Which is FALSE regarding the body's compensatory mechanisms for shock?

Correct answer: True

Vascular baroreceptors are specialized stretch-sensitive mechanoreceptors primarily located in the aortic arch and carotid sinuses. They detect changes in arterial blood pressure by sensing the degree of stretch in the vessel walls. When blood pressure rises, increased stretch of these receptors triggers afferent signals to the cardiovascular center in the medulla, leading to parasympathetic activation and sympathetic inhibition, which reduce heart rate and cause vasodilation. Conversely, a drop in blood pressure decreases baroreceptor firing, prompting sympathetic stimulation to increase heart rate, contractility, and vasoconstriction, helping maintain blood pressure within a normal range.

A. Large lumens and thin walls: This feature is characteristic of veins, which have larger lumens and thinner walls to accommodate higher blood volume at lower pressure. Arteries, in contrast, have thicker walls and smaller lumens to withstand high-pressure blood flow from the heart.

B. The tunica externa being the thickest layer: In veins, the tunica externa (adventitia) is often the thickest layer, providing structural support. In arteries, the tunica media is usually the thickest layer to handle pulsatile pressure, so this is not unique to arteries.

C. The presence of an external elastic membrane in larger vessels: Larger arteries have an external elastic (elastic lamina) layer between the tunica media and tunica externa, which allows them to stretch and recoil with each heartbeat. This feature is largely absent in veins and is distinctive of arteries, supporting their role in maintaining blood pressure and flow.

D. A smooth endothelium: Both arteries and veins are lined with a smooth endothelial layer to reduce friction and facilitate blood flow. This is not unique to arteries and is common to all blood vessels.