1 Mechanisms of Hormonal Regulation Chapter 20

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 3 The Endocrine System

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 5 Feedback

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 7 Cellular Mechanism of Hormone Action  Target cell  Up-regulation  Down-regulation  Hormone effects Direct effects Permissive effects

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 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)

Mosby items and derived items © 2006 by Mosby, Inc. 10 Cellular Mechanism of Hormone Action

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 12 Lipid-Soluble Hormones

Mosby items and derived items © 2006 by Mosby, Inc. 13 Structure and Function of the Endocrine Glands  Hypothalamic-pituitary axis Hypothalamus Pituitary gland  Anterior pituitary (adenohypophysis)  Posterior pituitary (neurohypophysis)

Mosby items and derived items © 2006 by Mosby, Inc. 14 The Pituitary Gland

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 16 Posterior Pituitary Hormones

Mosby items and derived items © 2006 by Mosby, Inc. 17 Anterior Pituitary Hormones  Adrenocorticotropic hormone  Melanocyte-stimulating hormone  Growth hormone  Prolactin  Thyroid-stimulating hormone  Luteinizing hormone  Follicle-stimulating hormone  β-lipotropin  β-endorphins

Mosby items and derived items © 2006 by Mosby, Inc. 18 Anterior Pituitary Hormones

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 20 Thyroid and Parathyroid Glands  Thyroid hormones 90% T 4 and 10% T 3 Bound to thyroxine-binding globulin, thyroxine- binding prealbumin, or albumin Affect growth and maturation of tissues, cell metabolism, heat production, and oxygen consumption

Mosby items and derived items © 2006 by Mosby, Inc. 21 Thyroid and Parathyroid Glands

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 23 Parathyroid Glands

Mosby items and derived items © 2006 by Mosby, Inc. 24 Parathyroid Glands

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 26 Endocrine Pancreas

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 29 Endocrine Pancreas

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 31 Endocrine Pancreas

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 34 Aldosterone

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 37 Catecholamines

Mosby items and derived items © 2006 by Mosby, Inc. 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

Mosby items and derived items © 2006 by Mosby, Inc. 39 Tests of Endocrine Function  Radioimmunoassay  Enzyme-linked immunosorbent assay (ELISA)  Bioassay

Mosby items and derived items © 2006 by Mosby, Inc. 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