Starter 14/03/24
9.4 Blood
Components of
blood
Plasma
Red blood cells
Cells and cell
fragments of
blood
White blood
cells
Platelets
Components of blood
•
Plasma: The liquid part of blood.
•
Red blood cells: Biconcave blood cells (like a flat disc that has been
pinched on both sides) with no nucleus, which transport oxygen.
•
White blood cells: Blood cells with a nucleus, which help to defend
against pathogens.
•
Platelets: Tiny cell fragments present in blood, which help with clotting.
Red blood cells
Which substance gives red blood cells their red colour?

Haemoglobin: A red pigment found in red blood cells, which
can combine reversibly with oxygen; it is a protein.

This protein contains iron.

It is this iron that readily combines with oxygen where the
oxygen concentration is high.
Which part of the human body has a very high concentration
of oxygen?

The alveoli in the lungs.

Blood capillaries take the blood close to the alveoli.

Oxyhaemoglobin: Haemoglobin that is combined
with oxygen.
Red blood cells

Oxyhaemoglobin releases its oxygen where the oxygen supply is
low.
Which part of the human body has a low concentration of
oxygen?

This happens when the blood passes through capillaries close
to cells that are respiring, using up oxygen.
Why does haemoglobin not have a nucleus?

The lack of nucleus provides more space for packing in millions
of molecules of haemoglobin.
Red blood cells
What is the purpose of the shape of the red blood cells?
•
Their shape together with their small size, gives
them a relatively large surface area compared
with their volume (high surface area to volume
ratio).
•
This speeds up the rate at which oxygen can
diffuse in and out of the red blood cell.
What is the purpose of the size of the red blood cells?

The small size of the red blood cells enables them to squeeze through even
the tiniest capillaries.

This means that oxygen can be taken very close to every cell in the body.
White blood cells

The nucleus of a white blood cell is often quite large.

White blood cells can squeeze out through the walls of blood
capillaries into all parts of the body.
What is the function of white blood cells?
•
Their function is to fight pathogens and
to clear up any dead body cells.
Phagocytosis

Some white blood cells engulf pathogens (take them
into their cytoplasm) and digest them with enzymes in
a vacuole.
•
This process is called phagocytosis.
•
Phagocytes: White blood cells that destroy
pathogens by phagocytosis.
Antibody production – lymphocytes

Some white blood cells produce antibodies.


These molecules fix onto pathogens and help to
destroy them.
Lymphocytes: White blood cells that produce
antibodies.
Practice question
Platelets

Platelets: Small fragments of cells (no
nucleus) that are involved in blot clotting.
•
They are made in the red bone marrow.
Blood clotting

Normally, skin provides a very effective barrier against the entry of pathogens.

When the skin is cut, blood vessels in it are severed and start to bleed.

The bleeding usually stops after a short time because of a process called clotting.

This process seals up the wound and prevents further loss of blood and blood pressure.

Clotting is also important because it prevents the entry of pathogens through breaks in the skin,
until new tissue has grown to heal the cut.
Platelets and blood clotting
1.
When a cut or other injury involving damage to blood
vessels occurs, platelets aggregate at the site forming a
temporary plug.
2.
They then release the clotting factors that trigger off the
clotting process.
3.
An enzyme that is produced after a chain of reactions
converts the soluble plasma protein fibrinogen into the
insoluble protein called fibrin.
4.
The fibrin forms fibres, which pile up on top of each other to
make a mesh in cuts that traps more platelets and also red
blood cells.

5.
The platelets stick together to form clumps.
The fibres, the trapped red blood cells and the clumps of
platelets form a blood clot.
Platelets and blood clotting
Practice question
Plasma
Water
Proteins
Components
of blood
plasma
e.g. fibrinogen,
antibodies
Lipids
e.g.
cholesterol
Carbohydrates
e.g. glucose
Excretory
substances
e.g. urea
Mineral ions
e.g. Na+ , Cl
Hormones
e.g. adrenaline
Dissolved
gases
e.g. 𝑪𝑶𝟐
−
Practice question
Plasma