After a few hours, the body's glycogen reserves are exhausted, and yet the nervous system continues to demand glucose. If a stressful situation is not resolved before the glycogen is gone, the body enters the stage of resistance, in which the first priority is to provide alternative fuels for metabolism. This stage is dominated
Saladin: Anatomy & 17. The Endocrine System Text © The McGraw-Hill
Physiology: The Unity of Companies, 2003 Form and Function, Third Edition
664 Part Three Integration and Control by cortisol. The hypothalamus secretes corticotropin-releasing hormone (CRH), the pituitary responds by secreting adrenocorticotropic hormone (ACTH), and this, in turn, stimulates the adrenal cortex to secrete cortisol and other glucocorticoids. Cortisol promotes the breakdown of fat and protein into glycerol, fatty acids, and amino acids, providing the liver with raw material for glu-coneogenesis (glucose synthesis). Like epinephrine, cortisol inhibits glucose uptake by most organs and thus has a glucose-sparing effect. It also inhibits protein synthesis, leaving the free amino acids available for gluconeogenesis. The immune system, which depends heavily on the synthesis of antibodies and other proteins, is depressed by long-term cortisol exposure. Lymphoid tissues atrophy, antibody levels drop, the number of circulating leukocytes declines, and inflammatory cells such as mast cells (see chapter 21) release less histamine and other inflammatory chemicals. Wounds heal poorly, and a person in chronic stress becomes more susceptible to infections and some forms of cancer. Cortisol stimulates gastric secretion, which may account for the ulcers that occur in chronic stress, but it suppresses the secretion of sex hormones such as estrogen, testosterone, and luteinizing hormone, causing disturbances of fertility and sexual function.
Was this article helpful?
This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.