Baroreceptors in the carotid artery walls and aorta respond to which of the following conditions?
A. Changes in blood pressure.
B. Changes in arterial oxygen tension.
C. Changes in arterial carbon dioxide tension.
D. Changes in heart rate.
Correct Answer: A. Changes in blood pressure.
Baroreceptors located in the carotid arteries and aorta sense pulsatile pressure. Baroreceptors are a type of mechanoreceptor allowing for the relay of information derived from blood pressure within the autonomic nervous system. Information is then passed in rapid sequence to alter the total peripheral resistance and cardiac output maintaining blood pressure within a preset, normalized range.
Option B: Peripheral chemoreceptors in the aorta and carotid arteries are primarily stimulated by oxygen. Peripheral chemoreceptors include the carotid and aortic bodies. The carotid bodies are located at the bifurcation of the common carotid arteries and send information to the respiratory center via cranial nerve IX, the glossopharyngeal nerve. The aortic bodies are situated within the aortic arch, and send information to the brain via cranial nerve X, the vagus nerve. While capable of sensing carbon dioxide and hydrogen ions, the peripheral sensory system primarily detects low arterial oxygen levels (hypoxemia).
Option C: Chemoreceptors in the medulla are primarily stimulated by carbon dioxide. Carbon dioxide is a lipid-soluble molecule that freely diffuses across the blood-brain barrier and forms hydrogen ions within the cerebrospinal fluid. Chemoreceptors, in turn, respond to pH changes as they become more acidic and send sensory input to the brain to stimulate hyperventilation. The result is a slow and deep breathing pattern that helps eliminate carbon dioxide from the body.
Option D: Decreases in pulsatile pressure cause a reflex increase in heart rate. Pulse pressure has been previously correlated with arterial compliance and with hemodynamic factors such as stroke volume and peak aortic blood flow. Left ventricular systolic dysfunction reduces stroke volume and therefore also PP and systolic BP.
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