venous systems in the body: the pulmonary, por-
tal, and systemic.
The PULMONARY SYSTEM comprises four
vessels, two from each lung, which empty into the
left atrium. These are the only veins in the body
that carry freshly oxygenated blood.
The PORTAL SYSTEM consists of the veins
that drain venous blood from the abdominal part
of the digestive tract (except the lower rectum),
spleen, pancreas, and gallbladder and deliver it
to the liver. There it is distributed by a set of
venous capillaries. The blood in the portal system
conveys absorbed substances from the intestinal
tract to the liver for storage, alteration, or detox-
ification. From the liver the blood flows through
the hepatic vein to the inferior vena cava.
The SYSTEMIC SYSTEM is divided into the
deep and superficial veins. The superficial veins
lie immediately under the skin, draining the skin
and superficial structures. The deep veins, usually
located in the muscle or deeper layers, drain the
large muscle masses and various other organs.
They usually lie close to the large arteries that
supply the various organs of the body (fig. 3-31)
and usually have the same name as the artery they
The superficial veins of the head unite to form
the external jugular veins. They drain blood from
the scalp, face, and neck, and finally empty into
the subclavian veins.
The veins draining the brain and internal facial
structures are the internal jugular veins. These
combine with the subclavian veins to form the in-
nominate veins, which empty into the superior
vena cava (fig. 3-31).
The veins of the upper extremity begin at the
hand and extend upward. An extremely valuable
vein, the median cubital, crosses the anterior sur-
face of the elbow. It is the vein most commonly
used for intravenous injections and infusions.
The deep veins of the upper arm unite to form
the axillary vein, which unites with the superficial
veins to form the subclavian vein. This later unites
with other veins to form the innominate and even-
tually, after union with still more veins, the
superior vena cava.
In the lower extremity (fig. 3-32), a similar
system drains the superficial areas. The great
saphenous vein originates on the inner aspect of
the foot and extends up the inside of the leg and
thigh to join the femoral vein in the upper thigh.
This vein is sometimes used for intravenous in-
jections at the ankle. The superficial venous
system of the leg often becomes varicose, or ex-
cessively dilated, particularly in persons whose
occupations require long periods of standing.
When this develops, the venous valves become in-
competent, allowing stagnation of blood in the
dependent extremity. Under these circumstances
varicose ulcers frequently develop. Ligation at
several points along the system will force the
venous return into the deep venous system and
restore normal venous circulation.
The veins from the lower extremities unite to
form the femoral vein in the thigh, which becomes
the external iliac vein in the groin. Higher in this
region, it unites with the hypogastric vein from
the lower pelvic region to form the common iliac
vein. The two common iliac veins unite to form
the inferior vena cava.
The veins from the abdominal organs, with
the exception of those of the portal system, empty
directly or indirectly into the inferior vena cava,
while those of the thoracic region eventually
empty into the superior vena cava.
All tissue cells of the body are continuously
bathed in interstitial fluid. This fluid is formed
by leakage of blood plasma through minute pores
of the capillaries. There is a continual interchange
of fluids of the blood and tissue spaces with a free
interchange of nutrients and other dissolved
substances. Most of the tissue fluid returns to the
circulation by means of venous capillaries, which
feed into larger veins. Large protein molecules
that have escaped from the arterial capillaries can-
not reenter the circulation through the small pores
of the venous capillaries. However, these large
molecules, as well as white blood cells, dead cells,
bacterial debris, infected substances, and larger
particulate matter, can pass through the larger
pores of the lymphatic capillaries and thus enter
the lymphatic circulation with the remainder of
the tissue fluid.
Lymph usually is clear, but following inges-
tion of a fatty meal the lymph contained in the
lymphatic that drain the small intestine appears
milky because of the fat globules that have been
absorbed. This milky lymph is called CHYLE.
Lymph vessels and lymph nodes form a net-
work throughout the body. Capillaries, like veins,