• Kidneys‘ objective is to maintain homeostatatic balance of blood volume, pressure, and ion concentrations via filtration of the blood, despite fluctuations in blood pressure throughout the day.
• GFR regulation achieves this balance through both intrinsic and extrinsic mechanisms.
• GFR is most easily regulated by adjusting the net filtration pressure, which is determined by the hydrostatic and oncotic forces at the filtration membrane.

Intrinsic vs Extrinsic Mechanisms

Intrinsic response

• Involve intra-renal mechanisms
• Structures within the kidneys initiate the intrinsic mechanisms
• Dominate as long as MAP is 80-180 mmHg
• Goal is to maintain nearly constant GFR over a wide range of mean arterial pressures
• Includes myogenic and tubuloglomerular feedback, which act primarily on afferent arteriole.

Extrinsic response

• Involve neural and hormonal mechanisms.
• Requires transport of neurotransmitters/hormones in bloodstream.
• Active when MAP is below 80 mmHg.
• Goal is to maintain blood volume and pressure; regulation of GFR is one facet of this.
• Sympathetic response acts primarily on afferent arteriole (Norepinephrine)
• Hormonal response acts primarily on efferent arteriole (Angiotensin II)