Diffusion through the capillary walls is a critical process that allows for the exchange of substances between the blood and surrounding tissues. Here’s how it works in the context of your statement:
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Waste removal: Waste products, such as carbon dioxide (CO2) and urea, are produced by cells during metabolism. These waste products diffuse from the cells into the blood within the capillaries. The blood then carries these wastes to organs like the lungs (for CO2 removal) and kidneys (for urea excretion) where they can be eliminated from the body. However, it's important to note that waste does not move from the heart to organs through diffusion; rather, it moves from tissues into the blood and then to excretory organs.
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Oxygen delivery: Oxygen diffuses from the blood into body cells through the capillary walls. When blood reaches the capillaries in tissues, the concentration of oxygen in the blood is higher than that in the surrounding tissues. As a result, oxygen moves from the blood (where it is dissolved and bound to hemoglobin) into the cells where it is needed for cellular respiration.
In summary, diffusion through capillary walls allows for the movement of oxygen from the blood to body cells and the movement of carbon dioxide and other waste products from the cells into the blood.