6.3 Defense against Disease

Question 1

Pathogens

Answer 1

Pathogens are disease-causing agent that disrupt the normal
physiology of infected organisms (i.e. homeostatic imbalance)
Pathogens may be species-specific or cross species barriers
* Diseases that can be naturally transmitted between
animals and humans are called zoonotic diseases

Question 2

Lines of Defense

Answer 2

Immune system can be divided into three lines of defense:
* 1st line of defense – Surface barriers (skin / mucus)
* 2nd line of defense – Innate immunity (non-specific)
* 3rd line of defense – Adaptive immunity (specific)

Question 3

Surface Barriers

Answer 3

The first line of defense against infectious disease is the
surface barriers that function to prevent pathogenic entry
Skin
* Protects external structures (i.e. outside the body)
* Thick, dry and composed predominantly of dead cells
* Glands secrete chemicals to restrict bacterial growth
Mucous Membranes
* Protects internal structures and cavities (inside body)
* Thin region composed of living cells that secrete fluid
(mucus) to trap pathogens (which may then be removed)

Question 4

Clotting

Answer 4

Clotting seals damaged vessels to prevent pathogenic entry
* Injured cells and platelets release clotting factors
* These factors convert prothrombin into thrombin
* Thrombin converts fibrinogen (soluble) into fibrin (insoluble)
* Fibrin forms a mesh of fibres that block the injured site
* Clotting factors also cause platelets to become sticky and
form a solid plug (called a clot), sealing the wound
* This process of events is called a coagulation cascade
* Clot formation in coronary arteries lead to heart attacks

Question 5

Antibiotics

Answer 5

Antibiotics are compounds that target prokaryotic features
but don’t harm eukaryotic cells (i.e. don’t affect host organism)
* May target structures (e.g. cell wall) or metabolic processes
Some strains of bacteria have evolved with genes that confer
resistance to antibiotics (some even have multiple resistance)
* Antibiotics can’t be used to treat viruses (no metabolism)
The first antibiotic identified was penicillin (Fleming – 1928)
* Its treatment use was demonstrated by Florey and Chain

Mice were infected with pathogenic bacteria
Conclusion: Penicillin has antibiotic properties