Download Topic 6.3 Defence against infectious disease

Topic 6.3
Defence against
infectious disease
Topic 6: Human Health and Physiology
A pathogen in an
organism or virus that
causes disease.
Some diseases are caused by genetic defects, others
by environmental stresses – not all diseases are
What is a pathogen?
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Patho = disease Gen = Producer
A pathogen is an organism or virus that
causes a disease.
Why aren’t viruses called organisms??
Organisms are living things. What are the
characteristics of living things?
Characteristics of living things
Properties of life
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Cellular Respiration
Reproduction
Metabolism
Homeostasis
Heredity
Responsiveness
Growth and development
Viruses infecting living cells
Viruses are not living organisms
Viruses do not
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Grow
Have homeostasis
Metabolize
Viruses do
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Infect cells and use the cell to make more
viruses
Cause disease in many organisms
Viruses
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Viruses are micro organisms consisting of
a strand of DNA or RNA surrounded by a
protein coat
They enter cells and hijack the cells
machinery to make more viruses.
They then burst out of the host cell,
destroying or damaging it.
Other pathogens
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Bacteria
Fungi
Protozoa
Animals
Prions
Flip over to I-biology ppt
Antibiotics
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Major medical improvement
Produced by fungi and bacteria
Work on bacteria but…
Cannot be used on viruses
antibiotics block specific metabolic pathways found in bacteria, but not eukaryotic cells
because viruses reproduce using the host cell (eukaryotic) metabolic pathways, they are
unaffected by antibiotics
antibiotics have produced great benefits world-wide in the control of bacterial diseases
 Staphylococcus infections controlled
 STD's, such as gonorrhea and syphilis controlled
antibiotic resistance has evolved in bacterial populations
In what form can pathogens enter the body?
6.3.3 Outline the role of skin and mucous
membranes in defence against pathogens
Skin
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Unbroken skin
provides a fantastic
barrier against
pathogens trying to
enter the body
Sebum (oil)
waterproofing
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You do not need to
learn the parts of this
diagram.
Mucous Membranes
(and other non-specific immunity)
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Anywhere on the body that is not protected by
skin has its own method of protection.
Lungs – Mucous
membranes and cilia
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Stomach – Acid
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Urethra – mucus
membranes + urine is
sterile
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Eyes – tears contain
lysozymes
Vagina – mucous
membranes and acid
Anus – mucous
membranes
Infection!
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This occurs if pathogens do get inside the
body.
The proteins on the surface of a pathogen
are immediately recognised as “foreign”.
Phagocytes (a type of leucocytes) will
ingest the pathogen by phagocytosis.
Phagocytosis
Phagocytes
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Phagocytes are found
in the blood and in
body tissues such as
the lungs.
After phagocytes
engulf pathogens,
they destroy them
with digestive
enzymes found in
lysosomes.
Phagocytosis
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damage to tissues allows invasion across 1st line of
defense
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phagocytes attracted to site by chemotaxis toward
histamine
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microbes successfully invade body fluids or tissues
damaged cells release histamine and other chemicals initiating
inflammation
phagocytes recognize microbes as foreign by antigen recognition
variety of phagocytic cells: neutrophils (small phagocytic &
macrophages (large phagocytic)
phagocytes endocytotically engulf microbes,which are
digested by enzymes held in lysosomes
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digested microbe fragments are displayed on cell membrane
phagocytes with microbe fragments displayed = antigenpresenting cells
antigens and antibodies
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antigen: a molecule recognized as foreign by the immune system; it
elicits an immune response; usually a foreign protien
antibody: =immunoglobulin
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a globular glycoprotein
recognizes an antigen by its complementary shape and charge
thus allowing it to attach to the antigen specifically
marking it for attack by the immune system
Antibodies
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Also known as immunoglobulins
Globular glycoproteins
The heavy and light chains are polypeptides
The chains are held together by disulphide
bridges
Each antiboby has 2 identical antigen binding
sites – variable regions.
The order of amino acids in the variable
region determines the shape of the binding
site
How Antibodies work?
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Some act as labels to identify
antigens for phagocytes
Some work as antitoxins i.e. they block
toxins for e.g. those causing diphtheria and
tetanus
Some attach to bacterial flagella making
them less active and easier for phagocytes
to engulf
Some cause agglutination (clumping
together) of bacteria making them less likely
to spread
Type
Number of Site of action
ag binding
sites
Functions
IgG
2
Increase
IgM
10
Blood
Tissue
fluid
CAN CROSS
PLACENTA
macrophage activity
Antitoxins
Agglutination
Blood
Agglutination
Tissue
fluid
IgA
2 or 4
Secretions
(saliva,
tears, small intestine,
vaginal, prostate,
nasal, breast milk)
Stop
bacteria
adhering to host
cells
Prevents bacteria
forming colonies on
mucous membranes
IgE
2
Tissues
Activate
mast cells
 HISTAMINE
Worm response
Lymphocyte with antigens
Blood types
Where do antibodies come from?=
Lymphocytes
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Produce antibodies
B-cells mature in bone marrow then
concentrate in lymph nodes and spleen
T-cells mature in thymus
B and T cells mature then circulate in the
blood and lymph
Circulation ensures they come into contact
with pathogens and each other
White Blood cells
WBC (Lymphocytes) are made in the bone marrow. The
cells divide and mature into 2 types:
T Lymphocytes
Develop in the thymus gland
B Lymphocytes
Develop in the bone marrow  lymph nodes
The Cell-Mediated Resopnse
Foreign, mutant or infected cells are
identified as ‘non-self’ by surface antigens.
T helper cell recognises antigens and
alerts the other T cells.
Killer (Cytotoxic) cells attack with perforin
or nitric oxide. T memory cells remember
the antigen for a later attack.
T suppressor cells switch off T and B cells
after attack over.
The Humoral (Antibody) Response
Plasma ɞ cells have a different shape
receptor on its membrane. There are about
10 million kinds in your body at any one
time! Each can detect any antigen of a
pathogen. Once activated they divide very
fast (clone) and start to secrete specific
antibodies. Antibodies slowly removed
from blood and lymph. Memory ɞ cells
remember antigens and can turn into
Plasma ɞ if re-infected.
HIV
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HIV is a virus that specifically attacks the
T lymphocytes.
This means the number of lymphocytes
decreases.
Less antibodies are made.
Predict the consequences…