Describe the kidney under position, coverings, relations and blood supply. Add a note on the ureter and its constrictions.

Position and General Features

• Extend from the upper border of T12 to the lower border of L3
• The right kidney is 1–2.5 cm lower than the left, because of the liver
• Each measures about 11 6 3 cm and weighs 150 g
• The hilum lies at the level of L1, on the transpyloric plane

Coverings

• The renal fascia encloses the kidney and the suprarenal gland in separate compartments, and is open inferiorly — which is why a perinephric abscess can track down into the pelvis, and why the kidney can descend (nephroptosis)
• Fat is the chief support of the kidney; rapid weight loss can cause a mobile kidney

Relations

• The left kidney is crossed posteriorly by the 11th and 12th ribs; the right by the 12th only, since it lies lower
• The pleura descends to the level of the 12th rib behind, so it is at risk in a posterior approach to the kidney

Hilum and Blood Supply

• Structures in the hilum, from anterior to posterior — renal vein, renal artery, renal pelvis (mnemonic VAP)
• Renal arteries arise from the aorta at L1–L2, just below the superior mesenteric artery
• The right renal artery is longer (it crosses behind the inferior vena cava); the left renal vein is longer (it crosses in front of the aorta)
• The left renal vein receives the left suprarenal and left gonadal veins; the right gonadal and suprarenal veins drain directly into the inferior vena cava
• Renal arteries are end arteries — segmental branches do not anastomose, so occlusion infarcts the segment

Internal Structure

• Cortex — outer; contains glomeruli and convoluted tubules; sends renal columns of Bertin between the pyramids
• Medulla — 8 to 18 renal pyramids, each ending in a papilla projecting into a minor calyx
• Minor calyces (7–13) → major calyces (2–3) → renal pelvis → ureter
• The renal sinus contains the calyces, pelvis, vessels and fat

The Ureter

• About 25 cm long, half abdominal and half pelvic
• Runs downward on psoas major, crossed by the gonadal vessels; enters the pelvis by crossing the bifurcation of the common iliac artery at the sacro-iliac joint
• In the female it is crossed by the uterine artery about 2 cm lateral to the cervix — "water under the bridge"; at risk in hysterectomy
• In the male it is crossed by the vas deferens

• Stones lodge at these three sites, and they are the points of difficulty in passing a ureteric catheter
• The oblique passage through the bladder wall acts as a valve preventing reflux

Development and Common Anomalies

Applied Aspects

• Ureteric colic — severe pain radiating "from loin to groin", and to the scrotum or labium, because the ureter is supplied by T11–L2
• Renal angle tenderness — elicited between the 12th rib and the lateral border of the erector spinae; a sign of renal inflammation
• Horseshoe kidney — fused lower poles caught beneath the inferior mesenteric artery during ascent, so it lies low; predisposes to obstruction and infection
• Renal transplantation places the graft in the iliac fossa extraperitoneally, anastomosed to the external iliac vessels — a superficial site that is easy to biopsy
• Renal cell carcinoma may extend along the renal vein into the inferior vena cava and even the right atrium; it classically presents with the triad of haematuria, loin pain and a mass, though this is now uncommon