How are the kidneys involved in controlling blood volume? How is the volume of blood in the body related to arterial pressure?

Explanation

1. Juxta glomerular apparatus (IGA) is a specialized tissue in the afferent arteriole of the nephron that consists of macula densa and granular cells.
2. The macula densa cells sense distal tubular flow and affect afferent arteriole diameter, whereas the granular cells secrete an enzyme called renin,
3. A fall in glomerular blood flow, glomerular blood pressure and glomerular filtration rate, can activate JG cells to release renin which converts a plasma protein, angiotensinogen (synthesized in the liver) to angiotensin I.
4. Angiotensin converting enzyme (ACH)converts : angiotensin 1 to angiotensin II. Angiotensin II ! stimulates Na* reabsorption in the proximal : convoluted tubule by vasoconstriction of the blood vessels and increases the glomerular blood pressure.
5. Angiotensin II acts at different sites such as ! heart, kidney, brain, adrenal cortex and blood vessels.
6. It stimulates adrenal cortex to secrete aldosterone that causes reabsorption of Na*, ! K* excretion and absorption of water from the distal convoluted tubule and collecting duct.
7. This increases the glomerular blood pressure and glomerular filtration rate. This complex mechanism is generally known as Renin- ! Angiotensin- Aldosterone System (RAAS).