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Unit 4 - Immunology and Public Health
CfE Higher Human Biology
21. Non-Specific Defences
Learning Intentions
I can describe non-specific defences.
I can describe physical and chemical defences. Epithelial cells form a
physical barrier and produce secretions against infection.
I can describe the inflammatory response which includes the release of
histamine by mast cells causing vasodilation and increased capillary
permeability. The increased blood flow and secretion of cytokines leads to
an accumulation of phagocytes and the delivery of antimicrobial proteins
and clotting elements to the site of infection.
I can describe the structure of Phagocytes and apoptosis by natural killer
(NK) cells.
I can state that Phagocytes and NK cells release cytokines which
stimulate the specific immune response. Phagocytes recognise surface
antigen molecules on pathogens and destroy them by phagocytosis. NK
cells induce the pathogen to produce self-destructive enzymes in
apoptosis.
I can describe specific cellular defences.
I can describe immune surveillance as a range of white blood cells
constantly circulate monitoring the tissues. If tissues become damaged or
invaded, cells release cytokines which increase blood flow resulting in
specific white blood cells accumulating at the site of infection or tissue
damage.
First Line Defences.
• The body defends itself against disease
causing organisms (pathogens), some
toxins, and cancer cells by using its
immune system. This can be in the form
of a physical defence or a chemical
defence.
• Immunity is the ability of the body to
resist infection by a pathogen or to
destroy the organism if it succeeds in
invading and infecting the body.
First line of defence of the body.
• Is Non-specific.
• Skin acts as a physical barrier to keep out
germs/microbes.
• Stomach acid made by the epithelial lining of the
stomach destroys the microbes swallowed
• Mucus in trachea traps microorganisms –the epithelial
cells lining the trachea are ciliated and sweep the
mucus up and away from the lungs .
• Tears and saliva have an enzyme called lysozyme that
digests the cell walls of bacteria and destroys them.
Epithelial cells – Physical Defence
Epithelial cells are our
first line of defence
against infection.
They line the surfaces
and cavities of the
entire body.
Form a physical barrier
against infection.
These cells cover
almost the entire
surface of the body.
They grow constantly
upwards and outwards
from the bottom layer
and by around 14 days
they have become
dead cells called
stratum corneum
which flake off taking
any bacteria or
pathogens with them.
Epithelial cells also produce secretions such as enzymes,
hormones and lubricating fluids that can defend against
infection.
Secretions – Chemical Defences
On all the inside
surfaces of the body
that can be exposed to
bacteria and pathogens
a substance called
mucus traps dirt and
germs, preventing them
from entering the
blood. Various glands
produce antimicrobial
secretions that help
kill microbes.
Other defences
• Tiny hairs at the entrance to the nose.
• Cough and sneeze reflexes.
• ‘Friendly’ bacteria.
The Inflammatory Response-mast
cells(second line of defence).
Chilblains –
inflammation of the
toes (or other
extremities) caused
by prolonged
exposure to moisture
and cold.
Acne –
inflammation of
the skin caused by
bacteria in the
pores
Tonsillitis –
inflammation of the
tonsils
Inflammation is a common
response to bee/wasp
stings
Inflammatory response-mast cells(second line of defence).
• This operates when the body suffers a physical
injury or invasion by microbes.
• Following injury mast cells are activated and
release large amounts of histamine which is a
chemical that dilates blood vessels that lets them
fill up with blood.
• Mast cells are made from the same stem cells that
make white blood cells and are found in connective
tissue throughout the body.
• Blood vessels in the injured area vasodilate and fill
full of blood which makes the area swollen, red and
inflamed.
• The tissues become swollen because the capillaries
become more permeable and tissue fluid leaks out.
Non-specific
inflammation
The inflammatory
response is
triggered when
something breaks
the skin.
Cytokines attract white blood cells called phagocytes to the area and
the release of antimicrobial proteins or clotting elements to the
damaged area.
Histamines are also released which cause the capillary to vasodilate
and become more permeable. Look at the following animation:
Video
Destroying invading pathogens
Self or non-self?
N5 revision
On the surface of a cell membrane, there are many
proteins partially embedded in the lipid bilayer. Some of
these proteins are called antigens and allow our immune
system to recognise our own cells.
Invading
bacteria and
viruses which
would cause
disease
(pathogens)
have different
antigens –
non-self.
Phagocytes
Phagocytes are cells which will engulf and digest a foreign
particle such as bacteria.
They recognise the foreign antigen molecules on its surface
then bind with the bacterium and engulf it by endocytosis.
Once the
bacterium is
inside the
phagocyte,
lysosomes fuse
with the
vesicle,
digesting the
bacterium.
VIDEO
Non-specific cellular responses-phagocytosis
(second line of defence).
• The process of phagocytosis is carried out by a type of white
blood cell called a phagocyte.
• Phagocytes can move and when they detect chemicals released
by a pathogen or detect antigens present on the surface of a
pathogen they move towards it.
• The pathogen is engulfed(taken in to the cell) and the cell
membrane folds in to form a vacuole with the pathogen inside it.
• Lysosomes which are vesicles filled with digestive enzymes fuse
with the vacuole and release their digestive enzymes into it.
• The pathogen is broken down and the products are absorbed by
the phagocyte.
• Cytokines are released by the phagocyte and they attract more
phagocytes to continue the battle.
• pus is dead bacteria and phagocytes that can form at a site of
injury.
Natural killer cells
Natural killer (NK) cells are found in the blood
and are constantly looking for signs of an
infection. They can also release cytokines but
they have an important role in destroying a
pathogen-infected cell.
They look for a cell which has not got the
normal surface antigens or self antigens and
knows that it must be infected.
It then destroys it with self-destructive
enzymes perforating the plasma membrane,
bursting it, a process called apoptosis.
Non-specific cellular responses-natural killer cells(second
line of defence)
• NK cells are not phagocytic.
• They attack virus-infected cells in general and
cancer cells.
• The NK cells releases molecules of a protein
which forms pores in the target cells of the
membrane .
• Signal molecules from the NK cell can then enter
the target cell and trigger a genetically controlled
series of events.
• The target cell produces cell destructive enzymes
and the cell’s DNA and vital proteins are broken
down and destroyed and the cell dies.
• This is called a programme of cell death and is
called apoptosis.
Cytokines.
• NK cells and phagocytes also release
cytokines after contact with a pathogen.
• These molecules move in the blood and
stimulate the specific immune response
by activating lymphocytes.
Inflammatory response-cytokines (in non-specific and specific
defences
).
• These are very important chemicals involved in this
response.
• They are called cell signalling protein molecules and can
be made by many types of cells including white blood
cells that have arrived at an injury.
• During the inflammatory response increased blood flow
and permeability of capillary walls at site of injury bring
about the following effects to help:
1. Cytokines attract more phagocytes to the damages
tissue and these engulf pathogens by phagocytosis and
clean up the injured site.
2. Fast delivery of anti-microbial proteins to the
infected site which amplify the immune system.
3. Rapid delivery of blood clotting chemicals to the
injured site to prevent other microbes entering and to
start repair.
Questions
1. Name a secretion made by the epithelial cells lining
the inside of the body.
2. What name is given to the immediate response of
the body to a cut?
3. What are mast cells?
4. Why do the capillaries vasodilate?
5. What general name do we give disease-causing
organisms?
6. Describe what an antigen is made of and where it is
found.
7. What is the name of the cell signalling molecule
produced by many immune cells?
Questions
8. Describe the process of phagocytosis.
9. What are NK cells?
10. Describe the stages involved in apoptosis.
Answers
1.
2.
3.
4.
5.
6.
7.
Name a secretion made by the epithelial cells lining the inside of the
body.
- Mucus
What name is given to the immediate response of the body to a cut?
- Inflammatory response
What are mast cells?
- Cells found under the epithelium containing histamines and
cytokines
Why do the capillaries vasodilate?
- Histamines causes this
What general name do we give disease-causing organisms?
- Pathogens
Describe what an antigen is made of and where it is found.
- An antigen is a protein marker found on the cell membrane surface
What is the name of the cell signalling molecule produced by many
immune cells?
- Cytokine
Answers
8. Describe the process of phagocytosis.
• Phagocyte recognises antigen on surface of pathogen as ‘non
self’
• Phagocyte attaches to antigen
• Phagocyte engulf pathogen into vacuole/vesicle
• Lysosomes containing digestive enzymes bind with
vacuole/vesicle.
• Pathogen digested
9. What are NK cells?
- Natural Killer Cells which recognise damaged or cancerous
cells
10. Describe the stages involved in apoptosis ( cell death )
• NK cell produces protein which punctures cell membrane of cell
• NK protein binds to ‘suicide gene’ in nucleus of cell
• Proteins produced by ‘suicide gene’ destroy cell
Glossary
Epithelial cells
Inflammatory response
Pathogen
Antigen
Non-self
Mast cells
Histamines
Cytokines
Vasodilation
Permeability
Phagocytes
Lysosomes
Natural killer cells
Apoptosis