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INTRODUCTION OF
CIRCULATORY SYSTEM PROCESS
Qi Lin
The Pennsylvania State University
INTRODUCTION OF CIRCULATORY SYSTEM PROCESS
Introduction
Cardiovascular Circulation
The circulatory system (shown in Figure
1), is an organ system that allows blood to
circulate and transport nutrients, oxygen,
carbon dioxide, hormones, and blood cells to
provide nourishment, fight disease, stabilize
temperature, and maintain homeostasis. The
circulatory system, as simply a highway for
blood, is made up of three independent
systems that work together: the heart
(cardiovascular
circulation),
lungs
(pulmonary circulation); and arteries, veins,
and coronary and portal vessels (systemic
circulation). The circulatory systems of
humans are close, which means that the blood
in humans’ body never leaves the network of
blood vessels. In contrast, oxygen, carbon
dioxide and nutrients diffuse cross the blood
and cells.
An average adult has a heart (shown in
Figure 2) that is about 14cm long by 9 cm
wide. It’s approximately the size of a man’s
closed fist. The heart pumps approximately
7,000 L of blood every day. Statistics show
that the heart will contract about 2.5 billion
times in an average person’s life. It contains
four chambers in total:
Figure 1: The diagram of the circulatory system
 Left atrium - the upper left chamber
of the heart
 Left ventricle - the lower left
chamber of the heart
 Light atrium - the upper right
chamber of the heart
 Right ventricle - the lower right
chamber of the heart
There is one atrium and one ventricle
involved in each circulation in the human
heart. For systemic circulation, the left
ventricle and the right atrium play important
roles. The left ventricle receives the
oxygenated blood from the lungs. Then, the
blood in the left ventricle will be pumped out
to the body through the aorta and return to
the right atrium. For pulmonary circulation,
the right ventricle and the left atrium play
important roles. The right ventricle receives
the deoxygenated blood from the body.
Then, the blood in the right ventricle will be
transferred to the lungs through the left and
right pulmonary artery.
INTRODUCTION OF CIRCULATORY SYSTEM PROCESS
Figure 2: The diagram of the cardiovascular
circulation
The blood from the left ventricular
pumps into the aorta, the body’s largest
artery. The aorta branches into major arteries
at the upper part of the body before passing
through the diaphragm. Then, these major
arteries branch further into smaller arteries
and arterioles at the lower parts of the body,
and finally capillaries. During the process of
systemic circulation, waste and carbon
dioxide diffuse out of the cell into the blood,
while oxygen in the blood diffuses out into
the cell. The deoxygenated blood continually
travel through the capillaries, which merge
into venules, then veins, and finally the vena
cava, to begin the pulmonary circulation,
exchanging the carbon dioxide and oxygen
with the alveoli in the lungs.
Systemic Circulation
The systemic circulation (shown in
Figure 3) is the circulation of the blood to all
parts of the body except the lungs. The main
components of the systemic circulation
including the aorta and its branches which
emitted from the left ventricle, and the vena
cava and it branches veins which returned to
the heart. The branches of the aorta include
arteries and arterioles, and the branches of
the vena cave include veins and venules. The
systemic venous system can be divided into
three major systems: the superior vena cava
system, the inferior vena cava system and
the coronary system. The superior vena cava
is the blood vessel that collects the blood
from the head, neck, and upper chest and
brings back to the heart. The inferior vena
cava is the blood vessel that collects the blood
from the lower part of the body including
abdomen, pelvic and lower extremity. The
cardiac vein is the blood vessel that collects
the venous blood in the heart.
Figure 3: The diagram of the systemic circulation
INTRODUCTION OF CIRCULATORY SYSTEM PROCESS
Pulmonary Circulation
Pulmonary circulation (shown in Figure
3) is the circulation of the blood from the
heart the lungs for oxygenation, then back to
the heart again. After the process of the
systemic system, oxygen-depleted blood
from the body enters the right atrium through
the superior and inferior vena cava. The
blood is then pumped into the right ventricle.
The pulmonary circulation is composed
of two main parts: pulmonary arteries and
veins. The pulmonary arteries are filled with
the venous blood, which are the only arterial
vessels in the body used to transport the
deoxygenated blood. The right ventricle in
the heart transports the deoxygenated blood
to the lung capillaries through the pulmonary
arteries. The deoxygenated blood in the lung
capillaries exchanges with gas within the
alveoli to inhale the oxygen and exhale the
carbon dioxide. Through this process, the
deoxygenated blood changes from dark red to
bright red. Then, it will return to the left
atrium through the pulmonary veins,
completing the pulmonary circuit. Pulmonary
veins are the only venous vessels in the body
that contain oxygenated blood. Once entering
the left atrium, the blood flows into the left
ventricle. From the left ventricle, the blood is
pumped into the aorta to begin the systemic
circulation, delivering oxygenated blood to
the body.
Figure 4: The diagram of the pulmonary
circulation
Key terms
Alveoli: Tiny sacs within lungs that allow oxygen
and carbon dioxide to move between the lungs
and bloodstream.
Aorta: The largest artery in the body, supplying
oxygenated blood to the circulatory system.
Arteries: Elastic vessels able to carry blood away
from the heart under high pressure.
Arterioles: A small diameter blood vessel in the
microcirculation that extends and branches out
from an artery and leads to capillaries.
Atrium: The upper chambers of the heart; they
receive blood returning to the heart.
Capillaries: The smallest blood vessel in a
human body; any of the fine branching blood
vessels that form a network between the arterioles
and venules.
Deoxygenated blood: The blood with a low
concentration of oxygen.
Homeostasis: The property of a system in which
variables are regulated so that internal conditions
remain stable and relatively constant.
INTRODUCTION OF CIRCULATORY SYSTEM PROCESS
Inferior vena cava: Along with the superior
vena cava, one of the two largest veins in the
body; it is formed by the joining of the common
iliac veins.
Nourishment: The food or other substances
necessary for growth, health, and good condition.
Oxygenated blood: The blood with a high
concentration of oxygen.
Superior vena cava: Along with the inferior
vena cava, one of the two largest veins in the
body; it is formed by the joining of the
brachiocephalic veins.
Veins: The blood vessels that carry blood back to
the atrium; they are less elastic than arteries.
Ventricles: The lower chambers of the heart;
they receive blood from the atria, which they
pump out into the arteries.
Venules: Macroscopic
capillaries to vein.
vessels
that
link
References:
Jones, and Bartlett. Anatomy and Physiology of
the Cardiovascular System.
"Systemic and Pulmonary Circulation
Boundless Open Textbook." Boundless.
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