Topic 6.3: Defence Against Infectious Disease

Question 1

Pathogens

Answer 1

Pathogens are disease-causing agent that disrupt the normal physiology of infected organisms

Question 2

Lines of Defense

Answer 2

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

First line of defense against infectious disease

Answer 3

Surface barriers that function to prevent pathogenic entry

• Skin
• Mucous Membranes

Question 4

Skin methods to fight against infectious diseases

Answer 4

1) Protects external structures by a layer of dead cells

2) Secretes enzymes and fatty acids to lower pH and inhibit bacterial growth.

Question 5

Mucous Membranes

Answer 5

1) Protects internal structures and cavities

2) Trap pathogens (which may then be removed)

Question 6

Function of clotting

Answer 6

Seal damaged blood vessels to prevent pathogenic entry

Question 7

Coagulation cascade (Clotting process)

Answer 7

a) Injured cells and platelets release clotting factors
b) These factors convert prothrombin into thrombin
c) Thrombin converts fibrinogen (soluble) into fibrin (insoluble)
d) Fibrin forms a mesh of fibers that block the injured site
e) Clotting factors cause platelets to become sticky and form a clot, sealing the wound

Question 8

Characteristics of innate immune responses (2)

Answer 8

a) Non-specific. It does not differentiate between different types of pathogens.
b) Non-adaptive. It responds to an infection the same way every time.

Question 9

Function of phagocytes

Answer 9

Engulf and digest foreign bodies

Question 10

Method used by phagocytes to fight against infectious diseases (4)

Answer 10

a) Phagocytes migrate via the blood to sites of infection (chemotaxis)
b) Pathogens are surrounded by extensions and are then internalized within a vesicle via phagocytosis
c) Vesicle may fuse with a lysosome to digest the pathogen
d) Fragments (antigens) are presented on the surface of the cell to active the third line of defense

Question 11

Characteristics of adaptive immune responses (2)

Answer 11

a) Specific. It can differentiate between different types of pathogens and respond accordingly.
b) Adaptive. It produces a heightened response upon re-exposure.

Question 12

Antigen definition

Answer 12

Substance that the body recognize as foreign and that can elicit an immune response

Question 13

Antibody definition

Answer 13

Globular protein produced by B lymphocytes that are specific to a given antigen

Question 14

Lymphocytes method used to fight against infectious diseases

Answer 14

a) B cells each produce one specific type of antibody
b) Macrophages present antigen fragments to helper T lymphocytes
c) TH cells release cytokines and activate the antigen specific B cells
d) The plasma cells make antibodies specific to the antigen
e) A small proportion of B cell clones differentiate into long-lasting memory B cells

Question 15

Antibiotics definition

Answer 15

Compounds that kill or inhibit the growth of prokaryotes by targeting prokaryotic metabolism or structure

Question 16

Effect of antibiotics on virus

Answer 16

Since viruses do not possess a metabolism, they must be treated with specific antiviral agents opposed to antibiotics

Question 17

First identified antibiotic

a) Name
b) Treatment

Answer 17

a) Penicillin (Fleming, 1928)

b) Florey and Chain in rats

Question 18

Why does strain resistance occur?

Answer 18

a) Bacteria mutate and resistance to an antibiotic naturally arises
b) Bacteria divide, so a resistant strain of bacteria can proliferate
c) Bacteria strains can become resistant to multiple antibiotics

Question 19

Causes of strain resistance

Answer 19

a) Antibiotics are often over-prescribed

b) Freely available without prescription

Question 20

Methods used to infect by Human Immunodeficiency Virus

Answer 20

a) HIV specifically targets the helper T lymphocytes which regulate the adaptive immune system
b) The virus undergoes a period of inactivity during which infected helper T cells reproduce
c) Eventually, the virus becomes active again and begins the spread, destroying the T lymphocytes
d) With a reduction in the number of helper T cells, antibodies are unable to be produced
e) When all plasma cells have been destroyed and a person’s ability to produce a specific immune response is gone, then it’s classified as AIDS

Question 21

Transmission of HIV

Answer 21

a) Sexual contact
b) Pregnancy
c) Childbirth
d) Injection drugs
e) Blood transfusion

Question 22

Lymphatic system

Answer 22

The lymphatic system is a secondary transport system that protects the body by producing and filtering lymph
* Lymph is a clear fluid rich in white blood cells that arises
from the drainage of interstitial fluid from the tissues
* Lymph is filtered at lymph nodes, whereby pathogens are removed and the fluid is returned to venous circulation