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The Circulatory System
Anatomy
The Circulatory System is the major
transportation system in the body.
It includes the heart, blood vessels
(capillaries, arteries ) and the blood.
Important in the exchange
between cells of tissues,
organs and systems.
The Heart
• This is the motor
(pump) that makes
the system work.
• Organ made up of muscle tissue.
• Size of a fist
• Located between the
two lungs, on the left side
and is protected by the
rib cage.
The Heart continued
• In adults, it beats between 65 and
85 times per minute.
• Over a lifetime it will beat about
2,500,000,000 times, twenty-four
seven, never stopping, just slowing
down.
• Movement of blood relies on the
heart because it propels blood with
sufficient pressure
The Heart Chambers (4)
The heart has four chambers
Right and Left Atrium in the upper part of the heart
where blood enters the heart.
Right and Left ventricles in the lower part contract to
send blood out of the heart. Bigger then atria!
Left atrium
Right atrium
Right ventricle
Left ventricle
(very muscular)
Functions of the Heart chambers
1. The right atrium: receives
deoxygenated blood from the entire
body.
2.The right ventricle: pushes blood to the
lungs so it is thinner then the left
3. The left atrium: receives oxygenated
blood from the lungs.
4. The left ventricle: wall thicker then right
ventricle because pushes blood to the
entire body. (larger chamber)
The heart also has valves which
control blood flow from one
chamber to the other and
prevent back flow.
Each atrium opens into the ventricle
located just below it through these
valves.
Blood Vessels of the Heart
• Blood vessels are the channels that blood
uses to circulate through the body
Two vessels leave the ventricles:
• Pulmonary trunk which divides into: Right
and left pulmonary arteries : brings
deoxygenated blood from the heart (right
ventricle) to the lungs
• Aorta brings oxygenated blood from the heart
(left ventricle) to the entire body.
• These are the larger vessels of the heart.
Two other blood vessels empty blood into
the atria of the heart
• Right and left pulmonary veins bring
oxygenated blood from the lungs to the
heart (left atrium)
• Superior and inferior vena cava bring
deoxygenated blood from the body (organs)
back to the heart (right atrium);
Other blood vessels are called coronary
vessels which supply blood to the heart.
They provide the heart with nutrients and
oxygen it needs to rid it of waste.
Main blood vessels
Aorta
(blood to body)
Superior vena cava
(blood from the
upper body)
Pulmonary
artery
(blood to the
lungs)
ri
Inferior vena cava
(blood from the
lower body)
Pulmonary
vein
(blood from
the lungs)
Septum
Blood vessels of the body:
• Their role is to distribute blood to
different parts of the body
• Arteries and arterioles(small
arteries): carry blood AWAY
from the heart to the organs of
the body.
• Have thick, muscular, elastic
walls to withstand high pressure.
• Starts with the aorta(largest artery)
which begins at the left ventricle.
• Divide into small arteries and
arterioles until they reach capillary
network.
• Capillaries: small branches at the
ends of arteries linking them to veins.
• They are permeable and have thin
walls of a single layer of epithelial
cells so gas exchange can happen
through diffusion between blood and
cells.
• Veins and venules(small veins):
•
•
•
•
•
carry blood from the organs to the heart.
Thinner walls and less elastic then
arteries because there is less pressure.
To help blood flow from the extremities
such as the legs, veins have one way
valves that prevent back flow.
Blood flows in the same direction from
arteries to arterioles, to the capillaries, to
the venules and veins.
Leg muscle contractions help pump blood
back to heart.
Capillaries turn into venules, enlarging
into veins and returning to the left atrium
from the large Vena Cava.
The Circulatory System
Physiology: How it works!!
• Blood vessels of body make up a network
that carry blood to all parts of the body.
• Two components form a double pump
– Pulmonary circulation = lungs
– Systemic circulation = all other organs
Function of the Heart in Circulation:
Contractions of the heart muscle causes blood
to circulate through the entire body.
Right and left sides of heart pump blood into
separate circuits at the same time.
For blood to enter the two atria, the muscles must
be at rest (muscles must be relaxed)
For blood to exit the atria, the two atria must
contract at the same time forcing blood to empty
into ventricles
Then the two ventricles contract at the same time
to push blood into arteries and towards body
organs or lungs
Pulmonary Circulation
• Carries blood that contains carbon
dioxide(deoxygenated blood) from the heart
to the lungs, where it gets rid of the waste
and is resupplied with oxygen and returned
to the heart.
Carbon dioxide diffuses out of the blood and
into the alveoli
Oxygen diffuses into the blood (gas
exchange)
When a heart beats, it
contracts the atria first and
then the ventricles.
1. Deoxygenated blood from the
body returns under pressure
via the Vena Cava into the
relaxed right atrium.
2. Contraction of right atrium
forces blood into the right
ventricle.
*
3. The contractions of the
right ventricles forces
blood through the Pulmonary
artery (only aretery carrying
deoxygenated blood) into
both lungs.
Blood travels through smaller
arteries then arterioles and
finally the capillaries in single file.
The capillaries surround the alveoli and allow the
exchange of gases.
 Oxygenated blood leaves the
lungs, first through the
venules, then veins returning
to the left atrium via the
pulmonary vein.

*
Thus during pulmonary circulation the
hearts contractions pump the blood
from:
• Right Atrium>Right ventricle 
pulmonary arteries (lead to the two
lungs) smaller arteries  arterioles
 pulmonary capillaries (gas
exchange/diffusion)  venules 
larger venules  pulmonary veins 
left atrium of heart.
Coloring of Veins and Arteries
• Pulmonary
• Arteries are blue
because blood is
deoxygenated and
the arteries are
sending the blood
to the lungs and
veins going back
to heart are red
because blood
has become
oxygenated
• Systemic
• Arteries leaving
heart are red, and
veins returning to
right ventricle are
blue
Systemic Circulation
• Carries oxygenated blood to
the cells from the heart to
supply them with oxygen and
nutrients and collects their
waste such as carbon dioxide
and water and brings them
back to the heart,
• Distance traveled by blood is
greater than in pulmonary
circulation.
• Gas exchange – O2 out of blood,
CO2 into blood, occurs in the cells
The Contractions of the
left atrium push blood
toward starting point of
systemic circulation into
the left ventricle.
4. Contraction of the left ventricle
forces the blood through the Aorta
and then throughout the body.
 Arteries branch off the aorta and
supply various organs and tissues
with oxygenated blood.

*
During Systemic Circulation the heart
contractions pump blood from:
Left ventricle  aorta  smaller
arteries  arterioles  capillaries
capillary networks surrounding
cells(exchanges/diffusion)  venules
 veins  inferior and superior vena
cava  right atrium of the heart.
• Right atrium contracts, pushing
blood in it’s chambers back to the
starting point of pulmonary
circulation (right ventricle)
The walls of the left ventricle are thicker (more
muscular) than those of the right ventricle
because the left ventricle has to push blood
into the entire body, whereas the right ventricle
only has to push blood as far as the lungs.
BLOOD ALWAYS LEAVES THE VENTRICLES,
GOES THROUGH THE BODY AND COMES
BACK INTO THE ATRIUMS!!
Blood Pressure
• Measures force with which blood pushes
against the walls of the arteries;
• It is measured in mm of mercury (mm Hg )
Blood Pressure has two types, Systolic and
Diastolic.
• Systolic pressure is when the
ventricular pressure is at its maximum.
During the contractions of the
ventricles, the arteries must expand
under pressure of the blood that is
being pumped out.
• Diastolic pressure is when the pressure
is at its lowest when the heart is not
contracting (at rest).
• Blood pressure is represented by the
systolic pressure(higher number)/
diastolic pressure(lower pressure);
• Normal blood pressure is 113 mm Hg/
65 mm Hg for adolescents.
Incompressibility of Blood
• Blood like water is an incompressible fluid,
• Liquid will move when pressure is applied
to it.
• Blood is an incompressible fluid that exerts
pressure on the walls of the arteries in
which it circulates. This is why it is called
blood pressure.
Heart rate
• What can affect your heart rate?
• Activity
• Emotions
• CO – slows your heart
• Drugs
Heart Health
• A healthy heart needs:
movie
Heart Health (movie)
• If blood pressure is to high, you have
Hypertension, to low, Hypotension.
• Hypertension is usually caused by a narrowing of
blood vessels due to cholesterol build up.
How to avoid high blood pressure:
Healthy diet, less salt
Exercise to lower stress
Decrease tobacco and
Alcohol consumption
Summary movie