Glomerular Filtration Rate and its Regulation

The glomerular filtration rate or GFR is the volume of filtrate formed per minute by the glomeruli.

Any changes in the local blood pressure and flow can affect the GFR; the kidneys adapt to maintain a constant GFR.  

This autoregulation involves two intrinsic mechanisms.

In the myogenic mechanism, smooth muscle in afferent arterioles contracts when blood pressure rises, reducing the glomerular blood flow and GFR.

Increased sodium levels in the filtrate detected by the macula densa cells initiate the tubuloglomerular feedback mechanism.

It triggers a signaling mechanism for vasoconstriction in afferent arterioles, reducing glomerular blood flow and GFR to maintain homeostasis.

However, under very low systemic blood pressure, extrinsic controls take over, including hormonal and neuronal mechanisms.

The sympathetic nervous system releases norepinephrine, which constricts the efferent and afferent arterioles, decreasing GFR.

The hormone angiotensin-II balances vasoconstriction in the afferent and efferent arterioles to maintain GFR.

In contrast, atrial natriuretic peptide triggers the dilation of afferent arterioles and the constriction of efferent arterioles, raising GFR.