Essentials of Anatomy and Physiology

ing arteries. The most important veins are dia-
grammed in Fig. 13–4 and listed in Table 13–2.

HEPATIC PORTAL CIRCULATION

Hepatic portal circulationis a subdivision of sys-
temic circulation in which blood from the abdominal
digestive organs and spleen circulates through the
liver before returning to the heart.
Blood from the capillaries of the stomach, small
intestine, colon, pancreas, and spleen flows into two
large veins, the superior mesenteric vein and the
splenic vein, which unite to form the portal vein (Fig.
13–7). The portal vein takes blood into the liver,
where it branches extensively and empties blood into
the sinusoids, the capillaries of the liver (see also Fig.
16–6). From the sinusoids, blood flows into hepatic
veins, to the inferior vena cava and back to the right
atrium. Notice that in this pathway there are two sets
of capillaries, and keep in mind that it is in capillaries
that exchanges take place. Let us use some specific
examples to show the purpose and importance of por-
tal circulation.
Glucose from carbohydrate digestion is absorbed
into the capillaries of the small intestine; after a big
meal this may greatly increase the blood glucose level.
If this blood were to go directly back to the heart and

then circulate through the kidneys, some of the glu-

cose might be lost in urine. However, blood from the

small intestine passes first through the liver sinusoids,

and the liver cells remove the excess glucose and store

it as glycogen. The blood that returns to the heart will

then have a blood glucose level in the normal range.

Another example: Alcohol is absorbed into the cap-

illaries of the stomach. If it were to circulate directly

throughout the body, the alcohol would rapidly impair

the functioning of the brain. Portal circulation, how-

ever, takes blood from the stomach to the liver, the

organ that can detoxify the alcohol and prevent its

detrimental effects on the brain. Of course, if alcohol

consumption continues, the blood alcohol level rises

faster than the liver’s capacity to detoxify, and the well-

known signs of alcohol intoxication appear.

As you can see, this portal circulation pathway

enables the liver to modify the blood from the diges-

tive organs and spleen. Some nutrients may be stored

or changed, bilirubin from the spleen is excreted into

bile, and potential poisons are detoxified before the

blood returns to the heart and the rest of the body.

FETAL CIRCULATION

The fetus depends upon the mother for oxygen and

nutrients and for the removal of carbon dioxide and

The Vascular System 301

Table 13–1 MAJOR SYSTEMIC ARTERIES (Continued)

Branches of the Abdominal Aorta

Artery Region Supplied

Testicular or ovarian a.

Common iliac a.

Internal iliac a.

External iliac a.

Femoral a.

Popliteal a.

Anterior tibial a.

Dorsalis pedis

Plantar arches

Posterior tibial a.

Peroneal a.

Plantar arches

• Testes or ovaries


• The two large vessels that receive blood from the
  abdominal aorta; each branches as follows:


• Bladder, rectum, reproductive organs


• Lower pelvis to leg


• Thigh


• Back of knee


• Front of lower leg


• Top of ankle and foot


• Foot


• Back of lower leg


• Medial lower leg


• Foot