Kidney Structure
The kidney has a precise internal architecture from outer cortex to renal pelvis. Understanding this layered structure explains patterns of disease on imaging and the functional significance of each zone.
✦ The Mnemonic
"Carefully Maintaining Perfectly Clear Priorities: Urinary"
Cortex · Medulla (pyramids) · Papilla · Calyx · Pelvis · Ureter — outer to inner
Clinical Breakdown
The kidney is a retroperitoneal organ located at T12–L3, with the right kidney slightly lower (displaced by the liver). Each kidney weighs ~150 g. The renal hilum (on the medial surface) transmits: renal vein (anterior), renal artery (middle), renal pelvis/ureter (posterior) — VAPe from anterior to posterior.
Renal papillary necrosis: ischaemic necrosis of the papillae, causing sloughed papillae that can obstruct the ureter. Risk factors: diabetes mellitus (most common), analgesic nephropathy (NSAIDs), sickle cell disease, pyelonephritis, and renal vein thrombosis. Presents with haematuria, renal colic, and pyuria.
Renal cortical scarring (reflux nephropathy) occurs when vesicoureteric reflux (VUR) allows infected urine to reach the renal papillae. The compound papillae at the poles (which have a concave tip rather than convex) allow intrarenal reflux — explaining why polar scars are most common.
⭐ Clinical Pearl
Renal cell carcinoma (RCC) arises from the proximal tubular epithelium of the cortex. The classic triad (haematuria, loin pain, flank mass) is present in only 10% of cases. RCC can invade the renal vein and IVC — a tumour thrombus extending into the right atrium is a surgical emergency. VHL gene mutation is associated with clear cell RCC.