Contents

What is Blood?

Plasma and cells in suspension

Plasma functions

Red blood cells

White blood cells

Blood cells

Summary quiz

2 of 50

Plasma and cells in suspension

The blood sample separates into two parts.

centrifuge

The top half is a straw coloured liquid called plasma.

The bottom half is a dark collection of blood cells.

If blood is separated it no longer looks like the red liquid that we recognise.

55%

45%

As blood is 55% plasma and only 45% cells, the cells are actually suspended within the plasma, a little like people would be suspended within a swimming pool.

How a suspension works

Contents

What is Blood?

Plasma and cells in suspension

Plasma functions

Red blood cells

White blood cells

Blood cells

Summary quiz

The plasma actually surrounds the cells and carries them along as it flows through the blood vessels.

This is the first function of plasma.

Blood flows around the body, transporting substances from one place to another.

First function of plasma

it usually picks up a substance from an exchange site

takes it to a place where it is used

reactiona reaction occurs

a useful product and a waste product is made

Transport role

7 of 50

The blood then transports one or both of these substances to another place in the body.

useful/waste product

cellblood vessel

Shifting the product

The cycle then starts again.

Products dissolved in plasma

blood flowing along a capillary

Blood has to rely on its plasma to transport some of these useful or waste products.

For example, plasma carries CO2 from the cells to the lungs.

CO2

CO2

CO2

CO2

CO2

plasma

blood cellblood cell

The third and fourth roles are also centred around the moving of a substance from one place to another.

Plasma is responsible for carrying dissolved food.

Dissolved digestive products

Our digestive system breaks down the food we eat to release the useful nutrients.

Remember!

MouthMouth

AnusAnus

food is eaten

waste is excreted

Useful products of digestion are absorbed from the digestive system and enter the blood.

Sugars

Amino acids

Glycerol

Fatty acids

Summary of absorption

The soluble food dissolves into the plasma and is carried from the small intestine to the cells of the body.

Here they diffuse into the cells and are used in various chemical reactions.

Leaving the plasma

body cell

sugars fatty acids

glycerol

amino acids

plasma

The final role of the plasma is to carry a particular waste product from the liver to the kidneys.

As urea is toxic, it must be removed from the body as quickly as possible!

The blood now has to help the body do this.

The waste product is called urea.

Urea is made in the liver by the breakdown of amino acids.

Removing urea

Plasma carries the urea from the liver to the kidneys that filter the blood. Urea is removed from the plasma of the blood and passes down a tube to the bladder.

This urea in the bladder is stored before it is excreted. The urea will leave the body within the liquid urine.

kidney

blood

ureaurea

Filtration and expulsion of urea

Reviewing the role of plasma

In summary, plasma has a principle role in transporting substances around the body.

substance moving from going to

CO2cells lungs

Cells all over the body

Dissolvedfood

smallintestine

cells

Urea liver kidney

Plasma – role summary

All this is being carried in just the plasma!

fatty acids

amino acids

urea

red blood cell

carbon dioxide

sugar

white blood cell

platelets

The full load

Contents

What is Blood?

Plasma and cells in suspension

Plasma functions

Red blood cells

White blood cells

Blood cells

Summary quiz

There are 3 types of blood cell within human blood.

They have different shapes and carry out different functions.

Red Blood Cells

White Blood Cells

(These are actually fragments of cells so we

can’t really call them cells)

Platelets

Blood cells

red blood cells

white blood cells

platelets

Image of the 3 constituents

Contents

What is Blood?

Plasma and cells in suspension

Plasma functions

Red blood cells

White blood cells

Blood cells

Summary quiz

Of all the cells these are the most numerous.

In fact, every cubic centimetre of blood contains…

1 cm

1 cm

1 cm5 000,000,000 cells

Red blood cells: erythrocytes

Therefore, it is not hard to realise that each red blood cell is extremely small.

In fact, each one is only on average 7 micrometers in diameter (one micrometer is a millionth of a metre).

This is a basic diagram of a red blood cell.

Basic diagram of a red blood cell

Actually, although the red blood cell is a “cell”, it does not contain one of the 3 parts of a “normal” cell.

Red blood cells have no nucleus.

This may seem odd but, there is a reason for it.

Inside the red blood cells

Red blood cells also contain a unique substance called haemoglobin.

This is a special iron based pigment whose presence is essential if the red blood cell is to perform its job.

Fe2+

The story begins in the lungs because this is where the oxygen gas enters the bloodstream.

Remember, during the process of breathing, oxygen gas enters the body and is exchanged for carbon dioxide gas.

The oxygen gas will be needed for the process of respiration.

Red blood cells carry OXYGEN (O2).

Oxygen for carbon dioxide

O2

O2O2

O2oxygen is inhaled

It passes through the breathing system and reaches an alveolus.

The oxygen gas diffuses across the lining of the alveolus and the capillary.

alveolus

O2

O2

O2

O2 diffusion

Here is a close up showing the diffusion of oxygen gas.

As the oxygen gas diffuses across the lining of the alveolus, it dissolves in the moist layer.

This speeds up the diffusion process.

lining of alveolus

moist layer

red blood cell

OO22 OO22

lining of capillary

Inside the alveoli

If we now concentrate on one red blood cell, we can see how important the haemoglobin molecule is to the process of transporting oxygen.

The oxygen molecule diffuses into the red blood cell.

Haemoglobin + O2

each red blood cell contains the pigment...

These two molecules bind together to produce this new substance.

Oxyhaemoglobin

Oxyhaemoglobin

It is important to remember that this reaction is happening in red blood cells at the alveolus.

This is how the red blood cells are able to bind hold of the oxygen and carry it within the blood.

Each red blood cell is now loaded with oxygen molecules.

OxyhaemoglobinOxyhaemoglobin

OxyhaemoglobinOxyhaemoglobin

OxyhaemoglobinOxyhaemoglobin

Oxygen binding at the alveolus

Order the following events

Once these red blood cells reach the cells of the body, they are travelling through tiny capillaries similar to those found in the alveolus.

cells

capillary

It is here that they offload their oxygen.

In order for this to happen, the oxyhaemoglobin molecule must be broken down.

Offloading the oxygen to body cells

Oxygen diffusion at the capillary bed

In the cell, the oxygen is used in the process of respiration which produces….

The oxyhaemoglobin breaks down to release the oxygen molecule.

It diffuses across the cell membrane and the lining of

the capillary and into the cell.

ENERGY

Oxygen use in the body

1 There are vast numbers of them.

The more cells there are, the more O2 can be carried and delivered to the cells.

Features of red blood cells

2 They have no nucleus.

This means they have more room for haemoglobin molecules and therefore each red blood cell can carry more oxygen gas.

Features of red blood cells

3They have a large surface area compared to their volume.

small volume

Through having a small volume compared to its surface area, the red blood cell is able to keep the oxygen close to its surface.

Features of red blood cells

large surface area

This means it can quickly release its oxygen by reducing the time it takes for the gas to diffuse out of the cell.

The distance for the gas to move is much smaller in a cell shaped like this.

O2

alternative cell design

The overall effect of this means that the blood can cope with the oxygen demands of the body.

Features of red blood cells

O2

4 The diameter of red blood cells is slightly larger than the average diameter of a capillary.

This means that the red blood cell is forced to slow down as it passes through the capillary.

This means the exchange of the gas will definitely happen.

It also means the surface of the red blood cell will be exposed to the surface of the capillary.

Features of red blood cells

red blood cell

capillary

Red blood cell features

Useful or useless?

Diffusion at the capillary bed level

Contents

What is Blood?

Plasma and cells in suspension

Plasma functions

Red blood cells

White blood cells

Blood cells

Summary quiz

Let’s now consider the white blood cell.

It has a much more varied shape and there are different types of white blood cell within the blood.

The white blood cell is bigger than the red blood cell.

White blood cell

White blood cells play a part in the defence system of the body.

They are designed to fight microbes such as bacteria and viruses.

There are far fewer white blood cells within the blood compared with red blood cells.

Role in defence

When the body fights disease, more white blood cells are produced. With some diseases, doctors can establish how healthy someone is by testing their blood to see how many white blood cells they have.

White blood cell count

white blood cell number is higher

testtest

white blood cell number is low

Disease

Match the cells to the correct functions

Blood cell differences

As we mentioned, the platelet is actually a fragment of a cell.

Therefore it does not have a nucleus.

They are also much smaller than both the white and red blood cells.

Their role is to help to clot the blood when the

body has a wound.cut

skin

Our final blood part is the platelet

Contents

What is Blood?

Plasma and cells in suspension

Plasma functions

Red blood cells

White blood cells

Blood cells

Summary quiz

Multiple-choice quiz