PSI Barbering Practice Exam 2026 – 400 Free Practice Questions to Pass the Exam

Capillaries are the smallest blood vessels in the body, and they play a critical role in the nutrient exchange process. Their walls are thin and permeable, allowing for easy diffusion of oxygen, carbon dioxide, nutrients, and waste products between the blood and surrounding tissues. As blood flows through the capillaries, nutrients from the bloodstream are delivered directly to the cells, providing them with the essential components needed for energy, growth, and repair.

In contrast, arteries carry oxygen-rich blood away from the heart and toward the tissues, but they do not directly exchange nutrients with the cells. Veins are responsible for returning deoxygenated blood back to the heart, and venules are smaller veins that collect blood from capillaries; while they have a role in the circulatory system, they are not involved in the direct delivery of nutrients.

Thus, capillaries are specifically designed for the exchange of nutrients and other substances, making them the correct answer to the question about what type of vessels bring nutrients to cells.