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Section 3 Thyroid Gland

Section 3 Thyroid Gland. I. Biological Actions of Thyroid Hormones. T 3 and T 4 bind with nuclear receptor, activate and initiate genetic transcription. ---- mRNA protein synthesis in cytoplasmic ribosomes ---- general increase in functional activity throughout the body. 1. On Metabolism.

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Section 3 Thyroid Gland

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  1. Section 3 Thyroid Gland

  2. I. Biological Actions of Thyroid Hormones • T3 and T4 bind with nuclear receptor, • activate and initiate genetic transcription. ---- mRNA • protein synthesis in cytoplasmic ribosomes ---- • general increase in functional activity throughout the body.

  3. 1. On Metabolism • Calorigenic action of thyroid hormones • Effect on metabolism of • protein • carbohydrate • fat

  4. Calorigenic action • increase O2 consumption of most tissues in the body, increasing heat production and BMR. • mechanism • A: Enhances Na+-K+ ATPase activity • B: Causes the cell membrane of most cells to become leaky to Na+ ions

  5. on metabolism of protein • Physiological level: stimulates synthesis of proteins and enzymes, • Hyperthyroidism: catabolism of protein, leads weigh-loss and muscle weakness • Hypothyroidism: myxedema (粘液性水肿） develops because of deposition of mucoprotein binding with positive ions and water molecules in the interstitial spaces while protein synthesis decreases

  6. On carbohydrate metabolism • Increase absorption of glucose from the gastrointestinal tract • Enhance glycogenolysis, and even enhanced diabetogenic effect of glucagon, cortisol and growth hormone. • Enhancement of glucose utilization of peripheral tissues.

  7. On fat metabolism • Fatty acids: • accelerate the oxidation of free fatty acids • increase the effect of catecholamine on decomposition of fat. • decrease plasma cholesterol concentration • promote synthesis • increase decomposition

  8. 2. on Growth and Development • essential for normal growth and development • especially skeletal growth and development. • stimulate formation of dendrites, axons, myelin and neuroglia. • Critinism • A child without a thyroid gland • growth and mental retardation.

  9. 3. Effects on Nervous System • increase excitability of • central nervous system • sympathetic nervous system • Hyperthyroidism: • extreme nervousness, • many psychoneurotic tendencies including anxiety complexes, extreme worry,paranoia （妄想）and muscle tremor . Hyperthyroidism

  10. Effects on Nervous System • Hypothyroidism • fatigue • extreme somnolence • poor memory • slow mentation （精神状态）

  11. 4. Other Effects • on cardiovascular system • increase heart rate and stroke volume, • (may through enhance calcium release from sarcoplasmic reticulum) • on gastrointestinal tract • increase the appetite and food intake by metabolic rate increased. • increase both the rate of secretion of the digestive juices and the motility of the gastrointestinal tract. • Lack of thyroid hormone can cause constipation.

  12. II Regulation of Thyroid Hormone Secretion • Hypothalamic Pituitary Thyroid Axis • Feedback Mechanisms • Autoregulation • Effect of Autonomic Nervous System

  13. Hypothalamic Pituitary Thyroid Axis • TSH (throid-stimulating hormone): • Increase secretion of T4 and T3 • Stimulate thyroid gland to growth, increasing size and number of thyroid cells

  14. Hypothalamic Pituitary Thyroid Axis • TRH（thyrotropin-releasing hormone) • causes the anterior pituitary to produce and release of TSH. • Cold and various emotional reactions can increase TRH secretion through nervous system

  15. Feedback Mechanisms of Thyroid Hormones • T3 and T4inhibitory proteinin anterior pituitary • reduces production and secretion of TSH • decrease response of pituitary to TRH • Negative feedback

  16. (Inhibitory Protein)

  17. In the absence of sufficient dietary iodide the thyroid cannot produce adequate amounts of T4 and T3. causes abnormally high level of the TSH secretion, which in turn stimulate the abnormal growth of the thyroid (a goiter).

  18. Autoregulation of Thyroid Hormone Secretion • thyroid gland adapt itself function to iodide uptake, • When iodine is insufficient, the thyroid gland increases formation of hormones • large doses of iodide act directly on the thyroid gland to produce a mild and transit inhibition of hormone synthesis. • In patients with hyperthyroidism • iodides cause the vascularity of hyperplastic gland to decrease (Wolff-Chaikoff effect) • making iodide treatment considerable in preparing patients for surgery.

  19. Effect of Autonomic Nervous System on Thyroid Activity • The thyroid gland is innervated by both sympathetic nerve and parasympathetic nerve. • sympathetic nerve increases formation of thyroid hormones • cholinergic fibers (vagus nerve) inhibits secretion of thyroid hormone

  20. Section 4 Adrenal Gland

  21. Adrenal Cortical Hormones • The mineralocorticoids are secreted by zona glomerulosa • regulates the concentration of the extracellular fluid. • Aldosterone is the principal mineralocorticoid.

  22. The glucocorticoids are secreted by both zona fasciculata and zona reticularis, • exhibiting an important effect on increasing blood glucose concentration • Cortisol is the principal glucocorticoid • Small amounts of sex hormones are secreted by the zona reticularis.

  23. 1. Biological Effects of Adrenocortical Hormones CBD, corticosteroid-binding globulin; GR, glucocorticoid receptor

  24. On metabolism • On carbohydrate metabolism. • A, Stimulation of gluconeogenesis by the liver cell • ----activates DNA transcription in the liver cell nuclei and increase the synthesis of enzymes required for gluconeogenesis. • ----causes mobilization of amino acids from extrahepatic tissues, mainly from muscle. • Result: a marked increase in glycogen storage in the liver cells.

  25. B, Reduction of glucose utilization by the cells. • by inhibition of response of cells to insulin. • Elevate blood glucose concentration

  26. 2) On protein metabolism • A. mobilizes amino acids from the nonhepatic tissues and diminishes the tissue stores of protein. • B. decreases protein synthesis and increases catabolism of protein in many extrahepatic tissues • especially in muscle and lymphoid tissue • In the presence of great excesses of cortisol, the muscles become weak and the immunity functions of lymphoid tissue decrease.

  27. 3) On fat metabolism A. Promote mobilization of fatty acids from adipose tissue and increases the concentration of free acids in the plasma B. Increases oxidationof fatty acids in the liver cells for energy.

  28. Cushing’s Syndrome People with excess cortisol secretion develop a peculiar type of obesity excess deposition of fat in the chest and head regions of the body a buffalo-like torso and a rounded “moon-face”.

  29. Cushing’s Syndrome “moon face” striae

  30. 4) Effects on water and electrolytes slight enhancement of sodium reabsorption and potassium excretion by distal tubules and colleting ducts in kidney. increases the rate of renal blood flow and then glomerular filtration rates, facilitating water excretion In patients with adrenal insufficiency, excretion of water is so slow that there is a danger of water intoxication and only glococorticoids can repair this deficit.

  31. (2) On blood cells • increase the production of red cells and platelets by stimulating bone marrow. • decrease the number of lymphocytes and eosinocytes (嗜酸性粒细胞） • causes atrophy of the all lymphoid tissues and promotion of destruction of lymphocytes and eosinocytes.

  32. (3) On cardiovascular system • necessary for maintenance of normal blood pressure. • Cause permissive action, enhancing the response of vascular muscle to catecholamines. • Inhibit synthesis of prostaglandins that have vasodilator effect. • Reduces the permeability of capillaries, which is useful to maintenance of blood volume.

  33. (4) Effect on stress. Almost any type of stress cause increase in ACTH secretion, and consequent cortisol secretion. essential for survival.

  34. (5) Other effects. increase in production of HCl and pepsin, promotion of synthesis of fetal surfactant. pharmacological effects including anti-inflammatory, antiallergic and antishock effect.

  35. 2. Regulation of Secretion of Adrenocortical Hormone • Hypothalamus – Anterior Pituitary – Adrenocortical Axis • Action of ACTH (adrenocorticotropin hormone) • control of cortisol secretion

  36. ACTH causes formation of adrenocortical adrenocortical secretion. hypertrophy and proliferation of the adrenocorticol cells.

  37. (2) CRH (corticotropin releasing hormone) A, Action of CRH promote synthesis and release of ACTH B, Regulation of CRH secretion

  38. Fluctuations in plasma ACTH and glucotorticoids throughout the day in a normal girl (age 16). The circadian rhythm is driven by impulses from the supra-chiasmatic nuclei 11-OHCS (11-hydroxycorticosteroids, １１－羟皮质类醇 )

  39. (3) Feedback mechanism Cortisol has direct negative feedbacks on the hypothalamus to decrease formation of CRH High circulating levels of cortisol inhibit secretion and formation of ACTH, decreasing response of anterior pituitary gland to CRH.

  40. High levels of ACTH also inhibit CRH secretion by a negative feedback mechanism. These feedbacks help regulate the plasma concentration of cortisol toward a normal control level.

  41. Clinical treatment of cortisol (large does and long time) always cause the atrophy of the adrenal gland.

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