How do the kidneys regulate blood volume and blood pressure?

Question

What will be an ideal response?

Answer 1

Fluids maintain the blood volume, which in turn influences blood pressure. The kidneys are central to the regulation of blood volume and blood pressure. All day, every day, the kidneys reabsorb needed substances and water and excrete wastes with some water in the urine. The kidneys meticulously adjust the volume and the concentration of the urine to accommodate changes in the body, including variations in the day’s food and beverage intakes. Instructions on whether to retain or release substances or water come from antidiuretic hormone, renin, angiotensin, and aldosterone.
Whenever blood volume or blood pressure falls too low, or whenever the extracellular fluid becomes too concentrated, the hypothalamus signals the pituitary gland to release antidiuretic hormone (ADH). ADH is a water-conserving hormone that stimulates the kidneys to reabsorb water. Consequently, the more water you need, the less your kidneys excrete. These events also trigger thirst. Drinking water and retaining fluids raise the blood volume and dilute the concentrated fluids, thus helping to restore homeostasis.
Cells in the kidneys respond to low blood pressure by releasing an enzyme called renin. Through a complex series of events, renin causes the kidneys to reabsorb sodium. Sodium reabsorption, in turn, is always accompanied by water retention, which helps to raise blood volume and blood pressure.
In addition to its role in sodium retention, renin hydrolyzes a protein from the liver called angiotensinogen to angiotensin I. Angiotensin I is inactive until another enzyme converts it to its active form—angiotensin II. Angiotensin II is a powerful vasoconstrictor that narrows the diameters of blood vessels, thereby raising the blood pressure.
In addition to acting as a vasoconstrictor, angiotensin II stimulates the release of the hormone aldosterone from the adrenal glands. Aldosterone signals the kidneys to excrete potassium and to retain more sodium, and therefore water, because when sodium moves, water follows. Again, the effect is that when more water is needed, less is excreted.