How do the kidneys help regulate blood pressure?

The kidneys play a crucial role in regulating blood pressure primarily through the maintenance of water balance and the production of hormones. When the kidneys filter blood, they not only remove waste products and excess substances but also manage the volume of blood by controlling the amount of water reabsorbed into the bloodstream.

This process is closely linked to the regulation of sodium levels; when sodium is reabsorbed, water follows osmotically, which can increase blood volume and, consequently, blood pressure. The kidneys also produce hormones such as renin, which initiates a cascade that leads to increased blood pressure by promoting sodium retention and water reabsorption.

Additionally, the hormone angiotensin II, formed from renin, constricts blood vessels, contributing further to the increase in blood pressure. Therefore, the kidney's ability to maintain the balance of fluids and electrolytes in the body directly impacts blood pressure regulation, making the choice of maintaining water balance and producing hormones the correct answer.