Chapter 72: Kidney & Ureter Anatomy

The kidneys are retroperitoneal organs positioned laterally to the vertebral column, with the right kidney typically lying slightly inferior to the left due to its relationship with the liver. Their long axis orientation is inferolateral, and the transverse axis is posteromedial, an appreciation of which is important in renal surgery. The kidneys are enclosed by perirenal fat, which is contained within the renal fascia, a multilaminar structure defining the perirenal space. Developmental abnormalities covered include single absent kidneys, ectopic kidneys often found in the pelvis, rare forms of crossed fused renal ectopia, and horseshoe kidneys, which are characterized by an isthmus connecting the lower poles, often below the inferior mesenteric artery, and are frequently associated with congenital ureteropelvic junction obstruction. The renal hilum, which opens anteromedially, transmits structures in a specific order from anterior to posterior: the renal vein, renal artery, and renal pelvis. Internally, the kidney is organized into the cortex, which arches over the bases of the renal pyramids in the medulla, where collecting tubules drain into minor calyces, major calyces, and eventually the renal pelvis. The rich blood supply, representing approximately 20% of cardiac output, originates from the renal arteries, which divide sequentially into segmental, lobar, interlobar, arcuate (at the corticomedullary junction), and interlobular arteries. The kidney is characterized by five primary arterial segments supplied by virtual end arteries, necessitating precise knowledge of vascular anatomy during procedures like partial nephrectomy. Venous drainage converges via interlobular and arcuate veins toward the renal veins, noting that the left renal vein is significantly longer than the right and is vulnerable to compression between the abdominal aorta and the superior mesenteric artery, a condition associated with anterior nutcracker syndrome. Microstructurally, urine formation begins in the renal corpuscle, where specialized podocyte cells and the glomerular basal lamina facilitate ultrafiltration from the plasma. The filtrate is refined in the renal tubule, where selective resorption of water and solutes occurs. Critical for water conservation is the countercurrent multiplier mechanism, which relies on the anatomical arrangement of the nephron loop and vasa recta to establish a steep osmotic gradient in the renal medulla. The juxtaglomerular apparatus regulates the filtration rate and systemic blood pressure through the release of renin by juxtaglomerular cells and osmoregulation by the macula densa. The ureters are muscular tubes 25 to 30 centimeters in length that transport urine via peristaltic contractions initiated by pacemaker cells located in the minor calyces. Ureteric calculi (stones) commonly become impacted at the three narrowest points: the ureteropelvic junction, the crossing of the iliac vessels at the linea terminalis, and the ureterovesical junction. In females, the ureter is closely related to the uterine artery as it travels toward the bladder, an important consideration during hysterectomy.