There are three major anatomical demarcations in the kidney: the cortex, the medulla, and the renal pelvis. The cortex receives most of the blood flow, and is mostly concerned with reabsorbing filtered material. The medulla is a highly metabolically active area, which serves to concentrate the urine. The pelvis collects urine for excretion.
The functional unit of the kidney is the nephron. There are five parts of the nephron: 1. The glomerulus, which is the blood kidney interface, plasma is filtered from capillaries into the Bowman’s capsule. 2. The proximal convoluted tubule, which reabsorbs most of the filtered load, including nutrients and electrolytes. 3. The loop of Henle, which, depending on it’s length, concentrates urine by increasing the osmolality of surrounding tissue and filtrate. 4. The distal convoluted tubule, which reabsorbs water and sodium depending on needs, 5. The collecting system, which collects urine for excretion. There are two types of nephrons, those localized to the cortex, and those extending into the medulla. The latter are characterized by long loops of Henle, and are more metabolically active.