The two adrenal glands are also called the suprarenal glands, because each sits on top of a kidney. The glands are organized into different sections, each of which is responsible for making substances that affect various functions within the body. Too much or too little of these substances can lead to disease.
Function
The adrenal gland secretes various hormones that affect different parts of the body. Some are necessary for survival, notes Frederic Martini, Ph.D., in “Fundamentals of Anatomy & Physiology.” The anterior pituitary of the brain regulates part of the gland, telling it when certain hormones need to be made. Parts of the nervous system and the kidneys stimulate the production of other adrenal hormones.
Structure
The outer part of the adrenal gland, the adrenal cortex, constitutes 90 percent of the gland. The cortex has three zones. The zona glomerulosa is the outermost zone and makes the hormone aldosterone from cholesterol. The next is the zona fasciculata, which makes hormone cortisol, also from cholesterol. The zona reticularis is the third area and is where androgens, or male hormones, are made from cholesterol. The inner part of the adrenal gland is called the adrenal medulla. It makes substances called epinephrine and norepinephrine.
Effects
People can lose a lot of water when they have diarrhea, are vomiting or are sweating. When this happens, aldosterone stimulates the kidneys to reabsorb sodium, as explained by Patricia Molina, M.D., in “Endocrine Physiology.” When the kidneys reabsorb sodium, water is also reabsorbed, restoring the fluid level. Cortisol, meanwhile, helps the body handle stress in many ways, including by raising the level of glucose in the bloodstream. The androgens are changed to testosterone or estrogen in the tissues. They promote sex characteristics. Epinephrine and norepinephrine give cells energy, increase the heart rate, make the pupils dilate and relax the smooth muscle in the lungs. All this prepares the body to handle stressful situations.
Disorders
If the adrenal gland secretes too much aldosterone, the result is a condition called Conn’s syndrome, which causes headaches, hypertension, muscle weakness and frequent urination. High levels of aldosterone lead to high levels of sodium in the bloodstream, with the resulting hypertension and headaches. The muscle weakness and frequent urination is due to chronic low levels of potassium in the blood.
The destruction of the adrenal glands causes Addison’s disease. Symptoms include weight loss, muscle weakness, nausea and vomiting from very low levels of sodium, because the gland cannot secrete enough aldosterone.
Expert Insight
Dehydroepiandrosterone, or DHEA, and androstenedione are the male hormones that are made in the zona reticularis. DHEA is changed to androstenedione in the adrenal gland. Androstenedione is then changed to testosterone or estrogen in the tissues. Molina writes in “Endocrine Physiology” that people have the highest levels of DHEA when they are 20 to 30 years old. By the time people reach 70, the level of DHEA in the bloodstream is only 20 percent of the level they had when they were in their 20s.
References
- “Endocrine Physiology”; Patricia Molina, M.D., Ph.D.; 2010
- “Fundamentals of Anatomy & Physiology”; Frederic Martini, Ph.D.; 1995
- The Merck Manual: Adrenal Disorders
