Problem 2 - Entrance Test

Significant blood loss leads to a decrease in blood volume and pressure. 1. Immediate Response (Neural): The decrease in blood pressure is detected by baroreceptors in the carotid sinus and aortic arch. This activates the sympathetic nervous system, leading to an increased heart rate (to pump more blood) and widespread vasoconstriction (to increase total peripheral resistance and redirect blood to vital organs), thereby increasing blood pressure. 2. Long-term Response (Hormonal): * ADH (Antidiuretic Hormone): Decreased blood pressure and increased osmolarity (due to fluid loss) stimulate osmoreceptors in the hypothalamus and baroreceptors, leading to increased ADH release from the posterior pituitary. ADH promotes water reabsorption in the collecting ducts, increasing blood volume and pressure. * RAAS (Renin-Angiotensin-Aldosterone System): Decreased renal perfusion pressure (due to low blood pressure) stimulates juxtaglomerular cells to release Renin. Renin converts angiotensinogen to Angiotensin I, which is then converted to Angiotensin II (a potent vasoconstrictor, also stimulates ADH and Aldosterone release). Aldosterone, released from the adrenal cortex, promotes Na+ and water reabsorption in the distal tubules and collecting ducts, increasing blood volume and pressure. Option A is incorrect because Angiotensin II causes vasoconstriction, not vasodilation, and decreased ADH would exacerbate fluid loss. Option C describes a response to increased osmolarity, but increased water excretion would further decrease blood volume, which is counterproductive in this scenario. ADH would increase, not decrease. Option D is incorrect as decreased blood volume would lead to decreased GFR (not increased), and ANF is released in response to increased atrial stretch (high blood volume/pressure), leading to decreased blood volume and pressure.