CorpusHuman Anatomy

Kidney — Coronal Section

Right kidney, anterior view (hilum faces medially, to the right)

Coronal (frontal) section of a right kidney seen from the front, with the hilum facing medially (to the right of the image). The parenchyma consists of an outer granular cortex, speckled with renal corpuscles, and an inner medulla made of conical, striated renal pyramids (8 shown; typically 8–18). Cortex dips between the pyramids as renal columns. The apex of each pyramid, the renal papilla, projects into a cup-shaped minor calyx; minor calyces unite into two or three major calyces, which join to form the funnel-shaped renal pelvis. The pelvis leaves through the hilum and narrows at the pelvi-ureteric junction into the ureter. Animated droplets trace urine from papilla to ureter.

For clarity the arterial tree is drawn in the lower half and the venous tree in the upper half. Renal artery → segmental arteries (in the renal sinus; end arteries) → interlobar arteries (in the renal columns) → arcuate arteries (over the pyramid bases at the corticomedullary junction) → cortical radiate (interlobular) arteries → afferent arterioles. Veins return in parallel but anastomose freely. At the hilum the order from anterior to posterior is renal Vein – Artery – Pelvis (VAP).

Step-by-step

  1. Capsule and cortex

    A tough fibrous capsule invests the kidney (outside it lie perirenal fat, renal fascia and pararenal fat). The outer cortex, ≈1 cm thick, contains every renal corpuscle (red dots) together with the proximal and distal convoluted tubules, which give it a granular appearance.

  2. Medulla: pyramids and columns

    The medulla is arranged as 8–18 renal pyramids whose striations are parallel loops of Henle, collecting ducts and vasa recta. Their bases face the cortex; their apices point into the sinus. Cortex extending between the pyramids forms the renal columns. One pyramid with its cap of cortex is a renal lobe.

  3. Renal artery → segmental arteries

    The renal artery arises from the aorta at ≈L1–L2; together the kidneys receive ≈20–25 % of cardiac output (≈1.1 L/min). At the hilum it divides into five segmental arteries (apical, anterosuperior, anteroinferior, inferior, posterior). Segmental arteries are end arteries — occlusion infarcts the segment they supply.

  4. Interlobar → arcuate arteries

    Segmental arteries give interlobar arteries that run outward in the renal columns, beside the pyramids. At the corticomedullary junction they bend through 90° to arch over the pyramid bases as arcuate arteries.

  5. Cortical radiate arteries → glomeruli

    Cortical radiate (interlobular) arteries run radially towards the capsule and give off afferent arterioles, each feeding one glomerulus. Efferent arterioles then form peritubular capillaries around cortical tubules or, from juxtamedullary glomeruli, the vasa recta of the medulla.

  6. Venous return

    Blood returns via cortical radiate, arcuate and interlobar veins, which anastomose freely, to the renal vein and then the inferior vena cava. The left renal vein is longer and crosses anterior to the aorta just below the superior mesenteric artery.

  7. Papilla → minor calyx

    Collecting ducts merge into papillary ducts (of Bellini) that open on the tip of each papilla (area cribrosa). Final urine drips into the minor calyx cupping the papilla; pacemaker cells in the calyceal wall initiate peristalsis.

  8. Major calyces → renal pelvis

    Two or three minor calyces unite to form a major calyx, and two or three major calyces join to form the funnel-shaped renal pelvis, which lies in the renal sinus and leaves through the hilum. Calyceal and pelvic capacity is only ≈5–10 mL.

  9. Hilum and renal sinus

    At the hilum the renal vein lies most anterior, the renal artery in the middle and the renal pelvis posterior (VAP). Inside, the vessels and collecting system are cushioned by renal sinus fat.

  10. Pelvi-ureteric junction → ureter

    The pelvis narrows at the pelvi-ureteric junction, the first of the three ureteric constrictions where calculi commonly lodge. Peristaltic waves, several per minute, propel urine down the ≈25–30 cm ureter to the bladder.

Labelled parts