The Heart
The aorta is the largest artery in the body. It extends upward from the left ventricle of the heart, arches over the heart to the left, and descends just in front of the spinal column. The first portion of the aorta is the "ascending aorta," which branches into the "arch of the aorta." Three major arteries originate from the aortic arch: the "brachiocephalic artery," which supplies blood to the brain and head; the left common carotid artery and the left subclavian artery. Internally, the heart is divided into four hollow chambers, two on the left and two on the right. The upper chambers, called "atria," have relatively thin walls and receive blood returning through the veins. The right atrium receives blood from two large veins: the "superior vena cava" and the "inferior vena cava." These veins return blood that is low in oxygen from various sites in the body. A smaller vein, called the "coronary sinus," also drains blood into the right atrium from the wall of the heart. The "atrioventricular" opening between the right atrium and the r
When the muscular wall of the right ventricle contacts, the blood inside the heart chamber is put under more pressure, and the tricuspid valve closes. As a result, the only exit is through the "pulmonary trunk," which divides to form the right and left "pulmonary arteries." At the base of this trunk is a "pulmonary semilunar valve" that is made up of three leaflets or cusps. This valve opens when the right ventricle contracts. When the right ventricular muscles relax, blood starts back up the pulmonary trunk, causing the valve to close to prevent the flow from returning into the ventricular chamber. The pulmonary vein travels parallel to the pulmonary artery as it carries the blood back up to the heart. When the left ventricle of the heart contracts, the bicuspid valve closes, and the only way out is through a large artery called the "aorta." The branches of the aorta distribute blood to all parts of the body (See Arch of the Aorta). At the base of the aorta, there is an "aortic semilunar valve" that has three leaflets or cusps. It opens to allow blood to l
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Approximate Word count = 719
Approximate Pages = 3 (250 words per page double spaced)
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