When a heart contracts and forces blood into the blood vessels, there is a certain path that the blood follows through the body. The blood moves throughpulmonary circulation and then continues on through systemic circulation. Pulmonary and systemic are the two circuits in the two-circuit system of higher animals with closed circulatory systems.Humans and other mammals have two-circuit circulatory systems: one circuit is for pulmonary circulation (circulation to the lungs; pulmo = lungs), and the other circuit is for systemic circulation (therest of the body). As each atrium and ventricle contract, blood is pumped into certain major blood vessels, and from there, continues through the circulatory system.
The intertwined circulatorysystem pathways: Pulmonary circulation and systemic circulation work together.
Blood that is lacking oxygen is said to be deoxygenated. This blood has just exchanged oxygen forcarbon dioxide across cell membranes, and now contains mostly carbon dioxide. Deoxygenated blood enters the right atrium through the superior vena cava and the inferior vena cava.
Superior meanshigher, and inferior means lower, so the superior vena cava is at the top of the right atrium, and the inferior vena cava enters the bottom of the right atrium.
From the right atrium, the deoxygenatedblood drains into the right ventricle through the right atrioventricular (AV) valve, which is so named because it is between the atrium and the ventricle. This valve is also referred to as thetricuspid valve because it has three flaps in its structure. When the ventricles contract, the AV valve closes off the opening between the ventricle and the atrium so that blood does not flow back up intothe atrium.
As the right ventricle contracts, it forces the deoxygenated blood through the pulmonary semilunar valve and into the pulmonary artery. Semilunar means half-moon and refers to the...