Haemoglobin — Haemoglobin is an iron and protein compound that is found within the Red Blood cells. It acts as the "oxygen-carrier".
Capillaries — Capillaries are the terminal branches of an artery, which rejoin to form a vein.
Aorta — The aorta is the largest artery in the body and carries oxygenated blood from the left ventricle to all parts of the body through its branches.
Universal donor — A person with O blood group can give blood to a person of any blood type and is therefore called a universal donor.
Blood pressure — The pressure exerted by the blood on the walls of the arteries while flowing through them is called blood pressure.