Kidneys and Suprarenal Glands
The two kidneys lie behind the peritoneum on either side of the upper lumbar vertebrae (Fig. 4.79). They are embedded in fat in the paravertebral gutters of the posterior abdominal wall and are placed obliquely, with their anterior surfaces directed slightly laterally (Fig. 4.80). The left kidney usually lies at a higher level than the right.
Each kidney is bean-shaped, flattened anteroposteriorly and approximately 11 cm long. The anterior and posterior surfaces are gently convex and the superior and inferior poles are rounded. The lateral border is convex, while the indented medial border bears an aperture, the hilum (Figs 4.81 & 4.82), which is traversed by the renal pelvis or ureter, the renal vessels, lymphatics and autonomic nerves. The hilum leads into a cavity within the kidney, the renal sinus, which is occupied by the calices and renal pelvis (Fig. 4.83), the renal blood vessels and a quantity of fat.
Covered by a thin capsule, the kidney comprises an outer cortex and an inner medulla. The medulla contains numerous pyramids, the apices of which project into the renal sinus as the renal papillae. Urine discharged from the papillae is collected by about 10 trumpet-shaped chambers, the minor calices (Fig. 4.83), which unite to form two or three major calices. These fuse into the single, funnel-shaped renal pelvis, which lies posterior to most of the vessels and is continuous with the ureter. Either of the kidneys and ureters may be duplicated and the two embryonic organs may fuse resulting in a ‘horseshoe kidney’.
Each kidney is surrounded by a layer of perinephric (perirenal) fat enveloped in a thin sheet of connective tissue, the renal fascia (Fig. 4.84). This fascia also encloses the suprarenal gland and the proximal part of the ureter. From the inferior pole of the kidney, the renal fascia tapers downwards into the iliac fossa. Around the fascia is a further layer of fat (paranephric or pararenal fat) lying against the posterior abdominal muscles and covered anteriorly by the peritoneum. The perirenal fascia can impede the spread of infection or cancer.
Relations of kidneys
The right and left kidneys have similar posterior relations (Fig. 4.80). The superior poles lie against the diaphragm and the twelfth ribs, below which run the subcostal nerves and vessels. On the left the upper pole is also related, through the diaphragm, to the pleura and eleventh rib. The medial border of each kidney overlaps psoas major (Fig. 4.79), while the inferolateral portion is related to quadratus lumborum and transversus abdominis and to the first lumbar nerve.
The anterior relations of the kidneys are asymmetric. On the right, from above downwards, they include the bare area of the liver, the second part of the duodenum (Fig. 4.80), the right flexure of the colon and coils of jejunum. The medial border of the right kidney is related to the inferior vena cava, the renal vessels and the upper part of the ureter (Fig. 4.84).
On the left, from above downwards, the anterior relations include the stomach and spleen, the splenic vessels, the tail of the pancreas, the left colic flexure and coils of jejunum. The medial border relates to the suprarenal gland, the renal and suprarenal vessels, the left gonadal vein and the proximal part of the ureter (Fig. 4.87).
At the level of the first lumbar vertebra the aorta usually supplies one renal artery to each kidney (Fig. 4.85). Each artery lies behind the corresponding vein, and the artery on the right crosses behind the inferior vena cava. However, there are often supernumerary (anomalous, aberrant or accessory) renal arteries arising from the aorta above or below the typical vessel. Regardless of its origin, each renal artery divides as it approaches the kidney and all the branches usually traverse the hilum. However, a polar artery may occasionally be found entering the medial border of the organ above or below the hilum (Figs 4.81 & 4.87). Stenosis of a renal artery can lead to systemic arterial hypertension.
Several veins unite near the renal hilum, anterior to the arteries, forming the renal vein. On the right, the vein runs a short course to terminate in the inferior vena cava. The left renal vein is longer and usually receives the suprarenal and gonadal veins before passing in front of the aorta to reach the inferior vena cava (Fig. 4.79). Because of its termination, the left gonadal vein may become dilated if the renal vein is obstructed. In the male, this can lead to swelling of the pampiniform plexus within the scrotum (varicocele; p. 150).
The suprarenal glands lie adjacent to the superior poles of the kidneys, embedded in the perinephric fat. On the right, the gland is tetrahedral and occupies the angle between the superior pole of the kidney and the inferior vena cava (Fig. 4.86). The left gland is crescentic and is applied to the medial border of the kidney above the hilum (Fig. 4.87).
The blood supply to the suprarenal glands is provided by branches of the renal and inferior phrenic arteries and the aorta. The right suprarenal vein is very short and enters the inferior vena cava directly while that on the left descends to enter the left renal vein.
The medulla of each suprarenal gland is richly innervated by preganglionic sympathetic nerves from the adjacent part of the sympathetic trunk.
Abdominal parts of ureters
From the pelviureteric region, each ureter descends through the retroperitoneal tissues of the posterior abdominal wall as far as the pelvic brim. Here it crosses in front of the external iliac vessels and continues down the lateral wall of the pelvis (p. 222). Within the abdomen, the ureter lies on psoas major (Fig. 4.84), behind which are the lumbar transverse processes (Fig. 4.82).
The right ureter commences behind the descending duodenum and is crossed by the root of the mesentery, the gonadal vessels and branches of the superior mesenteric artery and accompanying veins. This ureter is also related to coils of small intestine, and sometimes to the caecum and appendix. The left ureter is covered initially by the pancreas and is subsequently crossed by the gonadal vessels, branches of the inferior mesenteric artery and vein (Fig. 4.76) and coils of small intestine and sigmoid colon. At the pelvic brim, it passes behind the root of the sigmoid mesocolon.
Renal calculi may impact where the ureters narrow at the pelviureteric junction, near the pelvic brim and at the entrance to the bladder.
The blood supply to the abdominal part of the ureter is derived from branches of the renal artery, supplemented by minute peritoneal vessels.