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How do capillaries exchange oxygen and nutrients with body tissues?
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human cardiovascular system
The human heart is both a pump and a muscle. Its four chambers move blood efficiently, while cardiac muscle cells joined by intercalated disks synchronize each contraction.
Capillaries serve as the primary sites for the exchange of oxygen, nutrients, and waste products between the blood and body tissues. Their walls are extremely thin, consisting of a single layer of endothelial cells surrounded by a basement membrane, which acts as a semipermeable barrier.123
The exchange of substances is driven largely by differences in concentration and pressure. There are three primary modes of transport across these walls:2
- Diffusion: Substances soluble in the lipid membrane of the endothelial cells pass directly through the membrane.3
- Ultrafiltration: Water-soluble substances that are insoluble in the lipid membrane pass through minute pores in the capillary walls.3
- Receptor-mediated transport: Specific molecules, such as cholesterol, are transported by specialized receptors in the endothelium.3
Oxygen and nutrients typically pass into tissues at the arteriolar end of the capillary, while carbon dioxide and waste products enter the vessel at the venous end. The flow of blood into these networks is regulated by the constriction and dilation of arterioles and the action of sphincter muscles.3