(1) Left ventricle of the heart. The oxygen-saturated blood is moved from
the left atrium into the left ventricle. When the left ventricular wall contracts, the
pressure closes the mitral valve, which prevents blood from returning to the left atrium.
The contraction of the left ventricular wall therefore forces the blood through the aortic
semilunar valve into the aortic arch. Upon relaxation of the left ventricular valve, the
back pressure of the aortic arch forces the aortic semilunar valve closed.
(2) Arterial distributions. The blood then passes through the various
arteries to the tissues of the body. See Figure 2-5 for an illustration of the main arteries
of the human body.
(a) The carotid arteries supply the head. The neck and upper
members are supplied by the subclavian arteries.
(b) The aortic arch continues as a large single vessel known as the
aorta passing down through the trunk of the body in front of the vertebral column. It
gives off branches to the trunk wall and to the contents of the trunk.
(c) At the lower end of the trunk, the aorta divides into right and left
iliac arteries, supplying the pelvic region and lower members.
(3) Capillary beds of the body tissues. In the capillary beds of the tissues
of the body, materials (such as food, oxygen, and waste products) are exchanged
between the blood and the cells of the body.
(4) Venous tributaries. See Figure 2-6 for an illustration of the main veins
of the human body.
(a) The blood from the capillaries among the tissues is collected by a
venous system parallel to the arteries. This system of deep veins returns the blood
back to the right atrium of the heart.
(b) In the subcutaneous layer, immediately beneath the skin, is a
network of superficial veins draining the skin areas. These superficial veins collect, and
then join the deep veins in the axillae (armpits) and the inguinal region (groin).
(c) The superior vena cava collects the blood from the head, neck,
and upper members. The inferior vena cava collects the blood from the rest of the
body. As the final major veins, the venae cavae empty the returned blood into the right
atrium of the heart.
(d) The veins are generally supplied with valves to assist in making
the blood flow toward the heart. It is of some interest to note that the veins from the
head do not contain valves.