(2) Chambers. The heart can be described as being two pumps. Each side
(right half and left half) of the heart has a receiving chamber for the blood (the atrium)
and a pumping chamber (the ventricle). The two halves of the heart are separated by a
wall-like structure called the interventricular septum.
The plural of atrium is atria.
(3) Sinoatrial node. The sinoatrial (SA) node is a small bundle of nerve
tissue located at the junction of the superior vena cava and the right atrium. The
sinoatrial node is a natural pacemaker that produces an electrical stimulus. This
electrical stimulus causes the muscles of the ventricles to contract and pump blood.
b. Blood Vessels. The blood vessels are firm, elastic, muscular tubes that
carry the blood away from the heart and back to the heart again.
(1) Blood circulation systems. Since the heart is divided into two parts (the
right half consisting of the right atrium and the right ventricle and the left half consisting
of the left atrium and left ventricle), it is not surprising to find that there are actually two
blood circulatory systems--the systemic and the pulmonary.
(a) Systemic. The systemic (general) circulatory system is the larger of
the two systems. It takes the blood pumped by the left ventricle to all parts of the body
and returns the blood to the right atrium. The oxygen content of the blood is high when
it leaves the heart through the left ventricle and is low when it returns to the right atrium.
(b) Pulmonary. The pulmonary circulatory system takes the blood
pumped by the right ventricle to the lungs and returns the blood to the left atrium. The
oxygen content of the blood is low when it leaves the heart through the right ventricle
and high when it returns to the left atrium.
(2) Types of blood vessels. Both the systemic and the pulmonary
circulatory systems are composed of three major types of blood vessels--arteries,
capillaries, and veins.
(a) Arteries. The arteries carry blood pumped by the ventricles away
from the heart. The arteries of the systemic circulatory system carry oxygenated
(oxygen rich) blood to body tissues. The pulmonary arteries carry deoxygenated
(oxygen-poor) blood to the lungs. Arteries have the capacity to constrict and dilate.
This constricting and dilating helps to regulate the blood pressure.