Blood

Blood is the red fluid that flows in the arteries and veins of humans and other vertebrate animals; and also the fluid, not necessarily red, circulating in invertebrate performing similar function.

Colour of the blood is red when oxygenerated and purple when doxygenerated. It carries hemoglobin, the protein that gives blood its colour, and which can combine with oxygen enabling the blood to carry oxygen from lungs to the issues of the body. It carries carbon dioxide from the tissues of the body again to the lungs. Blood contains plasma, a mildly alkaline aqueous fluid, with suspended red blood cells ie erythrocytes, white blood cells ie leukocytes, and platelets in it. White blood cells protect the body against infection of foreign agents, such as from bacteria. Platelets and other factors present in plasma are responsible for preventing hemorrhage or in the clotting of blood.

In medieval physiology and medicine, blood was regarded as one of the four elemental bodily humours, believed to be associated with a confident, optimistic, and cheerful temperament.

A member belonging to the Black foot Confederacy of North American Indian people is also called a Blood.