AEMCA Practice Exam

What is a capillary?

1. The largest blood vessel in the body

2. A small blood vessel that is one cell thick

3. An artery that carries oxygenated blood

4. A blood vessel that connects arteries to veins

The correct answer is: A small blood vessel that is one cell thick

A capillary is defined as a small blood vessel that is notably one cell thick. This structural characteristic is crucial because it allows for the efficient exchange of oxygen, carbon dioxide, nutrients, and waste products between the blood and surrounding tissues. The thinness of the capillary walls facilitates this exchange, enabling gas and nutrient diffusion to occur readily. In contrast to larger blood vessels, such as arteries and veins, which are designed to transport blood over longer distances and under higher pressure, capillaries play a vital role in the microcirculation. They connect the arterial and venous systems, enabling blood to flow from arterioles (smallest branches of arteries) to venules (smallest branches of veins), thus completing the circulation process. The other choices describe different types of blood vessels or functions, but they do not accurately define a capillary. Understanding the specific function and structure of capillaries is fundamental to comprehending the overall functioning of the circulatory system.