Abdomen:Solid viscus:Kidneys

The **kidneys**are paired retroperitoneal organs that lie at the level of the T12 to L3 vertebral bodies, on the posterior abdominal wall. The long axis of the kidney is parallel to the lateral border of the psoas muscle on an oblique angle.

The kidney is bean-shaped with a superior and and inferior pole with a vertical slit depression that transmit the renal vessels and renal pelvis. In adults, each kidney is normally 10-12 cm in length, 3-5 cm in width and weighs 150-260 g.

The kidney has a fibrous capsule, which is surrounded by perinephric fat.

The kidney itself can be divided into

* Renal parenchyma
	+ cortex: lies peripherally under the capsule
	+ medulla. consists of 10-14 renal **pyramids**, which are separated from each other by an extension of renal cortex called **renal columns**
* Renal sinus containing renal pelvis, calyces, renal vessels, nerves, lymphatics and perirenal fat.
	+ The**renal hilum** is the entry to the renal sinus and lies vertically at the anteromedial aspect of the kidney, containing renal vessels (most anterior), nerve, fat and renal pelvis (posterior).

Urine is produced in the **renal lobes**, which consists of the renal pyramid with associated overlying renal cortex and adjacent renal columns. Each renal lobe drains at a papilla into a **minor calyx**, four or five of these unite to form a **major calyx**. Each kidney normally has two or three major calyxes, which unite to form the renal pelvis.

Relations

**Right kidney**

* anteriorly
	+ superiorly - right adrenal gland, liver
	+ inferiorly - hepatic flexure, small intestine
* medially - duodenum
* laterally - transversus abdominis
* posteriorly - diaphragm, quadratus lumborum, psoas major

**Left kidney**

* anteriorly
	+ superiorly - left adrenal gland, spleen
	+ inferiorly - splenic flexure, jejunum
* medially - pancreas
* laterally - transversus abdominis
* posteriorly - diaphragm, quadratus lumborum, psoas major

Arterial supply

* Renal arteries (from abdominal aorta). Supplies the five segments. The artery gives rise to an anterior/posterior division. The posterior division supply posterior segment, anterior division supply apical, upper, middle and lower segments.
* From these lobar and interlobar arteries arise which supply the renal lobes.
* This continues as the arcuate arteries located at the border of the renal cortex and renal medulla.
* Interlobular arteries arises at 90 degree from arcuate arteries into the cortical substance. In their outward course, they give off lateral branches, which are the afferent arterioles that supply the renal corpuscles. The afferent arterioles, then, enter Bowman's capsule and end in the glomerulus.

Venous drainage

* renal veins (to IVC). Branches from renal segments communicate and form five/six vessels that unite at the hilum as the renal vein.

Nerve supply

* Sympathetic T12-L1, pass to thoracic and lumbar splanchnic nerves. These synapse in the coeliac and renal ganglia
* Pain afferent accompany sympathetic nerves.
* Sympathetic and parasympathetic renal nerve plexus, which is derived from abdominopelvic splanchnic nerves

Lymph drainage

* drain into the para-aortic nodes at the level of renal arteries origin (L2)

Normal variant:

* Persistent fetal lobulation
* Column of Bertin
* Renal ectopia e.g. pelvic, iliac, lumbar
* Horseshoe kidney
* Agenesis/dysplasia of a single kidney
* Supernumery kidney
* Extrarenal pelvis
* Malrotation and subsequent change in renal axis