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The Circulatory System
The circulatory system is made up of the heart, the blood and the blood vessels (such as veins
and arteries)
Main functions of the circulatory system:
• To transport substances (e.g. food, oxygen) around the body
• To fight disease
• To maintain constant body temperature
Part of Blood
Function
Blood Plasma
To transport food, carbon dioxide and
heat around body
To transport oxygen from lungs to
other parts of body
To fight disease
Red Blood Cells
White Blood
Cells
Platelets
To clot the blood (to form a scab)
Function of the heart: to pump blood around the body
Difference between left and right ventricle:
The left ventricle has a thicker muscular wall than
the right ventricle.
• This is because blood in the left ventricle has to be
pumped all around the body.
• The blood in the right ventricle only has to be
pumped as far as the lungs.
Arteries and Veins
•
Arteries and veins are the blood vessels that
transport blood around the body.
Main arteries in the body:
 Aorta: Carries blood away from the heart to the
rest of the body.
 Pulmonary artery: Carries blood away from the
heart to the lungs, where oxygen passes into the
blood.
Main veins in the body:
• Vena Cava: Carries blood back into the heart
from the body.
• Pulmonary Vein: carries blood back into the
heart from the lungs. This blood now contains
oxygen.
Capillaries
•
•
Capillaries are tiny blood vessels that link arteries
to veins.
Capillaries have very thin walls so substances (e.g.
food, oxygen) can easily pass through them.
•
Blood flowing through arteries is usually rich in
oxygen and glucose.
•
When the blood flows into the capillaries, glucose
and oxygen pass out of the capillaries into the
cells of the body.
•
In the cells glucose and oxygen are converted into
carbon dioxide and energy during respiration.
•
This CO2 and other wastes pass out of the cells and into the capillaries.
•
This blood then flows into the veins. This blood is no longer rich in glucose and oxygen, but
is now rich in CO2 and wastes.
Valves
•
•
•
•
Veins carry blood at low pressure.
To prevent blood flowing backwards, veins
have valves.
Valves can open to allow blood to pass through
but close afterwards to prevent the blood going
backwards.
The heart also has valves to prevent the backflow
of blood.
Main differences between Arteries, Veins and Capillaries

Arteries carry blood Away
from the heart

Veins carry blood into the
heart

Capillaries connect
arteries to veins

Arteries carry blood at
high pressure

Veins carry blood at low
pressure

Capillaries carry blood at
medium pressure

Due to the high blood
pressure, arteries have
thick muscular walls

Due to the low blood
pressure, veins have thin
muscular

Capillaries have very thin
walls (only one cell thick)

Arteries do not have
valves

Veins have valves, to
prevent blood flowing
backwards

Capillaries do not have
valves

Most arteries carry
oxygenated blood, apart
from the pulmonary artery

Most veins carry
deoxygenated blood,
apart from the pulmonary
vein

As blood flows through the
capillaries, oxygen passes
from the capillaries into
the cells in the body
Vein
Artery
Capillary
Exercise and the Heart
The average pulse rate for an adult at rest is 70 beats per minute (b.p.m)
What causes a pulse?
The pumping of blood by the heart causes changes in the blood pressure in the arteries, which
causes a pulse.
Experiment: Investigating the effect of exercise on the
heart rate (pulse)
(1) Find a pulse, for example at the wrist.
(2) Count the number of beats in one minute (bpm) at rest.
(3) Run on the spot for 5 minutes.
(4) Count the bpm again.
(5) Rest for 5 minutes and count the bpm again.
Result: The bpm incareases during exercise, but goes back dowm to
normal again after rest.



The pulse rate increases during exercise. This is because the cells need more oxygen to
release energy during respiration.
After a period of rest, the pulse rate goes back to normal again. This is beacuse the cells
no longer need as much oxygen to release energy.
The fitter a person is, the quicker their pulse rate will return to normal after they have
finished exercising.
Body Temperature



The normal body temperature is 37 °C.
The circulatory helps to maintain this constant body temperature by transporting heat
around the body.
When people are ill however their body temperature often rises, as they are trying the
fight the infection.
Food and the Circulatory System
 Digested food enters the blood by passing into capillaries that surround the small intestine.
 The blood then transports the food to all the cells for respiration.
By the end of this section, you should be able to:
 describe the composition and functions of blood (white blood cells, red blood cells and platelets in
liquid called plasma)
 state the function of the heart, describe its structure identifying the four chambers
 explain the difference between the left and right ventricle
 describe the passage of blood through the heart and lungs via arteries and veins
 identify the pulmonary artery and vein, aorta and vena cava
 distinguish between arteries, veins and capillaries
 demonstrate the effect of exercise and rest on the pulse rate and appreciate that a balance of
each promotes good health
 recall that the average pulse rate id 70 b.p.m, and explain why exercise results in increased pulse
rates
 recall that the normal temperature of the human body is 37 °C and that illness may cause a change
in body temperature
 associate the circulation of the products of digestion around the body with their absorption into
the bloodstream