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many subdivisions of this route. Systemic refers to the fact
that it is carrying blood to all organs of all the sys-tems of
the body. Two of its significant subdivisions are the
coronary circulation and the hepatic portal
circulation routes. The coronary circulation route supplies
the myo-cardium of the heart. The hepatic portal circulation
route travels back and forth from the intestine of the
digestive tract to the liver. This route is used to store excess
sugars from digestion into the liver after a meal and to
release sugars stored in the liver as glycogen between
meals to maintain blood glucose levels.
The pulmonary circulation (see Figure 14-5) is the
route that goes from the right ventricle of the heart through
the pulmonary semilunar valve to the pul-monary trunk that
branches into the right and left pulmonary arteries, which
go to the lungs. Here the de-oxygenated blood loses its
carbon dioxide and picks up the oxygen and returns to the
left atrium of the heart via the four pulmonary veins.
The cerebral circulation is the blood circulatory
route that supplies the brain with oxygen and nutrients and
disposes of waste. Blood goes to the brain via the carotid
arteries that go into the head from the center neck region
and the vertebral arteries that go into the head from the
posterior neck region. The vertebral arteries fuse to form
the basilar artery on the brainstem. The carotid arteries and
the basilar artery form the cerebral arterial circle, which is
also known as the Circle of Willis. Branches from the
cerebral arterial circle carry the blood supply to the brain.
Chapter 14The fetal circulation, a temporary circulation, is the
circulation route that exists only between the developing
fetus and its mother. It contains special structures that allow
the fetus to exchange oxygen and nutrients with its mother
and to get rid of fetal waste products through this
connection.Anatomy of Blood Vessels
Blood vessels can be categorized into arteries, arterioles,
veins, venules, and capillaries. Arteries and veins have
walls composed of three layers: the tunica intima
(TYOO-nih-kah IN-tih-mah) composed of a single layer of
-endothelial cells, the tunica media made of smooth mus-
cle, and the tunica adventitia (ad-vin-TISH-ee-ah) com-
posed of white fibrous connective tissue (Figure 14 - 7).
Arteries have walls made of these three coats or
-tunics surrounding a hollow core known as a lumen
(LOO-men) through which blood flows. Arteries are
thicker and stronger than veins with two major proper-ties:
elasticity and contractility. This is necessary be-cause when
the two ventricles of the heart contract, they inject a large
amount of blood into the large aorta and pulmonary trunk.
These arteries must be able to expand to accommodate the
extra blood. Then while the ven-tricles relax, the elastic
recoil of the arteries pushes the blood forward. Most parts
of our body receive branches from more than one artery. In
these areas, the distal ends of these branches unite to form
one artery going intoHealthy AlertHealthy heartIn order to maintain a healthy heart, we need
to concentrate on both consistent, moderate
exercise and our diet. Our diets should contain
high levels of fresh fruit and vegetables, which
have a high fiber content. Cereal grains and
nuts are also good sources of fiber. Our diet
needs to be low in satu-rated fats; moderate
amounts of fish and skinless poultry and small
amounts of lean red meat will contribute to
keeping cho-lesterol levels low. We need to
avoid large intakes of both sugar and salt. A
guiding rule for diets should be “moderation in
all things.” A healthy diet leads to lesseningthe risk of arterial disease, which leads to a
healthy heart. Good side effects of a healthy
diet are better blood pressure rates, lower
blood cholesterol levels, and less excessive
weight.
Exercise is also important to maintain a
healthy heart. However, in older adults,
strenuous exercise can cause a heart attack,
usually by causing an unstable plaque to
dislodge or rupture, initiating the clotting
mechanism in an artery of the heart. Such risk
can be minimized by exercising regularly at a
low-to-moderate rate as we reach our older
years (50 and above).