Final answer:
The kidneys play a major role in the cardiovascular system by regulating blood volume and pressure, filtering blood, removing waste products through urine, and producing hormones for erythrocyte development and vitamin D synthesis.
Step-by-step explanation:
The kidneys play a major role in the cardiovascular system by regulating blood volume and pressure, as well as maintaining the osmolarity of the blood. They work with the circulatory system to filter blood and remove waste products through urine. Additionally, the kidneys produce hormones that help regulate erythrocyte (red blood cell) development and vitamin D synthesis.