Explain Blood Vessels that carry blood?
Blood vessels that carry blood away from the heart to the lungs or to the rest of the body are called arteries. The walls of arteries have a thick layer of muscle tissue sandwiched between two layers of elastic tissue. These two elastic layers are themselves bounded by an inner layer of endothelium (surface lining cells) and an outer layer of connective tissue. If you think of an artery as a pipe or hose, the inside of the artery is lined by the surface cell tissue called the endothelium, and the outside is made of connective tissue. Arteries divide into smaller branches called arterioles, which branch and become progressively smaller until they divide into tiny vessels called capillaries.
Blood is forced under pressure in the capillaries into small vessels called venules, that join to form veins in a return journey leading to the heart. Similar to the walls of arteries, the walls of veins contain a middle layer of muscle; but veins in general are much thinner and less elastic than arteries. Veins also contain one-way valves that keep blood flowing in one direction - back to the heart.