URINARY SYSTEM: GENERAL FEATURES OF THE URINARY SYSTEM

A. Components of the System: The urinary system includes the kidneys and the urinary tract.

1. Kidneys. These paired, bean-shaped, retroperitoneal organs are located in the posterior wall of the abdominal cavity. a. Structural and functional subdivisions, When sliced in the frontal plane, each kidney shows a dark-staining outer cortex and a light-staining inner medulla that partly surrounds the renal hilum, The hilum consists of a space, the renal sinus, that contains the larger renal blood vessels, the renal pelvis, and adipose tissue.

Each lobe consists of numerous renal lobules, each containing hundreds of nephrons, These are largely tubular structures that filter the blood, modify the filtrate to form urine, and empty into a series of collecting tubules and ducts which converge on the medulla and empty into the minor calyces. b. Blood supply. Because the kidneys are blood-filtering organs, their blood supply is crucial to their function. A pair of renal arteries--one to each kidney--branches from the aorta in the upper abdomen. Each artery undergoes successive branching to feed specialized capillary beds in both the cortex (glomeruli and peritubular capillaries) and medulla (vasa rectal).


B. General Functions of the System: The kidneys filter metabolic wastes and foreign sub stances from the blood; regulate the ion, salt, and water concentrations of the fluids that bathe the body's tissues; and produce renin and erythropoietin. It is followed by the reabsorption of important ions, small proteins, nutrients, and much of the water. These are returned to the blood in the peritubular capillaries and vasa recta in precise proportions.