- Kidney is a retroperitoneal organ, lying on the upper part of posterior abdominal wall. Each kidney is bean shaped with two poles (upper and lower), two borders (medial and lateral) and two surfaces (anterior and posterior). Left kidney is slightly higher, related to both 11thand12th ribs; right kidney is lower and related only to 12thrib.
- Lateral border is convex. The medial border is concave and shows a depression in middle part called hilus (or hilum). The hilum contains following structures, from anterior or posterior: - renal vein, renal artery, and renal pelvis. Hilum is 5 cm away from LI spine on the transphyloric plane.
Relation of the kidneys
- Upper pole of each kidney is related to the corresponding suprarenal gland. Upper pole is 2.5 cm away from midline, opposite to T11 spine. Lower pole is 7.5 cm away from midline, opposite to L3 spine, and lies 2.5 cm above highest point of iliac crest.
- Anterior surface is related to :-
- Left kidney :- Left suprarenal gland, spleen (visceral surface), stomach (posteroinferior surface), splenic flexure and descending colon, pancreas (body), coils of jejunum, splenic vessels and ascending branch of left colic artery. Out of these gastric, splenic and jejunal surfaces are covered with peritoneum.
- Right kidney- Right suprarenal gland, liver (right lobe), duodenum, hepatic flexure of colon, small intestine (jejunum). Out of these hepatic and intestinal surfaces are covered with peritoneum. Right kidney and liver are separated from each other by hepatorenal pouch of Morison (right sub hepatic space or right posterior intraperitoneal space).
- Posterior surface of both kidneys is related to diaphragm, medial and lateral arcuate ligament, psoas major, quadratuslumborum, transversus abdominis, subcostal vessels, subcostal nerve, iliohypogastric nerve, and ilioinguinal nerve. In addition, the right kidney is related to 12th rib and the left kidney is related to H" and 12th ribs.
- Medial border of each kidney is related to suprarenal gland above the hilus and ureter below the hilus.
- Lateral border of right kidney is related to the right lobe of liver and hepatic flexure of colon. On left side it is related to spleen and descending colon.
There are four coverings around the kidney (from within outwards):-
- True capsule (fibrous capsule) :-It is formed by the condensation of fibrous stroma of kidney:
- Perinephric fat (adipose capsule):- It occupies the interval between the fibrous capsule and renal fascia (false capsule or fascia of Gerota). This space (occupying perinephric fat) is called space of Gerota.
- False capsule (renal fasciaor fascia of Gerota):- It is formed by condensation of extra-peritoneal connective tissue around kidney and is continuous laterally with fascia transversalis. False capsule consists of two layers: anterior "fascia of Toldt" and posterior "fascia of Zuckerkendl".
- Perinephricfat:-It occupies the interval between the renal fascia and anterior layer of thoracolumbar fascia.
- Each kidney has two distinct zone
- The outer cortex
- The inner medulla
- The medulla comprises about 10 renal pyramids. Their apices form renal papillae which indent the minor calyces.
- The cortex is divided into two parts: -
- Cortical arches or cortical lobules, which form caps over the bases of the pyramids.
- Renal columns, which dip in between the pyramid.
- Each pyramid along with overlying cortical arch forms a lobe of the kidney.
- The renal sinus is a space that extends into kidney from the hilus.
- It contains:
- Branches of the renal artery.
- Tributaries of the renal vein.
- Renal pelvis: Pelvis divides into 2 to 3 major calyces, and these in their turn divide into 7-13 minor calyces.
- Each minor calyx ends in an expansion which is intended by one to three renal papillae.
- Renal pelvis and calyces are lined by transitional epithelium.
- Each kidney is supplied by renal artery (branch of abdominal aorta and is drained by renal vein to IVC,
- Renal artery: - Right renal artery is longer and passes behind IVC. Renal artery divides into: -
- Posterior division: - Supplies posterior segment.
- Anterior division: - Divides further into 4 branches to supply apical, upper anterior, middle anterior and lo~segments.
- Thus, there are five vascular segments in each kidney: - Posterior, apical, upper anterior, middle anterior and lower.
- Branches of renal artery are end arteries.
- Renal vein: - Left renal vein is longerand passes in front of abdominal aorta, behind the origin of superior mesenteric artery. Left renal vein also receives left inferior phrenic vein, left gonadal vein and left suprarenal (adrenal) vein. Each renal vein begins beneath the true capsule as stellate vein.
The kidney is supplied by renal plexus, an offshoot of coeliac plexus. It contains sympathetic (T10-L1) fiber which are chiefly vasomotor. The afferent nerves of the kidney belong to segments T10-T12.
The angle between the lower border of 12th rib and the outer border of erector spinae (sacrospinalis) is known as renal angle. It overlies the lower part of the kidney. Tenderness in the kidney is elicited by applying pressure over this angle with thumb.