part of the body that controls the activity of other parts Steroid Non-steroid Targets Each hormone has a specific target Environmental signals include at least 3 different categories of messengers. 1. Environmental signals may act at a distance between individuals, using chemicals called pheromones to allow communication between members of the same species. Insects use these chemicals in ant trails or moth sexual attractants. Invertebrate endocrine systems contain hormones produced only by specialized neurons called neurosecretory cells. Neurosecretory cells are capable of making and secreting hormones, discharging them directly into the blood. Neurosecretions have been particularly studied in insects. Insects undergo a series of larval stages with several molts before they pupate. The brain is necessary for maturation to occur, since it produces brain hormone. Dog urine contains pheromones used to mark territories. Studies are being done to determine if humans have pheromones. 2. Environmental signals may act at a distance between body parts of the same individual. These include the endocrine secretions that have been traditionally referred to as hormones. They also include the secretions of neurosecretory cells of the hypothalamus, endorphins, and norepinephrine released by the adrenal medulla. 3. Environmental signals may also act locally between adjacent cells. Neurotransmitters belong in this category.  Prostaglandins are sometimes referred to as local hormones. Histamine release when skin is cut is involved in promotion of the inflammatory response. Redefinition of a hormone has broadened it to include all types of chemical messengers, needed because hormones are actually produced in many more tissues than previously thought, as insulin production within the brain, and are even found in bacteria. Hormones are typically released directly into the bloodstream. The endocrine system acts mores slowly because hormones have to travel through the blood to reach a target organ. Cells of the target organ contain receptors that bind only to specific kinds of hormones in a lock-and-key fashion. (sound familiar?) Hormones may have different functions in different species or may be species specific and only functional in a particular species.Environmental signals include at least 3 different categories of messengers. 1. Environmental signals may act at a distance between individuals, using chemicals called pheromones to allow communication between members of the same species. Insects use these chemicals in ant trails or moth sexual attractants. Invertebrate endocrine systems contain hormones produced only by specialized neurons called neurosecretory cells. Neurosecretory cells are capable of making and secreting hormones, discharging them directly into the blood. Neurosecretions have been particularly studied in insects. Insects undergo a series of larval stages with several molts before they pupate. The brain is necessary for maturation to occur, since it produces brain hormone. Dog urine contains pheromones used to mark territories. Studies are being done to determine if humans have pheromones. 2. Environmental signals may act at a distance between body parts of the same individual. These include the endocrine secretions that have been traditionally referred to as hormones. They also include the secretions of neurosecretory cells of the hypothalamus, endorphins, and norepinephrine released by the adrenal medulla. 3. Environmental signals may also act locally between adjacent cells. Neurotransmitters belong in this category.  Prostaglandins are sometimes referred to as local hormones. Histamine release when skin is cut is involved in promotion of the inflammatory response. Redefinition of a hormone has broadened it to include all types of chemical messengers, needed because hormones are actually produced in many more tissues than previously thought, as insulin production within the brain, and are even found in bacteria. Hormones are typically released directly into the bloodstream. The endocrine system acts mores slowly because hormones have to travel through the blood to reach a target organ. Cells of the target organ contain receptors that bind only to specific kinds of hormones in a lock-and-key fashion. (sound familiar?) Hormones may have different functions in different species or may be species specific and only functional in a particular species.

6. Steroid Hormones Lipids No receptor Cross plasma membrane Production of new protein Ex: Progesterone Testosterone Check against Fig 13.2 pg. 285. Steroid hormones enter the cell freely, rather than binding to cell-surface receptors. Reproductive hormones, estrogen and progesterone, enter the cells of the reproductive organs and bind to receptors in the cytoplasm. Hormone-receptor complexes then enter the nucleus, where they bind to chromatin at a location that activates a particular set of genes. Steroid hormones act more slowly than peptide hormones because of the time required to produce new proteins as opposed to just activating proteins already in the cell. Steroids also have a more prolonged effect on the metabolism of the cell than do peptide hormones.Check against Fig 13.2 pg. 285. Steroid hormones enter the cell freely, rather than binding to cell-surface receptors. Reproductive hormones, estrogen and progesterone, enter the cells of the reproductive organs and bind to receptors in the cytoplasm. Hormone-receptor complexes then enter the nucleus, where they bind to chromatin at a location that activates a particular set of genes. Steroid hormones act more slowly than peptide hormones because of the time required to produce new proteins as opposed to just activating proteins already in the cell. Steroids also have a more prolonged effect on the metabolism of the cell than do peptide hormones.

7. Non-Steroid Hormones Receptor to cross plasma membrane Hormone is first messenger cAMP as the second messenger (also calcium) Enzyme cascade Check against Fig. 13.3 pg. 286. Peptide hormones include epinephrine, for which the effects were recognized by Earl W. Sutherland in the 1950s, winning him a Nobel Prize. Epinephrine binds to a cell-surface receptor, causing a chain reaction that involves ATP, cAMP, and sometimes calcium. The enzyme cascade can cause 1,000fold response. It is faster than the steroid response, but not as long lasting. Used for homeostatic controls that need to be quick (blood glucose level).Check against Fig. 13.3 pg. 286. Peptide hormones include epinephrine, for which the effects were recognized by Earl W. Sutherland in the 1950s, winning him a Nobel Prize. Epinephrine binds to a cell-surface receptor, causing a chain reaction that involves ATP, cAMP, and sometimes calcium. The enzyme cascade can cause 1,000fold response. It is faster than the steroid response, but not as long lasting. Used for homeostatic controls that need to be quick (blood glucose level).

8. Control of Hormonal Secretion: Negative Feedback Loops Check against Fig. 13.4 pg. 287. The hypothalamus is the part of the brain that regulates the internal environment, including heart rate, body temperature, water balance, and the secretions of the pituitary gland, located just under the hypothalamus. It sends out releasing hormones, which cause the pituitary to release stimulating hormones, which cause the target organ to release a homeostatic hormone. Negative feedback (shown) means that the hormone released stops production of the releasing or stimulating hormone. There is also production of antagonistic hormones at the target glands. These have opposite actions on homeostasis. An example of this type of control is the calcitonin/parathyroid hormone interaction which will be discussed later.Check against Fig. 13.4 pg. 287. The hypothalamus is the part of the brain that regulates the internal environment, including heart rate, body temperature, water balance, and the secretions of the pituitary gland, located just under the hypothalamus. It sends out releasing hormones, which cause the pituitary to release stimulating hormones, which cause the target organ to release a homeostatic hormone. Negative feedback (shown) means that the hormone released stops production of the releasing or stimulating hormone. There is also production of antagonistic hormones at the target glands. These have opposite actions on homeostasis. An example of this type of control is the calcitonin/parathyroid hormone interaction which will be discussed later.

9. Hypothalamus and Pituitary The posterior pituitary (neurohypophysis) is connected to the hypothalamus by a stalk-like structure, across which extends the neurosecretory cells (neurons) of the hypothalamus. These are cells that respond to neurotransmitters. They also produce hormones and release them in the posterior lobe of the pituitary. Antidiuretic hormone (ADH), also called vasopressin, is released in this way and controls the reabsorption of water from the collecting duct of the kidney nephron. Oxytocin is another hormone produced by the hypothalamus cells and released from within the posterior lobe of the pituitary; it is important in uterine contractions of labor and in stimulating the release of milk from the mammary glands of a nursing mother. Oxytocin is given to women to induce labor when they are over due or are having an abortion. Anterior pituitary:3 hormones don’t affect other endocrine glands (GH, PRL, and MSH). 4 hormones have target organs. The anterior pituitary produces and releases several other hormones that are controlled by the actions of hormones produced by the hypothalamus. A portal system of blood vessels connects the hypothalamus and the anterior pituitary capillary beds. A set of neurosecretory cells in the hypothalamus produces several hypothalamic-releasing hormones that pass by way of the portal system to the anterior pituitary system, where cells are stimulated to release pituitary hormones. At least 6 different types of hormones are produced and released by the anterior pituitary lobe, each produced by a distinct cell type.The posterior pituitary (neurohypophysis) is connected to the hypothalamus by a stalk-like structure, across which extends the neurosecretory cells (neurons) of the hypothalamus. These are cells that respond to neurotransmitters. They also produce hormones and release them in the posterior lobe of the pituitary. Antidiuretic hormone (ADH), also called vasopressin, is released in this way and controls the reabsorption of water from the collecting duct of the kidney nephron. Oxytocin is another hormone produced by the hypothalamus cells and released from within the posterior lobe of the pituitary; it is important in uterine contractions of labor and in stimulating the release of milk from the mammary glands of a nursing mother. Oxytocin is given to women to induce labor when they are over due or are having an abortion. Anterior pituitary:3 hormones don’t affect other endocrine glands (GH, PRL, and MSH). 4 hormones have target organs. The anterior pituitary produces and releases several other hormones that are controlled by the actions of hormones produced by the hypothalamus. A portal system of blood vessels connects the hypothalamus and the anterior pituitary capillary beds. A set of neurosecretory cells in the hypothalamus produces several hypothalamic-releasing hormones that pass by way of the portal system to the anterior pituitary system, where cells are stimulated to release pituitary hormones. At least 6 different types of hormones are produced and released by the anterior pituitary lobe, each produced by a distinct cell type.

10. Pg. 287.Pg. 287.

11. Antidiuretic Hormone (ADH) Function: water balance Target cells: kidney collecting ducts Stimulates reabsorption of water Fig. 13.5 pg. 288. SIADH is syndrome of inappropriate ADH secretion. With SIADH, too much water is retained. With diabetes insipidus, either lack of ADH or lack of receptors in the kidneys causes too much water to be released. People with this disease need to drink huge amounts of water.Fig. 13.5 pg. 288. SIADH is syndrome of inappropriate ADH secretion. With SIADH, too much water is retained. With diabetes insipidus, either lack of ADH or lack of receptors in the kidneys causes too much water to be released. People with this disease need to drink huge amounts of water.

12. Oxytocin Function: contraction of the uterus, milk ejection, sexual arousal Target cells: smooth muscle cells Fig. 13.6 pg 289. Oxytocin is also present in males, and is implicated in smooth muscle responses in arousal and orgasm. The neuroendocrine reflex is the somatic sensory stimulation of the neurons, causing release of oxytocin into the blood stream.Fig. 13.6 pg 289. Oxytocin is also present in males, and is implicated in smooth muscle responses in arousal and orgasm. The neuroendocrine reflex is the somatic sensory stimulation of the neurons, causing release of oxytocin into the blood stream.

13. Adrenocorticotropin (ACTH) “Fight or flight” blood volume & pressure blood glucose level The adrenal glands are located atop each kidney, with an inner region called the medulla and an outer region called the cortex. The adrenal medulla secretes epinephrine (adrenalin) and norepinephrine (noradrenalin) under conditions of stress. This produces the ``fight or flight'' responses that are initiated by the sympathetic nervous system and sustained by the secretions of the adrenal medulla. The adrenal cortex is absolutely necessary for life, while the adrenal medulla is not. Two classes of hormones are produced by the adrenal cortex: the glucocorticoids (regulate carbohydrate, protein, and fat metabolism; increase blood glucose level) and the mineralocorticoids (regulate salt and water balance; increase blood pressure & volume). The stimulation for mineralocorticoid’s release does NOT come from the hypothalamus (next slide). The cortex also produces a small amount of the steroid sex hormones of the male and a smaller amount of the female sex hormones. Cortisol is the glucocorticoid hormone with the greatest activity, promoting the breakdown of muscle protein to amino acids, thus increasing the blood glucose level. Cortisol opposes insulin and raises blood glucose levels. It also counters the inflammation response and reduces the pain and swelling of arthritis and bursitis. Aldosterone is the most significant of the mineralcorticoids. Aldosterone regulates the levels of sodium and potassium ions in the blood, acting primarily on the kidney to promote renal absorption of sodium and renal excretion of potassium.The adrenal glands are located atop each kidney, with an inner region called the medulla and an outer region called the cortex. The adrenal medulla secretes epinephrine (adrenalin) and norepinephrine (noradrenalin) under conditions of stress. This produces the ``fight or flight'' responses that are initiated by the sympathetic nervous system and sustained by the secretions of the adrenal medulla. The adrenal cortex is absolutely necessary for life, while the adrenal medulla is not. Two classes of hormones are produced by the adrenal cortex: the glucocorticoids (regulate carbohydrate, protein, and fat metabolism; increase blood glucose level) and the mineralocorticoids (regulate salt and water balance; increase blood pressure & volume). The stimulation for mineralocorticoid’s release does NOT come from the hypothalamus (next slide). The cortex also produces a small amount of the steroid sex hormones of the male and a smaller amount of the female sex hormones. Cortisol is the glucocorticoid hormone with the greatest activity, promoting the breakdown of muscle protein to amino acids, thus increasing the blood glucose level. Cortisol opposes insulin and raises blood glucose levels. It also counters the inflammation response and reduces the pain and swelling of arthritis and bursitis. Aldosterone is the most significant of the mineralcorticoids. Aldosterone regulates the levels of sodium and potassium ions in the blood, acting primarily on the kidney to promote renal absorption of sodium and renal excretion of potassium.

14. Thyroid Stimulating Hormone (TSH) Control of metabolism The thyroid gland is large and located in the neck, attached to the trachea below the larynx, where it produces hormones containing iodine. Triiodothyronine (T3) with 3 atoms of iodine. Thyroxin (T4) contains 4 atoms of iodine. Thyroxin is secreted in the greatest quantity of all the hormones produced by the thyroid gland. Iodine is actively transported into the thyroid for use in producing these hormones. When iodine is lacking in the body, a goiter forms as the thyroid enlarges in an effort to produce the necessary hormones. A low level of thyroxin in the blood stimulates release of TSH from the anterior pituitary, producing more thyroid tissue. This can be avoided by use of iodized salt. Thyroxin is necessary in vertebrates for proper growth and development. Thyroxine increases the number and activity of mitochondria in cells by binding to the cells’ DNA, increasing the basal metabolic rate. Administration of thyroid hormones, such as thyroxine, causes an increase in the rate of carbohydrate metabolism and a rise in the rate of protein synthesis and breakdown. The hormone, which excites the nervous system and leads to increased activity of the endocrine system, remains active in the body for more than a month. In frogs, metamorphosis will not occur without thyroxin. Cretinism occurs in humans with low thyroid function from birth, with reduced skeletal growth, sexual immaturity, abnormal protein metabolism, and mental retardation. Hypothyroidism in adults produces lethargy, weight gain, loss of hair, slow pulse, and decreased body temperature (Myxedema). Hyperthyroidism occurs with an enlarged and overactive thyroid, producing a goiter and bulging eyes with the patient becoming hyperactive, nervous, irritable, and suffering from insomnia; this may require removal of part of the thyroid or destruction of a portion by use of radioactive iodine.The thyroid gland is large and located in the neck, attached to the trachea below the larynx, where it produces hormones containing iodine. Triiodothyronine (T3) with 3 atoms of iodine. Thyroxin (T4) contains 4 atoms of iodine. Thyroxin is secreted in the greatest quantity of all the hormones produced by the thyroid gland. Iodine is actively transported into the thyroid for use in producing these hormones. When iodine is lacking in the body, a goiter forms as the thyroid enlarges in an effort to produce the necessary hormones. A low level of thyroxin in the blood stimulates release of TSH from the anterior pituitary, producing more thyroid tissue. This can be avoided by use of iodized salt. Thyroxin is necessary in vertebrates for proper growth and development. Thyroxine increases the number and activity of mitochondria in cells by binding to the cells’ DNA, increasing the basal metabolic rate. Administration of thyroid hormones, such as thyroxine, causes an increase in the rate of carbohydrate metabolism and a rise in the rate of protein synthesis and breakdown. The hormone, which excites the nervous system and leads to increased activity of the endocrine system, remains active in the body for more than a month. In frogs, metamorphosis will not occur without thyroxin. Cretinism occurs in humans with low thyroid function from birth, with reduced skeletal growth, sexual immaturity, abnormal protein metabolism, and mental retardation. Hypothyroidism in adults produces lethargy, weight gain, loss of hair, slow pulse, and decreased body temperature (Myxedema). Hyperthyroidism occurs with an enlarged and overactive thyroid, producing a goiter and bulging eyes with the patient becoming hyperactive, nervous, irritable, and suffering from insomnia; this may require removal of part of the thyroid or destruction of a portion by use of radioactive iodine.

15. Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) Primary and secondary sexual characteristics; menstrual cycle The gonads produce hormones that determine sexual characteristics. The testes produce the androgens, including testosterone, the main male sex hormone. The ovaries produce estrogen and progesterone, the female sex hormones. Secretion of these hormones is under control by the anterior pituitary. Secondary sex characteristics develop at puberty, with males typically having greater muscle strength. More in reproductive system. The gonads produce hormones that determine sexual characteristics. The testes produce the androgens, including testosterone, the main male sex hormone. The ovaries produce estrogen and progesterone, the female sex hormones. Secretion of these hormones is under control by the anterior pituitary. Secondary sex characteristics develop at puberty, with males typically having greater muscle strength. More in reproductive system.

16. Prolactin (PRL) Milk production (after birth) Usually suppressed by PIH from the hypothalamus Prolactin (PRL) is only produced in quantity after childbirth, when it causes the development of mammary glands and the production of milk; it is also involved in metabolism of fats and carbohydrates.Prolactin (PRL) is only produced in quantity after childbirth, when it causes the development of mammary glands and the production of milk; it is also involved in metabolism of fats and carbohydrates.

17. Growth Hormone (GH) Height Too little: pituitary dwarfism Too much: acromegaly Cell division, protein synthesis, bone growth Growth hormone (GH), or somatotropin, determines the height of an individual, with a pituitary dwarf or a pituitary giant produced by too little or too much GH in childhood, or acromegaly produced by too much GH production in an adult. Growth hormone promotes cell division, protein synthesis, and bone growth. GH also stimulates the liver to release hormones that stimulate growth of bone and cartilage.Growth hormone (GH), or somatotropin, determines the height of an individual, with a pituitary dwarf or a pituitary giant produced by too little or too much GH in childhood, or acromegaly produced by too much GH production in an adult. Growth hormone promotes cell division, protein synthesis, and bone growth. GH also stimulates the liver to release hormones that stimulate growth of bone and cartilage.

18. Pancreatic Hormones Insulin: beta cells Glucagon: alpha cells Somatostatin: delta cells The pancreas is a long abdominal organ that produces and secretes digestive juices that pass through the pancreatic duct to the duodenum; it also contains the islets of Langerhans, which produce and secrete the hormones insulin and glucagon into the blood. Again control is not through the hypothalamus, but is antagonistic hormones. Insulin is secreted when blood glucose is high, usually just after eating. It has 3 different actions that promote the storage of nutrients for use in leaner times, helping to lower the blood glucose level. 1. It stimulates fat, liver, and muscle cells to take up and metabolize glucose. 2. It stimulates the liver and muscles to store glucose as glycogen. 3. It promotes the buildup of fats and proteins and inhibits their use as an energy source. Glucagon is secreted between meals, and its effects oppose those of insulin, stimulating the breakdown of stored nutrients and causing the blood glucose level to rise. Somatostatin has many functions. Beyond scope of this course, but important in BMR, etc.The pancreas is a long abdominal organ that produces and secretes digestive juices that pass through the pancreatic duct to the duodenum; it also contains the islets of Langerhans, which produce and secrete the hormones insulin and glucagon into the blood. Again control is not through the hypothalamus, but is antagonistic hormones. Insulin is secreted when blood glucose is high, usually just after eating. It has 3 different actions that promote the storage of nutrients for use in leaner times, helping to lower the blood glucose level. 1. It stimulates fat, liver, and muscle cells to take up and metabolize glucose. 2. It stimulates the liver and muscles to store glucose as glycogen. 3. It promotes the buildup of fats and proteins and inhibits their use as an energy source. Glucagon is secreted between meals, and its effects oppose those of insulin, stimulating the breakdown of stored nutrients and causing the blood glucose level to rise. Somatostatin has many functions. Beyond scope of this course, but important in BMR, etc.

19. Blood Glucose Regulation Fig. 13.9 pg. 292Fig. 13.9 pg. 292

20. Diabetes Mellitus Type I: failure to produce insulin Type II: cells fail to respond to insulin Diabetes mellitus is a fairly common disease caused by a defect in insulin production or utilization. A common laboratory test for this is the presence of glucose in the urine. Untreated diabetes produces extreme thirst because of the high blood solute content. Breakdown of fat and protein leads to rapid weight loss, acid buildup in the blood, and respiratory distress, which may lead to coma and death without treatment. In Type I diabetes, the pancreas does not produce insulin, usually after a viral infection that sets off an autoimmune reaction leading to the destruction of insulin-producing cells in the islets of Langerhans of the pancreas; Type I diabetics must have daily insulin injections or a pancreas transplant. Type II diabetes is much more common, with continued production of insulin but failure of cells to respond properly to it; the best treatment for this is a low-fat, low-sugar diet and regular exercise, but oral medication can also be used to increase the effects or production of insulin.Diabetes mellitus is a fairly common disease caused by a defect in insulin production or utilization. A common laboratory test for this is the presence of glucose in the urine. Untreated diabetes produces extreme thirst because of the high blood solute content. Breakdown of fat and protein leads to rapid weight loss, acid buildup in the blood, and respiratory distress, which may lead to coma and death without treatment. In Type I diabetes, the pancreas does not produce insulin, usually after a viral infection that sets off an autoimmune reaction leading to the destruction of insulin-producing cells in the islets of Langerhans of the pancreas; Type I diabetics must have daily insulin injections or a pancreas transplant. Type II diabetes is much more common, with continued production of insulin but failure of cells to respond properly to it; the best treatment for this is a low-fat, low-sugar diet and regular exercise, but oral medication can also be used to increase the effects or production of insulin.

21. Adrenal Glands Two parts: Medulla: sympathoadrenal system Epinephrine, norepinephrine Cortex: corticosteroid hormones stimulated by ACTH Mineralocorticoids Glucocorticoids Adrenal glands are paired glands on the superior surface of the kidneys. Discussed under ANS, also will discuss under metabolism, so will not spend too much time here.Adrenal glands are paired glands on the superior surface of the kidneys. Discussed under ANS, also will discuss under metabolism, so will not spend too much time here.

22. Thyroid Glands Location: inferior to larynx, two lobes on either side of the trachea Basal Metabolic Rate (BMR) T3 and T4 =thyroxine Calcitonin Thyroids are the major controlling center for BMR. Remember TSH is a trophic hormone, so if not enough T3 and T4 produced, it will enlarge the thyroid trying to make more. GOITER results. T3 = triiodothryonine, T4 = thyroxine (most of what is released)Thyroids are the major controlling center for BMR. Remember TSH is a trophic hormone, so if not enough T3 and T4 produced, it will enlarge the thyroid trying to make more. GOITER results. T3 = triiodothryonine, T4 = thyroxine (most of what is released)

23. Gonads: Male Testosterone Seminiferous tubules with interstitial cells (Leydig cells) Lutenizing hormone (LH) acts on Leydig cells Testosterone is responsible for primary and secondary sexual characteristics Primary sex characteristics: development and maintenance of the male genitalia (penis, scrotum), accessory sex organs (prostate, seminal vesicles, epididymis, and vas deferens). 2ary characteristics are hair, musculature, larger larynx, etc.Primary sex characteristics: development and maintenance of the male genitalia (penis, scrotum), accessory sex organs (prostate, seminal vesicles, epididymis, and vas deferens). 2ary characteristics are hair, musculature, larger larynx, etc.

25. Gonads: Female During puberty: pituitary releases LH that stimulates ovaries to begin making estrogen and progesterone. Estrogen: breasts, pelvis, body fat. Progesterone: works with estrogen to regulate menstrual cycle.

26. Thymus, GI Tract Thymus: thymosin (one of several polypeptide hormones secreted) controls the maturation of T cells GI Tract: gastrin (acid secretion); neurotensin (inhibit acid secretion) Other endocrine glands include the thymus and the pineal glands. The thymus gland in the neck and thoracic cavity grows during childhood but gradually decreases in size after puberty. Lymphocytes that have passed through the thymus become competent as T cells. Thymic hormones called thymosins can aid in the production of new T cells. Thymosins are being investigated as part of the therapy for restoration of T cell function in AIDS and cancer patients. Other endocrine glands include the thymus and the pineal glands. The thymus gland in the neck and thoracic cavity grows during childhood but gradually decreases in size after puberty. Lymphocytes that have passed through the thymus become competent as T cells. Thymic hormones called thymosins can aid in the production of new T cells. Thymosins are being investigated as part of the therapy for restoration of T cell function in AIDS and cancer patients.

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