West Coast EMT Practice Test 2025 – Complete Exam Prep

Smooth muscle primarily regulates blood vessels, playing a crucial role in controlling blood flow and blood pressure. This is achieved through the contraction and relaxation of smooth muscle cells in the walls of the blood vessels. When smooth muscle contracts, it causes vasoconstriction, which narrows the vessel diameter, increasing resistance and blood pressure. Conversely, when the smooth muscle relaxes, it leads to vasodilation, increasing vessel diameter and reducing resistance and blood pressure.

In contrast, the heart is predominantly regulated by cardiac muscle, which has different control mechanisms, including electrical conduction through the pacemaker cells. The skeleton is composed of striated skeletal muscle that is under voluntary control and not directly regulated by smooth muscle. The diaphragm, while involved in respiration, is made of skeletal muscle as well and is not primarily regulated by smooth muscle. Thus, blood vessels are the correct answer, as they rely on smooth muscle to regulate their structure and function effectively.