Blood from the brachiocephalic trunk flows into which 2 arteries?

A. Blood flow increases: According to the relationship defined by Poiseuille’s law, blood flow is inversely proportional to resistance when pressure remains constant. Vasoconstriction decreases vessel radius, which dramatically increases resistance and therefore reduces flow rather than increasing it.

B. Blood flow decreases: When vascular smooth muscle constricts, the vessel lumen narrows, increasing resistance to flow. Because flow equals pressure divided by resistance (Q = ΔP/R), an increase in resistance results in decreased blood flow if the pressure gradient does not proportionally increase.

C. Blood flow remains unchanged: Blood flow cannot remain unchanged if resistance increases and the pressure gradient is stable. Physiologically, the body may compensate by increasing cardiac output or pressure, but in direct terms, increased resistance reduces flow.

D. Blood viscosity decreases: Vasoconstriction does not directly alter blood viscosity. Viscosity depends on factors such as hematocrit, plasma proteins, and temperature. The change in flow during vasoconstriction is due to altered vessel diameter, not changes in blood thickness.

Correct answer: True

Hypovolemic shock occurs when there is a significant reduction in intravascular circulating volume, leading to decreased preload, reduced stroke volume, and diminished cardiac output. Hemorrhage is one of the most common causes because acute blood loss reduces both plasma volume and red blood cell mass, impairing oxygen delivery to tissues. As circulating volume falls, venous return to the heart decreases, resulting in inadequate tissue perfusion. Without prompt fluid and blood replacement, this volume deficit progresses to hypotension, organ hypoxia, and shock.