The cortex region looks darker than the medulla's renal pyramids and the renal pyramids often look like a series of fine straight fibers. The innermost kidney region is called the renal pelvis . Each kidney contain 1-2 million functional units called nephrons . The nephrons and their associated blood vessels form the tissues of the renal cortex and renal medulla. The nephron is composed of several specialized regions.
Blood plasma is filtered across a very leaky capillary bed called a glomerulus .
All but cells and large plasma proteins normally filter into a renal capsule that surrounds the glomerulus. The glomeruli and renal capsules are located in the renal cortex of the kidney. The proximal tubule is specially designed with lots of microvilli to increase its surface area to aid this reabsorption. Other sections of the nephron may secrete unwanted substances into the filtrate. The body produces many types of metabolic wastes that must be removed from the body to maintain homeostasis.