Kidneys and Urinary System - LO 1

1. Describe the location of the kidneys within the abdomen. 

Retroperitoneal Space

The peritoneum is a serous membrane lining the abdominopelvic cavity, consisting of two layers: a parietal peritoneum that lines the walls of the cavity, and a visceral peritoneum which covers viscera suspended within the cavity. The retroperitoneal space is the region posterior to the parietal peritoneum and anterior to the posterior wall of the abdomen and vertebral column. Structures found within the retroperitoneal space are said to be 'retroperitoneal.'

The kidneys (as well as their associated suprarenal glands and ureters) are retroperitoneal. Each kidney is found within the ipsilateral perirenal space, a space surrounded be peri(renal) fascia (Gerota's fascia) and also filled with perirenal adipose tissue (fat). There is much variation of the perirenal space, but it is best conceptualized as an inverted cone, with a superior base and and inferior apex, which tapers along the course of the ureter. Surrounding a perirenal space are the ipsilateral pararenal spaces. The anterior pararenal space is found between the parietal peritoneum and the peri(renal) fascia. The posterior pararenal space is found between the peri(renal) fascia and the investing fascias of posterior and lateral muscles (e.g. quadratus lumborum m., internal abdominal oblique m., transversus abdominis m., etc.). The pararenal spaces are typically filled with pararenal adipose tissue (fat). 

Relative Spatial Relationships

The kidneys have:

Kidneys are located high in the abdomen on the posterior wall inferior to the diaphragm in the region of the lower ribs. The left kidney is located slightly higher than the right kidney – roughly from T11-L2 vertebral level, while the right kidney spans T12-L3 vertebral levels. The superior 1/3 of the posterior surface of the kidney lies against the diaphragm. The remaining 2/3 is inferior to the diaphragm, and is adjacent to the quadratus lumborum muscle. The subcostal nerve (T12) and vessels run posterior to the kidneys. And the 11th and 12th ribs run behind the upper portion of both kidneys. At rest, the hila of the kidneys coincide with the transpyloric plane, the midpoint between the jugular notch and the pubic symphysis, which corresponds to where the pyloric part of the stomach meets the duodenum (approximately at the L1 vertebral level). 

The anterior relationships are different on each side, except that both kidneys are capped superomedially by a suprarenal (adrenal) gland. The right kidney contacts the descending (2nd) portion of the duodenum, the right lobe of the liver, the right colic (hepatic) flexure, and some coils of jejunum. The left kidney contacts the pancreas, the stomach, the spleen, the left colic (splenic) flexure, and some coils of jejunum.

The medial border of the kidney contains the hilum – the space into which the renal arteries and veins pass and the renal pelvis and ureter emerge. The kidneys do not sit with their borders and surfaces in strict anatomical position. For example, the medial borders of the kidneys are oriented anteromedially, and the lateral borders are oriented posterolaterally.

Ureters pass retroperitoneally through the abdomen, and enter into the pelvis adjacent to the birfurcation of the common iliac aa. Ureters enter into the base/fundus of the bladder.