Final answer:
Sodium ions are reabsorbed into the blood from the nephron through active transport mechanisms facilitated by hormones such as aldosterone, which increases sodium reabsorption in the distal convoluted tubules.
Step-by-step explanation:
Sodium ions are returned to the blood from the nephron primarily via active transport. Reabsorption of sodium ions occurs when they are transferred from the filtrate back into the blood. This process involves an antiport mechanism in the apical membranes of cells lining the renal tubule, where sodium is exchanged for hydrogen ions. Aldosterone significantly influences this process by increasing sodium ion reabsorption in the distal convoluted tubules, thus helping to regulate blood pressure and fluid balance.
In addition, the blood capillaries, specifically the vasa recta, recover solutes and water, including sodium, while preserving the countercurrent multiplier system required for this process. This action is governed by two major hormones: aldosterone and angiotensin II. While more sodium is reabsorbed, more potassium is secreted into the filtrate.