Final answer:
Capillaries are the tiny blood vessels responsible for the exchange of oxygen and carbon dioxide between the bloodstream and the body's tissues. They provide a site for external respiration within the pulmonary capillaries of the lungs. Here, oxygen is absorbed into the blood and carbon dioxide is released.
Step-by-step explanation:
The microscopic blood vessels responsible for oxygen (O2) exchange are known as capillaries. These are the smallest blood vessels in the body, which connect arterioles and venules. Capillaries are integral to the body's microcirculation as they facilitate the exchange of gases and other substances between the blood and surrounding tissue fluid (interstitial fluid).
The external respiration process occurs when the pulmonary artery carries deoxygenated blood into the lungs and through to the pulmonary capillaries network adjacent to the alveoli. Here, oxygen is absorbed and carbon dioxide is expelled, allowing red blood cells to pick up oxygen and bind it to hemoglobin. This results in the bright red color of oxygenated blood, which is then carried back to the heart via the pulmonary veins.