RENIN- ANGIOTENSIN SYSTEM
RENIN:
- Protease enzyme
- Secreted by Juxta-Glomerular (JG) cells of afferent arterioles.
REGULATION OF RENIN SECRETION:
1. Renal pressure:
- Reduced renal perfusion pressure – Most powerful stimulus.
- Sensed by Juxtaglomerular cells themselves.
2. NaCl- concentration in distal tubules:
- Changes sensed by macula densa → signal transmitted to JG cells.
- Increased NaCl– → Decreases renin release.
- Decreased NaCl– → Increases renin release.
3. Innervation of JG cells:
- By sympathetic fibers.
- Release renin in response to sympathetic discharge.
4. Prostacyclin (PGI2):
- Stimulates renin secretion directly.
Renin from JG cells enters circulation.
↓
Acts on angiotensinogen (α2 -globulin secreted by liver).
↓
Converted to angiotensin I, decapeptide.
- (By splitting Leucine-Valin bond of angiotensinogen).
Angiotensin I → Angiotensin II (Octapeptide)
- By enzyme angiotensin-converting enzyme (ACE).
- By splitting phenylalanine-histidyl bond of angiotensin II.
- ACE found on surface of lung capillary endothelium.
- Hence, angiotensin II formed here.
Angiotensin II degraded to angiotensin III (hexapeptide)
- By splitting aspargine-arginine bond by aminopeptidase.
Actions of Angiotensin:
| TYPE | DESCRIPTION |
| Angiotensin I | Solely angiotensin II precursor without anyother established action. |
|
Angiotensin II
|
3 major peripheral actions:
1. Vasoconstriction – Most prominent action. 2. ↑ed aldosterone secretion:
3. Reducing GFR & RBF:
Central action:
|
|
Angiotensin III
|
Functions:
|
Exam Important
- Renin secreted by Juxta-Glomerular (JG) cells of afferent arterioles.
- Most powerful stimulus for renin release is reduced renal perfusion pressure.
- Increased NaCl in distal tubulesdecreases renin release.
- Renin releases in response to sympathetic discharge from JG cells.
- Renin acts on angiotensinogen secreted by liver, converting to angiotensin I.
– By splitting Leucine-Valin bond of angiotensinogen.
- Angiotensin I converted into Angiotensin II by ACE.
- ACE is found on surface of capillary endothelium of lung.
– Hence, angiotensin II is formed on lung capillary endothelium.
- Angiotensin I has no established function & is solely “Angiotensin II precursor”.
- Most prominent action of angiotensin II is Vasoconstriction.
- Angiotensin II cause,
– Na2+ & water retention in kidney by increasing aldosterone & ADH secretion.
– Reduces both GFR & RBF, by constricting both afferent & efferent arterioles.
- Angiotensin II acts centrally by increasing thirst.
- Angiotensin III (hexapeptide) is breakdown product of angiotensin II has about 40% of angiotensin II pressor activity & complete aldosterone stimulating activity.
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