An 18-year-old male with multiple stab wounds to his abdomen is brought by ambulance to the trauma bay. He is bleeding profusely, with HR 128 beats/min, BP 72/41 mm Hg, SpO2 92% on 15 L oxygen via nonrebreathing face mask. Of the following statements regarding this patient’s renin-angiotensin-aldosterone system (RAAS), which is FALSE?
A. Decreased oxygenation in the macula densa activates the RAASCorrect Answer: A
There are many compensatory biological and neuroendocrine mechanisms in response to acute hypovolemic shock. In the juxtaglomerular apparatus, renin is released in response to three stimuli:
Renin hydrolyzes angiotensinogen into angiotensin I, which is further cleaved in the lungs by endothelial-bound ACE into angiotensin II, a potent vasoconstrictor which acts directly on the AT1-receptor on arteriolar smooth muscles to maintain systemic perfusion. Angiotensin II also acts on glomerular arterioles, with greater vasoconstrictive effect on efferent arterioles than afferent. This preserves glomerular pressure and the glomerular filtration rate in shock states.
Angiotensin II also stimulates the adrenal glands to release aldosterone, which triggers the epithelial cells in the distal tubule and collecting ducts of the kidney to increase reabsorption of sodium and water and excretion of potassium and hydrogen ions.
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