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Mechanisms of Hormonal Regulation

Mechanisms of Hormonal Regulation. Chapter 20. Hormones. General characteristics Specific rates and rhythms of secretion Diurnal, pulsatile and cyclic, and patterns depending on circulating substances Operate within feedback systems Affect only cells with appropriate receptors

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Mechanisms of Hormonal Regulation

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  1. Mechanisms of Hormonal Regulation Chapter 20

  2. Hormones • General characteristics • Specific rates and rhythms of secretion • Diurnal, pulsatile and cyclic, and patterns depending on circulating substances • Operate within feedback systems • Affect only cells with appropriate receptors • The liver inactivates hormones, rendering the hormones more water soluble for renal excretion

  3. The Endocrine System

  4. Regulation of Hormone Release • Hormones are released: • In response to an alteration in the cellular environment • To maintain a regulated level of certain substances or other hormones • Hormones are regulated by chemical, hormonal, or neural factors • Negative feedback • Positive feedback

  5. Feedback

  6. Hormone Transport • Hormones are released into the circulatory system by endocrine glands • Water-soluble hormones circulate in free, unbound forms • Lipid soluble hormones are primarily circulating bound to a carrier

  7. Cellular Mechanism of Hormone Action • Target cell • Up-regulation • Down-regulation • Hormone effects • Direct effects • Permissive effects

  8. Cellular Mechanism of Hormone Action • Hormone receptors • Located in or on the plasma membrane or in the intracellular compartment of the target cell • Water-soluble hormones • High molecular weight • Cannot diffuse across the plasma membrane • Lipid-soluble hormones • Easily diffuse across the plasma membrane and bind to cytosolic or nuclear receptors

  9. Cellular Mechanism of Hormone Action • Water-soluble hormones • First messenger • Signal transduction • Second-messenger molecules • Calcium • Cyclic adenosine monophosphate (cAMP) • Cyclic guanosine monophosphate (cGMP)

  10. Cellular Mechanism of Hormone Action

  11. Cellular Mechanism of Hormone Action • Lipid-soluble hormones • Steroid hormones • Androgens, estrogens, progestins, glucocorticoids, mineralocorticoids, and thyroid hormones • Diffuse across the plasma membrane • Bind to cytoplasmic or nuclear receptors • Activate • RNA polymerase • DNA transcription and translation

  12. Lipid-Soluble Hormones

  13. Structure and Function of the Endocrine Glands • Hypothalamic-pituitary axis • Hypothalamus • Pituitary gland • Anterior pituitary (adenohypophysis) • Posterior pituitary (neurohypophysis)

  14. The Pituitary Gland

  15. Posterior Pituitary Hormones • Synthesized with their binding proteins in the supraoptic and paraventricular nuclei of the hypothalamus • Secreted by the posterior pituitary • Antidiuretic hormone (ADH) • Controls plasma osmolality • Oxytocin • Uterine contractions and milk ejection in lactating women

  16. Posterior Pituitary Hormones

  17. Anterior Pituitary Hormones • Adrenocorticotropic hormone • Melanocyte-stimulating hormone • Growth hormone • Prolactin • Thyroid-stimulating hormone • Luteinizing hormone • Follicle-stimulating hormone • β-lipotropin • β-endorphins

  18. Anterior Pituitary Hormones

  19. Thyroid and Parathyroid Glands • Thyroid gland • Two lobes lateral to the trachea • Isthmus • Follicles (follicle cells surrounding colloid) • Parafollicular cells (C cells) • Secrete calcitonin • Regulation of thyroid hormone secretion • Thyrotropin-releasing hormone and thyroid stimulating hormone

  20. Thyroid and Parathyroid Glands • Thyroid hormones • 90% T4 and 10% T3 • Bound to thyroxine-binding globulin, thyroxine-binding prealbumin, or albumin • Affect growth and maturation of tissues, cell metabolism, heat production, and oxygen consumption

  21. Thyroid and Parathyroid Glands

  22. Thyroid and Parathyroid Glands • Parathyroid glands • Small glands located behind the upper and lower poles of the thyroid gland • Produce parathyroid hormone • Regulator of serum calcium • Antagonist of calcitonin

  23. Parathyroid Glands

  24. Parathyroid Glands

  25. Endocrine Pancreas • The pancreas is both an endocrine and an exocrine gland • Houses the islets of Langerhans • Secretion of glucagon and insulin • Cells • Alpha—glucagon • Beta—insulin • Delta—somatostatin and gastrin • F cells—pancreatic polypeptide

  26. Endocrine Pancreas

  27. Endocrine Pancreas • Insulin • Synthesized from proinsulin • Secretion is promoted by increased blood glucose levels • Facilitates the rate of glucose uptake into the cells of the body • Anabolic hormone • Synthesis of proteins, lipids, and nucleic acids

  28. Endocrine Pancreas • Glucagon • Secretion is promoted by decreased blood glucose levels • Stimulates glycogenolysis, gluconeogenesis, and lipolysis • Somatostatin • Possible involvement in regulating alpha and beta cell secretions

  29. Endocrine Pancreas

  30. Adrenal Glands • Adrenal cortex • 80% of an adrenal gland’s total weight • Zona glomerulosa • Zona fasciculata • Zona reticularis • Adrenal medulla • Innervated by the sympathetic and parasympathetic nervous systems

  31. Endocrine Pancreas

  32. Adrenal Glands • Adrenal cortex • Stimulated by adrenocorticotropic hormone (ACTH) • Glucocorticoid hormones • Direct effects on carbohydrate metabolism • Anti-inflammatory and growth-suppressing effects • Influence awareness and sleep habits • Most potent naturally occurring glucocorticoid is cortisol

  33. Adrenal Glands • Adrenal cortex • Mineralocorticoid hormones • Affect ion transport by epithelial cells • Increase the activity of the sodium pump of the epithelial cells • Cause sodium retention and potassium and hydrogen loss • Most potent naturally occurring mineralocorticoid is aldosterone • Regulated by the renin-angiotensin system

  34. Aldosterone

  35. Adrenal Glands • Adrenal cortex • Adrenal estrogens and androgens • Estrogen secretion by the adrenal cortex is minimal • The adrenal cortex secretes weak androgens • Androgens are converted by peripheral tissues to stronger androgens such as testosterone

  36. Adrenal Glands • Adrenal medulla • Chromaffin cells (pheochromocytes) • Chromaffin cells secrete the catecholamines epinephrine (majority) and norepinephrine • Release of catecholamines has been characterized as a “fight or flight” response • Catecholamines promote hyperglycemia

  37. Catecholamines

  38. Neuroendocrine Response to Stress • The endocrine system reacts with the nervous system to respond to stressors • The stress response also involves the immune system • Influenced by corticotropin-releasing hormone from the hypothalamus

  39. Tests of Endocrine Function • Radioimmunoassay • Enzyme-linked immunosorbent assay (ELISA) • Bioassay

  40. Aging and the Endocrine System • Thyroid gland • Glandular atrophy, fibrosis, nodularity, and increased inflammatory infiltrates • Parathyroid glands • Related to alterations in calcium balance • Inadequate intake, malabsorption, or renal changes • Adrenal glands • Decreased clearance of cortisol

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