PROCESS DIAGRAM
M ineralocorticoids re g u la te m ineral
com position o f th e b lo o d
Cells in the
outer zone of the adrenal cortex secrete ste-
roid
hormones
called
mineralocorticoids
.
One of these, aldosterone, acts on the kid-
neys to reabsorb sodium into the blood and
mineralocorticoids
Steroid hormones secret-
ed by the adrenal cortex
that regulate the mineral
composition of the blood.
excrete potassium in response to dehydra-
tion, blood loss, or sodium deficiency. Aldoste-
rone acts in concert with the hormones renin
and angiotensin to change the mineral com-
position of the blood and influence both blood
volume and blood pressure (Figure 9.15).
R e n in -a n g io te n sin -a ld o stero n e sy stem • Figure 9.15
In a complex series of events involving several organs, the renin-angiotensin-aldosterone
system restores blood volume and blood pressure.
a.
R elease o f re n in
The kidney senses this
drop in blood pressure
and/or change in sodium
concentration and releases
an enzyme called renin.
Dehydration, sodium
. deficiency or blood loss
(hemorrhage) causes a
drop in blood volume
and blood pressure.
n
TT
b. P ro d u c tio n o f
a n g io te n s in o g e n
c. P ro d u c tio n o f a n g io te n s in
II
renin
angiotensinogen-------
>■
angiotensin I (AI)
Renin converts
The liver makes a protein
called angiotensinogen
and releases it into the
blood.
angiotensinogen into
angiotensin I (A I).
----- Lungs
ACE
çfc* «
ACE
I As the blood passes through the lungs,
another enzyme called angiotensin
converting enzyme (ACE) converts
angiotensin I into an active protein
called angiotensin II
(A
II).
angiotensin
I
d. A c tio n s o f a n g io te n s in
II
(A
II
)
6
A II acts on the adrenal cortex
to release aldosterone.
e. Actions of aldosterone
8
Aldosterone acts on the
kidney to reabsorb sodium
and water and to excrete
potassium.
A II constricts blood
vessels.
The reabsorption of sodium
and water increases blood ■
volume.
Kidney
Arterioles
f.
C o m b in e d e ffe c ts
o f a ld o s te ro n e
an d a n g io te n s in
TT
10 Increased blood volume
. and vasoconstriction increase
and restore blood pressure.
270 CHAPTER 9
The Endocrine System
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