15. The Endocrine System


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15. The Endocrine System

  1. 1. The Endocrine System
  2. 2. <ul><li>Describe the negative feedback system that controls production of hormones. </li></ul><ul><li>List the major endocrine glands and the hormones they produce. </li></ul><ul><li>Describe the structure and functions of the pituitary gland. </li></ul><ul><li>Describe the effect(s) of growth hormone, prolactin, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, melanocyte-stimulating hormone, antidiuretic hormone, and oxytocin. </li></ul>Learning Objectives
  3. 3. <ul><li>Describe the structure of the thyroid gland. </li></ul><ul><li>Describe the effects of thyroid hormone, calcitonin, and parathormone. </li></ul><ul><li>Differentiate between T 3 and T 4 . </li></ul><ul><li>List the three categories of hormones produced by the adrenal cortex. </li></ul><ul><li>List the hormones produced by the pancreatic islet cells and describe the effect(s) of each. </li></ul><ul><li>Describe the effect(s) of androgens, estrogens, and progestins. </li></ul><ul><li>List the hormones produced by the kidneys, stomach, small intestine, placenta, thymus, and pineal body. </li></ul>Learning Objectives
  4. 4. Endocrine System <ul><li>Works together with nervous system to maintain homeostasis </li></ul><ul><li>Primary function: produces hormones </li></ul><ul><li>Hormones act on specific target cells to produce specific effects . </li></ul>
  5. 5. <ul><li>Chemical messengers produced by endocrine glands and secreted directly into blood vessels </li></ul><ul><li>Produce effects when they find their specific receptors in or on cells </li></ul><ul><li>A cell that has receptors for a particular hormone is referred to as a target of that hormone . </li></ul>Hormones
  6. 6. Control of Hormone Secretion <ul><li>Negative feedback systems </li></ul><ul><li>When the level of a specific hormone drops below needed levels, the appropriate endocrine gland is stimulated to produce more hormone. </li></ul><ul><li>Once the proper hormone level is present in the bloodstream, stimulation of that endocrine gland is reduced and production of that hormone is reduced. </li></ul>
  7. 7. Control of Hormone Secretion <ul><li>Direct stimulation from the nervous system </li></ul><ul><li>Secretion of some hormones is stimulated by sympathetic nerve impulses when an animal feels threatened. </li></ul><ul><ul><li>“ Fight or flight&quot; response </li></ul></ul>
  8. 8. Major Endocrine Glands <ul><li>Anterior pituitary </li></ul><ul><li>Posterior pituitary </li></ul><ul><li>Thyroid </li></ul><ul><li>Parathyroid </li></ul><ul><li>Adrenal cortex </li></ul><ul><li>Adrenal medulla </li></ul><ul><li>Pancreas (islets) </li></ul><ul><li>Testis </li></ul><ul><li>Ovary </li></ul>
  9. 9. Hypothalamus <ul><li>Part of diencephalon section of the brain </li></ul><ul><li>Controls activities of the pituitary gland </li></ul><ul><li>Portal system of blood vessels links hypothalamus with anterior portion of pituitary gland </li></ul>
  10. 10. Hypothalamus <ul><li>Modified neurons in the hypothalamus secrete releasing and inhibiting factors into portal blood vessels </li></ul><ul><ul><li>Specific for a particular anterior pituitary hormone </li></ul></ul>
  11. 11. <ul><li>Modified neurons in hypothalamus also secrete antidiuretic hormone and oxytocin </li></ul><ul><li>Transported to posterior pituitary for storage </li></ul><ul><li>Released into the bloodstream by nerve impulses from the hypothalamus </li></ul>Hypothalamus
  12. 12. Pituitary Gland (Hypophysis) <ul><li>Two separate glands with different structures, functions, and embryological origins </li></ul><ul><li>Anterior pituitary - adenohypophysis; rostral portion </li></ul><ul><ul><li>Stimulated by hypothalamus and direct feedback from target organs and tissues to produce its hormones </li></ul></ul><ul><li>Posterior pituitary - neurohypophysis; caudal portion </li></ul><ul><ul><li>Stores and releases hormones produced in hypothalamus </li></ul></ul>
  13. 13. The Anterior Pituitary <ul><li>Known anterior pituitary hormones: </li></ul><ul><li>1. Growth hormone </li></ul><ul><li>2. Prolactin </li></ul><ul><li>3. Thyroid-stimulating hormone </li></ul><ul><li>4. Adrenocorticotropic hormone </li></ul><ul><li>5. Follicle-stimulating hormone </li></ul><ul><li>6. Luteinizing hormone </li></ul><ul><li>7. Melanocyte-stimulating hormone </li></ul>
  14. 14. Growth Hormone (GH) <ul><li>Also known as somatotropin and somatotropic hormone </li></ul><ul><li>Promotes body growth in young animals </li></ul><ul><li>Helps regulate the metabolism of proteins, carbohydrates, and lipids in all the body's cells </li></ul>
  15. 15. Prolactin <ul><li>Helps trigger and maintain lactation </li></ul><ul><ul><li>Secretion of milk by the mammary glands </li></ul></ul><ul><li>Prolactin production and release continues as long as the teat or nipple continues to be stimulated by nursing or milking. </li></ul><ul><li>When prolactin stimulation stops, milk production stops, and the mammary gland shrinks back to its nonlactating size. </li></ul>
  16. 16. Thyroid-Stimulating Hormone (TSH) <ul><li>Also known as thyrotrophic hormone </li></ul><ul><li>Stimulates growth and development of thyroid gland and causes it to produce its hormones </li></ul><ul><li>Secretion is regulated by feedback from the thyroid gland </li></ul><ul><ul><li>Has direct effects on anterior pituitary gland through changes in TSH-releasing factor produced by the hypothalamus </li></ul></ul>
  17. 17. Adrenocorticotropic Hormone (ACTH) <ul><li>Stimulates growth and development of the adrenal cortex and release of some of its hormones </li></ul><ul><li>Regulated by feedback from the hormones of the adrenal </li></ul><ul><li>ACTH can also be released quickly as a result of stimulation of the hypothalamus by other parts of the brain. </li></ul><ul><ul><li>Hypothalamus sends a burst of ACTH-releasing factor to the anterior pituitary through the portal system causing ACTH to be released quickly </li></ul></ul>
  18. 18. Follicle-Stimulating Hormone (FSH) <ul><li>In female, stimulates growth and development of ovarian follicles - oogenesis </li></ul><ul><ul><li>Also stimulates cells lining the follicles to produce and secrete estrogens </li></ul></ul><ul><li>In the male, stimulates spermatogenesis </li></ul>
  19. 19. Luteinizing Hormone (LH) <ul><li>Completes process of follicle development in ovary </li></ul><ul><li>Increasing amounts of estrogens feedback to the anterior pituitary and cause reduced production of FSH and increased production of LH </li></ul><ul><li>LH levels reach a peak when follicle is fully mature </li></ul><ul><ul><li>Usually causes ovulation </li></ul></ul>
  20. 20. Luteinizing Hormone (LH) <ul><li>After ovulation, LH stimulates cells in the empty follicle to multiply and develop into the corpus luteum. </li></ul><ul><ul><li>Corpus luteum produces progestin hormones necessary for the maintenance of pregnancy </li></ul></ul><ul><li>In the male, LH stimulates interstitial cells to develop and produce testosterone. </li></ul>
  21. 21. Melanocyte-Stimulating Hormone (MSH) <ul><li>Associated with control of color changes in the pigment cells (melanocytes) of reptiles, fish, and amphibians </li></ul><ul><li>Administration of artificially large amounts of MSH to higher mammals can cause darkening of the skin from melanocyte stimulation </li></ul>
  22. 22. The Posterior Pituitary <ul><li>Stores two hormones produced in the hypothalamus </li></ul><ul><li>Antidiuretic hormone and oxytocin </li></ul><ul><li>Transported from hypothalmus to posterior pituitary and stored in nerve endings </li></ul><ul><li>Periodically released into the bloodstream in response to nerve impulses from hypothalmus </li></ul>
  23. 23. Antidiuretic Hormone (ADH) <ul><li>Helps prevent diuresis </li></ul><ul><li>Receptors in hypothalamus detect changes in osmotic pressure of blood that result from dehydration/hemoconcentration </li></ul><ul><li>Generates nerve impulses - causes release of ADH </li></ul><ul><ul><li>ADH travels to the kidney - causes kidneys to reabsorb more water from the urine and return it to the bloodstream </li></ul></ul><ul><li>ADH deficiency causes diabetes insipidus. </li></ul>
  24. 24. Oxytocin <ul><li>Effects on uterus - causes contraction of the myometrium at the time of breeding and at parturition </li></ul><ul><ul><li>Induces uterine contractions that aid transport of spermatozoa to the oviducts </li></ul></ul><ul><ul><li>Stimulates uterine contractions that aid in the delivery of the fetus and the placenta </li></ul></ul>
  25. 25. Oxytocin <ul><li>Effect on active mammary glands - causes movement of milk down to the lower parts of the gland (milk letdown) </li></ul><ul><ul><li>Stimulation of the teat or nipple by nursing or milking causes oxytocin to be released into the bloodstream. </li></ul></ul><ul><ul><li>Causes contraction of the myoepithelial cells around the mammary gland alveoli and small ducts </li></ul></ul><ul><ul><li>Forces milk into the lower parts of the gland </li></ul></ul>
  26. 26. The Thyroid Gland <ul><li>Consists of two lobes on either side of larynx </li></ul><ul><ul><li>Lobes may be connected by isthmus </li></ul></ul><ul><li>Thyroid hormone is produced in follicles </li></ul><ul><ul><li>Simple cuboidal glandular cells surrounding globule of thyroid hormone precursor </li></ul></ul>
  27. 27. Thyroid Hormones <ul><li>T 3 (triiodothyronine) and T 4 (tetraiodothyronine, or thyroxine) </li></ul><ul><li>Produced when TSH from anterior pituitary reaches the thyroid gland </li></ul><ul><li>T 4 produced in greater abundance than T 3 but is mostly converted to T 3 before producing effects on target cells </li></ul>
  28. 28. Effects of Thyroid Hormones <ul><li>Influences development and maturation of CNS; growth and development of muscles and bones </li></ul><ul><li>Calorigenic effect - regulates the metabolic rate of all the body's cells </li></ul><ul><li>Allows animal to generate heat and maintain constant internal body temperature </li></ul>
  29. 29. Effects of Thyroid Hormones <ul><li>Production increases with exposure to cold and then increases metabolic rate to generate more heat </li></ul><ul><li>Affects metabolism of proteins, carbohydrates, and lipids much like GH does </li></ul>
  30. 30. Calcitonin <ul><li>Produced by C cells located between thyroid follicles </li></ul><ul><li>Helps maintain blood calcium levels </li></ul><ul><li>Prevents hypercalcemia by encouraging excess calcium to be deposited in the bones </li></ul><ul><li>Calcium is involved in muscle contraction, blood clotting, milk secretion, and formation and maintenance of the skeleton </li></ul>
  31. 31. Parathyroid Hormone (PTH) <ul><li>Also called parathormone </li></ul><ul><li>Produced by the parathyroid glands </li></ul><ul><ul><li>Small, pale nodules in, on, or near the thyroid glands </li></ul></ul><ul><li>Helps maintain blood calcium levels </li></ul><ul><li>Prevents hypocalcemia </li></ul><ul><ul><li>Causes kidneys to retain calcium and intestine to absorb calcium from food; withdraws calcium from bones </li></ul></ul>
  32. 32. The Adrenal Glands <ul><li>Located near the cranial ends of the kidneys </li></ul><ul><li>Consist of two glands: </li></ul><ul><ul><li>Adrenal cortex </li></ul></ul><ul><ul><li>Adrenal medulla </li></ul></ul>
  33. 33. Adrenal Cortex <ul><li>Produces numerous steroid hormones classified into three main groups: </li></ul><ul><ul><li>Glucocorticoids </li></ul></ul><ul><ul><li>Mineralocorticoids </li></ul></ul><ul><ul><li>Sex hormones </li></ul></ul>
  34. 34. Adrenal Cortex <ul><li>Glucocorticoids: cortisone, cortisol, and corticosterone </li></ul><ul><ul><li>Hyperglycemic effect </li></ul></ul><ul><ul><li>Also help maintain blood pressure and help the body resist the effects of stress </li></ul></ul><ul><ul><li>Mineralocorticoids (e.g., aldosterone) </li></ul></ul><ul><ul><li>Regulate the levels of important electrolytes (mineral salts) in the body </li></ul></ul><ul><li>Sex hormones - androgens and estrogens </li></ul>
  35. 35. Adrenal Medulla <ul><li>Produces epinephrine and norepinephrine </li></ul><ul><li>Secretion is controlled by the sympathetic portion of the autonomic nervous system </li></ul><ul><ul><li>“ Fight or flight&quot; response </li></ul></ul><ul><li>Increases heart rate and output, increases blood pressure, dilates air passageways in the lungs, and decreases GI function </li></ul>
  36. 36. Pancreas <ul><li>Located near the duodenum </li></ul><ul><li>Has both exocrine and endocrine functions </li></ul><ul><li>Endocrine component - small percentage of the total volume of the organ </li></ul><ul><li>Pancreatic islets (islets of Langerhans): groups of cells scattered throughout the pancreas </li></ul><ul><ul><li>Alpha cells - produce glucagon </li></ul></ul><ul><ul><li>Beta cells - produce insulin </li></ul></ul><ul><ul><li>Delta cells - produce somatostatin </li></ul></ul>
  37. 37. Pancreatic Hormones <ul><li>Insulin: lowers blood glucose levels by causing glucose, amino acids, and fatty acids to be absorbed into body cells </li></ul><ul><li>Glucagon: lowers blood glucose levels by stimulating liver cells to convert glycogen to glucose and by stimulating gluconeogenesis </li></ul><ul><li>Somatostatin: inhibits secretion of insulin, glucagon, and GH; diminishes GI activity </li></ul>
  38. 38. Testes <ul><li>Interstitial cells: clumps of endocrine cells </li></ul><ul><li>Produce androgens when stimulated by LH </li></ul><ul><ul><li>Interstitial cell stimulating hormone (ICSH) in the male </li></ul></ul><ul><li>Testosterone: primary androgen </li></ul><ul><ul><li>Provides for development of male secondary sex characteristics and accessory sex glands </li></ul></ul><ul><ul><li>Activates spermatogenesis </li></ul></ul>
  39. 39. Ovaries <ul><li>Produce ova and hormones in cycles </li></ul><ul><li>Controlled by follicle stimulating hormone (FSH) and luteinizing hormone (LH) </li></ul><ul><li>Hormone groups produced in the ovaries: </li></ul><ul><ul><li>Estrogens </li></ul></ul><ul><ul><li>Progestins </li></ul></ul>
  40. 40. Estrogens <ul><li>FSH stimulates ovarian follicles to develop </li></ul><ul><ul><li>Cells of follicles produce and release estrogens </li></ul></ul><ul><ul><li>Amount of estrogen produced increases as follicle grows </li></ul></ul><ul><li>Increasing estrogen levels accelerate physical and behavioral changes </li></ul>
  41. 41. Estrogens <ul><li>Feedback to anterior pituitary </li></ul><ul><ul><li>Cause anterior pituitary gland to reduce the production of FSH and increase the production of LH </li></ul></ul><ul><li>When follicle is fully mature, LH level peaks </li></ul><ul><ul><li>In most animal species, ovulation occurs when LH level peaks </li></ul></ul>
  42. 42. Progestins <ul><li>Group of hormones produced by corpus luteum </li></ul><ul><li>High LH level stimulates cells of empty follicle to multiply and develop into corpus luteum </li></ul><ul><li>Progesterone - principal progestin </li></ul><ul><ul><li>Helps prepare uterus to receive the fertilized ovum; needed to maintain pregnancy </li></ul></ul>
  43. 43. Progestins <ul><li>In pregnant female, hormone signal is sent from uterus, and corpus luteum is maintained </li></ul><ul><li>If no pregnancy occurs, lack of hormone signal causes corpus luteum to shrink and disappear </li></ul>
  44. 44. Kidneys <ul><li>Produce erythropoietin - stimulates red bone marrow to increase production of red blood cells </li></ul><ul><li>Production of erythropoietin stimulated by hypoxia </li></ul><ul><li>As red blood cell production increases, more oxygen feeds back to kidneys and slows the production of erythropoietin </li></ul>
  45. 45. Stomach <ul><li>Gastrin: produced by cells in the wall of the stomach </li></ul><ul><li>Secretion stimulated by presence of food in the stomach </li></ul><ul><li>Stimulates gastric glands to secrete hydrochloric acid and digestive enzymes </li></ul><ul><li>Encourages muscular contractions of the stomach wall </li></ul>
  46. 46. Small Intestine <ul><li>Secretin and cholecystokinin produced by cells in lining of small intestine </li></ul><ul><li>Secretion occurs in response to presence of chyme in duodenum </li></ul><ul><li>Secretin stimulates pancreas to secrete fluid to neutralize acidic chyme after it passes out of the stomach </li></ul><ul><li>Cholecystokinin stimulates pancreas to release digestive enzymes into the duodenum </li></ul>
  47. 47. Placenta <ul><li>Surrounds a developing fetus during pregnancy </li></ul><ul><li>Acts as an interface with the maternal circulation </li></ul><ul><li>Produces hormones to help support and maintain pregnancy </li></ul><ul><ul><li>Estrogen and progesterone </li></ul></ul><ul><ul><li>Chorionic gonadotropin (some species) </li></ul></ul>
  48. 48. Thymus <ul><li>Extends cranially from the level of the heart up into neck region along both sides of the trachea </li></ul><ul><li>Large in young animals, atrophies later in life </li></ul><ul><li>Function involves hormones or hormonelike chemical substances (e.g., thymosin and thymopoietin) </li></ul><ul><li>Seems to cause certain cells to be transformed into T-lymphocytes </li></ul>
  49. 49. Pineal Body <ul><li>Located at caudal end of the cleft that separates the two cerebral hemispheres </li></ul><ul><li>Influences cyclic activities in the body </li></ul><ul><li>Melatonin - hormonelike substance called that seems to affect moods and wake-sleep cycles </li></ul><ul><ul><li>May also play a role in the timing of seasonal estrous cycles in some species </li></ul></ul>
  50. 50. Prostaglandins <ul><li>Hormonelike substances derived from unsaturated fatty acids </li></ul><ul><li>Produced in a variety of body tissues (skin, intestine, brain, kidney, lungs, reproductive organs, and eyes) </li></ul><ul><li>Nine main groups - designated A through I </li></ul><ul><ul><li>Subscript numbers and Greek letters designate subgroups </li></ul></ul><ul><li>Influence blood pressure, blood clotting, inflammation, GI, respiratory, reproductive, and kidney function </li></ul>