The Circulatory System

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Circulatory System
The human circulatory system is
composed of three major components:
a.
the heart (pump)
b.
a system of vessels ( arteries, veins,
capillaries, venules and arterioles)
c.
fluid (blood)
Every part of the body is made up of
tiny units of living matter called
cells.
The human body has approximately
50 to 100 trillion cells which
require oxygen and nutrients.
These cells must also eliminate
waste gases and material.
Nutrients and oxygen are carried
to all body cells by the blood.
The blood is pumped by the heart
through various vessels.
• Waste material and carbon
dioxide are also eliminated from
the body by the circulatory
system.
As the blood is transported through
the body, most of it goes to the muscle
cells which remove food materials
and oxygen.
Large amounts also go to the brain
and smaller amounts to other parts
which also require food and oxygen.
There are two basic
circulatory patterns in
humans:
Systemic circulation
Pulmonary circulation
Systemic circulation carries
oxygenated blood from the left
ventricle to all parts of the body.
Blood from systemic circulation
returns in a deoxygenated form to
the right atrium.
•Pulmonary circulation takes
deoxygenated blood from
the right ventricle to the
lungs.
•The blood becomes
oxygenated and returns to
the left atrium.
The heart must beat constantly to
perform these functions.
Approximately 70 beats per
minute if the body is relaxed and
more beats when the body is
active or under stress.
The Heart:
The heart is a hollow muscular
pear-shaped organ located in the middle
of the chest beneath the sternum and
between the lungs.
• The heart pumps blood through
the body, supplying cells with
oxygen and nutrients and
removing carbon dioxide and
nitrogen containing waste.
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B
The heart is held in place
principally by its attachment
to the great arteries and
veins, and by its confinement
in the pericardium.
(pericardial sac)
The pericardium is a double walled
sac with one layer enveloping the
heart and the other attached to the
breastbone, the diaphragm, and the
membranes of the thorax.
The pericardium protects the heart
form friction and trauma.
The adult human heart is approximately the
size of a fist and about the shape of your hand.
In an average adult, it is about fifteen
centimeters long and seven centimeters across
at its broadest part, and it weighs less than onehalf a kilogram. (APPROXIMATELY .43 % OF
THE BODY MASS)
The outside layer of the heart is the epicardium
(ectocardium). This is a relatively thin layer but it is
extremely important.
The vascular system of the heart is located in this
layer.
Open heart surgery and angioplasty involves blood
vessels found in this layer.
Unlike other organs the heart is unable
to slow down when it does not receive
enough nourishment from the blood.
It must continue to beat, pumping blood, no
matter the demands placed upon it. This
may lead to serious heart problems,
including a potentially deadly heart attack.
Good coronary circulation is very important. Chest
pain (angina) will occur when the heart is not
receiving enough oxygen. This could possibly be a
result of a blocked artery, inhibiting the flow of
nutrient and oxygen rich blood to the heart. A
complete blockage results in a heart attack.
( coronary occulsion )
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The middle layer of the heart is the thickest
layer of the heart and consists mostly of
cardiac muscle and small amounts of nerve
tissue.
This layer is called the myocardium.
Cardiac muscles are myogenic (self
excitable) as they can generate their own
electrical impulses.
The inner layer of the heart is the
endocardium. In this layer the heart
valves are located.
The endocardium lines the atria ( upper
chambers) and the ventricles ( lower
chambers) in the interior of the heart.
The atria have thin walls and function as
collection chambers for blood returning
from the body.
The atria or upper chambers of the heart
have thin walls and function as
collection chambers for blood returning
from the body.
The ventricles or lower chambers have
thick, powerful walls that pump blood to
the lungs and organs.
Atrioventricular valves:
valves between each atrium and
ventricle
AV valves keep blood in the
ventricles from flowing
backwards into the atria.
The right AV valve is the
tricuspid
The left Av valve is the bicuspid
or mitrial.
Semilunar valves: valves between the
veins entering the right and left atria
and the arties leaving the right and
left ventricle.
Heart cycle:
Sequence of events during each heart
beat, lasts about 0.8 seconds.
Systole, heart muscles (ventricle)
contract and the chambers pump blood
in the aorta and the pulmonary artery.
Diastole, the ventricles relax and fill
with blood.
• Systole is the upper number in a blood
pressure reading .
• Systole readings are usually (young
adults)
• 100 + age +_ 10%.
• Diastole is the lower number in a blood
pressure reading.
• Desirable reading are in the range of 50
to 80.
Stronger hearts have a lower pulse
rate and weaker hearts have a
higher pulse rate.
Stroke volume = the amount of
blood pumped from the ventricles
with each contraction of the
ventricles
• Cardiac output is the volume (litre)
of blood that the heart can pump
from the ventricles in a given
amount of time ( minute).
• C.O = stroke volume * pulse rate
Cardiac Output
• Calculate the the cardiac output for
a student with a pulse rate of 60
beats / min and a stroke volume of
70 ml/ beat.
Stroke Volume
• What is the stroke volume for
a person with a pulse rate of 60
beats/min and who requires a
cardiac output of 5.25 L/min?
Pulse Rate
• A student requires a cardiac output
of 5.8 L/Min and has a stroke
volume of 60 ml/ beat. What is the
pulse rate for the student?
Cardiac Output
• Calculate the the cardiac
output for a student with a
pulse rate of 72 beats / min
and a stroke volume of 60 ml/
beat.
Stroke Volume
• What is the stroke volume for
a person with a pulse rate of 70
beats/min and who requires a
cardiac output of 5.50 L/min?
Pulse Rate
• A student requires a cardiac
output of 6.2 L/Min and has a
stroke volume of 70 ml/ beat.
What is the pulse rate for the
student?
Types of blood vessels
• Arteries( arterioles)
• Veins ( venules)
• Capillaries
Arteries and veins contain 3 layers of
tissue.
1.
Outer layer (epithelial layer)
2.
Middle layer - smooth muscle and
elastic fibers,
3.
Inner layer - endothelium
The internal opening in the blood
vessel through which blood passes is
called the lumen.
• Vasoconstriction = smaller lumen
size
• Vasodilation = larger lumen size
Arteries and veins
• Carry blood from
the heart
• Deep in the body
tissue
• Carry oxygenated
blood
• Carry blood to the
heart
• Close to the surface
• Carry deoxygenated
blood
• Arteries lack
valves
• Veins contain
valves to prevent
the back flow of
blood on its way
to the heart
• Arteries have small
•
veins
have
large
lumens
lumens
• Veins have oval
• Arteries have
spherical lumens lumens
• Veins are not under
• Arteries are under
pressure
pressure
• Arteries have
thick layers of
muscle and
elastic fibers
• Veins have thin
layers of
muscle and
elastic fibers
Capillaries
• Unlike the arteries and veins,
capillaries are very thin and fragile.
• The capillaries are actually only one
epithelial cell thick.
• Blood cells pass through capillaries in
single file.
• Despite the small size capillaries are
essential to survival.
• The exchange of oxygen and carbon
dioxide between the body cells and
the circulatory system takes place
through the thin capillary walls.
Capillaries connect veins to arteries. It
is here that any and all exchanges take
place between the blood and the body
cells.
Capillaries are one cell thick.
• The red blood cells inside the
capillary release their oxygen which
passes through the wall and into the
surrounding tissue.
• The tissue releases its waste
products, like carbon dioxide, which
passes through the wall and into the
blood vessel.
The arteries pass their oxygen-rich
blood to the capillaries which allow
the exchange of gases within the
tissue.
• The capillaries then pass their wasterich blood to the veins for transport
back to the heart.
• Capillaries are also involved in the
body's release of excess heat.
•
The major form of heart disease in
Western countries is atherosclerosis.
In this condition fatty deposits called
plaque, composed of cholesterol and
fats, build up on the inner wall of the
coronary arteries.
Gradual narrowing of the arteries
throughout life restricts the blood
flow to the heart muscles.
Symptoms of this restricted blood
flow can include shortness of
breath, especially during exercise,
and a tightening pain in the chest
called angina pectoris
The plaque may become large enough to completely
obstruct the coronary artery, causing a sudden decrease in
oxygen supply to the heart. Obstruction, also called
occlusion, can occur when part of the plaque breaks away
and lodges farther along in the artery, a process called
thrombosis. These events are the major causes of heart
attack, or myocardial infarction, which is often fatal
Heart Beat
• The heart has two nerve masses that
initiate muscular contraction:
• 1. the SA or sinoatrial node,
• 2. the AV or atrioventricular node.
The sinoatrial node (S-A
Node or the pacemaker)
which controls the rate of
contraction of the heart is
located in the right muscle
of the atrium wall.
• More specifically the SA node
(sinoatrial node) is located in the
wall of the right atrium, near the
junction of the atrium and the
superior vena cava.
The atrio-ventricular node (AV
node) is also located in the
myocardium but lower in the
atrial wall.
•
The AV node
(atrioventricular node) is
located near the bottom
centre of the right atrium
slightly above the right
ventricle.
• The nerve cells in the SA node
are connected to the medulla
oblongata by nerves.
• The medulla oblongata is the
section of the nervous system
which controls body functions
which occur automatically.
• Impulses from this region of the
brain (Medulla Oblongata) end up
in the SA node.
• The SA node in turn regulates the
contraction of the cardiac muscle
cells in the right and left atrium.
• Nerve fibers extend through the R.
and L. atrium causing
simultaneous contractions of the
upper chambers.
• The SA node is commonly refered
to as the pacemaker of the heart.
• When the SA node initiates a contraction, fibers
rapidly conduct the impulse to a large bundle of
nerve fibers called the AV node.
• Here the impulses move quickly through Purkinje
fibers (Bundle of His) via the septum that divides
the two ventricles in the ventricles themselves.
• From here, fibers run in two pathways one running
to the right ventricle, and one running to the left
toward the posterior apex of the heart.
• The result is that while the atria are
contracting, the impulse is carried quickly
to the ventricles.
• With the AV node holding up the impulse
just enough to let the atria finish their
contraction before the ventricles begin to
contract, blood can fill the ventricles.
• Since nerve fibers have carried the
electrochhemical impulse to the
(atrioventricular node) , the next impulse
generated by the heart proceeds into the
ventricles where the blood leaves
through the pulmonary arteries and the
aorta.
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