Chapter 36

1. Chapter 36 Endocrine Control: A Summary AP Biology Spring 2011

2. Categories of Signaling Molecules • Animal Hormones: cell products secreted from endocrine glands, endocrine cells, and a few neurons • Blood stream usually delivers them to target cells

3. Categories of Signaling Molecules • Neurotransmitters: secreted from neurons and act only in a synaptic cleft between axon endings and target cells • Local Signaling Molecules: secreted by many cells into extracellular fluid • Inactivated swiftly, effects localized in tissues

4. Categories of Signaling Molecules • Pheromones: signaling molecules that diffuse through water or air to targets in other individuals or of the same species • Help integrate social behavior, mate attraction

5. Overview of Endocrine System • W. Bayliss and E. Starling: in 1900, trying to figure out what triggers the secretion of pancreatic juices when food travels through canine gut • Sources of hormones in human body: • Pituitary gland • Adrenal gland (2) • Pancreatic islets (numerous cell clusters) • Thyroid gland • Parathyroid glands (4) • Pineal gland • Thymus gland • Gonads (2) • Endocrine cells of: hypothalamus, stomach, small intestine, liver, kidneys, heart, placenta, skin, adipose tissue, and other organs • Endorcine System: control system of cells, tissues, and organs that interacts intimately with the nervous system; secretes hormones and other molecules

6. Signal Reception, Transduction, Response • Signal activates a receptor on a target cell • Signal becomes transduced to a molecular form that acts within the receiving cell • Cell may make a functional response • Different classes of hormone can trigger the steps • Steroid hormones: derived from cholesterol • Amine hormones: modified amino acids • Peptide hormones: consist of two amino acids • Protein hormones: consist of a number of amino acids

7. Intracellular Receptors • Steroid hormones (lipids) diffuse across the bilayer of plasma membrane • Form hormone receptor complex by binding to receptors in cytoplasm or nucleus • Most often, complex binds to promoter region of hormonally regulated gene • Page 623 figure 36.3 (a)

8. Plasma Membrane Receptors • Peptide and protein hormones bind to membrane receptors and start cascade of reactions • Ex. Too little glucose in the blood  pancreas secretes glucagon • Certain liver cells have glucagon receptors that span plasma membrane • When activated, signal adenylatecyclasewhich converts ATP into cAMP (cyclic adenosine monophosphate) • cAMP is a second messenger, switches on protein kinases, which activate other enzymes, which activate others • Enzymes catalyze breakdown of glycogen to glucose are activated • Glucose is released from storage and enters interstital fluid, then blood • Helps return blood level of glucose to normal • Page 623 figure 36.3 (b) • Secondary messenger: molecules that form inside a cell and • mediate a signal from the outside

9. Plasma Membrane Receptors • Ex. Too much glucose in blood • Certain cells in pancreas secrete insulin • Protein hormone binds to receptors on muscle cells • Binding causes glucose transporters in cytoplasm to move to plasma membrane and insert themselves into it • With more transporters at surface, muscle cells can take in glucose more quickly • Glucose moves into cells, blood concentrations fall

10. Variations in Response • Cells will only respond if they have receptors to the specific hormone • One or more hormones may inhibit, enhance, or prime a target cells capacity to respond to another kind of hormone • Feedback mechanisms often influence the concentrations of different hormones in a tissue, which can alter cellular response • Even with receptors, certain components of its plasma membrane or its cytoplasm must be available to carry out the response • Environmental cues mediate the timing and extent of hormone secretions

11. Hypothalamus and Pituitary Gland • Hypothalamus: forebrain region, includes some neurons that secrete hormones, not neurotransmitters • Hypothalamus connected to pituitary gland by tissue stalk at base of hypothalamus • Pituitary Gland: size of a pea, axons of hormone secreting neurons extend down through stalk and into pituitary gland’s posterior lobe • Posterior lobe: stores and secrets their hormones • Anterior lobe: makes its own hormones, hypothalamic signals control their release • Intermediate lobe: (not humans) between posterior and anterior • Together hypothalamus and pituitary gland function as master control center that integrate the activities of many glands and the nervous system

12. Hypothalamus and Pituitary Gland

13. Posterior Pituitary Function • Some hypothalamic neurons secrete ADH (antidiuretic hormone) and oxytocin into posterior lobe of the pituitary • Hormone diffuse into adjacent capillary bed, then travel the bloodstream • In kidneys, ADH targets cell that adjust how much water is excreted in urine • Oxytocin makes uterus contact during childbirth and makes milk move into secretory ducts of mammary glands during lactation

14. Anterior Pituitary Function • Other hypothalamic hormones act on anterior pituitary cells • Releasers: induce secretions from target cells • Inhibitors: slow target cell secretions • Releasers and inhibitors diffuse out of hypothalamis neurons, are picked up by capillary bed in stalk above pituitary • Flow into second capillary bed in anterior pituitary, and there they diffuse out into tissues • Control secretions from 6 types of anterior lobe hormones • ACTH Adrenocorticotropin • TSH Thyrotropin • FSH Follicle stimulating hormone • LH Luteinizing hormone • PRL Prolactin • STH or GH Somatotropin or growth hormone

16. Thyroid Gland • Thyroid Gland: butterfly shaped, resting at base of neck, in front of trachea • Secretes two amines, triiodothronine and thyroxine (call both thyroid hormone)

17. Thyroid Gland Blood level of thyroid hormone falls below set point • Negative Feedback Loops • To the anterior pituitary and hypothalamus control thyroid hormone secretion Rise in blood level of thyroid hormone inhibits secretion of TRH and TSH

18. Thyroid Gland • Enlarged thyroid, simple goiter • Thyroid hormone synthesis requires iodine, low levels of iodine cause goiter • Hypothyroidism • Thyroid hormone level in blood remains too low, stunts growth and delays maturation of sexual organs, iodine deficiency • Hyperthyroidism, Graves, other toxic goiters • Excess of thyroid hormone in the blood

19. Parathyroid Glands and Calcium Levels • Parathyroid Glands: 4, located on thyroids posterior surface, release parathyroid hormone (PTH) in response to decline in the level of calcium in blood • PTH targets certain bone cells and kidney cells • Bones: induces osteoclasts to secrete bone-digesting enzymes; calcium and other minerals released from bone enter interstitial fluid, then blood • Kidneys: stimulates tubule cells to reabsorb more calcium • Also stimulates secretion of enzymes that activate Vitamin D3; stimulates cells in intestinal lining to absorb calcium from food • Vitamin D deficiencies: (young children) absorb too little calcium, cannot form enough bone tissue • Rickets: low calcium level triggers increase in PTH secretion, leads to breakdown of existing bones

20. Pancreatic Hormones • Pancreas: lies in abdominal cavity, in back of stomach, has exocrine and endocrine functions • Exocrine cells secrete digestive enzymes into a duct to the small intestines • Endocrine cells are grouped in clusters called pancreatic islets • Each islets contain 3 types of hormone secreting cells

21. Pancreatic Hormones • Alpha Cells: secrete peptide hormone glucagon • In between meals, cells throughout body take up glucose from blood • Blood glucose levels fall below certain point  alpha cells secrete glucagon, liver is main target • Glucagon activates many enzymes that break down glycogen to glucose • Glucagon raises level of glucose in blood

22. Pancreatic Hormones • Beta Cells: most abundant cells in pancreatic islets, secrete insulin, only hormone that causes target cells to take up and store glucose • After a meal, high levels of glucose in blood stimulate beta cells to release insulin • Targets mainly liver, fat, skeletal muscles • Activates enzymes that function in protein and fat synthesis, inhibits enzymes that catalyze protein and fat breakdown • Insulin lowers the level of glucose in the blood

23. The Adrenal Glands • Adrenal Glands: pair, one on top of each kidney • Adrenal Cortex: glands outer layer, secrete cortisol • Two negative feedback loops to the hypothalamus and to the anterior lobe of the pituitary keep blood level of cortisol from rising or falling too far

24. The Adrenal Glands • Negative feedback loops: • Blood level of cortisol falls below set point • Triggers secretion of CRH (corticotropin releasing hormone) from hypothalamus • CRH triggers anterior pituitary gland to release ACTH (adrenocorticotropin) • ACTH stimulates adrenal gland to secrete cortisol • Secretions continue until blood levels of cortisol rises above set point • Hypothalamus and anterior pituitary signal inhibition of secretion of CRH and ACTH, cortisol secretion slows

25. The Adrenal Glands Blood level of cortisol falls below certain point Both hypothalamus and pituitary detect rise in blood level of cortisol and slow its further secretion

26. The Adrenal Glands • Functions of Cortisol: • Maintains blood glucose levels when food is not being absorbed from gut • Induces liver cells to down glycogen stores, suppresses uptake of glucose • Keeps glucose continuously available to brain • Also breaks down fats and proteins from adipose and skeletal muscle cells • Amino acids and fatty acids used as alternative energy source • Injury, illness, anxiety  nervous system overrides feedback loops • Levels of cortisol can sore in blood • Helps body get enough glucose when sources low

27. Local feedback and Adrenal Medulla • Adrenal Medulla: inner region of adrenal gland, houses neurons • Secrete epinephrine and norepinephrine (act as neurotransmitters and hormones) • Act in fight or flight response

28. Hormones and Reproductive Behavior • Gonads: govern reproductive function by way of homeostatic feedback loops • Males: testes • Females: ovaries • Primary reproductive organs • Produce gametes and secrete sex hormones- estrogen, progesterone, androgens (testosterone)

29. Hormones and Reproductive Behavior • Puberty: postembryonic stage of development when reproductive organs and structures mature • Libido: desire for sex • Testosterone • Small amounts in women control libido • Small amounts of estrogen in males help sperm mature

30. Hormones and Reproductive Behavior • Pineal Gland: brain, secretes melatonin, an amine hormone that is part of internal timing mechanism (biological clock) • Melatonin decreases in response to light • Amount of light varies from day to night and varies with seasons, so does melatonin production • Variations in melatonin affect functions of gonads • Higher melatonin levels suppress sexual activity • Melatonin levels in humans: drop in melatonin correlates with onset of puberty • Also influences neurons that lower body temperature and make us drowsy in low light, more responsive in light

31. Reference • 36.12 Page 634-635, tables 36.3 and 36.4 • 36.7 • 36.9 • 36.11