Anatomy of the Adrenal Glands

Learning Objective: Differentiate between the hormones of the adrenal cortex and those of the adrenal medulla.
      The adrenal glands are located on the top of each kidney. The outer part of the gland is the adrenal cortex, and the inner part is called the adrenal medulla.

Adrenal Cortex
Learning Objective: Describe the adrenal cortex and the action of the hormones secreted.
The adrenal cortex produces cortical hormones, also called steroids. As a group, these three hormones are called corticosteroids:
            • Mineralocorticoids: Regulate the electrolytes in the body. Aldosterone, the most important mineralocorticoid, regulates the sodium and water balance in the body through the reabsorption of sodium and water in the kidneys. As the sodium is reabsorbed into the blood, hydrogen or potassium is excreted into the urine.
            • Glucocorticoids: Regulate protein, fat, and carbohydrate metabolism. They also hasten the breakdown of proteins into amino acids, which are converted to glucose in the liver. This process increases the blood glucose level. Norepinephrine and epinephrine need glucocorticoids to constrict blood vessels, which increases blood pressure. Glucocorticoids also have anti-inflammatory properties. The main glucocorticoid secreted is cortisol (also called hydrocortisone). Cortisone and corticosterone are produced in lesser amounts. Stress can also increase the number of glucocorticoids secreted.
            • Gonadocorticoids: Small amounts of male sex hormones (androgens) are secreted and responsible for some of the secondary sexual characteristics (e.g., pubic and axillary hair) in both males and females during puberty.
The hypothalamus and the anterior lobe of the pituitary gland (through the secretion of ACTH) regulate the corticosteroids secreted by the adrenal cortex.

24.2 Critical Thinking Application
The actions of mineralocorticoids and glucocorticoids confuse Cecilia. Summarize the actions of these two corticosteroids.

Adrenal Medulla
Learning Objective: Discuss the adrenal medulla and the action of the hormones secreted.
The hypothalamus, with the help of the sympathetic nervous system, stimulates the adrenal medulla to secrete these nonsteroid hormones:
            • Epinephrine (adrenaline): Secreted in response to physical or mental stress, providing the fight-or-flight response. It increases the heart rate and strength of the contractions, blood pressure, and blood glucose level. It also relaxes the smooth muscles in the bronchioles. These changes allow more glucose and oxygenated blood to get to the cells for the fight-or-flight response.
            • Norepinephrine (noradrenalin): Also secreted in times of stress. It increases the blood glucose level, heart rate, and the force of the heart’s contractions; in addition, it causes vasoconstriction, thus raising the blood pressure.