Adrenal Anatomy & Physiology
The adrenal glands, one located atop each of the kidneys, release hormones into the bloodstream, and are involved in the regulation of blood pressure and the levels of salt and water in the body. The right adrenal gland is pyramid-shaped, while the left is crescent-shaped. Each gland is approximately a mere 1 inch high, 2 inches wide, Ã?Â¼ inch thick, and weighs less than Ã?Â¼ ounce.
Each adrenal gland is composed of a medulla (inner part) and a cortex (outer part). The medulla releases epinephrine (adrenalin) and norepinephrine (noradrenalin), which play an important role in the body’s “fight or flight” stress response mechanism.
The cortex releases 3 major types of hormones:
1. Corticosteroids are hormones that affect metabolism, some physical characteristics, and chemicals in the blood. Corticosteroid hydrocortisone (cortisol) and corticosterone suppress inflammatory reactions in the body and also affect the immune system.
2. Aldosterone inhibits the level of sodium excreted into the urine, maintaining blood volume and blood pressure.
3. Androgen hormones, androgenic steroids, have minimal effect on the development of male characteristics.
The adrenal glands release their hormones under the instruction of adrenocorticotropic hormone (ACTH), released by the pituitary gland under instruction of the hypothalamus. This alliance, better known as the HPA Axis, acts as a negative feedback system much like the thermostat in a house. In a house, the thermostat senses the heat in the room and compares it to the desired temperature setting. When the temperature gets too low, the thermostat signals the relay switch to tell the furnace to ignite. Once the temperature has risen to the desired level, the thermostat then signals the furnace to quit. In the human body, the hypothalamus is analogous to the thermostat, the pituitary to the relay switch, and the adrenal glands to the furnace. The HPA Axis is one of the most important elements of homeostasis, the process that maintains a steady internal biochemical and physiological balance in the body.
There are several factors which affect the proper functioning of the adrenal glands. The most common adrenal strein is that caused by emotional stress. Other factors include the long-term use of corticosteroid medication, recreational drugs, chronic illness, and infection.
Pheochromocytoma is a rare benign tumor condition affecting the adrenal medulla. This condition may cause the “curable” form of hypertension. Related symptoms include: headache, heart palpitations, sweating, and anxiety.
Cushing’s syndrome is a common disorder affecting the cortex, caused by an excessive amount of glucocorticoids (e.g. hydrocortisone). The cause of this disorder is usually the presence of a tumor or the long-term administration of anti-inflammatory drugs. The catabolic effects of Cushing’s syndrome include: obesity, buffalo hump on a person’s back, fragile skin with red streaks, increased hair growth, osteoporosis, and decreased protein synthesis, which delays healing. Metabolic effects of Cushing’s syndrome include: increased gluconeogenesis and insulin resistance, glucose intolerance, and suppressed immune response.
Addison’s disease is a disorder related to a deficiency of adrenocortical secretions, often caused by autoimmune reactions, infection, or tumor. The effects of this disorder include: decreased blood glucose levels, poor stress response, fatigue, weight loss, decreased body hair, skin creases, and frequent infections. Addison’s disease can become serious, even fatal. If not treated properly, it can lead to low blood pressure, high potassium levels, and ultimately cardiac arrhythmia and failure.