Final answer:
Aldosterone is a hormone that regulates water and sodium reabsorption by the kidneys. It promotes sodium reabsorption, leading to water retention and increased blood volume. It also increases the excretion of potassium.
Step-by-step explanation:
Aldosterone is a hormone that regulates the amount of water and sodium reabsorbed by the kidneys. It is released in response to low water concentration in the blood or high blood potassium levels. Aldosterone causes the kidneys to reabsorb more sodium, which leads to water retention and increased blood volume. It also promotes the excretion of potassium.