Biology 102 Chapter 42 Animal Hormones 1. Compare the response times of the two major systems of internal communication: the nervous system and the endocrine system. ---nervous system is involved with high-speed messages ---endocrine system is slower and involves production, release, and movement of chemical messages 2. Describe the relationships among endocrine system components: Hormones, endocrine glands, target cells, and target cell receptors. ---most endocrine glands/tissues contain neurosecretory cells that secrete hormones --hormone is chemical signal that communicates regulatory messages within body ---hormones may reach all parts of body, but only certain types of cells, the target cells, are equipped to respond ---only target cells respond is because only they have receptors for the hormone 3. Describe hormonal regulation of insect development including the role of ecdysone, brain hormone, and juvenile hormone. ---in insects/crustaceans, molting triggered by ecdysone --secreted (insects) by prothoracic glands just behind head --also favors development of adult characteristics -from caterpillar to butterfly ---ecdysone production (insects) controlled by brain hormone (BH) ---balanced by juvenile hormone (JH) secreted by corpora allata (pair of small glands just behind brain) --promotes retention of larval characteristics 4. List the general chemical classes of hormones and give examples of each. ---peptide: oxytocin, ADH, calcitonin, PTH, thymosin ---protein: GH, prolactin, insulin, glucagon, ---glycoprotein: FSH, LH, TSH, ---amine: T3 and T4, epinephrine/norepinephrine, melatonin ---steroid: glucocorticoids, mineralocorticoids, androgens, estrogens, progesterone 5. State which of the two classes of hormones is lipid soluble, and explain how this property affects hormone action. ---nonsteroid hormones such as amines, peptides, and proteins usually combine with receptors in target cell membranes --first messenger and second messenger --signal-transduction pathways (convert extracellular chemical signal to specific intracellular response) ---steroid hormones are lipid soluble & can easily diffuse into cells --once inside target cell, steroid hormones may combine with specific protein molecules—the receptors 6. Describe the mechanism of steroid hormone action, and explain the location and role of steroid hormone receptors. (Chapter 15). ---steroid hormone easily crosses lipid bilayer of target cell ---binding of signal molecule with specific receptor (usually in nucleus) initiates signal transduction process --signal initiates cascade of events in which proteins interact with other proteins until final responses are achieved ---in many cases, signal-receptor complex binds to DNA to modify gene expression 7. Explain how to account for specificity in target cell response to hormonal signals. ---each chemical signal has specific shape recognized by that signal’s target cells ---signal’s action begins when it binds to specific receptor ---receptor protein may be in plasma membrane of target cell or inside the target cell ---diversity of responses of target cells depends on nature of target cells & affinity of receptor molecules on or within target cell ---cells are unresponsive to particular signal if they lack appropriate receptor(s) 8. Describe the location of the hypothalamus, and explain how its hormone-releasing cells differ from both endocrine gland secretory cells and other neurons. ---hypothalamus is region of lower brain ---hormone releasing cells are 2 sets of neurosecretory cells whose secretions are stored in posterior pituitary ---hormones released into capillaries in region at base of hypothalamus --capillaries drain into portal vessels; short blood vessels that subdivide into second capillary bed within anterior pituitary ---hypothalamic hormones have direct access to gland they control 9. Describe the location of the pituitary, and explain the functions of the posterior and anterior lobes. ---pituitary located at base of hypothalamus ---has 2 discrete parts that develop from 2 separate regions of embryo and have very different functions ---anterior pituitary (adenohypophysis) consists of endocrine cells that synthesize/secrete several hormones directly into blood ---posterior pituitary (neurohypophysis) is extension of brain --stores and secretes 2 hormones made by hypothalamus 10. List the posterior pituitary hormones, and describe their effects on target organs. ---oxytocin stimulates contraction of uterus and mammary gland cells; regulated by nervous system ---antidiuretic hormone (ADH) promotes water retention by kidneys; regulated by water/salt balance 11. Using antidiuretic hormone as an example, explain how a hormone contributes to homeostasis and how negative feedback can control hormone levels. ---osmoreceptors in hypothalamus monitor blood osmolarity ---plasma osmolarity >s, osmoreceptors shrink slightly and transmit nerve impulses to certain hypothalamic neurosecretory cells ---these cells respond by releasing ADH into general circulation from their tips in posterior pituitary ---target cells for ADH are cells lining collecting ducts of nephrons in kidneys ---ADH binds to receptors on target cells & activates signal-transduction pathway that increases water permeability of collecting ducts ---water retention is >ed as water exits collecting ducts and enters nearby capillaries ---osmoreceptors also stimulate thirst drive ---as more dilute blood (lower osmolarity) arrives at brain, hypothalamus responds by reducing ADH secretion and lowering thirst sensations ---this prevents overcompensation by stopping hormone secretion and quenching thirst ---this negative feedback scheme includes hormonal action and behavioral response 12. Define tropic hormone, and describe the functions of tropic hormones produced by the anterior pituitary. ---trophic hormones have other endocrine glands as their targets ---four of the hormones secreted by anterior pituitary gland are tropic hormones ---thyroid stimulating hormone (TSH) stimulates thyroid gland ---adrenocorticotropic hormone (ACTH) stimulates adrenal cortex to secrete glucocorticoids ---follicle-stimulating hormone (FSH) stimulates production of ova and sperm ---luteinizing hormone (LH) stimulates ovaries and testes 13. Explain how the anterior pituitary is controlled. ---set of neurosecretory cells in hypothalamus exerts control over anterior pituitary by secreting 2 kinds of hormones into the blood ---releasing hormones make the anterior pituitary secrete its hormones ---inhibiting hormones make the anterior pituitary stop secreting hormones ---is subtle blend (mix) of releasing and inhibiting hormones that control timing and amount of hormonal release 14. List hormones of the thyroid gland, and explain their role in development and metabolism. ---in humans and other mammals, thyroid gland consists of 2 lobes located on ventral surface of trachea ---produces 2 very similar hormones (from tyrosine) --triiodothyronine (T3) and tetraiodothyronine (also known as thyroxine (T4) ---in mammals, T3 is more active form ---thyroid important in human development --thyroid deficiency (cretinism) results in markedly retarded skeletal growth and poor mental development ---studies show thyroid hormones important for normal functioning of bone-forming cells and for branching of nerve cells during embryonic development of the brain ---in adult mammals, thyroid hormones help maintain normal blood pressure, heart rate, muscle tone, digestion, and reproductive functions ---hyperthyroidism (excessive secretion of thyroid hormones) produces symptoms of high body temperature, profuse sweating, weight loss, irritability, and high blood pressure ---hypothyroidism (too little secretion of thyroid hormones) produces cretinism in infants and symptoms of weight gain, lethargy, and intolerance to cold in adults --another condition associated with shortage of thyroid hormones is enlargement of thyroid called goiter -associated with deficiency of iodine in diet ---thyroid also produces calcitonin --lowers calcium levels in blood as part of calcium homeostasis 15. Diagram the negative feedback loop that regulates the secretion of thyroid hormones. ---hypothalamus-->TRH (thyroid releasing hormone) to anterior pituitary-->TSH (thyroid stimulating hormone) -->induces thyroid to manufacture and secrete T3 and T4 ---increases levels of TSH and T3 and T4 signal hypothalamus to reduce secretion of TRH 16. State the location of the parathyroid glands, and describe hormonal control of calcium homeostasis. ---four parathyroid glands embedded in surface of thyroid ---function in homeostasis of calcium ions ---parathyroid glands secrete parathyroid hormone (PTH) ---raises blood levels of calcium and has effect opposite of thyroid hormone calcitonin ---stimulates Ca2+ reabsorption in kidneys & induces specialized bone cells (osteoclasts) to decompose mineralized matrix of bone and release Ca2+ into blood ---vitamin D, synthesized in the skin and converted into active form by many organs, essential to PTH function ---lack of PTH causes blood levels of calcium to drop dramatically --leads to convulsive contractions of skeletal muscles --if unchecked, tetany, is fatal 17. Distinguish between and cells in the pancreas and explain how their antagonistic hormones (insulin and glucagon) regulate carbohydrate metabolism. ---pancreas has both endocrine and exocrine functions ---islets of Langerhans are cluster of endocrine tissue in pancreas ---secrete 2 hormones directly into circulatory system ---alpha () cells secrete peptide hormone glucagon ---beta () cells secrete the hormone insulin ---glucagon and insulin work together in antagonistic manner to regulate the [] of glucose in blood ---in humans, blood glucose levels must remain about 90 mg/100 mL for proper body functioning ---at glucose levels above set point, insulin secreted and lowers blood glucose [] by stimulating body cells to take up glucose from blood --also slows glycogen breakdown in liver and inhibits conversion of amino acids/fatty acids to sugar ---when blood glucose levels drop below set point, glucagon is secreted and increases blood glucose [] by stimulating liver to increase hydrolysis of glycogen, convert amino acids/fatty acids to glucose, and slowly release glucose into blood 18. List hormones of the adrenal medulla, describe their function, and explain how their secretion is controlled. ---medulla synthesizes/secretes catecholamines (epinephrine and norepinephrine) ---secreted in times of stress --nerve cells excited by stressful stimuli release the neurotransmitter acetylcholine in medulla --acetylcholine combines with cell receptors and stimulates release of epinephrine ---norepinephrine released independently of epinephrine ---have rapid and dramatic effects on several targets --glucose mobilized in skeletal and muscle cells --fatty acid released from fat cells --rate and stroke of heartbeat increased --delivery of blood changed --oxygen delivery to body cells increased 19. List the hormones of the adrenal cortex, describe their function, and explain how their secretion is controlled. ---adrenal cortex synthesizes and secretes corticosteroids ---stressful stimuli cause hypothalamus to secrete releasing hormone that simulates release of ACTH from anterior pituitary ---ACTH stimulates release of corticosteroids from adrenal cortex ---in humans, 2 primary types are glucocorticoids (cortisol) and mineralocorticoids (aldosterone) ---glucocorticoids promote glucose synthesis from noncarbohydrate substances such as proteins --also have immunosuppressive effects and are used to treat inflammation ---mineralocorticoids affect salt and water balance --aldosterone stimulates kidneys to reabsorb sodium ions and water from filtrate ---glucocorticoids/mineralocorticoids important to maintaining body homeostasis during extended periods of stress 20. Describe both the short-term and long-term endocrine responses to stress. ---short-term stress responses trigger release of epinephrine and norepinephrine ---long-term stress responses trigger the release of mineralocorticoids and glucocorticoids 21. Identify male and female gonads, and list the three categories of gonadal steroids. ---ovaries and testes ---androgens, estrogens, and progestins ---primary androgen is testosterone ---primary estrogen is estradiol ---progestins include progesterone ---gonadotropins from anterior pituitary (FSH & LH) control synthesis of both androgens and estrogens --FSH and LH controlled by gonadotropin-releasing hormone (GnRH) from hypothalamus 22. Describe the location of the pineal and thymus glands, list their hormone products, and describe their functions. ---pineal gland is small mass of tissue near center of mammalian brain ---secretes melatonin; regulates functions related to light and to seasons marked by changes in day length --called biorhythms ---pineal contains light-sensitive cells or has nervous connections from the eyes (depends on species) ---thymus is located just posterior to the sternum ---produces thymosin --promotes development and maturation of lymphocytes --important in immunity