Explain how a major drop in blood pressure caused by blood loss causes a decrease in the amount of urine lost.
What will be an ideal response?
Answer: The drop in blood pressure decreases urine production by multiple mechanisms. First, the drop in blood pressure directly reduces blood flow through the renal artery and the pressure in the afferent arteriole, reducing glomerular filtration rate. The drop in blood pressure is sensed by baroreceptors, leading to activation of the sympathetic nervous system, which constricts afferent arterioles, reducing glomerular filtration rate. The decreased pressure in the renal artery is also sensed by the juxtaglomerular cells, which secrete renin, and enzyme that converts angiotensin I to angiotensin II, which acts on the adrenal cortex to produce aldosterone, which acts on the cortical collecting ducts to increase sodium reabsorption. Because water follows salt, less urine is excreted. Also, the decrease in blood pressure causes the baroreceptors to increase vasopressin secretion by the posterior pituitary. Vasopressin acts on the collecting ducts to increase water reabsorption.
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