Structure of the kidney
On sectioning, the kidney has a pale outer region- the cortex- and a darker inner region- the medulla.The medulla is divided into 8-18 conical regions, called the renal pyramids; the base of each pyramid starts at the corticomedullary border, and the apex ends in the renal papilla which merges to form the renal pelvis and then on to form the ureter. In humans, the renal pelvis is divided into two or three spaces -the major calyces- which in turn divide into further minor calyces. The walls of the calyces, pelvis and ureters are lined with smooth muscle that can contract to force urine towards the bladder by peristalisis.
The cortex and the medulla are made up of nephrons; these are the functional units of the kidney, and each kidney contains about 1.3 million of them.
