Microorganisms and Health [2]: Physical Barriers and Phagocytes (A Level Biology)

Uploaded by freeeschool on 02.09.2012

A Level Biology: Microorganisms and Health 2 – Physical Barrier and Phagocytes
Hi! Welcome to my second video on the series about Microorganisms and Health. What we are
looking at today are the methods by which your body stops you getting ill.
The first of which are the physical barriers. These physical barriers include things like
your skin. You probably notice that if you feel your skin, it got an almost like a layer
of oil. Within that liquid that is produced, you have enzymes and you have chemicals which
actually can break down bacteria.
We also have tears, which inside these tears are specific chemicals which can break down
microorganisms. Obviously, if you were to ingest or swallow any microorganism and they
are able to get into your stomach which is quite likely, then the stomach acid, which
has a very, very low pH, is able to digest and break down microorganisms quite effectively.
What would happen if they got through the physical barriers and then got inside your
body, potentially through a cut or through a wound internally? Then, once it gets to
the bloodstream, what protects you on the inside?
We have a specific type of blood cell that actually deals with foreign infections and
these are called white blood cells, hence the drawing here. In this diagram here, it’s
got your red blood cells and the typical white blood cell here. Now, the specific name for
white blood cells is called leukocyte. You might have heard the word “leuko” before
in the word leukemia. So leukemia is a cancer of white blood cells. The only time you hear
the word leukocyte that means white blood cell.
The first type of white blood cell that the pathogen might encounter is called phagocyte.
The phagocytes work by ingesting and digesting microorganisms. The diagram here gives you
an indication of how phagocytes work. The blue blob here is a phagocyte and this is
the nucleus of a phagocyte here. The purple section here might be a particular microorganism,
probably bacteria.
Since what happens is the bacteria is recognized as being foreign and then it is engulfed into
the phagocyte, what will technically happen is the phagocyte will form a membrane around
the foreign pathogen and it will then release digestive enzymes that will break down the
pathogen and then obviously, eliminate the threat.
In order for the microorganism to be digested, we need to identify if it is foreign, first
of all. Basically, on a surface of a microorganism within the surface of most cells, you have
these things called antigens. These are surface protein markers. They’re a bit like an identification
method. So your cells, your red blood cells have a specific type of antigen and therefore,
your white blood cells recognize your red blood cells as being yours. This is what can
lead to problems when people have blood transfusions from different blood types because different
blood types have different antigens on them, therefore your white blood cells see them
as a problem and they therefore try to digest them and break them down, obviously leading
to serious complications. That’s why you can’t mix blood types. But it is also the
same reason why your white blood cells would target certain pathogens because they have
antigens on their surface that are foreign.
In summary, you have physical barriers that stop microorganisms getting inside your body
and those are things like your skin, the tears and the stomach acid. If they do gain an entry
into your body and into your bloodstream, then the first is met by a type of white blood
cell or leukocyte called a phagocyte. Phagocytes work by digesting and engulfing microorganisms.
If you will join me for the next video, then we will be looking at the next stage in your
immune response.
[end of audio – 03:59] A Level Biology: Microorganisms and Health
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