Final answer:
The kidneys regulate blood volume/pressure and erythropoiesis (red blood cell production) by controlling fluid loss and releasing hormones such as EPO and renin.
Step-by-step explanation:
The kidneys are responsible for several critical functions in the human body, particularly the regulation of blood composition. They regulate two key aspects of blood: blood volume/pressure and erythropoiesis. The regulation of blood pressure is achieved through the kidneys' ability to control fluid loss in the urine and by releasing the enzyme renin, which is part of the renin-angiotensin-aldosterone system. Erythropoiesis, the production of red blood cells, is regulated by erythropoietin (EPO), a hormone largely produced by the kidneys in response to low oxygen levels in the blood. EPO's role is to stimulate the bone marrow to produce red blood cells, which are essential for transporting oxygen throughout the body.