6.3 Defense against infectious Disease

Question 1

Mucous membranes

Answer 1

Thinner and softer type of skin

Question 2

Sticky Mucus

Answer 2

Sticky solution of glycoproteins traps pathogens; enzymes break down pathogens; pH not favourable to pathogens

Question 3

Skin

Answer 3

continuous (hard to find opening)

many layers/tough

dry

pH
Sebaceous glands secrete chemical called sebum that maintains skin moisture and lowers skin pH

Question 4

Skin clot

Answer 4

When the skin is cut, blood vessels are severed and start to bleed

Cuts to the skin causes opening through which pathogens can potentially enter the body

Blood clots at the site of a wound to prevent blood loss and the entry of pathogens.

Blood clotting involves a cascade of reactions and happens very quickly

Must be monitored carefully – blood clotting in blood vessels can cause blockages.

Platelets (small cell fragments) along with damaged tissue release clotting factors in response to a wound.

Platelets aggregate at the site of the injury and form a temporary plug, then release clotting factors

Question 5

Thrombin

Answer 5

The cascade results in the production of an enzyme thrombin.

Thrombin converts soluble protein fibrinogen into insoluble fibrous protein fibrin

Fibrin fibres form a mesh across the wound site which captures blood cells and platelets forming a clot

In the presence of air the clot dries to form a scab which shields the healing tissues underneath

Question 6

Coronary heart disease

Answer 6

blood clots sometimes form in coronary arteries —> coronary thrombosis

Heart tissues are not provided with supply of O2

Question 7

Atherosclerosis

Answer 7

occlusion (block) in coronary artery

Question 8

heart attack

Answer 8

Either condition may cause myocardial infarction

Coronary heart disease
Atherosclerosis

Question 9

Risk factors of blood clot formation in coronary artery

Answer 9

genetic
age
sex
smoking
diet
excercise
obesity
stress

Question 10

If a pathogen enters the body, the first line of defence are:

Answer 10

Phagocytic leukocytes

“eating” cell – white blood cell

Question 11

Phagocytosis

Answer 11

Step 1
Phagocytes can squeeze through the pores of capillaries and move to sites of infection
Chemotaxis (movement in response to chemicals) attracts the phagocytes to the area of invasion.

Step 2
The phagocyte attaches to the pathogen’s cell surface proteins.

Step 3
The pathogen is engulfed by endocytosis

Step 4
A phagosome forms. This is a vesicle that contains the pathogen. Lysosomes deposit the enzymes into the phagosome.

Step 5
The digestive enzymes break down the pathogen.

Step 6
Waste products are expelled from the cell by exocytosis.

Question 12

Antigen

Answer 12

a molecule, often found on a cell or virus surface, that causes antibody formation (characteristic to the surface of cell/cell type)

Question 13

Antibody

Answer 13

a globular protein that recognizes a specific antigen and binds to it as part of an immune response

Question 14

An immune response is triggered by “non-self” cells…

Answer 14

which is why matches are crucial in transplants and blood transfusions – and why stem cell technologies are so promising

Question 15

Many different lymphocytes exist. Each type recognizes…

Answer 15

one specific antigen

Question 16

When the immune system is challenged by the invasion of a pathogen…

Answer 16

the corresponding lymphocyte responds.

Question 17

It makes a clone of itself…

Answer 17

each of which produces antibodies to the pathogen.

Question 18

This process is called clonal selection…

Answer 18

as the right lymphocyte is selected and then cloned.

Question 19

Roles of antibodies

Answer 19

Make a pathogen more recognizable to phagocytes so they are more easily engulfed

Prevent viruses from docking to host cells so that they cannot enter the cells

Question 20

Antibodies only persist for…

Answer 20

a few weeks/months

Question 21

Some cloned cells remain as …

Answer 21

memory cells, ready for a second invasion by the pathogen. This is immunity.

Question 22

Antibiotics

Answer 22

drugs used in the treatment and prevention of prokaryotic bacteria

Question 23

Antibiotics are designed to disrupt structures or metabolic pathways in bacteria:

Answer 23

Cell walls and membranes
Protein synthesis (translation)
DNA/RNA synthesis
Other metabolic processes (e.g. enzyme function)

Question 24

Many antibacterial antibiotics were discovered in …

Answer 24

saprotrophic fungi. E.g. penicillin discovered in some strains of Penicillium fungi

Question 25

Florey and Chain’s experiments to test penicillin on bacterial infections in mice

Answer 25

For their work on penicillin Fleming, Florey and Chain were awarded the Nobel prize for medicine in 1945
An outline of the modern process of drug testing and clinical trials

Years of extensive laboratory research on animals and human cells to determine usefulness, likely dosage and possible side-effects

Assess the safety of the drug and the impact of side-effects on a small group of healthy volunteers – starting with a small dosage which is slowly increased

Test the effectiveness of the drug against a control on a small group of affected volunteers

Randomised and blind testing on a large group of affected volunteers against a placebo and competing drugs

Risks associated with scientific research: Florey and Chain’s tests on the safety of penicillin would not be compliant with current protocols and testing

Question 26

Viruses

Answer 26

non-living and can only reproduce when they are inside the living host cells

Use host cell metabolism – no effect of antibiotics
Protected by the host cell structure

Very different structure to prokaryote, just a protein capsid and genetic material - no cell wall or membrane to attack

Antibiotics should not be prescribed for viral infections

Antivirals can be used on some viruses to target virus enzymes

Question 27

Indiscriminate use of antibiotics is leading to antibiotic resistance in bacteria…

Answer 27

an example of evolution by natural selection

Question 28

Some bacteria have become resistant to multiple antibiotics:

Answer 28

E.g. methicillin-resistant Staphylococcus (MRSA)
E.g. multidrug-resistant tuberculosis (MDR-TB)

Question 29

How to avoid antibiotic resistance…

Answer 29

Prescribe antibiotics for only serious bacterial infections

Patients complete courses of antibiotics to eliminate infection completely

High standards of hygiene to eliminate cross-infection in patients

Farmers not using antibiotics on animal feeds to stimulate growth

Pharmaceutical companies developing new types of antibiotic – no new antibiotics since 1980s

Question 30

Human Immunodeficiency Virus (HIV)

Answer 30

gradually attacks the immune system

If a person becomes infected with HIV, they will find it harder to fight off infections and diseases.

Question 31

Acquired Immune Deficiency Syndrome (AIDS)

Answer 31

syndrome caused by HIV

Immune system is too weak to fight off infections, and develops when the HIV is advanced.

Last stage of HIV where the body can no longer defend itself and may develop various diseases and if left untreated, death.

No cure for HIV; however, with the right treatment and support, people can live long and healthy lives.

Question 32

Human Immunodeficiency Virus (HIV) methods of transport

Answer 32

sexual intercourse, muscus membranes of penis and vagina can cause minor bleeding

transfusion of infected blood, or blood products such as Factor VIII

sharing of hypodermic needles by intravenous drug users