Anaes · Applied cardiovascular & respiratory physiology

Renal: GFR & tubular function

Also known as Glomerular filtration rate · Filtration fraction · Clearance · Tubuloglomerular feedback · Proximal tubule · NHE3

The kidney filters plasma at the glomerulus and then selectively reabsorbs and secretes along the nephron, and the glomerular filtration rate (about 125 mL per minute) is the single best measure of kidney function. The framework rests on five exam-critical ideas: GFR is normally about 125 mL per minute and the filtration fraction (GFR over renal plasma flow) is about 20 percent, set by the balance of Starling forces across the glomerular capillary and the relative tone of the afferent and efferent arterioles; GFR is held constant across a range of blood pressures by autoregulation (myogenic and tubuloglomerular feedback from the macula densa); the clearance of a freely filtered, neither-reabsorbed-nor-secreted solute (inulin) equals GFR, and creatinine clearance approximates it clinically; the nephron segments each specialise — the proximal tubule reabsorbs about 65 percent of the bulk filtrate (including all glucose and amino acids and most bicarbonate and sodium, via the NHE3 sodium-hydrogen exchanger), the loop of Henle is the countercurrent multiplier that concentrates the medulla, and the distal nephron and collecting duct fine-tune sodium (aldosterone) and water (ADH); and the kidney is uniquely vulnerable to anaesthesia and nephrotoxins because it receives a high blood flow and depends on glomerular pressure and tubular energy. Built on the GFR-physiology review (Ayub 2026), the macula densa tubuloglomerular-feedback study (Li 2026), the renal NHE3 study (Nogueira Coelho 2026), the proximal-tubule-dysfunction study (Ikeme 2026), the SGLT2-inhibition study (Gao 2026), and the chloride-and-RAAS study (Adin 2026).