Emergency Medical Technician (EMT) Intermediate Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

The correct answer is the tunica media, which is the middle layer of the blood vessel wall. This layer is primarily made up of smooth muscle and elastic tissue, allowing it to regulate the diameter of the blood vessel. The smooth muscle cells in the tunica media enable vasoconstriction and vasodilation, which are critical for controlling blood flow and blood pressure throughout the circulatory system. The elastic tissue provides the ability to stretch and recoil, accommodating the pulsatile flow of blood that occurs with each heartbeat.

The tunica externa, also known as the adventitia, is the outermost layer of the blood vessel wall and is composed mainly of connective tissue, providing support and structure but not involved in blood vessel contraction or relaxation. The tunica intima, the innermost layer, consists of endothelium and a layer of connective tissue, primarily functioning as a barrier and interface between the blood and the vessel wall rather than in muscle contraction.