glomerulus

The glomerulus is a cluster of capillaries located in the cortex of the kidney. It forms part of the renal corpuscle along with Bowman's capsule and serves as the site of blood filtration to form the filtrate that becomes urine.

It receives blood via the afferent arteriole and drains into the efferent arteriole. The capillary tuft is supported by mesangial cells and is enclosed by the glomerular basement membrane and podocytes.

Filtration barrier: endothelial fenestrations, GBM, and podocyte slit diaphragms. The barrier is selectively permeable to water and small solutes, while restricting proteins; it bears a negative charge that repels negatively charged plasma proteins.

Filtration produces Bowman's space filtrate; GFR depends on hydrostatic pressure in glomerular capillaries, along with oncotic pressure; ultrafiltration rate is influenced by arteriolar tone and systemic blood pressure.

Regulation: Autoregulation via myogenic mechanism and tubuloglomerular feedback; renin-angiotensin system influences by constricting efferent arteriole, maintaining GFR during low renal perfusion. Sympathetic input reduces GFR during stress; mesangial cells can modify surface area.

Clinical note: Glomerular disease includes glomerulonephritis and diabetic nephropathy; damage to the filtration barrier can cause proteinuria, hematuria, and altered urine formation; nephrotic and nephritic syndromes reflect different patterns of injury.