Adrenal Glands

– Hello, BIO 242. This short video
will cover details on the structure and function
of the adrenal glands. The adrenal glands are also
known as the suprarenal glands because they are located
right on top of the kidneys like little hats. You have two adrenal
glands– the right and left. One hat for each kidney. Each adrenal gland is
really two glands in one. You have the adrenal cortex
and the adrenal medulla. The medulla is at the
center of the glands. The cortex wraps around it. The whole thing is wrapped in
a fibrous connective tissue– the capsule. This is showing you
a cadaver dissection of the adrenal gland. Here’s the kidney, here’s the
adrenal glands on top of it, the adrenal medulla
in the center, adrenal cortex around that,
and the capsule covering and protecting the whole thing. The images at the right
show the three regions of the adrenal gland
each highlighted in pink. The adrenal cortex
synthesizes over two dozen steroid-based hormones. Collectively, these are
known as the corticosteroids. We are just going to focus
on the main corticosteroids. The adrenal cortex can be
divided into three regions called zonas. From the capsule inward, you
have the zona glomerulosa, the zona fasciculata,
and the zona reticularis. The hormones
produced by each zone serve a different
function, and it may help you remember
which is which by thinking salt, sugar, sex. The zona glomerulosa
produces hormones called mineralocorticoids that
regulate sodium and potassium concentrations– salt. The main mineralocorticoid
is aldosterone. The zona fasciculata
produces hormones called glucocorticoids that
affect glucose metabolism– sugar. These hormones,
primarily cortisol, are released as part of the
body’s response to stress. The zona reticularis
produces hormones called gonadocorticoids,
sex hormones, including particularly,
the androgens that promote sperm maturation
and secondary male sexual characteristics. Aldosterone is the main
mineralocorticoid produced by the zona glomerulosa. Aldosterone is released
mainly in response to a drop in blood
volume or blood pressure. A drop in blood
pressure triggers activation of the
renin-angiotensin system in the kidneys. Angiotensin triggers
release of aldosterone from the zona glomerulosa. Aldosterone release can
also be triggered directly by a rise in blood
potassium concentration. Once released, aldosterone
increases the absorption of sodium and water, increases
the excretion of potassium, and brings blood volume
and blood pressure back up. Hyposecretion of aldosterone
is associated with a disorder called Addison’s disease. Some of the symptoms
of Addison’s disease are due to loss of
glucocorticoid secretion as well. The loss of aldosterone
in Addison’s causes sodium and water excretion. So your blood sodium levels
drop, you get dehydrated, and your blood pressure drops. John F. Kennedy is probably the
best known Addison’s patient. Hypersecretion of aldosterone
is known as aldosteronism. With aldosteronism, you see high
blood pressure and accumulation of fluids in the tissues. This is called edema. Also, loss of too
much potassium can interfere with the functioning
of your nervous system. Cortisol is the main
glucocorticoid produced by the zona fasciculata. Cortisol is part of the body’s
normal response to stress. Stress triggers release of
corticotropin-releasing hormone from the hypothalamus. CRH triggers release of
adrenal corticotropic hormone from the anterior pituitary. ACTH triggers the
release of cortisol from the zona fasciculata. Rising cortisol levels
turn off ACTH secretion. This is why patients
taking corticosteroid drugs pharmaceutically need to be
tapered off the medication. Pharmaceutical corticosteroids
shut off the adrenal cortex. So when a patient stops
taking the medication, they need to slowly
reduce the amount so that the adrenal glands can
recover their normal levels of secretion. Hyposecretion of
cortisol contributes to Addison’s disease. With low cortisol levels,
Addison’s patients can’t maintain their
blood glucose levels. Hypersecretion of cortisol
leads to Cushing’s disease, which we talked about when
we discussed ACTH back in the pituitary gland. The zona reticularis
secretes small quantities of androgens–
male sex hormones. These adrenal
androgens circulate at high levels in
the fetus where they help to maintain pregnancy. Adrenal androgen concentrations
go back down after birth and do not return until around
six or seven years of age. This is known as adrenarche. The role of adrenal
androgens after birth is still a bit unclear. There have been some
suggestions that adrenarche may play a role in
brain development and/or metabolic diseases, and low
levels of adrenal androgens have been found in
arthritis and fibromyalgia. We do know that the
adrenal androgens are important for
the development of pubic hair in adolescence. In adult males, the
adrenal androgens are drowned out by
the flood of androgens coming from the testes. In adult females,
the adrenal androgens seem to be important for the
sex drive and perhaps building muscle mass as well. The clinical importance
of hyposecretion of the gonadocorticoids is
still not well understood. But we do know that
hypersecretion can cause masculinization in females. Since men produce far more
androgens from the testes than from the
adrenal cortex, men see no effects of
hypersecretion. Moving deep to the
adrenal cortex, we have the adrenal medulla. The adrenal medulla
produces epinephrine and
norepinephrine in response to the sympathetic
nervous system. These hormones are part of
the short-term fight-or-flight response to stress. The cells that produce
norepinephrine and epinephrine are called chromaffin cells. Chromaffin cells are
modified neurons. They respond directly to
pre-ganglionic neurons from the sympathetic
nervous system by releasing epinephrine
and norepinephrine into circulation. This is neural stimulation
of hormone secretion. Hyposecretion of
norepinephrine and epinephrine does not seem to be a
problem, but hypersecretion can cause high blood sugar,
high heart rate, and high blood pressure, all of
which can be damaging to the cardiovascular system. Just remember,
when we’re talking about the adrenal
glands, we’re talking about two glands in one. You have the cortex
and the medulla. The cortex and the medulla
function very differently and produce very
different hormones. You can read up more on the
adrenal glands in your text on pages 615 to 619. (634-637 in the 11th edition)

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