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Cardiovascular
System
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Blood and Blood Vessels
The Heart
Blood and Blood
Vessels
Introduction
Good Cardiovascular
health is important in maintaining overall health and wellness.
Cardiovascular Health is a new section, which will teach you how
your heart and cardiovascular system work when healthy, and what
happens when diseased. We will also explore disease prevention,
therapeutic drug treatment, minimally invasive surgical procedures
and open surgical procedures for treating diseases, which affect
the heart and cardiovascular system.
The main role
of the cardiovascular system in the body is to transport oxygen
to all tissues in the body and for removing, from these same tissues,
metabolic waste products. The system itself consists of the blood,
the medium for exchanging oxygen, nutrients and waste products throughout
the body, the blood vessels, the pipes through which the blood flows
and the heart, the pump which forces blood to flow through the blood
vessels. First, Lets take a closer look at the components of blood.
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Components
of Blood
Health conscious
individuals should be especially concerned with maintaining a healthy
cardiovascular system. While the heart, which is a powerful automatic
pump, is the cardiovascular component we think of most often, the
blood and the blood vessels are also vital to maintaining good health.
The average
adult has between 5 to 6 liters of blood or blood volume. The blood
carries oxygen and essential nutrients to all of the living cells
in the body, and also carries waste products to systems that eliminate
them. Most of the blood is made up of a watery, protein-laden fluid
called plasma. A little less than half of this blood volume is composed
of red and white blood cells, and other solid elements called platelets.
Platelets are
responsible for coagulation of blood at the point of an injury to
a blood vessel.
Without platelets,
our blood would not be able to clot and hemorrhaging or uncontrolled
bleeding would result. Hemophilia is a genetic condition, which
results in individuals with no ability to clot. Also called bleeders,
these individuals must periodically administer a clotting factor
to their blood to prevent the constant bleeding, which occurs.
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How
Blood Clots
Let’s examine
how platelets work to form clots. Here's a cut section of a small
artery. The traffic going by includes red blood cells carrying oxygen;
platelets, which come from white blood cell fragments; and clotting
factors, which help the blood to clot. When a blood vessel becomes
damaged, as shown here, the blood cells and plasma begin oozing
out into the surrounding tissue. This begins the clotting process.
Platelets immediately begin to adhere to the cut edges of the artery;
they release chemicals to attract even more platelets. Eventually
a platelet plug is formed, and the external bleeding stops.
Inside, the
clotting factors take a much more active role by creating a cascade
of clotting activity. The clotting factors cause strands of blood-borne
material, called fibrin, to stick together and seal the inside of
the wound. Eventually, the cut blood vessel heals, and the blood
clot dissolves after several days.
While platelets
play an important role in clotting, red blood cells carry on the
important job of carrying oxygen and other nutrients to all the
tissues of the body and carrying waste products to the organs, which
remove them from the body.
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How
Red Blood Cells Carry Oxygen
Red blood cells
are the oxygen carriers. As they travel away from the heart, they
traverse smaller and smaller arteries, finally arriving at the collections
of microscopic blood vessels known as capillaries. Here, they exchange
nutrients and oxygen for cellular waste products. The waste products
are eventually eliminated from the blood stream through the urinary
and respiratory systems.
The exchange
of oxygen and nutrients between the red blood cells and the surrounding
tissues occurs through a process called diffusion. In diffusion,
when capillaries contain a high concentration of oxygen and nutrients,
while the surrounding tissues contain a lower concentration, Oxygen
and nutrients leave the capillaries and enter the tissues.
Conversely,
when body tissues contain high concentrations of carbon dioxide
and metabolic waste, while the capillaries contain a lower concentration,
the waste products diffuse from the tissues into the capillaries
and from there are carried by the venous system back toward the
heart.
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Blood
Pressure
The red blood
cells transport oxygen and waste products by flowing through the
blood vessels. What causes blood to flow through the vessels is
blood pressure. Just as water flows through pipes from areas of
greater pressure to lesser, so too the blood flows through the body
from areas of higher pressure to areas of lower pressure. Blood
pressure is measured both as the heart contracts, which is called
systole, and as it relaxes, which is called diastole. A systolic
blood pressure of 120 millimeters of mercury is considered right
in the middle of the range of normal blood pressures, as is a diastolic
pressure of eighty. In common terms, this normal measurement would
be stated as "120 over 80".
Normal blood
pressure is important for proper blood flow to the body's organs
and tissues. Each heartbeat forces blood to the rest of the body.
The force of the blood on the walls of the arteries is called blood
pressure. Blood pressure moves from high pressure near the heart
to low pressure away from the heart. Blood pressure depends on many
factors, including the amount of blood pumped by the heart. The
diameter of the arteries through which blood is pumped is also an
important factor. Generally, blood pressure is higher when more
blood is pumped by the heart, and the diameter of an artery is narrow.
Systolic pressure
is measured when the heart ventricles contract. Diastolic pressure
is measured when the heart ventricles relax. Stressful situations
can result in a temporary increase in blood pressure. If an individual
were to have a consistent blood pressure reading of 140 over 90,
he would be evaluated for having high blood pressure. If left untreated,
high blood pressure can damage important organs, such as the brain
and kidneys as well as lead to a stroke.
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The Heart
The
Heart (The Pump)
The pressure
and flow of the blood arise from the beating heart muscle, which
is the pump of the cardiovascular system. To understand how the
heart works lets take a brief look at the anatomy of the beating
heart.
The heart is
a four-chambered organ with four main vessels, which either bring
blood to or carry blood away from the heart. The four chambers of
the heart are: the right atrium, the right ventricle, the left atrium,
and the left ventricle.
The great vessels
that you see include the superior and inferior vena cava, which
bring blood from the body to the right atrium. The pulmonary artery,
which transports blood from the right ventricle to the lungs, and
the aorta, the body's largest artery, which transports oxygen-rich
blood from the left ventricle to the rest of the body.
If you look
carefully, you can see a series of one-way valves that keep the
blood flowing in one direction. The
blood first enters the heart into the right atrium. A contraction
of the right atrium then forces blood through the tricuspid valve
and into the right ventricle. When the right ventricle contracts,
the muscular force pushes blood through the pulmonary semilunar
valve into the pulmonary artery.
The
blood then travels to the lungs, where it receives oxygen. Next,
it drains out of the lungs via the pulmonary veins, and travels
to the left atrium. From the left atrium, the blood is forced through
the bicuspid valve into the critically important left ventricle.
The left ventricle is the major muscular pump that sends the blood
out to the body systems. When the left ventricle contracts, it forces
the blood through the aortic semilunar valves and into the aorta.
From here, the aorta and its branches carry blood to all the tissues
of the body.
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