Circulation
Body In action
SG Biology
What you need to know!
• Substances are transported around
the body, for example from where
they are taken into the body to cells;
or from cells to where they are
removed from the body, by the
circulation system, the heart, the blood
vessels and the blood.
Learning Outcomes
Lesson 1
• To be able to explain the circulation
system are a double circulation.
• To label a diagram of the body
showing the major blood vessels,
saying in each case if the blood is
oxygenated of deoxygenated.
• To understand the main features of
arteries, veins and capillaries
Why do we need a circulatory
system?
• Transport over short
distances is achieved by
diffusion, osmosis or active
transport.
• Situation in larger organisms
is different
• Giant redwoods need to
transport water to a height
of 100m without the
expenditure of energy
Why do we need a circulatory
system?
• Cell Metabolism – What do cells need?
– Amino acids, glucose, oxygen
– Removal of waste products
• What is important in determining whether an
organism has a transport system?
– Size
– Surface area to volume ratio
– Level of activity
Features of transport systems
• Suitable medium to carry materials
• Closed system of tubular vessels
• Mechanism to maintain flow in one
direction
• A mean of controlling the flow of the
transport medium to suit the changing
needs
Types of circulation
• Open circulation
– E.g. insects
• Closed circulation
– Single circulation
– e.g. fish
– Double circulation
– e.g mammals
Circulation System
Double Circulation
• The heart is divided into two halves, the left
and the right. The blood on the right side
does not mix with the blood on the left. So
the circulation is in two parts.
• The blood passes through the heart twice in
one circuit, this is called a double
circulation.
• Blood picks up oxygen in the lungs
(oxygenated), and gives up its oxygen to
the body cells (deoxygenated).
Double Circulation
Blood Vessels
• The blood flows from the heart to organs
through arteries and returns through
veins.
• Arteries have thick walls containing
muscle and elastic fibres, they carry
blood to the organs.
– Arteries contract and bounce back to force
the blood along, this bouncing back can be
felt as a “pulse” as the blood flows through.
• Veins have thinner walls and often have
valves to prevent the back-flow of
blood.
Blood Vessels
• In the organs the blood flows
through capillaries.
– These are very narrow, thin-walled
blood vessels, they are only one cell
thick.
– Substances needed by the cells in
body tissues pass out of the blood,
and substances produced by cells
pass into the blood through the walls
of the capillaries.
Learning Outcomes
Lesson 2
• To be able to label a diagram of the
heart
• To take part in a heart dissection,
demonstrating the main parts of the
heart.
• To be able to describe the events in
the cardiac cycle.
The Structure of the heart
Structure of heart
pulmonary artery
vena cava
right atrium
tricuspid valve
right ventricle
aorta
pulmonary vein
left atrium
semi-lunar valve
bicuspid valve
tendon supporting
valve
left ventricle
muscle
The Heart
• The heart pumps blood through the
circulatory system all round the body.
• The heart is a double pump.
– The right side collects blood from the body and
pumps it to the lungs.
– The left side collects blood from the lungs and
pumps it to the rest of the body.
Heart Dissection
Valves in the heart
• There are three main types of valves in the
heart. These are:
– Semi-lunar valves
• aorta and pulmonary artery
– Tricuspid valves
– Bicuspid valves
• The valves are attached to the wall of the
heart by tendons (heart strings), which
prevent the valves being turned inside out.
What do these valves do?
• Each valve has a particular function
– Semi-lunar valves – these prevent
blood sucking back into the ventricles
when they stop contracting.
– Tricuspid valve (between the right
atrium and ventricle) and bicuspid
valve (between the left atrium and
ventricle) these prevent blood passing
up into the atria when the ventricles
contract.
The Cardiac Cycle
• Draw a flow chart to demonstrate the
blood flow through the heart.
– Mention which muscles are contracted
– Which valves are open
– Which valves are closed