Red blood cells are the majority of cells in the blood. They are also known as erythrocytes and are disc shaped with a dipped center. All red blood cells carry oxygen, they transport oxygen from the heart to all parts of the body. Red blood cells play a very important role in the body as all body tissues need oxygen. Without blood flow bringing through oxygen, the various bodily tissues will die.
Hemoglobin makes up about 97% of the red blood cells weight and gives the red blood cells their color. Hemoglobin is a protein containing iron and carries the structure to hold the oxygen in the red blood cells. The circulatory system takes the oxygen from the heart through the red blood cells and circulates through the body and returns to the heart for replenishment of oxygen. This constant circulation takes just 20 seconds per cycle from the heart to other body tissues.
Every second, about 2.4 million new red blood cells are developed by the bone marrow and pushed into the circulatory system. They circulate through the body moving from the heart to other organs for up to about 120 days before they recycled.
Due to the importance of red blood cells in the body, certain disease that affect them may be harmful to the rest of the body. These diseases include anemias which cause abnormalities in the red blood cells so that they are unable to carry enough oxygen. The moist common anemias are iron deficiency anemia and sickle cell disease.