What are the two major portions of the circulatory system? Describe the structure of the heart and its relation to each of these major portions. Describe what occurs in during pulmonary circulation.
The heart pumps blood through the two major, independent portions of the circulatory system, the pulmonary circulation and the systemic circulation. Consequently, the heart has four chambers: the two atria which collect the blood from the two portions of the circulatory system and the two ventricles which take the blood from the atria and pump it back out into the body. The right atrium or auricle collects the deoxygenated blood from the systemic circulation. When the right atrium contracts, it forces the blood through the tricuspid valve into the right ventricle. When the right ventricle contracts, it sends the blood through the pulmonary semilunar valve into the pulmonary circulation. The pulmonary artery carries the blood to the lungs where the arteries branch numerous times connecting with capillary beds around the lungs' alveoli. Here, carbon dioxide is discharged into the air contained in the alveoli, and oxygen is picked up by the hemoglobin contained in the red blood cells of the blood. The pulmonary veins transport the oxygenated blood from the capillaries to the left atrium or auricle of the heart. When this atrium contracts, the blood flows through the mitral or bicuspid valve into the left ventricle. When the left
