The adrenal glands are triangular in shape and measure about 7.6 cm (3 inches) in length and 1.2 cm (half an inch) in height. They sit atop the kidneys at the back of the abdomen and are covered in a layer of fatty tissue. These glands are made up of an inner part called the adrenal medulla and an outer part called the adrenal cortex.
Role of the Adrenal Glands in the Body
The adrenal medulla is the primary source of adrenaline in the body, a hormone that raises blood pressure, increases the heart rate, and acts as a neurotransmitter (a chemical messenger in the nervous system) when the body is subject to stress or danger.
The adrenal cortex secretes many different hormones into the bloodstream that deal with the body's use of fats, proteins, and carbohydrates. The cortex also produces the male sex hormone, testosterone, and small amounts of estrogen. Aldosterone, a hormone involved in regulation of blood pressure, and water and salts in the body, is also secreted by the adrenal cortex.
How They Work
The adrenal glands produce hormones and other chemicals that are released directly into the bloodstream in response to nerve impulses and hormones produced by other organs.
The cells of the adrenal medulla are actually specialized nerve cells that respond to nerve impulses. These cells release the hormones adrenaline (epinephrine) and noradrenaline (norepinephrine) into the bloodstream in response to stress or danger. Adrenaline serves to increase heart rate and blood pressure and helps the body prepare for a "fight-or-flight" response.
The adrenal cortex responds to hormones produced elsewhere in the body. The cortex makes up part of the hypothalamic-pituitary-adrenal axis, a major functional unit of the endocrine system. This system controls hormone production that is involved with reactions to stress and regulation of digestion, the immune system, mood and emotions, sexual drive, and energy storage and expenditure.
Other cells in the adrenal cortex produce testosterone and small amounts of estrogen, both necessary for sexual maturation in men and women, and aldosterone, a hormone involved in blood pressure regulation and water and electrolyte balance.
Diseases of the Adrenal Glands
Cushing syndrome is a hormonal disorder caused by prolonged exposure of the body's tissues to high levels of the hormone cortisol which is produced by the adrenal cortex. Sometimes called hypercortisolism, it is relatively rare and most commonly affects adults aged 20 to 50. An estimated 10 to 15 of every million people are affected each year.
Symptoms vary, but most people have upper body obesity, rounded face, increased fat around the neck, and thinning arms and legs. Children tend to be obese with slowed growth rates.
Other symptoms can include thinning of the skin with easy bruising, poor healing of the skin, and purplish pink stretch marks on the abdomen, thighs, buttocks, arms, and breasts. The bones are weakened, and routine activities such as bending, lifting, or rising from a chair may lead to backaches, or rib and spinal column fractures.
Women usually have excess hair growth on their faces, necks, chests, abdomens, and thighs. Their menstrual periods may become irregular or stop. Men have decreased fertility with diminished or absent desire for sex.
In Cushing syndrome, the adrenal cortex produces too much cortisol, either because of an abnormality in the adrenal cortex itself, such as an adrenal tumor, or because the pituitary gland, located in the brain, is producing too much ACTH (a hormone that causes the adrenal cortex to produce cortisol). Pituitary adenomas cause most cases of Cushing syndrome. They are benign, or non-cancerous, tumors of the pituitary gland which secrete increased amounts of ACTH usually presenting as a single adenoma. This form of the syndrome, known as Cushing disease, affects women five times more frequently than men. 
Addison disease, also called adrenal insufficiency, or hypocortisolism, is an endocrine or hormonal disorder that occurs in all age groups and afflicts men and women equally. It occurs when the adrenal cortex does not produce enough of the hormone cortisol and, in some cases, the hormone aldosterone and it is characterized by weight loss, muscle weakness, fatigue, low blood pressure, and sometimes darkening of the skin in both exposed and nonexposed parts of the body.
Failure to produce adequate levels of cortisol can occur for different reasons. The problem may be due to a disorder of the adrenal glands themselves (primary adrenal insufficiency) or to inadequate secretion of ACTH by the pituitary gland (secondary adrenal insufficiency).
Addison disease affects about 1 in 100,000 people. Most cases are caused by the gradual destruction of the adrenal cortex, the outer layer of the adrenal glands, by the body's own immune system.
Symptoms of Addison disease can include chronic tiredness, muscle weakness, loss of appetite, weight loss, nausea, vomiting, diarrhea, dizziness or fainting from low blood pressure, and skin changes such as darkening of the skin on scars, skin folds, elbows, knees, knuckles, toes, and lips. Addison disease can also cause irritability and depression. Salt-craving can also be seen if aldosterone levels are affected.
In some cases, symptoms may be mild and are often ignored. A stressful event like an illness or accident can then cause symptoms to worsen suddenly. This is called an addisonian crisis, or acute adrenal insufficiency. Without prompt treatment, an addisonian crisis can be fatal. 
Congenital adrenal hyperplasia
Congenital adrenal hyperplasia, also known as CAH or 21-hydroxylase deficiency, is a genetic disorder of the adrenal glands. In people with congenital adrenal hyperplasia, the body doesn’t make enough of the hormone cortisol, and they may also not make aldosterone. Instead, their adrenal glands make too much androgen.
Congenital adrenal hyperplasia is caused by an error on a single gene. It is inherited, meaning it is passed down from parents to their children. Congenital adrenal hyperplasia is the most common autosomal recessive genetic disorder in humans, and many states require mandatory newborn screening for the deficiency of the enzyme.
Symptoms of congenital adrenal hyperplasia range from mild to serious. Some people with mild congenital adrenal hyperplasia might never be diagnosed because their symptoms do not cause them any problems. Mild symptoms include shorter height in children, early signs of puberty in children, acne, excess facial hair, and irregular menstrual periods and possible trouble getting pregnant for women. Severe symptoms include dehydration, low blood sugar, low blood pressure, trouble keeping enough sodium in the body, and benign testicular tumors and infertility in men.
Primary aldosteronism is a rare condition in which the adrenal cortex produces too much aldosterone, the hormone involved in blood pressure, and salt and water regulation. This can lead to hypertension and sometimes low blood pressure when standing from a lying position. Other symptoms can include excessive urination and thirst, muscle weakness, constipation, and headache. 
Symptoms include acute adrenal gland insufficiency and profound shock. It is deadly if not treated immediately.
An endocrinologist is a medical doctor (M.D.) who specializes in the endocrine system and it's diseases. An endocrinologist has completed training in internal medicine and specialized training in endocrinology.
- ↑ Orth, David N; "Cushing's Syndrome;" New England Journal of Medicine, Volume 332:791-803 March 23, 1995 Number 12 Full Text
- ↑ The National Endocrine and Metabolic Diseases Information Service, NIH; "Addison's disease;" NIH Publication No. 04–3054 June 2004 Available Online
- ↑ Mayo Clinic, "Diseases and Conditions: Primary aldosteronism" Available Online
- Medline Plus: Adrenal Gland Disorders
- NIH - National Institute of Child Health and Human Development
- American Urological Association: Adrenal Gland Disorders
- National Institutes of Health (NIH): Managing Adrenal Insufficiency (PDF)