C ontrol o f glucocorticoid secretio n
by th e h yp o th alam u s and p itu itary glan d • Figure 9.16
PLANNEF
The hypothalamus and pituitary gland control secretion of glucocorti-
coids from the adrenal gland through negative feedback.
^
In response to changes in metabolism and
stress, the hypothalamus secretes
corticotropin-releasing hormone (CRH).
I ACTH acts on the adrenal
cortex to secrete cortisol.
| Cortisol acts on various tissues
to increase metabolism.
Hypothalamus
I CRH stimulates the anterior pituitary
to secrete adrenocorticotropic
hormone (ACTH).
Anterior
pituitary
'I
&
Increased circulating cortisol in the blood inhibits
further CRH and ACTH secretions from the
hypothalamus and pituitary gland.
Cortisol
j
If blood pressure is restored to normal, then renin
and aldosterone secretions stop. With severe blood loss,
the renin-angiotensin-aldosterone system cannot fully
compensate for the drop in blood volume and pressure.
Secretions of renin and aldosterone will stop only when
the blood loss is fixed (for example, when a wound is
repaired) and when blood volume is restored by other
means (such as transfusion).
G lucocorticoids re g u la te e n e rg y b alan ce
The
cells in the middle layer of the adrenal cortex secrete
glu-
cocorticoids
, mainly
cortisol
. Cortisol acts on many tis-
sues to mobilize energy resources: •
Skeleta l muscle.
Cortisol causes the breakdown of muscle
proteins into amino acids, which get released into the
blood.
T he liver.
Cortisol stimulates liver cells to convert amino
acids into glucose, which is released into the blood.
F a t (adipose) tissue.
Cortisol stim-
ulates fat cells to break down
triglycerides into fatty acids,
which are
released into
the
blood. Other cells can use the
fatty acids to make ATP.
Glucocorticoids also suppress white blood cells from
participating in the inflammatory response. In high doses,
cortisol suppresses immune responses. Therefore, cortisol
(hydrocortisone) is often prescribed as an anti-inflamma-
tory treatment for rashes and allergic responses. In addi-
tion, cortisol is used to treat chronic inflammations, such
as arthritis, and to decrease the risk of tissue rejection by
the immune system in organ transplant recipients.
The hypothalamus and pituitary gland control secre-
tion of glucocorticoids from the adrenal gland through a
negative feedback loop involving corticotropin-releasing
hormone (CRH), adrenocorticotropic hormone (ACTH),
and cortisol (Figure 9.16).
glucocorticoids
Steroid hormones se-
creted by the adrenal
cortex that regulate
energy balance.
Endocrine Glands Regulate Other Key Body Functions
271
PROCESS DIAGRAM
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