c. The blood is carried through the lung tissues, exchanging its carbon dioxide
for oxygen in the alveoli. This oxygenated blood is collected from the main pulmonary
veins and delivered back to the left side of the heart to the left atrium.
d. As the left atrium contracts, the oxygenated blood flows through the open
bicuspid (mitral) valve into the left ventricle.
e. As the left ventricle contracts, the bicuspid valve is closed. The aortic
semilunar valve opens as a result of the force and movement of the blood, and the left
ventricle pumps oxygenated blood through the aortic semilunar valve into the aorta, the
main artery of the body. Oxygenated blood now starts its flow to all of the body cells
and tissues. The systemic circulation starts from the left ventricle, the pulmonary
circulation from the right ventricle.
BLOOD AND NERVE SUPPLY OF THE HEART
a. Coronary Arteries. The heart gets its blood supply from the right and left
coronary arteries (Figure 1-3). These arteries branch off from the aorta just above the
Aortic Valve, then subdivide into many smaller branches within the heart muscle. If any
part of the heart muscle is deprived of its blood supply through interruption of blood flow
through the coronary arteries and their branches, the muscle tissue deprived of blood
cannot function and will die. This is called myocardial infarction (MI). Blood from the
heart tissue is returned by coronary veins to the right atrium via the coronary sinus.
Figure 1-3. The coronary arteries.