Chapter 15

1. Chapter 15 Biology 25: Human Biology Prof. Gonsalves Los Angeles City College Based on Mader’s Human Biology,7th edition and Fox’s 8th ed Powerpoints

4. Hormones • Regulatory molecules secreted into the blood or lymph by endocrine glands. • Lack ducts. • Carry hormone to target tissue where it produces its effects.

5. Chemical Classification of Hormones • Amines • Polypeptides • Glycoproteins • Steroids

6. Amines • Hormones derived from tyrosine and tryptophan. • Include hormones secreted by adrenal medulla, thyroid, and pineal glands.

7. Polypeptides • Chains of amino acids (< 100 amino acids in length). • ADH • Insulin

8. Glycoproteins • Long polypeptides (>100) bound to one or more carbohydrate (CHO) groups. • FSH • LH

9. Steroids • Lipids derived from cholesterol. • Are lipophilic hormones. • Testosterone • Estradiol • Cortisol • Progesterone

10. Thyroid Hormones • Tyrosine derivatives bound together. • Contain 4 iodine atoms (T4). • Contain 3 iodine atoms (T3). • Small, non-polar molecules. • Soluble in plasma membranes.

11. Hormone Precursors • Prohormone: • Precursor is a longer chained chemical that is cut and spliced to make the hormone. • Preprohormone: • Prohormone derived from larger precursor molecule. • Prehormone: • Molecules secreted by endocrine glands that are inactive until changed to hormones by target cells.

12. Anterior and posterior pituitary glands.

13. Posterior Pituitary • Also called the neurohypophysis. • Formed by downgrowth of the brain during fetal development. • Is in contact with the infundibulum. • Nerve fibers extend through the infundibulum.

14. Hypothalamic Control of Posterior Pituitary • Hypothalamus produces: • ADH: supraoptic nuclei. • Oxytocin: paraventricular nuclei. • Hormones transported along the hypothalamo-hypophyseal tract. • Stored in posterior pituitary. • Release controlled by neuroendocrine reflexes.

15. Anterior Pituitary • Master gland (also called adenohypophysis). • Derived from a pouch of epithelial tissue that migrates upward from the mouth. • Consists of 2 parts: • Pars distalis: anterior pituitary. • Pars tuberalis: thin extension in contact with the infundibulum.

16. Anterior Pituitary • Trophic effects: • Health of the target glands, depends upon stimulation by anterior pituitary for growth. • High plasma hormone concentration causes target organ to hypertrophy. • Low plasma hormone concentration causes target organ to atrophy.

19. Hypothalamic Control of the Anterior Pituitary • Hormonal control rather than neural. • Hypothalamus synthesizes releasing hormones and inhibiting hormones. • Hormones are transported to axon endings of median eminence. • Delivers blood and hormones to anterior pituitary via portal system.

20. Hypothalamic Control of the Anterior Pituitary • Hormones secreted into the hypothalamo-hypophyseal portal system regulate the secretions of the anterior pituitary.

21. Feedback Control of the Anterior Pituitary • Anterior pituitary and hypothalamic secretions are controlled by the target organs they regulate. • Negative feedback inhibition by target gland hormones.

22. Feedback Control of the Anterior Pituitary • Negative feedback at 2 levels: • The target gland hormone can act on the hypothalamus and inhibit releasing hormones. • The target gland hormone can act on the anterior pituitary and inhibit response to the releasing hormone.

25. Growth Hormone (GH) - Somatotrophic Hormone (STH) • Increases Growth and Maintenance of Organs by: • stimulating protein anabolism • promotes fat catabolism (use of fat rather than sugars for energy) •  Abnormal Secretions of STH • Giantism -- hypersecretion during childhood (before epiphyseal plates close) • Acromegaly -- hypersecretion during adulthood • Dwarfism -- hyposecretion during childhood • Cachexia (Simmond's Disease) - hyposecretion during adulthood causes premature aging and atrophy of organs

27. Thyroid Hormones • Thyroid gland located just below the larynx. • Thyroid is the largest of the pure endocrine glands. • Follicular cells secrete thyroxine. • Parafollicular cells secrete calcitonin.

28. Production of Thyroid Hormones • I- (iodide) actively transported into the follicle and secreted into the colloid. • Oxidized to (Io) iodine. • Iodine attached to tyrosine. • Attachment of 1 iodine produces monoiodotyrosine (MIT). • Attachment of 2 iodines produces diiodotyrosine (DIT). • MIT and DIT or 2 DIT molecules coupled.

29. Production of Thyroid Hormones • T3 and T4 produced. • TSH stimulates pinocytosis into the follicular cell. • Enzymes hydrolyze to T3 and T4 from thyroglobulin. • Attached to thyroid-binding protein and released into blood.

31. T3 Effects • Stimulates cellular respiration by: • Production of uncoupling proteins. • Stimulate active transport Na+/ K+ pumps. • Lower cellular [ATP]. • Increases metabolic heat. • Increases metabolic rate. • Stimulates increased consumption of glucose, fatty acids and other molecules.

35. Parathyroid Hormone • Parathyroid glands embedded in the lateral lobes of the thyroid gland. • Only hormone secreted by the parathyroid glands. • Single most important hormone in the control of plasma Ca++ concentration. • Stimulated by decreased plasma Ca++ concentration.

37. Disorders of the Thyroid Hyperthyroidism (Grave's disease) • elevated PBI • increases nervousness and irritability • elevated BMR • exophthalmos - results in edema behind the eyes • Hypothyroidism • Cretinism - occurs if the hyposecretion is during fetal or early developmental life. • results in reduced metabolism • results in reduced growth • results in mental retardation • Myxedema - occurs if the hyposecretion is during adult life • results in reduced metabolism • results in reduced mental & physical activity • results in increased blood pressure • results in accumulation of subcutaneous fluids

39. Adrenal Glands • Paired organs that cap the kidneys. • Each gland consists of an outer cortex and inner medulla. • Adrenal medulla: • Derived from embryonic neural crest ectoderm (sympathetic ganglia). • Synthesizes and secretes: • Catecholamines (mainly epinephrine but some norepinephrine).

41. Adrenal Glands • Adrenal cortex: • Does not receive neural innervation. • Must be stimulated hormonally. • Consists of 3 zones: • Zona glomerulosa: • Aldosterone: regulate Na+ and K+ balance. • Zona fasciculata: • Cortisol: regulate glucose metabolism. • Zona reticularis: • Androstenedione and DHEA: supplement sex steroids.

43. Adrenal Medulla • Innervated by sympathetic nerve fibers. • Increase respiratory rate. • Increase heart rate, cardiac output; and vasoconstrict blood vessels, thus increasing venous return. • Stimulate glycogenolysis. • Stimulate lipolysis.

44. General Adaptation Syndrome (GAS) • Stress stimulates pituitary-adrenal axis • Alarm phase: • Adrenal glands activated. • Stage of resistance: • Stage of readjustment. • Stage of exhaustion: • Sickness and/or death if readjustment does not occur.

48. Abnormal Adrenal Cortical Function: • Addison's Disease - caused by Hyposecretion of Cortical hormones • results in increased blood potassium levels • results decreased sodium retention and dehydration • results decreased blood glucose levels • results decreased blood pressure • results decreased stress resistance • results increased risk of kidney failure • Cushing's syndrome - causes by Hypersecretion of Cortical Hormones • results in shifts of the body fat to the face and shoulders • results in general body weakness • results in altered carbohydrate & electrolyte metabolism • Adrenogenital Syndrome - caused by Hypersecretion of Gonadotropins • results in premature sexual development in both males and females • results in masculinization of females