Lung–kidney system ↗Renal blood flow arrives
Renal arteries branch toward afferent arterioles, delivering plasma to glomerular capillaries under autoregulatory and systemic control.
KIDNEYS / 05
Filter broadly.
Reclaim selectively.
A nephron combines a pressure-driven filter with metabolically active tubular segments. Final urine is what remains after extensive, regulated reabsorption and secretion.
Pressure produces ultrafiltrate
Hydrostatic and oncotic forces across the glomerular capillary determine net filtration pressure.
The barrier excludes cells and most proteins
Fenestrated endothelium, basement membrane, and podocyte slit structures provide layered selectivity.
Efferent flow feeds peritubular vessels
Blood leaving the glomerulus supplies capillaries that support tubular reabsorption, secretion, and oxygen delivery.
Proximal tubule reclaims bulk load
Most filtered water, sodium, bicarbonate, glucose, amino acids, and small proteins are returned to blood here.
Loop builds a medullary gradient
Segment-specific water and salt permeability plus countercurrent flow create the conditions for concentration or dilution.
Distal segments refine electrolytes
Distal tubule and connecting segments adjust sodium, chloride, calcium, and the solute delivery reaching collecting ducts.
Collecting ducts set final urine
ADH, aldosterone, flow, potassium, acid–base transport, and the medullary gradient determine the final excreted fluid.