Adrenal Glands
The adrenal glands are a pair of glands which are located on or very near the kidneys in most vertebrates. In humans, an adrenal gland perches on top of each kidney, like a cap. The adrenal glands have two separate parts, the cortex and the medulla. Although the cortex and medulla are structurally close, they do not interact functionally. They each have their own unique characteristics and functions.
The adrenal cortex is the outer "rind" of the adrenal gland. It is made up of tissue which is similar to that found in the ovaries and testes. The cortex is responsible for producing three types of hormones: sex hormones, mineralocorticoids, and glucocorticoids. The most important sex hormones produced in the adrenal cortex are male sex hormones, or androgens. These hormones increase in both males and females at puberty, resulting in oily skin and hair in the armpits and pubic area. In males, androgens are also responsible for the development of the penis and testicles, and for increased muscle bulk. Mineralocorticoids are hormones which regulate the way the kidneys process sodium and potassium. Glucocortiocoids affect the way the body processes, uses and stores carbohydrates, fats, and proteins.
The core of the adrenal gland is called the adrenal medulla. It is made up of the same kind of tissue found in an area of the nervous system. The adrenal medulla produces two very important hormones called epinephrine and norepinephrine. These hormones are responsible for a mechanism called the "fight-or-flight" response.
When a person or animal is confronted with some type of danger, the adrenal glands pump out large quantities of norepinephrine and epinephrine (also called adrenaline). This adrenaline rush resets a variety of the body's systems, so that the frightened individual can respond quickly: heart rate increases, sugar is brought out of storage for a quick burst of energy, blood vessels which feed the muscles expand, bodily functions which are unnecessary for facing the danger at hand (such as digestion in the stomach and intestines) are temporarily shutdown, the bronchial tubes leading to the lungs increase in size so that more oxygen can be taken in.
A number of disorders can affect the adrenal glands. An overactive adrenal cortex is called Cushing syndrome, named after Harvey Williams Cushing. Individuals with this disorder are often obese, with abnormal hair growth and high blood pressure. An underactive adrenal cortex is called Addison's disease; President John F. Kennedy suffered from this disorder. A tumor in the adrenal medulla (called a pheochromocytoma) can result in sudden spikes of blood pressure, with accompanying headache, sweats, anxiety, and nausea.
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