Download TOPIC 6.3

TOPIC 6.3
Defence Against Infectious
Disease
Chapter 24
6.3.1 Define pathogen.
• An organism or virus that causes a
disease
• Types = viruses, fungi, bacteria,
protozoa and worms of various types
6.3.2
Antibiotics are effective against
bacteria, but not viruses
• Antibiotics are chemicals that work against living
bacterial cells, but do not affect our body cells
• Bacteria are prokaryotic, body cells are eukaryotic
– Different biochemical rxs and pathways
– Protein synthesis not exactly the same
– Bacteria have a cell wall, body cells don’t
• Many types of antibiotics
– One type blocks protein synthesis in bacteria
– Another type inhibits cell wall production so they can’t
grow and divide
Antibiotics have no effect on viruses
• Antibiotics disrupt metabolism in bacteria
• Viruses make use of our body cells’
metabolism to create new viruses
• Viruses have no metabolism of their own
• Any chemical that would inhibit this would
damage our body cells
• Antibiotics are chemicals with the ability to
damage or kill prokaryotic cells, but not
eukaryotic cells or their metabolism
Antibiotics
• Availability varies widely in various parts of
the world
• Some places infections from bacteria are
devastating, whereas people in other areas
barely give these infections a second thought
• Overuse of antibiotics has led to strains that
are resistant to many antibiotics
6.3.3
Role of skin and mucous membranes
• Skin is a barrier to infection
– 2 primary layers: dermis and epidermis
– Under layer is the dermis which contains sweat glands,
capillaries, sensory receptors and dermal cells that give
structure and strength to the skin
– Top layer is the epidermis which is constantly replaced
as dermal cells die and move upwards. These dead cells
are a good barrier and prevent pathogens from entering
living tissue. It is important to cleanse and cover cuts
and abrasions.
Stomach acid
• When pathogens enter the body in
food and water the acidic
environment in the stomach helps to
kill most of these ingested
pathogens.
Mucus
• Pathogens may enter in the air we breathe through the
nasal passage or mouth
• This route of entry is lined with tissue known as mucous
membrane
Area with mucous What it is and does
membrane
Trachea
Nasal passages
Tube which carries air to & from lungs
urethra
Tube which carries urine from bladder to
the outside
vagina
Reproductive tract leading from uterus to
the outside
Tubes which allow air to enter the nose
and then the trachea
Mucous Membranes
• Produce and secrete a lining of sticky mucus
• Traps incoming pathogens and prevents them
from reaching cells they could infect
• Some mucous membrane tissue is lined with cilia
– Hair-like extensions capable of wave-like movement
– This movement moves trapped pathogens up and out
of mucous-lined tissues like the trachea
• Cells that secrete mucus also secrete an enzyme
called lysozyme which chemically damages
pathogens
6.3.4 Phagocytic Leucocytes
• Leucocytes = white blood cells in the bloodstream
which help us fight off pathogens that enter our bodies
and provide immunity for many pathogens
• One type of leucocyte = macrophage- large WBCs that
can change their cellular shape to surround an invader
and take it in through the process of phagocytosis
• Moves similar to an amoeba (pseudopods), so it is
referred to as amoeboid motion
• Macrophages can squeeze in and out of small blood
vessels = can fight invaders outside of the bloodstream
Macrophages
• Can recognize a cell as a natural part of the body
(“self”) or not a part of the body (“not-self”)
– Based on proteins molecules that make up part of the
surface of all cells, bacteria (cell membrane) and viruses
(protein coat)
• If “not-self” the macrophage engulfs invader by
phagocytosis
• Phagocytes contain many lysosome organelles to
help chemically digest the pathogen
• Non-specific response = identity of pathogen not
known, just that it is “not-self”
6.3.5 Antigens and Antibodies
• Antigens are molecules our bodies recognise as
“not-self”
• ex. bacteria (cell membrane proteins) and viruses
(protein coat) – foreign proteins are antigens
• Most pathogens have several different antigens on their
surface
• Antibodies are protein molecules that we produce
in response to a specific type of antigen
• Measles, flu, etc.
• Each type of antibody is different in response to a
different pathogen
6.3.6 Antibody Production
Similar to each other
Each antibody is a protein that is Y shaped
Binding site at the end of each fork of the Y
Binding site is where antibody attaches itself to an
Cytoplasm containing
antigen
ribosomes and plasmids
mesosome
Y
Antibodies specific
for an antigen on
surface of bacterium
B Lymphocytes
• Leucocytes that produces antibodies
• We each have many types of B lymphocytes
• Each produces only a small number of antibodies
relative to a massive infection that may occur;
however, our immune response has a way of
producing many antibodies
• Steps of a typical immune response:
1. Specific antigen identified (e.g. a particular cold virus)
2. Specific B lymphocyte identified to produce an
antibody which will bind to the antigen (proteins on
the cold virus protein coat)
3. The B lymphocytes clone themselves (divide
repeatedly by mitosis) to rapidly the number of
the same type of B lymphocyte
4. The newly formed “army” begins antibody
production
5. Newly released antibodies circulate in the
bloodstream and find their antigen match (the
proteins of the pathogen)
6. Using various mechanisms, the antibody helps
eliminate the pathogen
7. Some of the cloned antibody-producing
lymphocytes remain in the bloodstream and give
immunity from a second infection by the same
pathogen. These are called memory cells.
6.3.7 Effects of HIV on Immune System
• HIV = human immunodeficiency virus
– Results in a set of symptoms collectively called AIDS
(acquired immune deficiency syndrome)
– Viruses must find a type of cell in the body that
matches their own proteins in a complementary way
• Only certain body cells are damaged by certain viruses
• Reflected in the symptoms associated with a particular
infection
• Ex. a cold virus locates proteins on mucous membrane
cells in your nasal region and damages those cells
resulting in swelling of the area and excess mucus
production- this virus does not affect other body cells that
do not have the same protein
• Only certain cells in the body have protein in their
membrane that HIV recognizes
• One of these cells function as a communicator cell in
the bloodstream – called a helper-T cell (this is the
cell that HIV infects
• HIV has a latency period (infection occurs, but cells
remain alive)….i t is usually many years after HIV
infection that the symptoms called AIDS develop
• Helper- T cells are the cells that communicate which
cells need to undergo cloning and begin antibody
production
• When helper-T cells begin to die, communication no
longer occurs and antibodies do not get produced
• Secondary infections (cancer, pneumonia, etc.)
ultimately take the life of someone with AIDS.
Topic 6.3.8 Cause, Transmission & Social
Implications of AIDS
• Causes already outlined in previous slides
– HIV infection of the helper-T cells
• Difficult to find vaccine or cure because HIV “hides
away” inside host cells for years
• Body’s immune responses continue to work against
other pathogens, but not to combat the HIV
because it is already inside body cells waiting for a
chemical signal to become active
• The virus also mutates relatively quickly for a virus
– Body’s immune responses or vaccines may not even
recognize HIV after several mutations
• Adding to the difficulty of developing medication is
the association of HIV with sexual activity and drug
abuse
– This led to some reluctance to allocate $$$ for HIV
research
– Today huge sums of $$$ are allocated for HIV/AIDS
research, but this is a relatively new development
• Transmission of HIV has another historical
significance which has affected how society has
responded to the disease
– Transmitted from person to person by body fluids
– Body fluid exchanges during sex and reusing unsterile
syringe needles for legal or illegal drug injections
• AIDS was originally labeled as a disease affecting
homosexuals and drug abusers
• At one time, blood for transfusions wasn’t tested
for blood-borne diseases like HIV
• People became HIV positive from transfusions
• Today, in countries with reasonable medical care,
blood is routinely tested
• AIDS is rapidly spreading by way of heterosexual
encounters and everyone is at risk
• HIV positive individuals may be discriminated
against:
– Employment
– Insurance
– Education access
– Social acceptance
• Not every country has the education and
medical facilities to deal with this disease
• Until a cure is found, perhaps the best that
can be accomplished is to:
1. Continue to lengthen the lifespan of those
infected
2. Educate people on how to decrease their risk of
exposure to HIV
• AIDS is truly a global problem – effective
treatment and education must not be limited
to certain countries
Diagnosis of HIV
• Enzyme-linked immunosorbent assays (ELISA)
are used to detect the presence or absence of
a particular protein
• For example, people recently infected with
HIV will initially produce antibodies against
HIV. These antibodies can be detected by
ELISA to determine if a patient is HIV positive
or negative
Assignment
• On the night of August 28th 1987, a small home
in the town of Arcadia, Florida was burned in a
fire that was determined to have been started on
purpose.
• Report on this event by reading the handouts
– What, where, when, why, how and your reaction.
• You could also search the internet for more
about the Ray family
• This is due Friday 5-14