It's referred to as Carbon dioxide. It is the main cellular waste product that is carried in the blood to the lungs through the heart.
Carbon Dioxide (CO2)
Carbon dioxide is the waste substance that is transported back to the lungs from the cells in the body. It is exhaled out as a waste product of cellular respiration.
Haemoglobin?
Oxygen
Oxygen
oxygen
Oxygen
Oxygen
Carbon Dioxide
The pulmonary artery takes carbon dioxide (CO2) from the heart to the lungs. Oxygen is then carried back to the heart by the pulmonary vein. Finally, the aorta/arteries carry oxygen to the body.
The blood absorbs oxygen from the lungs - enabling it to be transported throughout the body.
The circulatory system for one needs oxygenated blood to be transported from the lungs to the heart, and it needs the body to get rid of carbon dioxide from the blood through the lungs. :)