6.3 - Defence against infectious diseases Flashcards
1
Q
what is a disease?
A
- the condition that negatively affects the structure or function of an organism.
- Sometimes, the microorganism is opportunistic whilst others are highly specialised
2
Q
what are the Microorganisms that cause disease?
A
- in the host (the one who is being infected) is called a pathogen
3
Q
what are humans primary defence system?
A
- against pathogens is the skin and mucous membranes as it prevents majority of pathogens from entering the body.
- It acts as physical barrier
4
Q
how does the skin protect the body from pathogens?
A
- it is extremely tough by providing both a physical and chemical barrier
- skin contains sebaceous glands that secrete sebum to maintain skin moisture and lowers the skin pH slightly to inhibit the growth of bacteria and fungi
5
Q
what are Mucous membranes?
A
- are thinner and softer than skin
- Mucous membranes secrete mucous and this acts as a barrier by trapping and either swallowing or expelling pathogens and harmful particles
- Mucous contains antibacterial enzyme lysozyme that has antiseptic properties
6
Q
what do cuts do?
A
- when tissues are injured, the break in the physical barrier allows pathogens to enter
7
Q
what do clots do?
A
- blood vessels are also commonly injured
- A non-specific defence takes place called clotting
- Clotting serves to seal up the wound and it prevents further loss of blood and blood pressure
- Clotting is also important as it temporarily reseals the damaged site on the skin and prevent further entry of pathogens
8
Q
how does blood clotting work?
A
- involves a cascade of reactions (at least 12), where each produces a product that catalyses the next reaction
- tightly controlled and very quick so there are no clots in vessles
9
Q
how do blood clots form?
A
- blood contains two components that form clots: thrombocytes and fibrinogen.
- Thrombocytes, also called platelets, are fragments of cytoplasm pinched off from larger cells in the bone marrow.
- Platelets will aggregate at the site of a cut to form a temporary plug that prevents any further bleeding, so then triggers the release of clotting factors that triggers the clotting process
10
Q
what is Fibrin production?
A
- platelets release the enzyme and the enzyme together with clotting factors in the plasma convert a plasma protein called prothrombin to its active form thrombin
- final reaction involves thrombin, which converts soluble fibrinogen protein into strands of insoluble fibrin.
11
Q
what is Fibrinogen?
A
- Fibrinogen is a membrane-wrapped protein found in blood plasma, which is the liquid part of blood
- Fibrin forms a mesh of fibres across the wound that traps platelets and blood cells to form a semi-solid clot or scab at the surface of the skin as it is air-dried
12
Q
what is Coronary thrombosis?
A
- arteries with atherosclerosis have a rough inner surface and this tends to cause blood clots to form
- arteries with atherosclerosis have a rough inner surface and this tends to cause blood clots to form
- deprives the heart of oxygen and other nutrients, and the cells in this area of the heart are unable to
respire to produce ATP - the heart becomes irregular or stops
13
Q
what happens because of Coronary thrombosis?
A
- The wall of the heart makes quivering movements called fibrillation that do not pump blood effectively
- can be fatal unless stent insertion
- Atherosclerosis causes occlusion in the coronary arteries, and it may lead to a myocardial infarction (MI) or a heart attack
- factors that are correlated with an increased risk of coronary thrombosis and heart attacks include: smoking, high blood cholesterol concentration, high blood pressure, diabetes, obesity and a lack of exercise
14
Q
what are Phagocytes?
A
- they are white blood cells that are the next line of defence
- a non-specific response to pathogens
- can move through the capillary pores (extravasation) and into sites of infection to ingest the pathogen
- A phagosome is formed around the pathogen, and it fuses with lysosomes that contain digestive enzymes that destroy the foreign pathogen.
- Waste material is expelled - pus
15
Q
what is phagocytosis?
A
- Phagocytes recognise and engulf pathogens by a transport mechanisms known as endocytosis
16
Q
what is an antigen?
A
- a foreign substance that stimulates a specific immune response
- they can be molecules on the surface of viruses or foreign cells, or toxins produced by microorganisms
- When the immune response detects an antigen, it produces proteins called antibodies (Ab)
17
Q
what are antibodies?
A
- part of the specific immune response
- a protein found in blood plasma that recognises and binds to a specific antigen and helps to counter its effects by clearing the pathogen
18
Q
how are antigens fought in the body?
A
- enters body and is recognised by white blood cell called a B-cell with a specific receptor to the antigen
- B-cell matures and produces antigen-specific antibodies
- Antigen-presenting cells (macrophages and dendritic cells) can activate helper T-cells (TH cells)
- Another white blood cell - TH cells gives processed antigen to the B-cell as a foreign antigen. TH cells also secrete chemicals (cytokines) to activate B-cells
- compatible B-cell is activated and it undergoes proliferation (increase in cell numbers) and differentiates into plasma cells and memory B-cells
- plasma B-cells produce antibodies that destroy the antigen. These are shortlived cells
- memory B-cells remain in circulation for many years to provide immunity against the same antigen if it is encountered again by proliferating and differentiating into plasma cells very rapidly
19
Q
what are antigen-presenting cells?
A
- macrophages and dendritic cells
20
Q
what is HIV?
A
- Human immunodeficiency virus (HIV) is a retrovirus that infects helper T-cells - essential for production of antibodies
- Antibody production involves complex processes and uses different types of lymphocytes: B and T cells
21
Q
what does HIV do?
A
- the virus undergoes a period of clinical latency where it is inactive
- virus becomes active and spreads where it destroys helper T-cells and stops production of antibodies
- Without a functioning immune system, the body is vulnerable to pathogens that would
normally be effectively controlled, - prone to opportunistic pathogens
22
Q
what happens because of HIV?
A
- secondary infection such as pneumonia that results in death because immune system is down
23
Q
where did HIV come from?
A
- a global issue especially in developing countries.
- It was first identified in 1983.
- HIV is a retrovirus with RNA as its genetic material.
- It uses reverse transcription during the replication phase in host cells.
- It embeds its genetic material in the host’s DNA to avoid host detection
- HIV is transmitted through the exchange of body fluids
- antivirals can be taken to slow down infection
24
Q
what do antibiotics do?
A
- inhibit the growth of microorganisms
- blocks specific metabolic pathways just for bacteria and not eukaryotes such as bacterial DNA replication, transcription, translation, ribosome functions and cell wall formation
- Most antibiotics destroy bacterial cells by disrupting the cell membranes or puncturing a hole (lysis).
- Antibiotics do not inhibit eukaryotic cell functions, and therefore it can be used to treat bacterial infections in humans without causing any harm.
25
how were antibiotics discovered?
- discovered in saprotrophic fungi that compete with saprotrophic bacteria for dead organic matter
26
how was penicillin found?
- by Scottish scientist Alexander Fleming in 1928 in the fungus Penicillium rubens
- development of penicillin as an antibiotic used in medicine was Australian scientist Howard Florey and German scientist Ernst Chain
27
how did they test penicillin?
- 1939-1940, Florey and Chain tested the effect of penicillin on bacterial infections in mice (in vivo)
- Eight mice were infected with Streptococcus bacteria with a known concentration to cause death from pneumonia, of which, four were injected with penicillin.
- Within 24 hours, the 4 untreated mice died whilst the 4 penicillin-treated mice remained healthy
- then tested on human and it worked
28
what is a virus?
- Viruses are non-living and must exist inside host cells.
- Viruses do not have cell walls and rely on host cell’s metabolic pathways to reproduce as they lack a metabolism.
- viruses are not affected by antibiotics but antivirals will inhibit some viruses’ disease progression in hosts
- if use antibiotic for virus it kills good bacteria
- Overuse of antibiotics may potentially develop antibiotic-resistant strains of bacteria
29
what is antibiotic resistance?
- because of evolution the bacteria can resist the antibiotics
- Golden Staph, Staphylococcus aureus (MRSA) which has infected the blood or surgical wounds of hospital patients and resists all commonly used antibiotics
- Another example is MDR—TB.
- The problem is certainly avoidable if:
* Doctors prescribe antibiotics only for serious bacterial infections.
* If patients complete full courses of antibiotics.
* If hospital staff maintain high standards of hygiene.
* If farmers do not use antibiotics in livestock feed.
