Defense from Illness or Injury
Defense against Disease/Illness
Germ Theory of Disease
 Disease is caused by pathogens
 Examples: bacteria, fungi, protists, viruses
 Spread by: physical contact, contaminated food and water,
infected animals
Nonspecific Defense -does not discriminate between one threat
and another; includes physical and chemical barriers
First Line of Defense – keep pathogens out of the body
 Skin (the most important nonspecific barrier to disease)
 Secreted Fluids (mucus, tears, saliva)
Second Line of Defense – the Inflammatory Response
 Patrolling cells & proteins attack invaders that
penetrate body’s outer barriers
 Triggered by tissue damage
 Increased blood supply delivers extra white blood cells,
red blood cells, platelets, and clotting agents
 Causes inflammation – swelling, redness
 Fever helps the body fight infection by increasing
temperature and raising heart rate
Specific Defense – specific to the threat
Third Line of Defense – the Immune Response
 Triggered by antigens (foreign invader; pathogen)
 Antibodies bind to specific antigens (your body either
makes antibodies to fight the antigen or already has the
antibodies required)
o Each antibody is unique to match a particular
antigen

A good immune system has specificity, diversity, memory,
and the ability to distinguish self from non-self
Outside Help
1. Vaccination – the immune system is exposed to a harmless
version of a pathogen
a. Vaccines stimulate the body to produce antibodies
so there will be a rapid response if there is a future
exposure to the antigen
b. Vaccines are particularly useful to prevent viral
disease; also used for bacterial and fungal disease,
but not as effective
c. Jenner used the first successful vaccine (to prevent
smallpox)
2. Antibiotics – drugs that combat living cells by interfering
with various cellular functions
a. Penicillin, the first antibiotic used, was discovered
by Alexander Fleming by accident
Antibiotics only work on things that are made of cells: bacteria,
protists, fungi. They don’t work on viruses.
Defense against Injury (Healing)
Healing happens in overlapping stages.
1. Hemostasis – Platelets in blood stick to the injury and to
each other, forming a clot to slow and stop bleeding
2. Inflammation – White blood cells clear out damaged or
dead body cells and also work to remove bacteria or other
debris.
3. Proliferation (growth of new tissue) – Cells around the
wound divide, forming new cells. Cells pull together,
helping to close the wound.
4. Maturation (remodeling) – Alignment of cells to resume
original shape/condition. Unneeded cells undergo
apoptosis (programmed cell death.)