Chapter 31 Endocrine Control (Sections 31.6 - 31.11)

1. Chapter 31Endocrine Control(Sections 31.6 - 31.11)

2. 31.6 Thyroid and Parathyroid Glands The thyroid gland regulates metabolic rate, and the adjacent parathyroids regulate calcium levels thyroid gland Endocrine gland at the base of the neck Produces thyroid hormone, which increases metabolism parathyroid glands Four small endocrine glands whose hormone product increases the level of calcium in blood

3. Thyroid Function The thyroid secretes thyroid hormone (two iodine-containing molecules: triiodothyronine and thyroxine) which increases metabolic activity of tissues throughout the body The thyroid gland also secretes calcitonin, a hormone that causes deposition of calcium in bones of growing children The anterior pituitary gland and hypothalamus regulate thyroid hormone secretion by a negative feedback loop

4. Feedback Control of Thyroid Function A low level of thyroid hormone causes the hypothalamus to secrete thyroid-releasing hormone (TRH) TRH causes the anterior pituitary to secrete thyroid-stimulating hormone (TSH) TSH stimulates the secretion of thyroid hormone When the blood level of thyroid hormone rises, secretion of TRH and TSH declines

5. Negative Feedback Loop

6. Negative Feedback Loop STIMULUS RESPONSE Hypothalamus Blood level of thyroid hormone falls below a set point. TRH 4 1 Anterior Pituitary Rise of thyroid hormone level in blood inhibits the secretion of TRH and TSH. TSH 2 Thyroid Gland 3 Thyroid hormone is secreted. Fig. 31.7, p. 511

7. RESPONSE STIMULUS + Blood level of thyroid hormone falls below a set point. Hypothalamus TRH Anterior Pituitary Rise of thyroid hormone level in blood inhibits the secretion of TRH and TSH. TSH Thyroid Gland Thyroid hormone is secreted. Negative Feedback Loop Stepped Art Fig. 31.7, p. 511

8. Hypothyroidism A diet deficient in iodine can cause thyroid hormone deficiency (hypothyroidism) Hypothyroidism can also arise when the body’s immune system mistakenly attacks the thyroid In either case, ongoing stimulation of the thyroid can lead to thyroid enlargement, or goiter

9. Goiter Enlarged thyroid (goiter) caused by a dietary iodine deficiency

10. Parathyroid Glands and Calcium Levels Four parathyroid glands located at the rear of the thyroid gland are the main regulators of calcium levels in the blood When blood calcium level declines, the glands release parathyroid hormone (PTH), which increases breakdown of bone – blood calcium level rises PTH also encourages calcium reabsorption by kidneys and activation of vitamin D, which helps the intestine take up calcium from food

11. Rickets Rickets caused by a lack of vitamin D Parathyroid hormone softens the bones, causing bowed legs

12. ANIMATION: Parathyroid hormone action To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

13. 31.7 The Adrenal Glands • There are two adrenal glands, one above each kidney • An adrenal gland has two functional zones, controlled by different mechanisms: • The outer cortex secretes steroid hormones • The inner medulla releases molecules that function as neurotransmitters

14. Key Terms • adrenal gland • Endocrine gland that is located atop the kidney • adrenal cortex • Outer portion of adrenal gland • Secretes aldosterone and cortisol • adrenal medulla • Inner portion of adrenal gland • Secretes epinephrine and norepinephrine

15. The Adrenal Cortex • The adrenal cortex secretes two steroid hormones: • Aldosterone controls sodium and water reabsorption in the kidneys • Cortisol helps maintain blood glucose available to the brain by inducing the liver to break down glycogen, adipose cells to degrade fats, and skeletal muscles to degrade proteins

16. Negative Feedback and Cortisol • Cortisol secretion is governed by a negative feedback loop to the anterior pituitary gland and hypothalamus • In times of stress, the central nervous system overrides the feedback controls so that cortisol levels rise • Over the long term, excess cortisol has negative impacts on health

17. Negative Feedback Mechanism • A decrease in cortisol triggers secretion of CRH (corticotropin-releasing hormone) by the hypothalamus • CRH stimulates secretion of ACTH by the anterior pituitary • ACTH causes release of cortisol from the adrenal cortex • Cortisol level increases, causing hypothalamus and anterior pituitary to secrete less CRH and ACTH, and cortisol secretion slows

18. Negative Feedback Mechanism

19. STIMULUS RESPONSE Negative Feedback Mechanism Hypothalamus Blood level of cortisol declines. CRH 1 4 Anterior Pituitary adrenal cortex Rise of cortisol level in the blood inhibits the secretion of CRH and ACTH. ACTH 2 adrenal medulla Adrenal Cortex 3 Cortisol secretion increases and has the following effects: Cellular uptake of glucose from blood slows in many tissues, especially muscles (but not in the brain). Protein breakdown accelerates, especially in muscles. Some of the amino acids freed by this process get converted to glucose. Fats in adipose tissue are degraded to fatty acids and enter blood as an alternative energy source, indirectly adrenal cortex adrenal medulla kidney conserving glucose for the brain. kidney Fig. 31.9, p. 512

20. STIMULUS + RESPONSE A Blood level of cortisol falls below a set point. Hypothalamus adrenal cortex D Hypothalamus and pituitary detect rise in blood level of cortisol and slow its secretion. ACTH adrenal medulla Adrenal Cortex C Cortisol is secreted and has the following effects: Cellular uptake of glucose from blood slows in many tissues, especially muscles (but not in the brain). Protein breakdown accelerates, especially in muscles. Some of the amino acids freed by this process get converted to glucose. Fats in adipose tissue are degraded to fatty acids and enter blood as an alternative energy source, indirectly conserving glucose for the brain. Negative Feedback Mechanism B CRH Anterior Pituitary Stepped Art Fig. 31.9, p. 512

21. The Adrenal Medulla • The adrenal medulla contains specialized neurons of the sympathetic division that release norepinephrine and epinephrine that enter the blood and function as hormones • Like sympathetic stimulation, norepinephrine and epinephrine cause a fight-flight response: they dilate the pupils, increase breathing, and make the heart beat faster

22. Stress, Elevated Cortisol, and Health • When an animal is frightened or under physical stress, commands from the nervous system trigger increased secretion of cortisol, epinephrine, and norepinephrine • Physiological responses to chronic stress interfere with growth, the immune system, sexual function, and cardiovascular function • Chronically high cortisol levels harm cells in the hippocampus, a brain region central to memory and learning

23. Elevated Cortisol: Cushing Syndrome • Before and after removal of a adrenal gland tumor

24. Hypocortisolism: Addison’s Disease • Tuberculosis and other infectious diseases can damage adrenal glands, resulting in adrenal insufficiency • President John F. Kennedy had an autoimmune form of Addison’s Disease

25. 31.8 Pancreatic Hormones • The pancreashas both exocrine and endocrine functions: • Exocrine cells secrete digestive enzymes into a duct to the small intestine • Endocrine cells are grouped in pancreatic islets; each islet contains three types of hormone-secreting cells • pancreas • Organ that secretes digestive enzymes into the small intestine and hormones into the blood

26. The Pancreas and Digestion • Delta cells in pancreatic islets secrete somatostatin • Somatostatin helps control digestion and nutrient absorption

27. The Pancreas and Digestion Fig. 31.12a, p. 514

28. The Pancreas and Digestion stomach pancreas small intestine Fig. 31.12a, p. 514

29. The Pancreas and Blood Sugar • Two pancreatic hormones with opposing effects work together to regulate the level of sugar in the blood • Insulin (secreted by beta cells) stimulates glucose uptake by muscle and liver cells and thus lowers the blood glucose • Glucagon (secreted by alpha cells) stimulates the release of glucose, which increases blood levels

30. Regulating High Blood Sugar • Blood glucose rises • Glucagon is blocked • Insulin is secreted • Glucose is taken up • Blood glucose level decreases

31. Regulating High Blood Sugar Stimulus 1 Increase in blood glucose PANCREAS 3 2 glucagon insulin LIVER MUSCLE FAT CELLS Body cells, especially in muscle and adipose tissue, take up and use more glucose. Cells in skeletal muscle and liver store glucose in the form of glycogen. 4 Response 5 Decrease in blood glucose Fig. 31.12b, p. 514

32. Regulating Low Blood Sugar • Low blood glucose • Glucagon is secreted • Insulin is blocked • Liver breaks down glycogen into glucose • Blood glucose increases

33. Regulating Low Blood Sugar Stimulus 6 Decrease in blood glucose 7 8 glucagon insulin Cells in liver break down glycogen faster. The released glucose monomers enter blood. 9 Response 10 Increase in blood glucose Fig. 31.12c, p. 514

34. ANIMATION: Hormones and glucose metabolism To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

35. 31.9 Diabetes • Diabetes mellitus is a disorder in which the body does not make or does not respond to insulin • When cells do not take up and store glucose as they should, high blood sugar (hyperglycemia) disrupts normal metabolism • Cells have to use proteins and fats for energy – breakdown of these substances yields harmful waste products

36. Some Complications of Diabetes

37. Type 1 Diabetes • Type 1diabetes develops after white blood cells wrongly identify insulin-secreting beta cells as foreign (nonself) and destroy them (autoimmune response) • All affected individuals require injections of insulin, and must monitor their blood sugar level carefully • When fats and proteins are used as energy sources, ketones accumulate in the blood and urine (ketosis)

38. Insulin Pump • An insulin pump helps smooth out fluctuations in blood sugar, lowering risk of complications

39. Type 2 Diabetes • In type 2 diabetes insulin levels are normal or even high • However, target cells do not respond to the hormone as they should, and blood sugar levels remain elevated • Western diets and sedentary life-styles are contributing factors in type 2 diabetes – diet, exercise, and oral medications can control most cases

40. 31.10 Gonads, Pineal Gland, and Thymus • Outputs from gonads, pineal gland, and thymus all change as an individual enters puberty • gonads • Primary reproductive organs (ovaries or testes) that produce gametes and sex hormones • pineal gland • Endocrine gland deep inside the brain that secretes melatonin when the retina is not stimulated by light • thymus • Endocrine gland beneath the breastbone; secretes hormones that encourage maturation of T lymphocytes

41. The Gonads • Gonads are primary reproductive organs, which produce gametes (eggs or sperm) • Gonads produce steroid sex hormones with roles in reproduction and development of secondary sexual traits • Male gonads (testes) secrete mainly testosterone • Female gonads (ovaries) secrete mainly estrogens and progesterone

42. Location of Human Gonads

43. Location of Human Gonads testis (where sperm originate) Fig. 31.14a, p. 516

44. Location of Human Gonads ovary (where eggs develop) Fig. 31.14b, p. 516

45. Control of Sex Hormone Secretion • The hypothalamus and anterior pituitary control secretion of sex hormones

46. The Pineal Gland • The pineal gland lies deep within the vertebrate brain • Melatonin secreted by the pineal gland affects the daily sleep/wake cycle and the onset of puberty • Melatonin also protects against some cancers • Melatonin secretion declines when the retina detects light and sends action potentials along the optic nerve to the brain

47. The Thymus • The thymus lies beneath the breastbone • It secretes thymosins that encourage maturation of infection-fighting white blood cells (T lymphocytes, or T cells) • At puberty, the surge of sex hormones causes the thymus to shrink, and its secretions decline – this can be a problem for people with HIV infection, because AIDS kills T cells

48. Key Concepts • Other Hormone Sources • Endocrine glands throughout the body respond to signals from the hypothalamus and the pituitary • Others secrete hormones in response to internal changes such as a shift in blood glucose level • Poor diet, immune problems, and genetic factors can cause hormone disorders

49. 31.11 Invertebrate Hormones • Vertebrate hormone receptor proteins often resemble similar receptor proteins in invertebrates and probably evolved from them • Invertebrates also have hormones with no vertebrate counterpart, such as the steroid hormone ecdysone, which regulates molting in arthropods such as crabs and insects

50. Evolution of Receptor Diversity • Genetic analysis has revealed the invertebrate ancestry of some vertebrate hormone receptors • Sea anemones have receptors that are structurally similar to vertebrate receptors for TSH, LH, FSH, and other signaling molecules • Genes that encode these receptors have similar nucleotide sequences in vertebrates and invertebrates, and have the same number and type of introns in similar regions