Download 6.3 Defence Against Infectious Disease

Outcomes
6.3 Defence Against
Infectious Disease
IB Biology
6.3.1 Define pathogen.
6.3.2 Explain why antibiotics are effective against
bacteria but not against viruses.
6.3.3 Outline the role of skin and mucous membranes
in defence against pathogens.
6.3.4 Outline how phagocytic leucocytes ingest
pathogens in the blood and in body tissues.
6.3.5 Distinguish between antigens and antibodies.
6.3.6 Explain antibody production.
6.3.7 Outline the effects of HIV on the immune system.
6.3.8 Discuss the cause, transmission and social
implications of AIDS.
Pathogens
A pathogen can be defined as an organism
or virus that causes a disease.
A pathogen enters the body of a host and
causes damage.
Pathogens can be
viruses, bacteria,
protozoa, fungi,
and various types
of worms.
Antibiotics
Many disease caused by bacteria can be
effectively treated with antibiotics because they
block or interfere with the metabolic pathways of
the bacterium that is causing the disease without
having the same effect on human cells.
This is because
bacteria are
prokaryotic
cells and human
cells are eukaryotic.
Viruses
Viruses are not composed of cells and they
reproduce using the metabolic pathways and cell
contents of its host therefore the antibiotics do
not have any effect on the virus.
In other words, the
viruses use the
same metabolic
pathway as the
eukaryotic cells.
Antibiotics take advantage of
the fact that prokaryotic cells
are different from eukaryotic
cells in structure and in
function.
Some antibiotics interfere with
protein synthesis in bacteria.
Others focus on preventing the
bacterium from building new
cell walls therefore blocking
the ability of the bacterium to
grow and divide.
Defence!
The Skin
Our skin and mucus membranes act as
our primary line of defence against
invading pathogens!
The skin is a barrier that covers that entire
body and prevents pathogens from entering
the body. Your skin has two layers.
A very tough outer layer known as the
epidermis that is constantly being replaced
by new cells from the dermis layer
underneath.
Mucus Membranes
Skin cont’d…
As long as the epidermis stays
intact it is an excellent line of
defence against pathogens.
The skin itself is a tough outer
barrier but it also contains
defences within.
The sebaceous glands in the
pores of our skin secrete lactic
acids and fatty acids.
These acids create an
unwelcoming environment
on the surface of our skin
that prevents the growth
of most bacteria.
Mucous membranes are located in and around
openings in the body with areas of soft skin such as
the vagina, urethra, nose, and trachea.
The mucous contains an enzyme called lysozyme
that can kill many bacteria that try to enter.
The trachea also
contains cilia which
can sweep or push
the mucus and trapped
bacteria out of the
trachea.
More protection…
Although the human body has these outer defences
some pathogens will still enter the body so internal
defences are needed.
Acids in the stomach are one of those defences.
If a pathogen enters
the body in food or
water the acidic
environment of the
stomach often kills
the pathogen.
Leukocytes…
Leukocytes
Human
blood contains leukocytes also
known as white blood cells.
There are several different types of blood
cells and they are involved in the body’s
defence system or immune system.
These cells have the ability to recognize foreign
invaders in our system using the protein molecules
that are part of the surface of every cell and virus.
They determine if a substance or cell is part of the
body and recognize it as “self” or they may
determine it is not part of the body and therefore “not
self”.
Anything that is
determined to be
“not self” is flagged
as something that
should be removed.
Phagocytes
One type of blood cell known as phagocytes
will consume or ingest pathogens that enter
the body.
There are lysosomes
inside the phagocytes
that contain digestive
enzymes which
destroy the ingested
pathogen.
Phagocytic Leukocytes…
Phagocytes also have the ability to slip through the
spaces between the cells in the walls of the capillaries
and enter the body tissues.
From here they can target areas of infection and
engulf the pathogens that are
responsible for the
infection.
When there is a large
amount of phagocytes
at an infection site
they form pus.
A Phagocyte animation!
http://www.mydr.com
.au/healthimages/animationphagocytosis
Antigens
Antigens are foreign substances that stimulate an
immune response in the body.
Different parts of pathogens can be antigens that will
stimulate the response such as cell walls of bacteria
and fungi or the protein coats
of viruses.
Antigens are molecules
that our immune
system recognizes
as “not self”.
Unfortunately
not all pathogens can be
stopped by phagocytes and general (nonspecific) protection so again, more and
more specific/targeted defences are
needed.
Antibodies
Antibodies are composed of proteins and they target
certain antigens.
For example, in human blood types, anti-A antibodies
target A antigens on the surface of red blood cells.
Most antibodies have
a specific antigen that
they target and they
are produced in
response to that
specific antigen.
Pathogens
Antibody Production
Pathogens contain proteins on their outer surface
that the immune system recognizes as antigens and
these non-self proteins trigger and immune response.
Most pathogens contain
more than one protein or
antigen on their surface so
this triggers the
production of more than
Lymphocytes, a type of leukocytes are responsible
for making antibodies.
Each lymphocyte can only produce one type of
antibody so a tremendous number of different
lymphocytes are needed.
one type of antibody.
Antigen-Antibody recognition
Antibodies…
Although there are many different types of antibodies
their structure is quite similar.
They are Y shaped
proteins that each
contain a binding site
at the end of the Y
where the antibody
will attach to the
The cell membrane of each lymphocyte contains
some of the antibody that it is responsible for
producing.
They also contain antigen-combining or bonding sites
that project out from the cell membrane surface.
antigen.
B Cells produce antibodies…
B Lymphocytes
Leucocytes that produce antibodies are known as B
lymphocytes.
Humans contain many different types of B cells
because each B lymphocyte can only produce one
type of antibody.
A problem arises because we do not contain high
numbers of each type of B cell and they can only
produce a small number of antibodies which are not
high enough in numbers for the invasion that is
occurring.
Despite this hurdle
our immune system
has a way of
producing many
antibodies.
Typical Immune Response
4.
The newly formed B cells being the production
of antibodies which circulate in the bloodstream in
search of the matching antigen they were produced
for.
5.
The antibodies use several different methods to
eliminate the pathogen from the body.
6.
When the pathogen has been eliminated some of
the B cells will remain in the blood stream to provide
immunity from a second invasion of that pathogen.
These cells are known as memory cells.
1.
Immune Response
Let’s see this in action!
Once a pathogen enters the body,
the specific antigen of the pathogen is
identified.
2.
The B lymphocyte is identified that
matches the antigen and can produce the
antibody to bind to the antigen.
3.
That B cell and several others begin
rapid cell division by mitosis to increase
the numbers of that B cell.
AIDS
AIDS is a syndrome that is
caused by the HIV virus.
AIDS is categorized as a
syndrome and not a
disease because
syndromes are a group of
symptoms that occur
together.
This syndrome attacks the
body’s defences and
destroys the immune
system leaving the body
weak and defenceless.
http://www.youtube.com/watch?feature=
player_embedded&v=lrYlZJiuf18
HIV
The human immunodeficiency virus (HIV) infects
white blood cells known as lymphocytes.
The virus targets the lymphocyte known as the helper
T-cells which play a very important role in producing
antibodies.
The Virus
HIV
Over a period of time the
virus will destroy the
lymphocytes and
antibodies can no longer
be produced.
This destroys the body’s
immune system and the
infected individual is very
susceptible to pathogens
that cause disease that
would be easy to control
under normal
circumstances.
The HIV virus cannot survive long outside of a host
and it cannot pass easily across the skin.
Transmission of the virus involves an exchange of
fluids between an infected person and an uninfected
person.
The most common
methods of
transmission are:
HIV
http://highered.mcgrawhill.com/sites/0072495855/student_view
0/chapter24/animation__hiv_replication.
html
Method of Transmission
The virus can be transmitted during sexual
intercourse through small cuts or tears in the vagina,
penis, mouth or intestines.
Through the sharing of hypodermic needles with
traces of blood.
The virus can be transmitted from mother to child
across the placenta, through cuts during childbirth, or
in breast milk.
The virus can be transmitted during a blood
transfusion using infected blood.
Social/Ethical Implications
The social implication of living with HIV can be
devastating.
The infected individual will suffer injustices associated
with the disease such as loss of job, income,
insurance, and housing.
Their families and
friends will suffer
grief and they may
lose both friends
and family.
We love Ted! (10 minutes)
http://www.ted.com/talks/lang/en/hans_r
osling_the_truth_about_hiv.html