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Adrenal glands are a pair of ductless glands located above the kidneys. Through hormonal secretions, the adrenal
glands regulate many essential functions in the body, including biochemical balances that influence athletic training
and general stress response. The glucocorticoids include corticosterone, cortisone, and hydrocortisone or cortisol.
These hormones serve to stimulate the conversion of amino acids into carbohydrates which is a process known as
gluconeogenesis, and the formation of glycogen by the liver. They also stimulate the formation of reserve glycogen
in the tissues, such as in the muscles. The glucocorticoids also participate in lipid and protein metabolism. The cortex
of the adrenal gland is known to produce over 20 hormones, but their study can be simplified by classifying them
into three categories: glucocorticoids, mineralcorticoids, and sex hormones.
They are triangular-shaped glands located on top of the kidneys. They produce hormones such as estrogen,
progesterone, steroids, cortisol, and cortisone, and chemicals such as adrenalin (epinephrine), norepinephrine, and
dopamine. When the glands produce more or less hormones than required by the body, disease conditions may occur.
The adrenal cortex secretes at least two families of hormones, the glucocorticoids and mineral corticoids. The
adrenal medulla secretes the hormones epinephrine (adrenalin) and norepinephrine (noradrenalin).
Adrenal Cortex: The hormones made by the Adrenal Cortex supply long-term responses to stress. The two major
hormones produced are the Mineral Corticoids and the Glucocorticoids. The Mineral Corticoids regulate the salt
and water balance, leading to the increase of blood volume and blood pressure. The Glucocorticoids are monitoring
the ACTH, in turn regulating carbohydrates, proteins, and fat metabolism. This causes an increase in blood glucose.
Glucocorticoids also reduce the body's inflammatory response.
Cortisol is one of the most active glucocorticoids. It usually reduces the effects of inflammation or swelling
throughout the body. It also stimulates the production of glucose from fats and proteins, which is a process referred
to as gluconeogenesis.
Aldosterone is one example of a mineralcorticoid. It signals the tubules in the kidney nephrons to reabsorb sodium
while secreting or eliminating potassium. If sodium levels are low in the blood, the kidney secretes more renin,
which is an enzyme that stimulates the formation of angiotensin from a molecule made from the liver. Angiotensin
stimulates aldosterone secretion. As a result, more sodium is reabsorbed as it enters the blood.
Aldosterone, the major mineralcorticoid, stimulates the cells of the distal convoluted tubules of the kidneys to
decrease re-absorption of potassium and increase re-absorption of sodium. This in turn leads to an increased
re-absorption of chloride and water. These hormones, together with such hormones as insulin and glucagon, are
important regulators of the ionic environment of the internal fluid.
The renin-angiotensin-aldosterone mechanism can raise blood pressure if it tends to drop. It does this in two ways.
Angiotensin is a vasoconstrictor, decreasing the diameter of blood vessels. As vessels constrict, blood pressure
increases. In addition, as sodium is reabsorbed, the blood passing through the kidney becomes more hypertonic.
Water follows the sodium into the hypertonic blood by osmosis. This increases the amount of volume in the blood
and also increases the blood pressure.
Adrenal Medulla: The hypothalamus starts nerve impulses that travel the path from the bloodstream, spinal cord,
and sympathetic nerve fibers to the Adrenal Medulla, which then releases hormones. The effects of these hormones
provide a short-term response to stress.
Excessive secretion of the glucocorticoids causes Cushing's syndrome, characterized by muscle atrophy or
degeneration and hypertension or high blood pressure. Under secretion of these substances produces Addison's
disease, characterized by low blood pressure and stress.
Epinephrine and norepinephrine produce the "fight or flight" response, similar to the effect from the sympathetic
nervous system. Therefore, they increase heart rate, breathing rate, blood flow to most skeletal muscles, and the
concentration of glucose in the blood. They decrease blood flow to the digestive organs and diminish most digestive
processes.
The adrenal sex hormones consist mainly of male sex hormones (androgens) and lesser amounts of female
sex hormones (estrogens and progesterone). Normally, the sex hormones released from the adrenal cortex are insignificant
due to the low concentration of secretion. However, in cases of excess secretion, masculine or feminine
effects appear. The most common syndrome of this sort is "virilism" of the female.
Should there be an insufficient supply of cortical hormones, a condition known as Addison's disease
would result. This disease is characterized by an excessive excretion of sodium ions, and hence water, due to lack
of mineralcorticoids. Accompanying this is a decreased blood glucose level due to a deficient supply of glucocorticoids.
The effect of a decreased androgen supply cannot be observed immediately. Injections of
adrenal cortical hormones promptly relieve these symptoms.
Hormonal production in the adrenal cortex is directly controlled by the anterior
pituitary hormone called adrenocorticotropic hormone (ACTH).
The two adrenal glands lie very close to the kidneys. Each adrenal gland is actually a double gland, composed of an
inner core like medulla and an outer cortex. Each of these is functionally unrelated.
The adrenal medulla secretes two hormone, adrenalin or epinephrine and noradrenalin or norepinephrine, whose
functions are very similar but not identical. The adrenal medulla is derived embriogically from neural tissue. It has
been likened to an overgrown sympathetic ganglion whose cell bodies do not send out nerve fibers, but release their
active substances directly into the blood, thereby fulfilling the criteria for an endocrine gland. In controlling
epinephrine secretion, the adrenal medulla behaves just like any sympathetic ganglion, and is dependent upon
stimulation by sympathetic preganglionic fibers.
Epinephrine promotes several responses, all of which are helpful in coping with emergencies: the blood pressure
rises, the heart rate increases, the glucose content of the blood rises because of glycogen breakdown, the spleen
contracts and squeezes out a reserve supply of blood, the clotting time decreases, the pupils dilate, the blood flow to
skeletal muscles increase, the blood supply to intestinal smooth muscle decreases and hairs become erect. These
adrenal functions, which mobilize the resources of the body in emergencies, have been called the fight-or-flight
response. Norepinephrine stimulates reactions similar to those produced by epinephrine, but is less effective in
conversion of glycogen to glucose.
The significance of the adrenal medulla may seem questionable since the complete removal of the gland causes few
noticeable changes; humans can still exhibit the flight-or-fight response. This occurs because the sympathetic
nervous system complements the adrenal medulla in stimulating the fight-or-flight response, and the absence of the
hormonal control will be compensated for by the nervous system.
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