CCH The circulatory system introduction

The circulatory system is so named because the blood flows in a circle (from the Latin circus—the next time the circus is in town notice that it plays in the middle of a big circle as well). The heart, arteries, veins, and capillaries are the key components Of the system (Freberg, 2016). The human heart with its muscular myocardium walls is about the size Of a clenched fist, sits just beneath our breastbone, and is protected by a fibrous sac called the pericardium. The heart has two main halves. The right half receives blood low in
oxygen from all over the body and pumps it to the lungs. The left half receives blood rich in oxygen from the lungs and pumps it back all over the body. Each half of the heart is further divided into two chambers. The upper and thinner-walled chambers on each side are called the atria; the lower, thickerwalled chambers on each side are called ventricles. Blood vessels that carry blood away from the heart are called arteries, and the vessels that carry blood to the heart are called veins. envo large veins, the superior (from the upper parts of the body) and the inferior (from the lower parts of the body) venae cavae, carry deoxygen- ated blood into the heart. A large artery carries oxygenated blood to the rest of the body. "IAvo other vessels carry blood between the heart and the lungs. The pulmonary artery carries deoxygenated blood from the heart to the lungs, and the pulmonary vein carries blood from the lungs to the heart. What keeps everything separate? The heart's valves. A system of valves ensures that the blood flows in one direction only (a nice idea that would work great to keep backwash to a minimum when one is sipping from a can or bottle). Each valve consists of flaps of connective tissue; the actual sound of a heartbeat is the sound of the valves closing. The first sound is buh, which is when the valves between the atria and ventricles close. The second sound