The renal fascia is a protective covering surrounding each kidney that is composed of connective tissue, which is a form of strong fibrous tissue found throughout the human body. Gerota's capsule or Gerota's fascia are alternative names for the renal fascia. Two layers of adipose tissue surround the renal fascia, one layer above it and one layer below it. The function of the renal fascia is to securely contain the layers of adipose and other types of tissue that lay beneath it, and protect them from injury-causing collisions such as organ damage sustained from a fall or other type of bodily impact.
Fasciae are found throughout the body and are a type of dense regular connective tissue that contain thickly crowded bundles of collagen fibers arranged in a single direction. The purpose of fasciae is to bind structures together much like the cover of a book binds and protects the pages within. Fasciae encapsulate a number of bodily structures such as muscles, organs, nerves, and blood vessels. Although fasciae are flexible structures, they can only resist tension from a single direction because their collagen fibers are unidirectional unlike dense irregular connective tissue which can resist tension coming from multiple directions.
Humans have two kidneys that are bean-shaped. Both kidneys have a concave and a convex surface. The concave surface, called the renal hilum, is the place where the renal artery enters the kidney, and is also where the renal vein and ureter exit the kidney.
Each of the kidneys are enclosed and protected by the renal capsule, which is a layer of strong fibrous tissue. Below the renal capsule sits the renal cortex, which is the part of the kidney that's responsible for the process of ultrafiltration. The blood supply for the entire body passes through the areas of the renal capsule where toxins get removed from the bloodstream and eventually are excreted in urine. Below the renal cortex is the innermost part of the kidney called the renal medulla.
Surrounding the renal capsule is perinephric fat, which is also known as perirenal fat or the adipose capsule of the kidney, and it is considered a part of the renal capsule. The layer of tissue surrounding the perirenal fat is the renal fascia, which itself is surrounded by a layer of adipose tissue called paranephric fat. Surrounding the pararenal fat is the peritoneum, which is a membrane of tissue that lines the abdominal cavity.