Q.Nitya has been admitted to hospital after heavy blood loss. Till proper treatment could be given; how did Nitya's body must have tackled the situation?

Heavy blood loss sharply reduces both blood volume and blood pressure, and the body has two closely coordinated hormonal systems, both covered in this chapter, that respond to exactly this emergency.

Step 1. The drop in blood flow/pressure reaching the afferent arteriole is sensed by the juxtaglomerular apparatus in the kidney, which releases renin.

Step 2. Renin converts angiotensinogen (from the liver) to Angiotensin I, which is then converted to the active Angiotensin II.

Step 3. Angiotensin II constricts arterioles throughout the kidney (and elsewhere), directly raising blood pressure, and it also stimulates PCT cells to reabsorb more Na+, Cl− and water.

Step 4. Angiotensin II further stimulates the adrenal cortex to release aldosterone, which makes the DCT and collecting ducts reabsorb even more Na+ and water, expanding blood volume.

Step 5. In parallel, hypothalamic osmoreceptors (and the fall in blood volume/pressure itself) trigger release of ADH from the posterior pituitary, which increases water reabsorption in the late DCT and collecting duct, further conserving the body's remaining water and helping sustain blood volume. …

Apply the RAAS and ADH pathways (already explained in the chapter for normal homeostasis) to the eme …

• Naming only one of the two hormonal systems (just ADH, or just RAAS) instead of explaining that they act together in this kind of emergency. …