Diseases and Immunity
Part 2
Background
• Focusing on transmissible diseases (can be passed on from one host
to another)
• This type of diseases are caused by pathogens
• Pathogen: disease-causing organism (bacteria, viruses, fungi,
protozoa/protist)
• Transmissible disease: disease in which the pathogen can be passed
on from one host to another
Transmission
DIRECT
Involve transfer through blood
and other body fluids
i.e. HIV and Malaria
INDIRECT
Involve infection from pathogen
on contaminated surfaces
i.e Salmonella food poisoning,
contaminated water, waste
disposal, contamination by
houseflies, Tinea (‘ringworm’) a
fungal parasite, Amoebic
dysentery, Airborne, ‘droplet’ or
aerosol infection.
Defences against diseases
MECHANICAL
BARRIERS
*skin
*hairs in the nose
*ciliated cells in the
trachea
First line of defence
Non-specific
CHEMICAL
BARRIERS
*Acid in stomach
*Moist lining of nasal passages
& mucus produced by the lining
of the trachea & bronchi
Defences against diseases
IMMUNE
CELLS
When pathogen passes the
first defence
*Phagocytes – phagocytosis
*Lymphocytes – antibody
and anti-toxin production
Second line of defence
Specific
VACCINATION
To enhance the body’s defences
*Involves harmless form of the
pathogen being introduced into the
body by injection or swallowing
Lymphocytes
B-CELLS
Different functions
but inter dependent
T-CELLS
‘Helper’ T-cells
‘Killer’ T-cells
From bone marrow
From the Thymus gland
*become short-lived plasma cells
& produce antibodies that are
released into blood
*some B cells remain in the
lymph nodes as memory cells
*have receptor molecules on their
surface, which attach them to
antibodies
*T cells kill the infected
cells/pathogen
*Helper T-cells stimulate B-cells to
divide and produce antibodies
Antibodies & Immunity
• Lock on to antigens leading to direct destruction of pathogen or
marking of pathogens for destruction by phagocytes
• Each pathogen has its own antigens, which have specific shapes.