Which structural layer of blood vessels is most responsible for maintaining blood pressure?

• A. Endothelium
• B. Tunica adventitia
• C. Tunica media
• D. Internal elastic lamina

Answer: (C)

Blood pressure is kept up primarily by the smooth muscle in the tunica media, which sets the vessel’s radius. This layer can constrict or relax in response to neural signals and local factors, changing peripheral resistance. When the tunica media constricts (vasoconstriction), resistance increases and blood pressure rises; when it relaxes (vasodilation), resistance falls and pressure drops. The endothelium helps modulate tone with vasoactive substances, but it isn’t the main structural mechanism maintaining pressure. The internal elastic lamina contributes to elastic recoil in large arteries, not ongoing pressure control, and the tunica adventitia mainly provides support and anchoring. So, the tunica media is the key layer responsible for maintaining blood pressure.