Blood is a connective tissue made up of millions of cells. It flows throughout the body in the blood vessels and supplies nutrients and oxygen to cells and tissues. Blood also collects waste products excreted by the cells and filters them out of the body. It constitutes around seven percent of the total body weight. The heart pumps blood at a constant rate and supplies it to the whole body. Blood has four components: red blood cells, white blood cells, platelets, and plasma. Red Blood Cells Red blood cells
(RBCs) are small, flat, disk-shaped cells, also called erythrocytes. They contain a type of protein called hemoglobin that gives blood
its red color. It is responsible for carrying oxygen throughout the body. The level of hemoglobin in the blood also determines its
WORDS TO UNDERSTAND
antibodies: proteins produced by white blood cells to fight off infections. hemoglobin: a protein that carries oxygen around the body. marrow: the substance inside bones, where blood cells are created. platelets: small, oval-shaped cells.
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