Topic 6: Human health & physiology
6.2 The transport system
Draw in the route of blood through the heart
 The two sides of the heart (left and right) are separated by the septum
 Blood in the right side is deoxygenated (oxygen-poor)
 Blood in the left side is oxygenated (oxygen-rich)
 The right side of the heart is less muscular as the blood is pumped to the
nearby lungs
 Blood is under less pressure
 The left side of the heart is more muscular as the blood is pumped to the
rest of the body
 Blood is under higher pressure
Direction of blood
flow
To the heart
From the heart
Vessels
Veins
Arteries
Pressure
Low
High
Low (exception is the
pulmonary vein)
High (exception is the
pulmonary artery)
Oxygen content
Blood is pumped
around the body by the
heart.
It takes about 30
seconds for blood to go
once around the body.
Starting with the left
side of the heart, what
route does the blood
follow to complete one
circuit of the body?
The left side of
the heart pumps
oxygen-rich blood
to the rest of the body.
This blood supplies
the body’s cells with
oxygen.
What gas does the
blood then pick up from
the body’s cells and
where does the blood go
next?
body’s
cells
Blood picks up
carbon dioxide from
the body’s cells.
This oxygen-poor
blood then travels
back to the right side
of the heart.
The oxygen-poor
blood needs to lose
the carbon dioxide and
pick up more oxygen.
body’s
cells
Next, the right side
of the heart pumps
oxygen-poor blood
to the lungs.
lungs
In the lungs the blood
gets rid of the waste
carbon dioxide and
collects more oxygen.
body’s
cells
The oxygen-rich
blood then returns
to the left side of the
heart.
lungs
This completes the
blood’s journey
around the body.
body’s
cells
During one complete
circuit of the body,
blood passes through
the heart twice.
lungs
The heart has two
jobs to do and so the
circulatory system
involves a double
circulation.
body’s
cells
The heart is full of blood but also needs its own blood supply so
that the muscle can keep pumping.
muscle
tissue
blood vessels
supply blood
to muscle tissue
The blood vessels on the outside of the heart carry oxygen-rich blood
to the heart muscle cells.
Oxygen-poor blood is then carried away from these cells by outer blood
vessels and back into the heart.
 All the parts of the heart on either
side, work together in a repeated
sequence.
 The two atria contract and relax;
then the two ventricles contract and
relax.
 This is how blood moves through
the heart and is pumped to the lungs
and the body.
 One complete sequence of
contraction and relaxation is called a
heartbeat.
 When the heart muscles are
relaxed – diastole
 Blood flows from veins into atria
 When the heart muscles contract –
systole
 Atria contract first to pump blood
into ventricles (valve between
atrium and ventricle opens)
 Ventricles contract to pump blood
into the arteries
(forces valve to shut)
Normal blood pressure:
120 Systolic pressure
80 Diastolic pressure
The beating of the heart is due to myogenic
muscle contraction...
• This means that the myoctye (muscle cell) is the origin of
the contraction and it is not controlled externally.
A region of myocytes, called the sinoatrial
node (SA node) controls the rate of the
heartbeat.
• This region is also called the pacemaker.
A wave of excitations is sent from the SA nose,
causing the atria to contract. This excitation is
conducted to the atrioventricular (AV) node,
where it is passed through the nerves to the
muscles of the ventricles, causing them to
contract.
http://drugline.org/img/term/sa-node-13124_3.jpg
The heart muscle is indefatigable.
Heart rate can be controlled by the autonomic nervous system – the part of the
nervous system that responds automatically to changes in body conditions.
Where mycocardial contraction maintains the beating of the
heart, we may need to speed up or slow down heart rate.
When exercising, more CO2 is present in the blood. This is
detected by chemoreceptors in the brain’s medulla
oblongata, resulting in a nerve signal being sent to the SA
node to speed up the heart rate.
When CO2 levels fall, another nerve reduces heart rate.
The hormone adrenaline causes a rapid increase in heart rate in fight-or-flight reponses,
preparing the body for action.
• This effect can be mimicked by stimulant drugs.
Arteries
 Carry blood away from the heart
 Except for the pulmonary artery, transport oxygenated blood
 Artery walls are thick and elastic so they can stretch under
the high pressure of blood
 As the arteries stretch, they “pulse”
thick outer wall
thick inner layer
of muscle and
elastic fibres
narrow central
tube
Veins
 Carry blood to the heart
 Except for the pulmonary vein, carry deoxygenated blood
 Wider than arteries, with thinner walls
 Blood under lower pressure
 Valves prevent the back-flow of blood
thin outer
wall
thin inner layer
of muscle and
elastic fibres
wide
central tube
Capillaries
 Capillaries are the tiny blood vessels that carry a blood supply
to and from the body’s cells.
artery
 Capillaries are the
vein
only blood vessels where substances can be
exchanged between the blood and body cells.
 The liquid part of the circulatory system
 Blood cells are suspended in plasma
 An adult human has about 5.5L of blood in their body
The four components
of blood
Plasma [55%]
Leucocytes (WBCs) and
platelets [0.09%]
Erythrocytes (RBCs) [44.91%]
 Blood plasma carries three types of blood cells.
 They have different shapes and carry out different functions.
red
blood cell
white
blood cell
platelet
Components of
blood
Micrographs of blood
Platelet
Lymphocyte (WBC)
Erythrocyte (RBC)
Scanning electron micrograph of blood
http://www.webmd.com/heart/anatomy-picture-of-blood
• nutrients,
• oxygen,
• carbon dioxide,
• hormones,
• antibodies,
• urea,
• heat