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Chapter 23

Chapter 23. Endocrine Control of Growth and Metabolism. About this Chapter. How several key hormone pathways influence metabolism How cortisol is produced & regulated; how it impacts many tissues How thyroid hormones are regulated and their effect on targets

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Chapter 23

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  1. Chapter 23 Endocrine Control of Growth and Metabolism

  2. About this Chapter • How several key hormone pathways influence metabolism • How cortisol is produced & regulated; how it impacts many tissues • How thyroid hormones are regulated and their effect on targets • The role of growth hormone in growth & development • Calcium metabolism and its role in bones and cell regulations

  3. Endocrine Control in Review • Hypothalamic – pituitary: feedback loop & trophic control • Hormones can have receptors on many diverse tissues • Usually initiating protein change or synthesis in target cells • Problems come from too much or too little hormone

  4. Adrenal Cortex: Steroid Hormone Production Figure 23-2: Synthesis pathways of steroid hormones

  5. Cortisol Effects: Body Responses to Stress • Permissive effect on glucagon • Memory, learning & mood • Gluconeogenesis • Skeletal muscle breakdown • Lipolysis, calcium balance • Immune depression • Circadian rhythms

  6. Cortisol Effects: Body Responses to Stress Figure 23-4: Circadian rhythm of cortisol secretion

  7. Control of Cortisol Secretion: Feedback Loops • External stimuli • Hypothalamic • Anterior Pituitary • Adrenal cortex • Tissues Figure 23-3: The control pathway for cortisol

  8. Endocrine Control: Three Levels of Integration Figure 7-13: Hormones of the hypothalamic-anterior pituitary pathway

  9. Cortisol: Role in Diseases and Medication • Use as immunosuppressant • Hyperimmune reactions (bee stings) • Serious side effects • Hypercortisolism (Cushing's syndrome) • Tumors (pituitary or adrenal) • Iatrogenic (physician caused) • Hypocortisolism (Addison's disease)

  10. Thyroid Gland: Hormones and Iodine Metabolism • C-cells – calcitonin (covered later) • Follicle cells • Amine hormones: • thyroxine, T1, T2 & T3 •  growth •  metabolism • Thermogenic

  11. Effects of Thyroid Hormone • TH is concerned with: • Glucose oxidation • Increasing metabolic rate • Heat production • TH plays a role in: • Maintaining blood pressure • Regulating tissue growth • Developing skeletal and nervous systems • Maturation and reproductive capabilities

  12. Thyroid Hormone • Thyroid hormone – the body’s major metabolic hormone • Consists of two closely related iodine-containing compounds • T4 – thyroxine; has two tyrosine molecules plus four bound iodine atoms • T3 – triiodothyronine; has two tyrosines with three bound iodine atoms

  13. Thyroid Gland: Hormones and Iodine Metabolism Figure 23-7b: The thyroid gland

  14. Thyroxine and its precursors: Structure & Synthesis Figure 23-8: Thyroid hormones are made from tyrosine and iodine

  15. Thyroxine and its precursors: Structure & Synthesis Figure 23-9: Thyroid hormone synthesis

  16. Synthesis of Thyroid Hormone • Thyroglobulin is synthesized and discharged into the lumen • Iodides (I–) are actively taken into the cell, oxidized to iodine (I2), and released into the lumen • Iodine attaches to tyrosine, mediated by peroxidase enzymes, forming T1 (monoiodotyrosine, or MIT), and T2 (diiodotyrosine, or DIT) • Iodinated tyrosines link together to form T3 and T4 • Colloid is then endocytosed and combined with a lysosome, where T3 and T4 are cleaved and diffuse into the bloodstream

  17. Transport and Regulation of TH • T4 and T3 bind to thyroxine-binding globulins (TBGs) produced by the liver • Both bind to target receptors, but T3 is ten times more active than T4 • Peripheral tissues convert T4 to T3 • Mechanisms of activity are similar to steroids • Regulation is by negative feedback • Hypothalamic thyrotropin-releasing hormone (TRH) can overcome the negative feedback

  18. T3 & T4 Control Pathways & Diseases from Malfunction • Hypothalamus • Anterior Pituitary • Thyroid • Hypothyroidism • Goiter (TSH ) • Grave's disease

  19. T3 & T4 Control Pathways & Diseases from Malfunction Figure 23-12: Thyroid hormone pathway

  20. Growth Hormone (GH): Functions & Malfunctions • Polypeptide H from hypothalamus/anterior pituitary •  growth (with T4, sex Hs, paracrines) •  metabolism •  protein & bone synthesis • Regulation – hypothalamus • Dwarfism • Acromegaly

  21. Metabolic Action of Growth Hormone Figure 16.6

  22. Growth Hormone (GH): Functions & Malfunctions Figure 23-16: Growth hormone pathway

  23. Multiple Hormones Can Target a Cell/Tissue • Growth H • Somatomedins • Thyroxin • All have receptors on many tissues • Stimulate pathways for growth Figure 7-17: A complex endocrine pathway

  24. Bone Growth and Calcium Metabolism • Epiphyseal plate – new bone growth site • Chondrocytes, osteoblasts & calcification build bone

  25. Bone Growth and Calcium Metabolism Figure 23-19: Bone growth at the epiphyseal plate

  26. Calcium Metabolism: • Maintain [plasma]: from diet, from bone "storage", recycled • Key roles: muscle contraction, bone support, cell signaling

  27. Calcium Metabolism: Figure 23-20: Calcium balance in the body

  28. Control of Calcium Balance & Metabolism • Parathyroid H • Calcitrol • Vitamin D • Sun/diet • Calcitonin • Thyroid • C-cells • (Phosphate balance) Figure 23-23: Endocrine control of calcium balance

  29. Osteoporosis: Disease of Bone Growth & Calcium Metabolism • Bone reabsorption exceeds deposition • Osteoclasts mobilize Ca++ to plasma • Factors: inadequate Ca++ intake, genes, hormones, smoking Figure 23-21: Osteoclasts are responsible for bone resorption

  30. Summary • In addition to insulin and glucagon, metabolism is influenced by hormones from adrenal, thyroid, parathyroid and hypothalamus • Cortisol  catabolic activities responding to stress • Growth H  anabolic activities to promote growth • PTH, cacitrol, & calcitonin balance plasma [Ca++] for bone synthesis, muscle contraction, & cell signaling • Endocrine diseases result from pathway or glandular hypo or hyper secretion

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