Question

Describe how glomerular filtration rate is regulated. Be sure to include both intrinsic and extrinsic mechanisms, and explain how and when they operate.

Describe the mechanism for reabsorption of water, glucose and Na+ in the PCT.

Answer 1

• Glomerular filteration rate (GFR)is defined as the amount of filterate formed by glomerular filtering membrane of both the kidneys in a uinit time.Normally it is 125ml/min.
• Regulation of glomerular filteration involves neural mechanism,hormonal mechanism,myogenic mechanism and tubuloglomerular feedback.

Neural mechanism

1. The sympathetic activity in the renal nerve is less when the blood volume is normal.When blood volume decreases,increases renal sympathetic activity and increased circulating catecholamines cause renal vasoconstriction that in turn decreases GFR.
2. Activation of sympathetic fibers causes constriction of afferent arteriole that decreases blood flow to glomerulus.

Hormonal Mechanism

• Various hormones affect GFR are :- Angiotensin,Histamine,Dopamine,ANP,Endothelin,Bradykinn,Nitric oxide,Adenosine,Glucocorticoids,and prostaglandins.

​​​​​​​Autoregulatory Mechanism

• The autoregulation of GFR maintains a constant rate of glomerular filteration despite changes in systemic arterial pressure within the range of 80-180mmHg.This is mainly due to Myogenic theory anf theory of tubuloglomerular feedback.

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• Myogenic theory :- Myogenic mechanism controls renal blood flow and GFR.When arterial pressure increases,the afferent arteriole is stretched and stretch induced contraction of smooth muscles of afferent arteriole decreases GFR.
• Tubuloglomerular Feedback :- Increased renal arterial pressure increases pressure in the glomerular capillaries. - This increase GFR and flow of fluid in the tubule,which is sensed by macula densa cells.   - Tubular cells provide signal to glomerular apparatus that causes afferent arteriolar constriction to decrease GFR and bring it back to normal and maintain the constancy of load deliverd to the tubule.

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