Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

Oxygen transfers to tissues from blood primarily through which structure?

1. Lymphatic vessels

2. Arteries

3. Arterioles

4. Capillaries

The correct answer is: Capillaries

Oxygen transfer to tissues from the blood occurs primarily through capillaries. Capillaries are the smallest blood vessels in the body and have walls that are only one cell thick. This thin structure facilitates the efficient exchange of gases, nutrients, and waste products between the blood and surrounding tissues. When blood reaches the capillaries, oxygen that is bound to hemoglobin in red blood cells diffuses out of the blood, across the capillary walls, and into the tissues where there is a lower concentration of oxygen. The close proximity of capillaries to nearly every cell in the body ensures that oxygen can be delivered effectively. The other choices represent different components of the circulatory system that are not primarily responsible for the direct transfer of oxygen to tissues. Lymphatic vessels are part of the immune system and involved in transporting lymph fluid, while arteries and arterioles are responsible for transporting blood away from the heart but do not facilitate the actual exchange of oxygen with tissues. The functionality of capillaries is crucial in ensuring that oxygen transfer occurs efficiently at the cellular level.