The Journey of a red blood cell is a long one, a whole loop that starts at any given point and doesn’t end, ever! It just keeps circling on and on and on and on…. Thus forth until death. Today we will begin our story at the point where the red blood cell is created, inside the bones. Red blood cells travel through capillaries. The deoxygenated red blood cell makes its way into the heart through the Vena Cava. then it enters the right atrium. Once the red blood cell is in the right atrium, the right atrium contracts and pushes the blood cell through the tricuspid valve and into the right ventricle. The right ventricle will then push the red blood cell through the pulmonary valve and up through the pulmonary artery to the lungs. The pulmonary artery carries the blood to the lungs through pulmonary arterioles which branch into capillaries which surround the alveoli in the lungs. The capillary walla and the alveoli walls are very thin so that rapid diffusion can happen, carbon dioxide going into the alveoli from the red blood cells and oxygen from the alveoli going into the red blood cells.
Once the red blood cell is in the lungs it picks up oxygen and drops off carbon dioxide then goes back into the heart through the pulmonary veins and then into the left atrium. Once in the left atrium, the left atrium contracts and sends the red blood cell through the mitral valve and into the left ventricle. Now it's time for the red blood cell to leave the heart again. The left ventricle contracts and sends the red blood cell flying through the aortic valve and into the aorta. The blood branches off from the aorta into arteries.Arteries make up smaller arterioles and then capillaries. These capillaries diffuse the oxygen into the cells of the body and pick up carbon dioxide The red blood cell travels from the aorta to to capillaries of the abdominal organs and lower limbs. The red blood cell drops off the oxygen to the cells. And finally the deoxygenated red blood cell travels back up through the Vena Cava and the loop starts again.
*The purpose of this whole cycle and the red blood cells themselves is to carry oxygen from the lungs to the rest of the body.
*deoxygenated blood comes back to the heart through the vena cava