Download KS4 Blood Vessels

Contents
Blood Vessels
What blood vessels do
Arteries
Veins
Capillaries
Summary quiz
What blood vessels do
We can get an idea of what they could look like from
considering the job they have to do.
Let us look at a small section of the circulatory system.
There seems to be 3 types of blood vessel present.
one joins the
other two
together
one takes
blood away
from the
heart
Lungs
one takes
blood to the
heart
Three broad types of vessels
1.
Blood vessels that take blood away from
the heart are known as ARTERIES.
Remember, arteries (away)
2.
Blood vessels that take blood back to
the heart are known as VEINS.
Remember, veins (into the heart)
and in between…
3.
Finally, if arteries take blood away from the
heart and veins take blood back to the heart,
when does an artery turn into a vein?
Well, our third type of blood vessel links the two.
We find it present where an artery finishes and a
vein is about to begin.
This third type of blood vessel
is known as a CAPILLARY.
Contents
Blood Vessels
What blood vessels do
Arteries
Veins
Capillaries
Summary quiz
Artery cross-section
small
lumen
thick muscle
and elastic
fibres
Arteriole pressure
The small size of the lumen means that
blood will be under high pressure.
The thick fibrous wall strengthens
the artery.
Imagine using a water hose and
putting your thumb half over the
open end.
The water is released under higher
pressure and it flows faster.
Properties of arteriole walls
thick arteriole wall
lumen
The elastic allows the artery to stretch under pressure
whilst the muscle can contract to push the blood along.
The human pulse
This stretching of the artery is what allows us to feel a pulse.
As the heart beats, it releases regular surges of blood. As
these pass along the arteries, the vessel must stretch to
allow the increased blood flow to pass.
This stretching pushes on the skin, which we sense as a
pulse.
blood
flow
blood
flow
Blood flow in arteries
The blood flowing through an artery will be under high
pressure and moving extremely fast.
There is no chance that the blood will turn around and
start travelling in the opposite direction.
Therefore, there are no valves present in arteries.
Contents
Blood Vessels
What blood vessels do
Arteries
Veins
Capillaries
Summary quiz
Veins: cross-section
large lumen
thin muscle and
elastic fibres
Walls of veins
The lumen of a vein is much
thicker than the wall that
surrounds it.
There is less of a need to
maintain a high pressure.
The walls still contain elastic and muscle but there is
far less present compared to the artery.
You will appreciate that the blood is flowing far less quickly
through veins compared to arteries.
Getting another boost
The veins are carrying blood back towards the heart.
Materials have been exchanged and now it is running
out of energy.
It needs to return to the heart to receive another pump.
Unfortunately, this could lead to a real
problem...
Preventing backflow
Q. What would happen if blood loses so
much energy that it stops and turns around?
leg
gravity
vein
Normal
direction of
blood flow
This situation could arise where blood is flowing against
gravity.
However, there is a solution to this problem and it comes in
two parts.
Valves
1.
Firstly, veins have valves which act to stop the blood
from going in the wrong direction.
(These valves are similar to those found in the heart)
valves close
valves open
blood
Muscular massage
2.
The second part of the solution has to get the
blood flowing again whilst overcoming the problem
of a lack of muscle in the lining of the vessel.
The solution comes in the
form of general body
muscles that surround the
veins. When these muscles
contract to move the body,
they also squeeze the veins
and push the blood along
the vessel.
→
Contents
Blood Vessels
What blood vessels do
Arteries
Veins
Capillaries
Summary quiz
Capillaries: role and position
These vessels link arteries with veins.
They are found all over the body and are essential for
the exchange of materials between the blood and other
body cells.
artery
vein
capillaries
Capillary bed
Capillaries are so small
that they can only be seen
using a microscope.
A collection of capillaries is
known as a capillary bed.
body cell
The wall of a capillary is
only one cell thick!
very narrow lumen
Diffusion and exchange
Substances can diffuse across the lining of the capillary.
This allows useful substances which are dissolved within
the blood to move into surrounding cells whilst cellular
waste moves in the opposite direction.
3
1
2
The exchange of materials between the blood and the
body can only occur through capillaries.
Exchange of dissolved gases
Oxygen and carbon dioxide
exchange in the capillaries.
Vessel test. Part 1
Reaching all parts
Vessel test. Part 2
Blood characteristics
Contents
Blood Vessels
What blood vessels do
Arteries
Veins
Capillaries
Summary quiz
Multiple-choice quiz