Renin-Angiotensin-Aldosterone System
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
1. 2.
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
3.
Renin-Angiotensin-Aldosterone System
It is a glycoprotein synthesized and secreted into the bloodstream by the liver Angiotensinogen Renin angiotensin I ACE Angiotensin III Angiotensin II
Angiotensinogen
Renin-Angiotensin-Aldosterone System
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
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 Angiotensin III Stmulates aldosterone production without vasoconstriction
Renin-Angiotensin-Aldosterone System
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.
Role of Angiotensin II Hypertensive
Effects of Angiotensin II
Renin-Angiotensin-Aldosterone SystemAldosterone: It is a mineralocorticoid produced in the adrenal cortex Increases cortical collecting tubule reabsorption of Na+ and secretion of K+ and H+
Regulation of Aldosterone
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.
Angiotensin II
Renin
JGA
Kidney
Angiotensin III
Distal Tubules Na & H2O
ANP
Aldosterone
EndothelinADH
Blood VolumeOsmolarity
Aldosterone Hypertensive
Stimulates Na+ reabsorption and K+ excretion
Aldosterone-mediated responses in the Kidney
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.
Renin-Angiotensin-Aldosterone System