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How does the human cardiovascular system remove carbon dioxide and other wastes from tissues?

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Silhouette diagram of the human body highlighting the heart and major blood vessels, with labeled arteries in red and veins in blue to show the structure of the cardiovascular system. — Circulatory system Human circulatory system.

The human cardiovascular system removes carbon dioxide and other metabolic wastes from tissues through a process of exchange facilitated by the capillary network.1

Exchange at the Capillaries

Capillaries are microscopic vessels with extremely thin, semipermeable walls that allow waste products to move from the tissues into the bloodstream. Because the partial pressure of carbon dioxide is higher in the tissues than in the blood, it diffuses across the capillary membrane into the vessel.12

Transport of Carbon Dioxide

Once in the blood, carbon dioxide is transported to the lungs primarily through chemical conversion:23
* Bicarbonate: The majority of carbon dioxide (about 88 percent) is converted into bicarbonate ions. This process is catalyzed by the enzyme carbonic anhydrase within red blood cells. Through the chloride shift, bicarbonate is moved into the plasma for transport.24
* Carbamate: A portion binds to blood proteins, specifically hemoglobin, to form carbamates.2
* Dissolved Gas: A small amount remains dissolved directly in the blood.2

Elimination of Other Wastes

Other metabolic waste products, such as urea, creatinine, and uric acid, are transported by the blood to the kidneys, where they are filtered and excreted in urine. Additionally, the liver processes certain substances, such as bilirubin, for excretion into the gastrointestinal tract.5