b. Via the Major Veins.
(1) In general, the major veins pass through the body in proximity to the
arteries, and in most cases, have the same names. Blood from the veins of the heart
drains through the coronary sinus into the right atrium. Blood from the head and neck
drains into the jugular veins, and that from the upper extremities into the subclavian
veins. On each side, these veins join to form the right and left brachiocephalic veins,
which, in turn, unite into the superior vena cava that opens into the right atrium. The
superior vena cava also receives the azygos vein which, with its tributaries, returns
blood from the thorax to the superior vena cava. The azygos vein begins in the
abdomen as an extension of one of the tributaries of the inferior vena cava and serves
as a connection between the superior and inferior venae cavae in the return of blood to
the heart. The major veins are shown in figure 3-26.
(2) From the lower extremities and abdomen, two venous routes lead to the
heart. In the direct route, blood from the lower extremities moves through the right and
left common iliac veins, which join at the level of the fifth lumbar vertebra to form the
inferior vena cava. This major vein passes through the abdominal cavity in proximity to
the aorta along the posterior abdominal wall. It receives the lumbar, genital, renal,
adrenal, hepatic, and inferior phrenic veins as it ascends through the abdominal cavity
before it enters the right atrium of the heart.
(3) Blood from the spleen and the abdominal organs of the
gastrointestinal tract is not returned directly to the heart by way of the inferior vena
cava. Instead, the veins draining the small intestine, stomach, lower esophagus, and
spleen join to form the portal vein, which enters the liver. Blood from the tissues of the
liver enters the hepatic vein which then drains into the inferior vena cava en route to the
3-43. PULMONARY CIRCULATION
The pulmonary arteries arise from the right ventricle and carry deoxygenated
blood to the lungs where gaseous exchanges occur. The lungs are drained by the
pulmonary veins, which carry oxygenated blood to the left atrium of the heart.
3-44. PATHOLOGICAL CONDITIONS
A thrombus is a clot of blood lodged at its point of formation in a blood vessel or
the heart. If a clot or any foreign material travels from its point of origin until it becomes
lodged in a smaller vessel, it is called an embolism. Arteriosclerosis is a condition of
arteries that results from a collection of cholesterol and fats on the interior wall,
narrowing the lumen. Arteriosclerosis is a hardening of the arterial wall. An aneurysm
is a ballooning of an artery or vein.