Distended veins are an example of which transmural pressure state?

• A. Low transmural pressure
• B. Negative transmural pressure
• C. Zero transmural pressure
• D. High transmural pressure

Answer: (D)

Transmural pressure is the pressure difference across a vessel wall, calculated as inside pressure minus outside pressure. When this difference is positive and sizable, the wall is stretched and the vessel distends. Distended veins occur because the intraluminal pressure exceeds the external pressure, producing a high transmural pressure. If the transmural pressure were negative, the outside pressure would overwhelm the inside, causing collapse; if it were zero, there would be no net distension; if it were only low, the wall would not be significantly stretched.