1 adj Social means relating to society or to the way society is organized. ADJ n. ...the worst effects of unemployment, low pay and other social problems., ...long-term social change., ...changing social attitudes., ...the tightly woven social fabric of small towns., ...research into housing and social policy.
The human circulatory system (simplified). Red indicates oxygenated blood carried in arteries, blue indicates deoxygenated blood carried in veins. Capillaries, which join the arteries and veins, and the lymphatic vessels are not shown.
Simply the heart, a big muscle, is connected to a series of tubes, the arteries and the veins, which carry blood to the various parts of the body. Arteries carry the blood away from the heart, while veins bring blood back to the heart. The arteries are connected to the veins via very small vessels called capillaries. Electrical and chemical signals to the heart cause it to pump the blood into the arteries. Further, a number factors can cause the blood vessels to expand (dilate) or contract. In doing so they can increase or decrease the amount of effort the heart needs to put forth to deliver the blood.