How do the kidneys help regulate blood pressure?

The kidneys play a crucial role in regulating blood pressure primarily through their ability to adjust blood volume via urine production. When blood volume decreases, for example, due to dehydration or blood loss, the kidneys respond by conserving water and reducing urine output. This helps to maintain or increase blood volume, which in turn helps to raise blood pressure back to normal levels.

Conversely, when there is excess fluid volume, the kidneys will produce more urine, removing the excess fluid from the body. This process reduces blood volume and can lead to a decrease in blood pressure. Additionally, the kidneys release the hormone renin, which is part of the renin-angiotensin-aldosterone system (RAAS), further influencing blood pressure regulation by causing blood vessels to constrict and increasing blood volume.

The other choices do not directly relate to the regulation of blood pressure in the same way. While hormones related to heart rate, glucose filtration, and red blood cell production are important functions, they do not directly affect blood pressure regulation through fluid balance as urine production does.