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Chapter 8: Endocrine Physiology

The Endocrine System

Overview

A hormone is a chemical that is produced by the body and has a specific regulatory effect on a target cell or organ. Classic endocrinology was concerned with the functions of anatomically defined glands such as the thyroid gland or the pituitary gland. It is now recognized that almost every organ secretes hormones and that endocrine cells may be dispersed throughout the body (e.g., in the gut mucosa). The more recent study of endocrinology encompasses all processes concerned with the physiology of hormones. Certain diseases commonly encountered in general medical practice, such as diabetes mellitus or thyroid disorders, are caused by a deficiency or an excess of specific hormones. Many other common diseases not directly caused by endocrine dysfunction have prominent endocrine components, including cancer and atherosclerosis. Table 8-1 summarizes the hormones produced by the major endocrine organs.

Table 8-1Summary of Hormones Produced by the Major Endocrine Organs
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Table 8-1Summary of Hormones Produced by the Major Endocrine Organs
Endocrine Gland Hormone(s) Produced Chemical Structure Overview: Major Function(s)
Hypothalamus Corticotropin-releasing hormone (CRH) Peptide

  • Stimulates adrenocorticotropic hormone (ACTH)
Growth hormone-releasing hormone (GHRH) Peptide

  • Stimulates growth hormone (GH) release
Growth hormone inhibitory hormone (GHIH; also known as somatostatin) Peptide

  • Inhibits GH release
Gonadotropin-releasing hormone (GnRH) Peptide

  • Stimulates luteinizing hormone (LH) and follicle-stimulating hormone (FSH) release
Prolactin-inhibiting factor (PIF; also known as dopamine) Peptide

  • Inhibits prolactin release
Thyrotropin-releasing hormone (TRH) Peptide

  • Stimulates thyroid-stimulating hormone (TSH) and prolactin release
Anterior pituitary ACTH Peptide

  • Trophic to adrenal cortex

  • Stimulates synthesis and secretion of cortisol, aldosterone, and androgens
FSH Peptide

  • Promotes sperm maturation via Sertoli cells in testes

  • Stimulates ovarian follicle development
GH Peptide

  • Acute metabolic effects oppose insulin

  • Chronic growth-promoting effect via insulin-like growth factor 1 (IGF-1)
LH Peptide

  • Stimulates Leydig cells of testes to secrete testosterone

  • LH surge important for ovulation & formation of corpus luteum
Prolactin Peptide

  • Required in lactation for mammary growth, initiation of milk secretion, and maintenance of milk production
TSH Peptide

  • Stimulates synthesis and secretion of thyroid hormones
Posterior pituitary Antidiuretic hormone (ADH) (also called arginine vasopressin, or AVP) Peptide

  • Increases water retention at kidney

  • Vasoconstricts arterioles
Oxytocin Peptide

  • Stimulates uterine contractions during labor

  • Milk ejection in lactation
Thyroid Triiodothyronine (T3) & thyroxine (T4) Amine

  • Increase metabolic rate

  • Required for normal growth and development
Adrenal cortex Aldosterone Steroid

  • Decreases urinary Na+ excretion

  • Increases urinary K+ and H+ excretion
Cortisol Steroid

  • Released in response to stress

  • Multiple metabolic actions
Endocrine Gland Hormone(s) Produced Chemical Structure Overview: Major Function(s)
Adrenal medulla Epinephrine & norepinephrine Amine

  • Produces effects similar to actions of the sympathetic nervous system
Pancreas Insulin (β cell) Peptide

  • Promotes storage of glucose as glycogen in liver and muscle

  • Promotes uptake of glucose and storage as triglyceride in adipose tissue and liver
Glucagon (α cell) Peptide

  • Increases blood glucose by promoting glycogenolysis, gluconeogenesis, and ...

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