ABSTRACT
Course of the circulation Postnatally the pulmonary circulation is completely separated from the systemic circulation. Well-oxygenated arterial blood ejected by the left ventricle flows through the systemic arteries to supply all tissues of the body with oxygen and nutrients. Blood then enters the systemic venous system and returns to the right atrium and ventricle; it is ejected into the pulmonary arterial circulation and returns to the left atrium and ventricle through the pulmonary veins. Blood thus flows serially through the circulation and, apart from passage of a small amount of coronary venous blood into the left ventricular cavity through Thebesian veins, no mixing of arterial and venous blood occurs.
