alteration, or detoxification. 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. Deep veins commonly lie close to the large arteries
that supply the various organs of the body and typically
have the same name as the artery they accompany.
V E I N S O F T H E H E A D , N E C K , A N D
BRAIN.The superficial veins of the head unite to
form the external jugular veins. The external jugular
veins 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
innominate veins, which empty into the superior
vena cava (fig. 1-36).
V E I N S O F T H E U P P E R E X T R E M -
ITIES.The veins of the upper extremities begin at
the hand and extend upward. A vein of great interest to
you is the median cubital, which crosses the anterior
surface of the elbow. It is the vein most commonly used
for venipuncture. Also found in this area are the basilic
and cephalic veins, which extend from the midarm to
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 vein later unites with
other veins to form the innominate and eventually,
after union with still more veins, the superior vena cava
VEINS OF THE ABDOMEN AND THO-
RACIC REGION.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 (fig.
V E I N S O F T H E L O W E R E X T R E M -
TIES.In the lower extremities (fig. 1-36), 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. The great
saphenous vein is used for intravenous injections at the
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,
external iliac unites the internal iliac (hypogastric)
vein from the lower pelvic region to form the common
iliac veins. The right and left common iliac veins unite
to form the inferior vena cava.
THE LYMPHATIC SYSTEM
LEARNING OBJECTIVE: Identify the parts
of the lymphatic system and their function.
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 circulatory system by means of
capillaries, which feed into larger veins. Large protein
molecules that have escaped from the arterial
capillaries cannot reenter the circulation through the
small pores of the 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
circulatory system with the remainder of the tissue
The lymphatic system also helps defend the tissues
against infections by supporting the activities of the
lymphocytes, which give immunity, or resistance, to
the effects of specific disease-causing agents.
PATHWAYS OF THE LYMPHATIC SYSTEM
The lymphatic pathway begins with lymphatic
capillaries. These small tubes merge to form lymphatic
vessels, and the lymphatic vessels in turn lead to larger
vessels that join with the veins in the thorax.
Lymphatic capillaries are closed-ended tubes of
microscopic size (fig. 1-37). They extend into
interstitial spaces, forming complex networks that
parallel blood capillary networks. The lymphatic
capillary wall consists of a single layer of squamous
epithelial cells. This thin wall makes it possible for
interstitial fluid to enter the lymphatic capillary. Once