244. ADRENAL CORTEX
The adrenal cortex, the outer layer of each adrenal gland, secretes three types of
hormones: mineralocorticoids, glucocorticoids, and androgens.
a. Mineralocorticoids, such as aldosterone, regulate electrolytes (especially
sodium). Aldosterone, mentioned previously in the section on the urinary system,
promotes the active reabsorption of sodium ions in the kidney tubules. This in turn
decreases the reabsorption of potassium and increases the reabsorption of chloride and
b. Glucocorticoids, such as hydrocortisone, function to enhance resistance to
physical stress. Hydrocortisone promotes both protein and fat metabolism. It affects
protein metabolism by increasing the rate of transfer of amino acids from cells into the
blood and interstitial fluids. The amino acids can thereby be transported to specific
bodily areas where they are momentarily in demand. Hydrocortisone also mobilizes fat
from fat depots in much the same manner as it mobilizes amino acids from cells.
Hydrocortisone affects glucose metabolism through a process called gluconeogenesis.
In this process, both proteins and lipids are converted into glucose. Glucose can then
be rapidly broken down into water and carbon dioxide with the release of several
adenosine triphosphate (ATP) molecules.
c. Androgens are hormones that affect male secondary sexual characteristics.
The testes are the primary source of male hormones; however, the adrenal cortex also
secretes minute quantities.
2-45. ADRENAL MEDULLA
The adrenal medulla is the innermost region of the adrenal gland. Epinephrine
(Adrenalin) is the primary hormone secreted by the adrenal medulla. Epinephrine
stimulates the sympathetic nervous system. Epinephrine is responsible for preparing an
individual for vigorous physical and mental activity. It prepares the system for strenuous
activity by (1) increasing the metabolism of all cells, (2) increasing heart rate, (3)
inhibiting peristalsis in the gut, (4) initiating sweating, and (5) dilating the pupils (see
Table 21). Epinephrine elevates the blood sugar concentration by stimulating the
release of glucose from both the liver and muscle glycogen. A similar hormone
released by the adrenal medulla in small amounts is norepinephrine, which is released
in response to hypotension (low blood pressure).
246. PANCREAS (ISLETS OF LANGERHANS)
The pancreas is comprised mainly of pancreatic acinar (saclike) tissue that secretes
enzymes for the chemical digestion of food in the small intestine. Scattered throughout
pancreatic tissue, however, are small epithelial masses known as islets of Langerhans.
Basically two types of cells, alpha and beta cells, are found within the islets. The beta
cells secrete insulin, which is necessary for the transfer of sugar from extracellular fluids