MAIN FUNCTION :
* It helps in maintaining volume and blood pressure .
RENIN :
* Renin is acid protease which is glycoprotein in nature .
* Renin is the substance secreted by the J.G cells of the kidney .
* Renin activates angiotensinogen ( inactive form )to angiotensin - l ( precursor of angiotensin - ll )
# PROCESS OF SYNTHESIS OF RENIN :
* There are some specialised cells in the DCT called " macula densa " , which can sense the concentration of sodium in tubular fluid .
*In afferent arteriole there are specialised smooth muscle cells called polkisen cells .
* These polkisen cells can sense the pressure , they act as baro receptors . *Macula densa and polkisen cells are held together by lacis cells forming juxtra glomerular apparatus .
* When blood flow to kidney decreases then J.G. apparatus get activated and releases renin along with prostaglandins , nitric oxide etc ..
# CONDITIONS WHICH LEAD TO SECRETION OF RENIN :
* Reduced blood volume and pressure .
* Increased sympathetic activity .
* Decreased electrolytes concentrations in plasma of sodium , potassium etc...
# FACTORS WHICH INCREASES SYNTHESIS OF ANGIOTENSINOGEN :
* Glucocoticoids , thyroid hormones , estrogen in the blood increases synthesis of angiotensinogen by liver .
# MECHANISM OF ACTION OF ANGIOTENSIN - II :
* Liver produces many proteins ,one among them is angiotensinogen ( inactive form ).
* In the presence of renin , angiotensinogen will be converted to angiotensin - l .
* This angiotensin- l reaches lungs via blood.
* In the surface epithelium of pulmonary capillaries , there is Angiotensin Converting Enzyme .
* Angiotensin Converting Enzyme converts angiotensin - l to angiotensin - ll .
* Angiotensin converting enzyme also inactivates bradykinin ( bradykinin is vasodilator ) .
* ACTIONS OF ANGIOTENSIN - II
1) ACTION OF ANGIOTENSIN - II ON BLOOD VESSELS :
* Potency of angiotensin - II is about eight times of norepinephrine .
* It is potent vasoconstrictor .
* It acts on venous smooth muscles and constrict them , which leads to increase in pressure in veins .
* Which eventually leads to increased cardiac filling and increases blood pressure .
2) ACTIONS OF ANGIOTENSIN - II ON ADRENAL CORTEX ( Zonaglomerulosa ) :
* It acts on zonaglomerulosa and increases the secretion of aldosterone .
* Aldosterone have receptors on principle cells of DCT .
* Where it activates genes related to synthesis of Na+k+ ATPases , sodium chanels , potassium chanels .
* These channels get embedded into basolateral membrane ( Na+ K+ ATPases ) and luminal membrane ( Na+ and K+ channels).
* Presence of these chanels leads to retention of salt and water which leads to increase in blood pressure and blood volume .
3) ACTION OF ANGIOTENSIN -II ON CENTRAL NERVOUS SYSTEM :
* Angiotensin - II stimulates sympathetic nervous system .
* It activates sympathetic ganglia .
* Angiotensin - II acts on nerve endings and stimulate the release of norepinephrine , amount of norepinephrine at synapse increases .
* Increase in norepinephrine leads to increase in strength of constriction of blood vessels .
* These are the mechanisms by which angiotensin - II regulates blood volume and blood pressure . MECHANISM :
MAIN FUNCTION :
* It helps in maintaining blood volume and blood pressure .
RENIN :
* Renin is acid protease which is glycoprotein in nature .
* Renin is the substance secreted by the J.G cells of the kidney .
* Renin activates angiotensinogen ( inactive form )to angiotensin - l ( precursor of angiotensin - ll )
# PROCESS OF SYNTHESIS OF RENIN :
* There are some specialised cells in the DCT called " macula densa " , which can sense the concentration of sodium in tubular fluid .
*In afferent arteriole there are specialised smooth muscle cells called polkisen cells .
* These polkisen cells can sense the pressure , they act as baro receptors . *Macula densa and polkisen cells are held together by lacis cells forming juxtra glomerular apparatus .
* When blood flow to kidney decreases then J.G. apparatus get activated and releases renin along with prostaglandins , nitric oxide etc ..
# CONDITIONS WHICH LEAD TO SECRETION OF RENIN :
* Reduced blood volume and pressure .
* Increased sympathetic activity .
* Decreased electrolytes concentrations in plasma of sodium , potassium etc...
# FACTORS WHICH INCREASES SYNTHESIS OF ANGIOTENSINOGEN :
* Glucocoticoids , thyroid hormones , estrogen in the blood increases synthesis of angiotensinogen by liver .
# MECHANISM OF ACTION OF ANGIOTENSIN - II :
* Liver produces many proteins ,one among them is angiotensinogen ( inactive form ).
* In the presence of renin , angiotensinogen will be converted to angiotensin - l .
* This angiotensin- l reaches lungs via blood.
* In the surface epithelium of pulmonary capillaries , there is Angiotensin Converting Enzyme .
* Angiotensin Converting Enzyme converts angiotensin - l to angiotensin - ll .
* Angiotensin converting enzyme also inactivates bradykinin ( bradykinin is vasodilator ) .
* ACTIONS OF ANGIOTENSIN - II
1) ACTION OF ANGIOTENSIN - II ON BLOOD VESSELS :
* Potency of angiotensin - II is about eight times of norepinephrine .
* It is potent vasoconstrictor .
* It acts on venous smooth muscles and constrict them , which leads to increase in pressure in veins .
* Which eventually leads to increased cardiac filling and increases blood pressure .
2) ACTIONS OF ANGIOTENSIN - II ON ADRENAL CORTEX ( Zonaglomerulosa ) :
* It acts on zonaglomerulosa and increases the secretion of aldosterone .
* Aldosterone have receptors on principle cells of DCT .
* Where it activates genes related to synthesis of Na+k+ ATPases , sodium chanels , potassium chanels .
* These channels get embedded into basolateral membrane ( Na+ K+ ATPases ) and luminal membrane ( Na+ and K+ channels).
* Presence of these chanels leads to retention of salt and water which leads to increase in blood pressure and blood volume .
3) ACTION OF ANGIOTENSIN -II ON CENTRAL NERVOUS SYSTEM :
* Angiotensin - II stimulates sympathetic nervous system .
* It activates sympathetic ganglia .
* Angiotensin - II acts on nerve endings and stimulate the release of norepinephrine , amount of norepinephrine at synapse increases .
* Increase in norepinephrine leads to increase in strength of constriction of blood vessels .
* These are the mechanisms by which angiotensin - II regulates blood volume and blood pressure .
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