Structure of kidney

A kidney is wrapped in three protective layers - an outer renal fascia, a perirenal fat capsule, and an inner fibrous capsule - that anchor it in place and cushion it from injury. Cut lengthwise, a kidney shows two clearly distinct regions: a pale outer cortex and a darker inner medulla. The medulla is not uniform either - it is divided into a number of cone-shaped renal (medullary) pyramids, with tongues of cortical tissue, the renal columns of Bertini, dipping down between adjacent pyramids. All of this tissue is built around a central drainage system: the inner concave surface of the kidney has a notch, the renal hilum, through which the renal artery, renal vein, nerves and ureter all pass. Just inside the hilum is a broad, funnel-shaped cavity, the renal pelvis, which branches into smaller cup-like extensions called major and minor calyces. Each renal pyramid empties its urine into a minor calyx; the smooth muscle in the walls of the calyces, pelvis and ureter contracts rhythmically to keep pushin …