The majority of blood is made up of a liquid called plasma. Plasma comprises proteins that carry things through the blood, aid in blood clotting, and carry out other tasks. Additionally, glucose and other dissolved nutrients are present in blood plasma. 

Blood cells make up around half of the volume of blood: 

White blood cells combat pathogens, while red blood cells transport oxygen to the tissues. 

• Platelets, which are tiny cells that aid in blood clotting.

White blood cells fight infections, while platelets, which are smaller cells, aid in blood clotting. Red blood cells carry oxygen to the tissues. 

Blood is transported by blood vessels (arteries and veins). The blood arteries' smoothness and the carefully calibrated balance of clotting factors prevent blood from clotting there.