6.3 Defense against infectious Disease Flashcards
Mucous membranes
Thinner and softer type of skin
Sticky Mucus
Sticky solution of glycoproteins traps pathogens; enzymes break down pathogens; pH not favourable to pathogens
Skin
continuous (hard to find opening)
many layers/tough
dry
pH
Sebaceous glands secrete chemical called sebum that maintains skin moisture and lowers skin pH
Skin clot
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
Thrombin
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
Coronary heart disease
blood clots sometimes form in coronary arteries —> coronary thrombosis
Heart tissues are not provided with supply of O2
Atherosclerosis
occlusion (block) in coronary artery
heart attack
Either condition may cause myocardial infarction
Coronary heart disease
Atherosclerosis
Risk factors of blood clot formation in coronary artery
genetic
age
sex
smoking
diet
excercise
obesity
stress
If a pathogen enters the body, the first line of defence are:
Phagocytic leukocytes
“eating” cell – white blood cell
Phagocytosis
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.
Antigen
a molecule, often found on a cell or virus surface, that causes antibody formation (characteristic to the surface of cell/cell type)
Antibody
a globular protein that recognizes a specific antigen and binds to it as part of an immune response
An immune response is triggered by “non-self” cells…
which is why matches are crucial in transplants and blood transfusions – and why stem cell technologies are so promising
Many different lymphocytes exist. Each type recognizes…
one specific antigen
When the immune system is challenged by the invasion of a pathogen…
the corresponding lymphocyte responds.
It makes a clone of itself…
each of which produces antibodies to the pathogen.
This process is called clonal selection…
as the right lymphocyte is selected and then cloned.
Roles of antibodies
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
Antibodies only persist for…
a few weeks/months
Some cloned cells remain as …
memory cells, ready for a second invasion by the pathogen. This is immunity.
Antibiotics
drugs used in the treatment and prevention of prokaryotic bacteria
Antibiotics are designed to disrupt structures or metabolic pathways in bacteria:
Cell walls and membranes
Protein synthesis (translation)
DNA/RNA synthesis
Other metabolic processes (e.g. enzyme function)
Many antibacterial antibiotics were discovered in …
saprotrophic fungi. E.g. penicillin discovered in some strains of Penicillium fungi
Florey and Chain’s experiments to test penicillin on bacterial infections in mice
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
Viruses
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
Indiscriminate use of antibiotics is leading to antibiotic resistance in bacteria…
an example of evolution by natural selection
Some bacteria have become resistant to multiple antibiotics:
E.g. methicillin-resistant Staphylococcus (MRSA)
E.g. multidrug-resistant tuberculosis (MDR-TB)
How to avoid antibiotic resistance…
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
Human Immunodeficiency Virus (HIV)
gradually attacks the immune system
If a person becomes infected with HIV, they will find it harder to fight off infections and diseases.
Acquired Immune Deficiency Syndrome (AIDS)
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.
Human Immunodeficiency Virus (HIV) methods of transport
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
