Body
defences:
2. Physical ways our body defend itself against
pathogens
Doc Brown's Biology exam study revision notes
There are various sections to work through, after 1 they can be read and studied in any order.
Sub-index of notes: Our body's defence mechanisms against infections from
pathogens, help from vaccines & drugs
(2) How do our bodies
defend themselves against infectious diseases?
Physical defence mechanisms of protection from
pathogens
Your skin and hairs and mucous
in the respiratory tract can stop a lot of the pathogen cells from entering
your body.
When breathing, you cannot
help taking in all sorts of fine particles of dust and microbes.
The whole of the
respiratory tract from the nasal passage, down
the trachea and into the lungs is covered with mucous and lined with ciliated
cells. Cilia are fine
hairs that can move freely at their ends.
The
hairs and mucous in your
nose traps
dust and any other particles that might contain pathogens like
bacteria, before they can get down into the lungs.
The trachea and bronchi
have ciliated epithelium
- shown in the diagram below.
In between the ciliated
epithelial cells are goblet cells that secrete mucus onto
the surface of all the respiratory airways.
This sticky mucus traps
particles like dust or microbe pathogens and the cilia
(hairs) move the mucous along..
The hair-like structure of
the cilia
of the ciliated cells work together and move-push the mucous up to the back of the throat
where it can be swallowed.
The ciliated cells have
lots of mitochondria, they have a lot of work to do!
Cells that line the
trachea and bronchi have cilia. These hair-like
structures can move the
mucous along from the lungs up to the nasal passage and back of the throat
where it can be swallowed, coughed out or blow
your nose, into a tissue!
Note that smoking can
damage and paralyse the cilia reducing the ciliated cell's
capacity to remove harmful particles, so another reason why
smokers are more susceptible to respiratory diseases.
Skin in good condition acts as a
very effective physical barrier against pathogens.
The outer layer of epidermis
skin cells are dry and dead and pathogens cannot easily get
through this layer.
The skin also protects the
body from physical damage and dehydration.
As well as acting as a
physical barrier, your skin also has sebaceous glands that secrete antimicrobial
molecules that can kill pathogens.
The sebaceous glands are
an 'offshoot' of the hair shaft, out of which the hair
grows.
What happens if the skin is
damaged?
When a cut in the skin occurs,
small fragments of cells called platelets help the blood to clot quickly
to seal the wound - the seal becomes the covering scab when dry, and prevent microorganisms entering
the skin tissue or blood stream.
When the platelets are
exposed to air through a cut, they become 'activated' and
make protein fibres called fibrin, that form a mesh over the
wound, and the mesh traps platelets and red blood cells to
form a clot.
Clotting also reduces blood loss.
The greater the concentration of platelets
in the blood the faster the clotting process ('sealing') can occur.
These
physical
defences are non-specific and can counteract a variety of types of
pathogens.
Learning objectives for this section on the physical ways the body defends
itself against pathogens
Be able to describe physical ways in which the body defends
and protects itself against pathogens.
Be able to describe how
cilia hairs and mucous in the respiratory tract and the barrier of our skin
help protects us against pathogens.
Be able to explain how the human body can be effective against attack from
pathogens, including:
-
The body has different physical and chemical ways of protecting itself
against pathogens.
-
Physical barriers – skin, cilia, mucus
-
Physical protection from
pathogens
-
Your skin and hairs and mucous
in the respiratory tract can stop a lot of the pathogen cells from entering
your body. The whole of the respiratory tract from the nasal passage, down
the trachea and into the lungs is covered with mucous and lined cilia (fine
hairs that can move freely at their ends). The mucous traps dust and
bacteria before they can get down into the lungs and the cilia move the
mucous along from the lungs up to the nasal passage -and then you can blow
your nose!
-
Skin in good condition acts as a
very effective barrier against pathogens. When a cut in the skin occurs,
small sections of cells called platelets help the blood to clot quickly to
seal the wound (seal = scab when dry) and prevent microorganisms entering
the skin tissue or blood stream. The greater the concentration of platelets
in the blood the faster the clotting process ('sealing') can occur.
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