Red blood cells and heart. Computer artwork of a heart on the silhouette of a person and red blood cells (erythrocytes). The heart is a hollow muscle that pumps blood around the body. Red blood cells are biconcave, giving them a large surface area for gas exchange, and highly elastic, enabling them to pass through narrow capillary vessels. The cell's interior is packed with haemoglobin, a red iron-containing pigment that has an oxygen carrying capacity. The main function of red blood cells is to distribute oxygen to body tissues and to carry waste carbon dioxide back to the lungs.
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