THE
CIRCULATORY SYSTEM
Arteries Veins Artery-Vein Comparison Capillaries Summary Of
Blood Vessels The Heart
The Blood Flow Through The Heart The Double Circulation System Blood For The Heart
To Use
Heartbeat Control Stages Of Heartbeat Sounds Of The Heart
Blood
Pressure Lifestyle
Effects On Heart
Click here to view a
general animation of the circulatory system
Click here to view an
animation of the formation of the heart in an embryo
Functions of the Circulatory System
- To carry digested food from the small intestine
to all areas in the body which need it.
- To carry oxygen from the lungs to the rest of the
body.
- To aid in the disposal of all wastes from the
body.
- To distribute heat.
- To fight diseases by using white blood cells to
fight off infection.
Arteries and Veins have many differences:
1. Carry blood away from the heart always.
2. Have thick muscular walls
3. Have a pulse
4. Deep under the skin
5. Have no valves
6. Arteries branch at their ends, into tiny arterioles those then join
capillaries.
1. Carry blood to the heart.
2. Have thin walls
3. Do not have a pulse
4. Near surface of the skin
5. Have valves to stop back-flow of blood.
6. Veins branch at their beginnings into tiny venules
which join capillaries.
Veins have valves which stop the blood from flowing
backward. Compared to the arteries, pressure in the veins is very low. The
blood is being pushed through the arteries as the heart squeezes the blood out.
This is not true for the veins. Blood is pushed through the veins when body
muscles contract and squeeze the veins. In this way the blood moves.
The contraction/relaxation cycles of
skeletal muscles squeeze the veins forcing the contained blood towards the
heart.
Artery-Vein Comparison
Arteries Veins
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Transport blood away from the heart; |
Transport blood towards the heart; |
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Carry Oxygenated Blood |
Carry De-oxygenated Blood |
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Have relatively narrow lumens (see diagram above); |
Have relatively wide lumens (see diagram above); |
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Have relatively more muscle/elastic tissue; |
Have relatively less muscle/elastic tissue; |
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Transports blood under higher pressure (than veins); |
Transports blood under lower pressure (than arteries); |
|
Do not
have valves (except for the semi-lunar valves of the pulmonary
artery and the aorta). |
Have
valves throughout the main veins of the body. These are to
prevent blood flowing in the wrong direction, as this could (in theory)
return waste materials to the tissues. |
Capillaries
Capillaries are small blood vessels acting as
veins and arteries. They surround the body cells at the ends of the arteries
and at the beginning of the veins. The walls of capillaries are only one cell
thick so substances (Food or cells) can easily get through them and into the
blood or out. If all the capillaries of the body were set end to end they would
be 100,000 km long!
SUMMARY OF BLOOD VESSELS
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Arteries
The
Heart
The heart is
located slightly to the left of the centre of your chest between the 2 lungs.
It is made of cardiac muscle and is surrounded by a double membrane called the
pericardium. There is fluid between these 2 membranes called pericardial fluid.
This fluid helps to reduce friction when the heart beats. The heart is about
the size of a clenched fist.
The
human heart is primarily a shell. There are four cavities, or open spaces,
inside the heart that fill with blood. Two of these cavities are called atria.
The other two are called ventricles. The two atria form the curved top of the
heart. The ventricles meet at the bottom of the heart to form a pointed base
which points toward the left side of your chest. The left ventricle contracts
most forcefully, so you can best feel your heart pumping on the left side of
your chest.
The
left side of the heart houses one atrium and one ventricle. The right side of
the heart houses the others. A wall, called the septum, separates the right and
left sides of the heart. A valve connects each atrium to the ventricle below
it. The bicuspid valve connects the left atrium with the left ventricle. The
tricuspid valve connects the right atrium with the right ventricle. The
semilunar valves allow the blood to flow out of the heart into the 2 main
arteries (aorta and pulmonary artery). They prevent blood from returning to the
heart.
The
top of the heart connects to a few large blood
vessels. The largest of these is the aorta, or main artery, which
carries nutrient-rich blood away from the heart. Another important vessel is
the pulmonary artery which connects the heart with the lungs as part of the pulmonary
circulation system. The two largest veins that carry blood into the
heart are the superior vena cava and the inferior vena cava. They are called
"vena cava" because they are the "heart's veins." The
superior is located near the top of the heart. The inferior is located beneath
the superior.
The
heart's structure makes it an efficient, never-ceasing pump. From the moment of
development through the moment of death, the heart pumps. The heart, therefore,
has to be strong. The average heart's muscle, called cardiac muscle, contracts
and relaxes about 70 to 80 times per minute without you ever having to think
about it. As the cardiac muscle contracts it pushes blood through the chambers
and into the vessels. Nerves connected to the heart regulate the speed with
which the muscle contracts. When you run, your heart pumps more quickly. When
you sleep, your heart pumps more slowly.
Considering
how much work it has to do, the heart is surprisingly small. The average adult
heart is about the size of a clenched fist and weighs about 11 ounces (310
grams). Located in the middle of the chest behind the breastbone, between the
lungs, the heart rests in a moistened chamber called the pericardial cavity
which is surrounded by the ribcage. The diaphragm, a tough layer of muscle,
lies below. As a result, the heart is well protected.
THE FLOW
OF BLOOD THROUGH THE HEART
Day and night, the muscles of your heart contract
and relax to pump blood throughout your body. When blood returns to the heart,
it follows a complicated pathway. If you were in the bloodstream, you would
follow the steps below one by one.
|
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SUMMARY
OF BLOOD FLOW:
FROM
BODY:
1.
Superior and inferior
vena cava (deoxygenated)
2.
Right atrium
3.
Tricuspid valve
4.
Right ventricle
5.
Semilunar valve
6.
Pulmonary artery
7.
Lungs
8.
Pulmonary veins (oxygenated)
9.
Left atrium
10.
Bicuspid valve
11.
Left ventricle
12.
Semilunar valve
13.
Aorta
TO BODY and then back to the superior and inferior
vena cava (Step #1)
Click here to see a
general animation of blood flow
THE DOUBLE CIRCULATION SYSTEM
The heart has a double circulation system. The pulmonary circuit pumps blood to the lungs and the systemic circuit pumps blood to the body systems (i.e. The head limbs, and trunk).
This system separates the oxygenated and the deoxygenated blood. (See diagram below)
The right ventricle pumps blood through the shorter pulmonary circuit while the left ventricle pumps blood through the longer systemic circuit. As a result, the left ventricle’s walls are thicker and stronger.
The Systemic System can be
divided into THREE SUBSYSTEMS
A.
CORONARY CIRCULATION - SUPPLIES BLOOD TO THE HEART.
B.
RENAL CIRCULATION - SUPPLIES BLOOD TO THE KIDNEYS. Nearly
one-forth of the blood that is pump into the Aorta by the Left Ventricle flows
to the Kidneys. The Kidneys Filter Waste From the Blood.
C.
HEPATIC PORTAL CIRCULATION - Nutrients are picked up by
capillaries in the small intestines and are transported to the Liver.
Excess nutrients are stored in the Live for future needs. The Liver
receives oxygenated blood from a large Artery that branches of the Aorta.
The
heart also needs a supply of blood for its nourishment. It does not use the
blood it pumps for itself. The blood flowing through the heart does not directly
serve the heart. Like all other organs the heart muscle has its own blood
circuit. The heart gets blood from the
coronary arteries that emerge directly from the aorta. Two coronary arteries
arise from the aorta just beyond its semilunar valve. The right coronary artery
mostly serves the right atrium and right ventricle. The left coronary artery is
much larger and supplies the left atrium and left ventricle. The blood then goes through arterioles into
capillaries and then to the heart’s cells. Venules then carry the blood to the
coronary veins and back to the right atrium.
HEARTBEAT
CONTROL
The
pumping action of the heart is controlled by the pacemaker (also known
as the sino-atrial node (SA). It is in the wall of the right
atrium. The pacemaker receives messages from the brain. Two nerves from the
medulla oblongata connect to it influencing its rate of contraction. One nerve
quickly accelerates the heart rate and the other can quickly reduces it back to
resting rate. These messages are transmitted as electrical
impulses that cause the atria (both left and right) to contract. This
contraction is called atrial systole. Contraction
of the atria sends blood to the ventricles.
The electrical impulse
then enters the ventricles at the atrio-ventricular node and travels through
the septum to the ventricles at the atrio-ventricular node (AV).
The ventricles contract and force the blood towards the openings of the
arteries, pulmonary artery and aorta. This is called ventricular systole.
The rate of heartbeat is very important. The average healthy
person will have a heart rate of about 70-80 beats per minute. Brain impulses
and hormones can change this rate. Also, exercise, temperature, emotions, and
shock will increase the heart rate. Relaxation and sleep decrease the rate.
STAGES OF THE HEARTBEAT
A heartbeat is a
two-part pumping action that takes about a second. As blood collects in the
upper chambers (the right and left atria), the heart's natural pacemaker (the
SA node) sends out an electrical signal that causes the atria to contract. This
contraction pushes blood through the tricuspid and bicuspid valves into the
resting lower chambers (the right and left ventricles). This part of the
two-part pumping phase (the longer of the two) is called atrial systole.
The second part of
the pumping phase begins when the ventricles are full of blood. The electrical
signals from the SA node travel along a pathway of cells to the ventricles,
causing them to contract. This is called ventricular systole. As the
tricuspid and bicuspid valves shut tight to prevent a back flow of blood, the
semilunar valves are pushed open. While blood is pushed from the right
ventricle into the lungs to pick up oxygen, oxygen-rich blood flows from the
left ventricle to the heart and other parts of the body.
After blood moves
into the pulmonary artery and the aorta, the ventricles relax, and the
pulmonary and aortic valves close. The lower pressure in the ventricles causes
the tricuspid and bicuspid valves to open, and the cycle begins again. This
series of contractions is repeated over and over again, increasing during times
of exertion and decreasing while you are at rest.
When the atria are
contracting the ventricles are relaxing. This is called ventricular diastole.
Likewise, when the ventricles are contracting the atria are relaxing. This is
called atrial diastole.
The sounds of the heart are
caused by the closing of the valves.
1.
The “lub” sound- quieter, longer, lower
pitched- caused by the bicuspid and tricuspid valves closing.
2.
The
“dub” sound- louder, shorter, higher pitched- caused by the semi lunar
valves closing.
3. A heart murmur is an abnormal sound of the heart. It is usually an indication of damaged valves.
Blood Pressure
Blood
pressure is the
blood pressing against the blood vessel walls. It is measured by a sphygmomanometer.
The pressure varies along the circuit –
decreasing from artery to arteriole to capillary to venule to vein.
Pressure is highest at the start of the
artery and lowest at the entrance to the atrium.
Blood pressure is much
higher in the aorta than in the pulmonary artery.
The measures
of a person’s blood pressure it taken at a large artery in the upper arm. It is
the pressure need to stop blood flow in this artery and is measured at diastole
and systole. Standard healthy readings are 80 mm Hg diastolic, 120 mm Hg
systolic.
People with a diastolic number at or above
95 have hypertension (high blood pressure). It is usually caused by blockages
in the arteries.
Click here to view an
animation about blood pressure
Effect of Smoking
1. Hardening of the arteries.
2. Increased risk of heart disease.
3. Raised blood pressure.
- Increased risk of
stroke.
Click here to see an
animation of smoking’s effects on arteries
Click here to see an
animation about strokes
Effect of Diet
- High Blood Pressure:
excessive salt.
- Clogged arteries from
fatty foods.
- Low Blood Pressure:
lack of protein.
Click here to see an
animation of clogged arteries
Effect of Exercise
1. Lower resting heart rate –
more efficient heart.
2. Dilated arteries caused by aerobic exercise –
improved blood flow to all the organs and less risk of heart disease.