Glomerular filtration barrier

The specialized interface between glomerular blood and the nephron that filters water and small solutes while restricting blood cells and most plasma proteins.

Glomerular endothelium: Fenestrated endothelial cells lining glomerular capillaries, with a surface layer that influences filtration. Its fenestrae admit plasma while its glycocalyx contributes to the barrier's selectivity.
Proteinuria: An abnormal amount of protein in urine, often reflecting kidney filtration or reabsorption dysfunction. Increased urinary protein can signal that the barrier no longer retains plasma proteins effectively.
Glomerulus: A tuft of capillaries in the kidney nephron where blood filtration begins. The barrier is built into the capillary wall of this filtering structure.
Tubular reabsorption: The transfer of water and solutes from nephron fluid back into the blood. Unlike barrier filtration, reabsorption retrieves selected substances after filtrate enters the nephron.
Glomerular basement membrane: A specialized extracellular matrix sheet between glomerular endothelial cells and podocytes. Its matrix forms the central structural layer traversed by filtrate.
Albuminuria: The presence of excess albumin in urine, used as a marker of kidney damage. Albumin leakage is a common measurable consequence of glomerular barrier injury.
Bowman's space: The space within Bowman's capsule that receives fluid filtered from glomerular capillaries. Filtrate crosses the barrier into this space before entering the renal tubule.
Tubular secretion: The transfer of substances from blood or tubule cells into nephron fluid. Secretion adds substances to tubular fluid rather than filtering them across the glomerular interface.
Podocyte: A specialized epithelial cell whose interdigitating foot processes wrap around glomerular capillaries. Podocyte foot processes form the outer surface of the filtration barrier.
Hematuria: The presence of red blood cells in urine, visible or detectable by laboratory testing. Red-cell passage can occur when glomerular capillary structures are damaged.

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