507
CHAPTER THIRTEEN
Endocrine System
ion concentration and blood volume (f
g. 13.31). Angiotensin
II is also a powerFul vasoconstrictor and thereby helps main-
tain systemic blood pressure.
ACE inhibitors are a class of drugs used to treat some forms of high blood
pressure (hypertension). They work by competing with angiotensin-
converting enzyme, blocking formation of angiotensin II and pre-
venting inactivation of bradykinin, a vasodilator. Both eF
ects dilate
blood vessels, lowering blood pressure.
Cortisol
Cortisol
(hydrocortisone) is a
glucocorticoid,
which means it
aFFects glucose metabolism. It is produced in the middle zone
(zona Fasciculata) oF the adrenal cortex and has a molecular
structure similar to aldosterone
(f
g. 13.32)
. In addition to
aFFecting glucose, cortisol infl
uences protein and Fat metabo-
lism. Among the more important actions oF cortisol are the
Following:
1. It inhibits the synthesis oF protein in various tissues,
increasing blood concentration oF amino acids.
2. It promotes the release oF Fatty acids From adipose
tissue, increasing the use oF Fatty acids and decreasing
the use oF glucose as energy sources.
3. It stimulates liver cells to synthesize glucose From
noncarbohydrates (gluconeogenesis), such as circulating
amino acids and glycerol, thus increasing blood glucose
concentration.
FIGURE 13.31
Aldosterone increases blood volume and pressure by promoting conservation of sodium ions and water (steps
1–4
).
Kidney
Angiotensin II stimulates
adrenal cortical cells
to secrete aldosterone
Aldosterone
Bloodstream
Angiotensin-converting
enzyme (ACE)
Angiotensinogen
Renin
Angiotensin I
Angiotensin II
Release into
bloodstream
Stimulation
Inhibition
1
2
Decreasing blood pressure
and/or sodium ion concentration
stimulate secretion of the
enzyme renin
4
Blood pressure and/or sodium
ion concentration return toward
normal, inhibiting further
secretion of renin
3
Aldosterone acts on the
kidney to conserve sodium
ions and (by osmosis) water
Cortisol
O
H
3
C
H
3
C
HO
OH
CO
CH
2
OH
Aldosterone
O
H
3
C
C
H
HO
CO
O
CH
2
OH
FIGURE 13.32
Cortisol and aldosterone are steroids with similar
molecular structures.
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