1. The Endocrine System

2. Thyroid Gland  Found at the base of the throat  Consists of two lobes and a connecting isthmus  Produces two hormones

3. Thyroid Gland Figure 9.7a

4. Thyroid Gland  Thyroid hormone  Major metabolic hormone  Composed of two active iodine-containing hormones  Thyroxine (T 4 )—  Triiodothyronine (T 3 )—

5. Thyroid Gland Figure 9.7b

6. Thyroid hormone disorders Goiters  Thyroid gland enlarges due to lack of iodine Cretinism  Caused by hyposecretion of thyroxine (T4)

7. Goiter Figure 9.8

8. Cretinism Figure 9.8

9. Thyroid hormone disorders Myxedema  Caused by hypothyroidism in adults Graves’ disease  Caused by hyperthyroidism

10. Myxedema

11. Grave’s Disease

12. Thyroid Hormone Calcitonin (CT)  Decreases blood calcium levels by causing its deposition on bone

13. Thyroid Gland Figure 9.7b

14. Parathyroid Glands  Tiny masses on the posterior of the thyroid  Secrete parathyroid hormone (PTH)

15. Hormonal Regulation of Calcium in Blood Figure 9.10 Calcium homeostasis of blood 9–11 mg/100 ml Rising blood Ca 2+ levels Thyroid gland releases calcitonin Osteoclasts degrade bone matrix and release Ca 2+ into blood PTH Calcitonin Calcitonin stimulates calcium salt deposit in bone Parathyroid glands release parathyroid hormone (PTH) Thyroid gland Parathyroid glands Falling blood Ca 2+ levels Imbalance

16. Adrenal Glands  On top of the kidneys  Two regions  Adrenal cortex—  Mineralocorticoids secreting area  Glucocorticoids secreting area  Sex hormones secreting area  Adrenal medulla—

18. Hormones of the Adrenal Cortex Figure 9.11

19. Hormones of the Adrenal Cortex  Mineralocorticoids (mainly aldosterone)  Produced in outer adrenal cortex

20. Hormones of the Adrenal Cortex Figure 9.12

21. Hormones of the Adrenal Cortex  Glucocorticoids (including cortisone and cortisol)  Middle layer of the adrenal cortex  Normal cell metabolism

22. Roles of the Hypothalamus and Adrenal Glands in the Stress Response Short termMore prolonged Stress Hypothalamus Nerve impulses Adrenal cortex Releasing hormone Corticotropic cells of anterior pituitary ACTH MineralocorticoidsGlucocorticoids 1.Retention of sodium and water by kidneys 2.Increased blood volume and blood pressure 1. Proteins and fats converted to glucose or broken down for energy 2. Increased blood sugar 3. Suppression of immune system Long-term stress response Short-term stress response Spinal cord Adrenal medulla Preganglionic sympathetic fibers Catecholamines (epinephrine and norepinephrine) 1. Increased heart rate 2. Increased blood pressure 3. Liver converts glycogen to glucose and releases glucose to blood 4. Dilation of bronchioles 5. Changes in blood flow patterns, leading to increased alertness and decreased digestive and kidney activity 6. Increased metabolic rate

23. Hormones of the Adrenal Cortex Sex hormones  Inner layer of the adrenal cortex  Small amounts are made throughout life

24. Adrenal cortex disorders Addison’s disease  Hyposecretion of all adrenal cortex hormones Hyperaldosteronism  May result from an ACTH-releasing tumor

25. Adrenal cortex disorders Cushing’s syndrome  “Moon face,” “buffalo hump” on the upper back, high blood pressure, hyperglycemia, weakening of bones, depression Masculinization  Results from hypersecretion of sex hormones  Beard and male distribution of hair growth

26. Cushing’s Syndrome

28. Hormones of the Adrenal Medulla  Produces two similar hormones (catecholamines)  Epinephrine (adrenaline)  Norepinephrine (noradrenaline)

29. Hormones of the Adrenal Medulla  These hormones prepare the body to deal with short- term stress (“fight or flight”) by:

30. Hormones of the Adrenal Cortex Figure 9.11

31. Pancreatic Islets  Both endocrine and exocrine functions  The pancreatic islets produce hormones  Insulin—  Glucagon—

32. Pancreatic Islets Figure 9.14a–b

33. Pancreatic Islets Figure 9.14b–c

34. Figure 9.15 Insulin-secreting cells of the pancreas activated; release insulin into the blood Elevated blood sugar levels Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts) Rising blood glucose levels return blood sugar to homeostatic set point; stimulus for glucagon release diminishes Blood glucose levels decline to set point; stimulus for insulin release diminishes Stimulus: declining blood glucose levels (e.g., after skipping a meal) Low blood sugar levels Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver Uptake of glucose from blood is en- hanced in most body cells Liver breaks down glycogen stores and releases glucose to the blood Liver takes up glucose and stores it as glycogen Homeostasis: Normal blood glucose levels (90 mg/100ml) Imbalance

35. Pineal Gland  Found on the third ventricle of the brain  Secretes melatonin

36. Thymus Gland  Located posterior to the sternum  Largest in infants and children  Produces thymosin

37. Gonads Ovaries  Produce eggs  Produce two groups of steroid hormone Testes  Produce sperm

38. Hormones of the Ovaries Estrogens  Stimulate the development of secondary female characteristics With progesterone, estrogens also  Promote breast development

39. Hormones of the Ovaries Progesterone  Acts with estrogen to bring about the menstrual cycle

40. Hormones of the Testes  Produce several androgens  Testosterone is the most important androgen  Responsible for adult male secondary sex characteristics