Circulatory system

• Arteries have thick, elastic walls that allow them to withstand the high pressure of blood pumped by the heart.
• Veins are thinner than arteries but still contain smooth muscle tissue and valves to prevent backflow of blood.
• The heart has four chambers: the two atria on top (right atrium and left atrium) and the two ventricles on bottom (right ventricle and left ventricle).
• Blood carries oxygen from the lungs to all parts of the body and removes carbon dioxide produced during cellular respiration.