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Kidneys regulate blood volume through a combination of filtration, reabsorption, and the actions of hormones such as aldosterone and anti-diuretic hormone (ADH). Filtration occurs in the nephron’s glomerulus, where water, electrolytes, glucose, and waste products are separated from large molecules. The filtrate then passes through the renal tubule, where water and essential substances are reabsorbed back into the bloodstream based on the body's needs. Aldosterone controls the amount of sodium reabsorbed in the renal tubule, influencing water reabsorption and thus blood volume. ADH increases the nephron's collecting ducts' permeability to water, allowing more water to be reabsorbed into the bloodstream, increasing blood volume. Together, these processes help maintain proper blood volume and overall body homeostasis.