Transcript AngiotensinReninAldost

Renin-Angiotensin-Aldosterone
System
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Juxtaglomerular apparatus secretes renin.
Renin acts on angiotensinogen (gamma
globulin from the liver) giving angiotensin I
Angiotensin converting enzyme (ACE) acts
on angiotensin I giving angiotensin II
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2.
3.
Renin-Angiotensin-Aldosterone
System
Renin:
It is secreted by the juxtaglomerular cells in
Kidney
Changes in secretion is in response to
changes in renal arterial pressure,
sympathetic nervous system signals and
some hormones
Its substrate is angiotensinogen
Renin-Angiotensin-Aldosterone
System
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Angiotensinogen
It is a glycoprotein synthesized and secreted into
the bloodstream by the liver
Angiotensinogen
Renin
angiotensin I
ACE
Angiotensin III
Angiotensin II
Renin-Angiotensin-Aldosterone
System
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Angiotensin converting enzyme (ACE) is
also known as kinanase II
It converts angiotensin I to II
(vasoconstrictor) and inactivates bradykinin
(vasodilator)
The principal site of its action is vascular
epithelium
It is inhibited by synthetically produced
Captopril drug
Renin-Angiotensin-Aldosterone
System
Angiotensin II
1. Stimulates aldosterone production
2. Stimulates ADH secretion from pituitary
3. Highly potent vasoconstrictor
4. Stimulates thirst
5. Stimulates release of catecholamines by
adrenal medulla
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Angiotensin III
Stmulates aldosterone production without
vasoconstriction
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Role of Angiotensin II
Hypertensive
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Angiotensin ll is a powerful vasoconstrictor.
It constricts the blood vessels and raises the
peripheral resistance, thereby acting to
restore blood pressure.
Angiotensin ll also increases the secretion of
aldosterone leading to Na+ reabsorption.
Effects of Angiotensin II
Renin-Angiotensin-Aldosterone
System
Aldosterone:
It is a mineralocorticoid produced in the
adrenal cortex
Increases cortical collecting tubule
reabsorption of Na+ and secretion of K+
and H+
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Regulation of Aldosterone
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Angiotensin II and III stimulate aldosterone release
Changes in volume ( long Negative feedback loop)
Inhibition of renin secretion by angiotensin II (short
negative feedback loop)
Endothelin and vasopressin stimulate aldosterone
secretion
ANP is a potent inhibitor, dopamine also inhibits it.
Endothelin
ADH
Blood Volume
Osmolarity
Kidney
ANP
Aldosterone
Distal
Tubules
Na & H2O
Angiotensin III
JGA
Renin
Angiotensin II
Aldosterone
Hypertensive
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Stimulates Na+ reabsorption and K+
excretion
Aldosterone-mediated responses in
the Kidney
Renin-Angiotensin-Aldosterone
System
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High Na intake suppresses the system
Acute decrease in Na activates RAS which in
turn stimulates aldosterone, leading to Na
retention by kidneys.
Prolonged Na restriction increases sensitivity
of adrenal to angiotensin
( aldosterone)
and decreases sensitivity of vasculature.