| Noun | 1. | Hb - a hemoprotein composed of globin and heme that gives red blood cells their characteristic color; function primarily to transport oxygen from the lungs to the body tissues; "fish have simpler hemoglobin than mammals"erythrocyte, RBC, red blood cell - a mature blood cell that contains hemoglobin to carry oxygen to the bodily tissues; a biconcave disc that has no nucleus oxyhaemoglobin, oxyhemoglobin - the bright red hemoglobin that is a combination of hemoglobin and oxygen from the lungs; "oxyhemoglobin transports oxygen to the cells of the body" | |