Question

describe the auto regulation of GFR and list extrinsic influences that affect GFR

Answer 1

AUTOREGULATION OF GFR : It is by two mechanism

1) Myogenic mechanism

2) Tubuloglomerulo feedback mechanism

Myogenic Mechanism - It is the intrinsic property of afferent arteriolar smooth muslce. When there is increased blood flow the afferent arteriolar smooth muscle streches. This leada to increased calcium influx in smooth mucle which lead to vasoconstriction and hence decreases the blood flow.

Tubuloglomerular feedback - It is mediated by macula densa cells, which are specialised epitheilial cells located in the thick ascending limb of loop of Henle. Macula densa sense Na concentration, by Na+K+2Cl- co transporter. In response to increased Na concentration, macula densa release Adenosine. This adenosine act on the afferent arteriole and causes vasoconstirciton, leading to decrease in Renal blood flow and hence the GFR.

Increased GFR --> Increased NaCl in tubule --> sensed by Macula densa --> release of Adenosine -> constirition of afferent --> Decrease in GFR.

EXTRINSIC FACTOR INFLUENCING THE GFR ::

1) Mesenglial Cells - by contration or relaxation :

Mesenglia cell contration - Angiotensin II, Endothelins , Adenosine, NE, ADH

Mesenglial cell relaxation - cAMP, Dopamine, ANP, NO

2) Glomerulotubular balance

3) Hormones