Urinary Tract: Renal Arteries, Ureters and Bladder

Renal arteries and segments

Each renal artery arises from the side of the aorta at about L1–L2 and, near the hilum, divides into anterior and posterior divisions that give five segmental arteries. The segmental arteries do not anastomose, so each supplies a surgically separable segment of kidney.

A relatively avascular plane between the anterior and posterior territories, along the lateral border, can be used to open the kidney. Segmental arteries give interlobar, arcuate and interlobular arteries and finally the afferent arterioles of the glomeruli. The renal veins, unlike the arteries, anastomose freely inside the kidney.

The right renal artery is longer and passes behind the inferior vena cava. The left renal vein is longer, crosses in front of the aorta below the superior mesenteric artery and receives the left gonadal and left suprarenal veins; on the right, the gonadal vein drains straight into the cava. Accessory renal arteries are common.

Ureters: course and relations

Each ureter is a muscular tube about 25–30 cm long that runs from the renal pelvis to the bladder, half in the abdomen and half in the pelvis.

Abdominal part

The ureter runs down on psoas major, retroperitoneally, roughly along the tips of the lumbar transverse processes on a radiograph. The gonadal vessels cross in front of it. On the right it lies behind the duodenum, the right colic and ileocolic vessels and the root of the mesentery; on the left, behind the left colic vessels and the sigmoid mesocolon.

Pelvic part

The ureter enters the pelvis by crossing the bifurcation of the common iliac artery, in front of the sacro-iliac joint. It runs down the lateral pelvic wall in front of the internal iliac artery to about the level of the ischial spine, then turns forwards and medially to the bladder.

• Males: the ductus deferens crosses above and in front of it near the bladder.
• Females: the uterine artery crosses above and in front of it, about 1.5–2 cm lateral to the cervix, in the base of the broad ligament.

It passes obliquely through the bladder wall, which acts as a valve against reflux.

Narrowings

The ureter narrows at the pelviureteric junction, where it crosses the pelvic brim, and at the vesicoureteric junction, the narrowest point. These are where stones lodge.

Bladder and urethra

The bladder is a muscular reservoir that lies behind the pubic symphysis when empty and rises into the abdomen, outside the peritoneum, as it fills. The empty bladder has an apex pointing forwards, attached to the median umbilical ligament (the obliterated urachus), a base facing backwards, and a neck, where it joins the urethra.

The wall is made of interlacing smooth muscle, the detrusor. The trigone is a smooth triangle of mucosa on the inside of the base, between the two ureteric openings and the internal urethral orifice. Elsewhere the empty mucosa is folded.

The female urethra is about 4 cm long and opens in front of the vagina. The male urethra is about 18–20 cm long and has intramural, prostatic, membranous and spongy parts.

Blood supply and innervation

The ureter takes branches from every artery it passes, and the bladder is supplied by branches of the internal iliac artery. In the abdomen, ureteric branches come from the renal, gonadal, aortic and common iliac arteries and approach from the medial side. In the pelvis they come from the internal iliac, vesical and uterine arteries and approach from the lateral side, which guides where to mobilise the ureter safely.

The bladder is supplied by the superior and inferior vesical arteries, with vaginal branches in females. Its veins form the vesical venous plexus, draining to the internal iliac veins.

• Parasympathetic (pelvic splanchnic nerves, S2–S4): contract the detrusor for voiding.
• Sympathetic (T10–L2): relax the detrusor and, in males, close the internal sphincter during ejaculation.
• Somatic (pudendal nerve, S2–S4): voluntary control of the external urethral sphincter.

Ureteric pain is referred along the lower thoracic and first lumbar dermatomes, from the loin to the groin.

Clinical relevance

Stones, iatrogenic ureteric injury and segmental infarction follow directly from this anatomy.

• Renal colic: stones impact at the three narrowings, most often the vesicoureteric junction.
• Ureteric injury at hysterectomy happens where the uterine artery crosses the ureter, the site summed up as water under the bridge.
• Segmental infarction follows occlusion of a segmental artery, because they are end arteries.
• Bladder rupture: a blow to a full bladder tears the dome into the peritoneal cavity; a pelvic fracture usually gives an extraperitoneal tear.
• Suprapubic catheterisation is possible because the full bladder rises above the pubis without peritoneum in front of it.

On the specimen

This station shows the kidneys in situ with the whole abdominal aorta and its visceral branches, so it tests the arterial pattern as much as the kidneys.

• Kidney surfaces and poles: the anterior surface faces forwards and laterally; the upper pole is broader and nearer the midline than the lower.
• Right renal artery and segmental arteries: follow the renal artery laterally behind the inferior vena cava; its branches fanning out at the hilum are the segmental arteries.
• Coeliac trunk, common hepatic and splenic arteries: the short trunk divides; the common hepatic runs right and the splenic runs left along the pancreas.
• Superior mesenteric artery and its jejunal and ileal branches: the jejunal and ileal arteries leave its left side and run into the mesentery; jejunal arteries form few arcades with long straight vessels, ileal arteries more arcades with short ones.
• Inferior mesenteric artery: the small anterior branch low on the aorta, running down and left.
• Left common iliac artery: one of the terminal branches at the L4 bifurcation.
• Left gonadal vein: a thin vein running vertically up on psoas to join the left renal vein, not the cava.