Blood

"Blood is a constantly circulating fluid providing the body with nutrition, oxygen, and waste removal. Blood is mostly liquid, with numerous cells and proteins suspended in it, making blood ""thicker"" than pure water. The average person has about 5 liters (more than a gallon) of blood.
A liquid called plasma makes up about half of the content of blood. Plasma contains proteins that help blood to clot, transport substances through the blood, and perform other functions. Blood plasma also contains glucose and other dissolved nutrients.
About half of blood volume is composed of blood cells:
• Red blood cells, which carry oxygen to the tissues.
• White blood cells, which fight infections.
• Platelets, smaller cells that help blood to clot.
Blood is conducted through blood vessels (arteries and veins). Blood is prevented from clotting in the blood vessels by their smoothness, and the finely tuned balance of clotting factors."

Haematoma

A haematoma, or hematoma, is a localized collection of blood outside the blood vessels,[1] usually in liquid form within the tissue. This distinguishes it from an ecchymosis, which is the spread of blood under the skin in a thin layer, commonly called a bruise. Internal bleeding is generally considered to be a spreading of blood within the abdomen or skull, not within muscle. Hematomas can occur within a muscle. Some hematomas form into hard masses under the surface of the skin. This is caused by the limitation of the blood to a subcutaneous or intramuscular tissue space isolated by fascial planes. This is a key anatomical feature that prevents such injuries from causing massive blood loss. In most cases the sac of blood or hematoma eventually dissolves; however, in some cases they may continue to grow or show no change. If the sac of blood does not disappear, then it may need to be surgically removed. Hematomas can occur when heparin is given via an intramuscular route; to avoid this, heparin must be given intravenously or subcutaneously.