The human kidneys filter waste products and excess water from the blood. This filtration maintains the body’s internal balance and health. A constant blood supply is necessary for the kidneys to function effectively, as their continuous operation relies on precise blood delivery and removal.
The Renal Arteries
Blood’s journey to the kidneys begins with the renal arteries, the primary vessels for this delivery. These arteries originate directly from the abdominal aorta, the body’s largest artery, which descends from the heart. One renal artery supplies each kidney, branching off the aorta just below the superior mesenteric artery.
These arteries are short but wide. The kidneys receive high blood flow, accounting for approximately 20-25% of the heart’s total output at rest. As the renal arteries approach the kidney, they divide into several smaller branches before entering the organ at a central indentation called the hilum.
Blood Flow Within the Kidneys
Once inside the kidney, the main renal artery branches further into smaller vessels. The renal artery first divides into segmental arteries, which then give rise to interlobar arteries that ascend between the renal pyramids. These interlobar arteries then arch over the bases of the pyramids, becoming the arcuate arteries.
From the arcuate arteries, smaller interlobular arteries extend outwards into the renal cortex, the outer region of the kidney. These interlobular arteries give rise to the afferent arterioles, which are vessels that lead directly to the glomerulus. The glomerulus is a specialized capillary network where the initial filtration of blood occurs. After passing through the glomerulus, blood then flows into efferent arterioles, which branch into a dense capillary network surrounding the renal tubules, known as the peritubular capillaries.
Blood’s Exit from the Kidneys
After the processes of filtration and reabsorption have occurred within the kidney, blood exits the organ to return to circulation. The peritubular capillaries, having exchanged substances with the renal tubules, converge to form venules. These venules then merge into larger veins, mirroring the arterial branching pattern in reverse.
The venules drain into interlobular veins, which then flow into arcuate veins, followed by interlobar veins. These larger veins ultimately coalesce to form the main renal vein at the kidney’s hilum. The renal vein, one for each kidney, carries deoxygenated blood away from the kidney. These renal veins then empty directly into the inferior vena cava, a major vein that transports blood back to the heart.