Glomerular Filtration and Regulation Mechanisms

Filtration barriers in the glomerulus

Endothelium of fenestrated capillaries, basal lamina, podocytes with filtration slits.

Filtration favorability in the glomerulus

Glomerular blood pressure is higher than in other capillaries, creating greater hydrostatic pressure, leading to filtration along the entire length of the glomerular capillaries.

Forces involved in glomerular filtration

PH: Hydrostatic pressure of blood in capillary (favors filtration), Π: Colloid osmotic pressure of blood in capillary (opposes filtration), PFluid: Hydrostatic pressure of fluid in Bowman's capsule (opposes filtration).

Net filtration pressure into Bowman's capsule

10 mmHg into Bowman's capsule.

Average glomerular filtration rate (GFR)

125 mL/min.

Myogenic autoregulation

A mechanism where decreased BP and GFR cause decreased stretch of smooth muscle in afferent arterioles → vasodilation → increased GFR.

Tubuloglomerular feedback

A form of intrinsic GFR control: Increased GFR → increased tubular flow, Macula densa detects more NaCl, Sends paracrine signal to afferent arteriole → constriction, Increased resistance → decreased glomerular hydrostatic pressure → decreased GFR.

Macula densa cells

Detect NaCl delivery and transport in the tubule.

Extrinsic controls of GFR

Neural and hormonal mechanisms that act to maintain systemic BP.

Sympathetic nervous system effect on GFR

It can stimulate granular cells in the juxtaglomerular apparatus (JGA) to release renin.

Role of renin in the renin-angiotensin mechanism

Renin catalyzes a cascade that produces angiotensin II.

Effects of angiotensin II

Vasoconstriction and increased Na⁺ reabsorption, which increase blood pressure and blood volume.