Kidney
Latin: Ren sinistrum
Location: Retroperitoneal, T12–L3
Paired structure: one on the left and one on the right side of the body.
View the kidney in 3DFunction
Together the two kidneys filter about 180 L of plasma a day and make about 1.5 L of urine — roughly a million nephrons in each kidney, filtering the whole plasma volume about 60 times daily. The glomerulus' 50 mmHg hydrostatic pressure forces filtrate through a three-layer sieve; the tubule then reclaims 99% of it, fine-tuned by aldosterone, ADH and natriuretic peptides.
Beyond filtration, the kidney is an endocrine organ: erythropoietin drives red cell production in the marrow, renin couples it to blood pressure control, and the 1-alpha-hydroxylase activates vitamin D for bone. The left kidney sits higher than the right, cradled by the spleen above and psoas behind, and its hilum delivers renal vein, artery and pelvis in that anterior-to-posterior order.
Blood supply
Renal artery directly from the aorta — the two kidneys together receive ~20–25% of cardiac output though they are under 1% of body weight; renal vein to the IVC (left vein crosses the aorta, longer and vulnerable).
Nerve supply
Sympathetic T10–L1 (renal plexus); visceral afferents travel with the lesser and least splanchnic nerves — flank pain radiating to the groin.
Clinical relevance
- Renal colic
- A stone in the ureter's three narrowings spasms smooth muscle — severe loin-to-groin pain with haematuria, writhing not still.
- Chronic kidney disease
- Diabetes and hypertension scar nephrons silently over years; anaemia, bone disease and acidosis follow the filtration decline.
Related conditions
Educational anatomy reference, not medical advice. About this content.