Kidneys 

Position and Shape:

• Bean-shaped organs.

• Located retroperitoneally in the posterior part of the abdomen, lateral to the vertebral column.

• In the supine position, they extend from T12 to L3.

• The right kidney lies lower than the left due to the presence of the liver.

• The left kidney is longer, thinner, and closer to the midline.

Anterior Relations:

Right kidney:

• Upper pole: in contact with the right adrenal gland.

• Upper anterior surface: contacts the liver (separated by peritoneum).

• Medial side: in direct contact with the descending duodenum (retroperitoneal).

• Lower pole:

• Lateral side: contacts the right colic flexure.

• Medial side: covered by small intestine (intraperitoneal).

Left kidney:

• Upper pole (medial part): in contact with the left adrenal gland.

• Remaining upper pole: covered by the stomach and spleen (intraperitoneal).

• Central part: covered by the pancreas (retroperitoneal).

• Lower part:

• Lateral side: covered by the left colic flexure and descending colon.

• Medial side: in contact with the jejunum (intraperitoneal).

Posterior Relations (both kidneys):

• Superiorly: diaphragm.

• Muscles (from medial to lateral):

• Psoas major

• Quadratus lumborum

• Transversus abdominis

• Ribs:

• Right kidney: in front of the 12th rib

• Left kidney: in front of the 11th and 12th ribs

• Also posteriorly related to:

• Pleural recesses and costodiaphragmatic recess

• Subcostal vessels and nerves

• Iliohypogastric and ilioinguinal nerves

Renal Fat and Fascia:

• Each kidney is surrounded by perinephric (perirenal) fat, which completely encases it.

• This fat is enclosed by a renal fascia, a fibrous membrane.

• The adrenal glands lie within the same fascial compartment but are separated by a thin septum.

• During surgery, the renal fascia must be incised.

Renal Fascia and Fat – Key Notes:

Fusion of fascial layers:

• At the lateral margin of each kidney, the anterior and posterior layers of the renal fascia fuse and may connect with the transversalis fascia.

• Superiorly, above the adrenal gland, layers fuse with the diaphragmatic fascia.

• Medially, the anterior layer continues over the renal vessels and joins the connective tissue of the abdominal aorta and IVC.

• In some cases, it may cross the midline and fuse with the opposite side.

• The posterior layer runs between the kidney and quadratus lumborum, and joins the psoas fascia.

• Inferiorly, the layers enclose the ureter.

Fat layers around the kidney:

• Perinephric (perirenal) fat: surrounds the kidney inside the renal fascia.

• Paranephric (pararenal) fat: located behind and lateral to the kidney, outside the renal fascia.

Kidney Structure – Summary

Capsule:

• Each kidney is covered by a fibrous capsule, easily removed except in disease.

Renal Hilum:

• Located on the medial border of the kidney.

• A deep vertical slit through which renal vessels, lymphatics, and nerves pass.

• Leads internally to the renal sinus.

• Perinephric fat extends into the hilum and sinus, surrounding all internal structures.

Internal structure:

• Renal cortex: outer pale layer forming a continuous ring.

• Renal medulla: inner tissue arranged in renal pyramids.

• Renal columns: extensions of cortex separating the pyramids.

Renal Pyramids and Urine Drainage System:

• Base of pyramids: faces outward, toward the cortex.

• Apex (renal papilla): projects inward, into the renal sinus.

• Renal papilla: surrounded by a minor calyx.

• Minor calyces: collect urine; first part of the drainage system.

• Major calyces: formed by union of minor calyces.

• Renal pelvis: funnel-shaped structure formed by 2–3 major calyces, continues as the ureter.

Vascular Supply and Lymphatic Drainage:

• Renal artery: originates from the abdominal aorta, just below the superior mesenteric artery (around L1–L2).

• Left renal artery: arises higher.

• Right renal artery: longer; passes behind the IVC.

• Divides near the hilum into anterior and posterior branches.

• Accessory renal arteries (extra-hilar): common, may enter the kidney at various levels.

• Renal veins:

• Located anterior to renal arteries.

• Left renal vein: longer; crosses in front of the aorta and behind the superior mesenteric artery (may be compressed by aneurysm).

• Lymphatic drainage: to lateral aortic (lumbar) lymph nodes, near the origin of the renal artery.

Ureters – Structure and Course

• Function: Muscular tubes that carry urine from the kidneys to the urinary bladder.

• Origin: Continuation of the renal pelvis.

• Renal pelvis: formed by 2–3 major calyces, which arise from minor calyces.

• Position: Ureters descend retroperitoneally on the medial surface of the psoas major muscle.

3 narrowing points (common sites for kidney stones):

1. Ureteropelvic junction (between renal pelvis and ureter)

2. Crossing of the common iliac vessels (at the pelvic brim)

3. Entry into the bladder wall.