PSL201Y1 Lecture Notes - Zona Fasciculata, Zona Reticularis, Zona Glomerulosa

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20 Apr 2012
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The adrenal glands
The adrenal glands are pair structures that sit above each kidney. Both
the adrenal glands and the kidneys are located in a potential space
called the retroperitoneum that lies deep within the abdominal cavity.
Although it appears as if the adrenal glands are attached to the
kidney, they have their own blood supply. Each adrenal gland consists
of an outer layered portion called the cortex which constitutes of 80%
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of the glands’ total mass. The other area is the inner core called the
adrenal medulla. The cortex and the medulla operate as two distinct
glands in one, as they are structurally and functionally distinct. The
adrenal cortex secretes a number of hormones that are collectively
called adrenal corticoids named for their origin of release and their
chemical class. They are all of the steroid family. The adrenal
corticoids include three families of hormones: he mineralcorticoids, the
glucocorticoids and the sex hormones. The adrenal medulla is formed
of chromaffin cells which secrete a family of hormones known as the
catecholamines.
The adrenal gland has a thin outer shell called the capsule and
beneath this, the three layers of adrenal cortex. The outer one is
called the zona glamerulosa, the middle layer is the zona fasciculate
and the inner one is the zona reticularis. In the inner core of the gland
we see the chromaffin cells of the adrenomedulla.
Adrenal cortex hormones
The adrenal corticoids include three families of hormones: he
mineralcorticoids, the glucocorticoids and the sex hormones.
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Mineralcorticoids
These hormones are synthesized and secreted from the outermost
layer of the cortex called the zona glamerulosa. Chief among these
hormones is called the aldosterone.
Glucocorticoids
Glucocorticoids are synthesized and secreted by the two inner
layers of the cortex: the zona fasciculata and the zona reticularis.
The most important glucocorticoid is called the cortisol.
Sex hormones
The sex hormones are also synthesized and secreted by the two inner
layers of the cortex: the zona fasciculata and the zona reticularis. The
most important sex hormones are the androgens.
Aldosterone
Aldosterone is synthesized by the outer layer of the adrenal cortex, the
zone glamerulosa. The aldosterone controls the osmolarity of the outer
fluid by its ability to stimulate the reabsorption of sodium at the
kidneys. It controls our plasma osmolarity. This is performed at two
levels of the kidney tubule. This sodium reabsorption is coupled with
potassium secretion. Aldosteron also plays a role in blood pressure
regulation. The aldosterone in response to a signal is secreted and
arrives by the circulation to its target cell, the principal cell. The
aldosterone is a hydrophobic molecule and so uses cyclosopic
receptors. The binding forces the sodium and potassium channels to
open, the synthesis of new sodium and potassium channels and the
synthesis and insertion of more sodium and potassium pumps. These
events provide channels through which sodium can move from the
tubular filtrate to the circulation and channels for potassium to move
from the circulation to the tubular filtrate.
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