Physiology_dept. Unical

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RENAL BLOOD FLOW
The kidneys receive an astonishing 20–25% of cardiac output, despite their small size. This massive blood flow is essential because the kidneys perform filtration, waste removal, electrolyte regulation, acid–base balance, and hormone production.
Blood enters through the renal artery, which branches into progressively smaller vessels until it reaches the afferent arteriole of each nephron. From here, blood flows into the glomerulus, a tuft of capillaries where filtration begins. The efferent arteriole then carries blood away and into the peritubular capillaries and vasa recta, which aid reabsorption and concentration of urine.
Renal blood flow must be tightly controlled. If it drops too low, filtration fails; if it becomes too high, the delicate capillaries can be damaged. The kidneys use autoregulation—including the myogenic mechanism and tubuloglomerular feedback—to keep blood flow stable even when systemic blood pressure changes.
Hormones like angiotensin II, nitric oxide, and prostaglandins also help fine-tune blood flow.
Understanding renal blood flow helps explain how conditions like dehydration, hypertension, shock, or kidney disease affect the entire body. The kidneys are true guardians of internal balance, and their blood supply is the lifeline that keeps them functioning.