The kidneys continuosly cleanse the blood and adjust its composition, so it is not surprising that they have a rich blood supply. under normal resting conditions, the large renal arteries deliver one-fourth of the total cardiac output (about 1200 ml) to the kidneys each minute.
The renal arteries issue at right angles from the abdominal aorta and the right renal artery is longer than the left because the aorta lies to the left of the midline. As each renal artery approaches a kidney, it divides into five segmental arteries. Within the renal sinus, each segmental artery branches further to form several interlobar arteries.
At the medulla-cortex junctions, the interlobar arteries branch into the arcuate arteries that arc over the bases of the medullary pyramids. Small cortical radiate arteries radiate outward from the arcuate arteries to supply the cortical tissue. More than 90% of the blood entering the kidney perfuses the renal cortex.
Afferent arterioles branching from the cortical radiate arteries begin a complex arrangement of microscopic blood vessels. These vessels are key elements of kidney function, and we will examine them in detailed later when we describe the nephrons.
Veins pretty much trace the pathway of the arterial supply in reverse. Blood leaving the renal cortex drains sequentially into the cortical radiate, arcuate, interlobar and finally renal veins (there are no segmental veins). The renal veins issue from the kidneys and empty into the inferior vena cava. Because the inferior vena cava lies to the right of the vertebral column, the left renal vein is about twice as long as the right.
The renal plexus, a variable network of autonomic nerve fibers and ganglia, provides the nerve supply of the kidney and its ureter. An offshoot of the celiac plexus, the renal plexus is largely supplied by symphatetic fibers from the most inferior thoracic and first lumbar sphlanchnic nerves, which course along with the renal artery to reach the kidney. These sympathetic vasomotor fibers regulate renal blood flow by adjusting the diameter of renal arterioles and also influence the urine-forming role of the nephrons.