External Anatomy of the Kidney

The kidneys are located at the T12 to L3 vertebrae level, positioned on either side of the vertebral column in the retroperitoneal space. They are partly protected posteriorly by the eleventh and twelfth ribs. The right kidney typically sits slightly lower than the left due to the liver's position superiorly.

An adult kidney typically measures approximately 10 to 12 centimeters in length, 5 to 7 centimeters in width, and 2 to 3 centimeters in thickness. Males' kidneys weigh approximately 125 to 175 grams, while females' kidneys weigh approximately 115 to 155 grams. These measurements can vary slightly between individuals.

The renal hilum is a vertical cleft on the concave medial border of the kidney where several vital structures enter and exit. These include the renal artery, which delivers unfiltered blood; the renal vein, which carries filtered blood away; the ureter, which transports urine to the bladder; lymphatic vessels; and nerves.

The three protective layers are the renal capsule, a transparent dense connective tissue layer providing protection and maintaining kidney shape; the perirenal fat capsule, a fatty tissue mass that cushions the kidney and holds it in place; and the renal fascia, a superficial connective tissue layer that firmly anchors the kidney to surrounding structures and the abdominal wall.

The renal capsule is the innermost protective layer, a transparent sheet of dense irregular connective tissue that directly surrounds the kidney and is continuous with the ureter's outer coat. The renal fascia, also called Gerota's fascia, is a superficial layer of connective tissue that encapsulates both the kidneys and adrenal glands, anchoring them firmly to surrounding structures and the abdominal wall.

The perirenal fat capsule, also called adipose capsule, is a layer of fatty tissue surrounding the renal capsule that acts as a protective cushion for the kidneys. It absorbs shock from physical movements and provides additional protection against trauma. This fatty layer also helps hold the kidney in place within the retroperitoneal space.

Various disorders can affect kidney protective layers: renal artery stenosis or renal vein thrombosis affect the hilum; perinephric abscess, where pus accumulates between the renal capsule and kidney, affects the capsule; perinephric fibrosis, inflammation of the renal fascia, can cause chronic pain; and excessive fat buildup around kidneys from obesity can lead to renal sinus lipomatosis.