6.3 Defense against infectious diseases Flashcards
(97 cards)
1
Q
What is the primary way that the human body prevents infection?
A
By preventing the entry of organisms and viruses that cause disease.
2
Q
How do the oil and pH in the skin act as growth inhibitors for certain bacteria?
A
- The skin has pores for sweating, hair follicles and sebaceous glands that produce oils (called sebum) to keep the skin supple and at a slightly lower pH.
- The oil and low pH both act as growth inhibitors for certain bacteria.
- Populations of bacteria found on healthy skin also prevent growth of harmful bacteria by out-competing them.
3
Q
Cross-sectional diagram of the human skin
A
4
Q
Which parts of the body are open to the outside world and therefore potential entry points for pathogens?
A
- The nose and mouth give access to the nasal passages, sinuses, lungs and the gastrointestinal tract.
- Also, the eyes, the vagina, the urethra and head of the penis are entry points too.
5
Q
What protects the openings on the human body that are potential entry points for pathogens?
A
In these places, mucous membranes help to protect your body.
6
Q
Explain how mucous membranes work
A
- These membranes produce a sticky mucus that contains glycoproteins and lysozymes, enzymes that attack bacterial cell walls.
- Both types of molecules have antiseptic properties (properties that discourage or prevent the growth of microorganisms).
- The mucus itself also forms a barrier, trapping organisms which can be killed by white blood cells that are found in the mucous membranes too.
7
Q
Define mucous membranes
A
- They are made up of a surface layer of epithelial cells over a deeper layer of connective tissue.
- They produce mucus for protection and lubrication.
8
Q
___ and ___ act as physical barriers forming a primary defence against pathogens that cause infectious disease.
A
The skin
Mucous membranes
9
Q
The eyes and the respiratory tract are both protected against infections by ___
A
The secretion of lysozyme onto their surfaces.
10
Q
Mucous membranes act as barriers to pathogens by ___
A
Secreting mucus that traps bacteria for ultimate destruction by phagocytes.
11
Q
Describe how scabs form
A
- Unless you have hemophilia, you will not bleed to death if you cut yourself by accident.
- Normally, the bleeding will stop after a short time due to blood clotting.
- If you observe this process closely, you will see that the blood becomes thicker and starts to gel.
- After a while, a soft scab forms and form a protective layer under which the skin can heal itself.
- The scab also prevents the entry of pathogens into the body.
12
Q
Explain the reactions involved in blood clotting that are triggered by damage to a blood vessel
A
-Clotting factors cause platelets to become sticky and adhere to the damaged region to form a solid plug
-These factors also initiate localized vasoconstriction to reduce blood flow through the damaged region
-Additionally, clotting factors trigger the conversion of the inactive zymogen prothrombin into the activated enzyme thrombin
-Thrombin in turn catalyzes the conversion of the soluble plasma protein fibrinogen into an insoluble fibrous form called fibrin
-The fibrin strands form a mesh of fibers around the platelet plug and trap blood cells to form a temporary clot
13
Q
What is the last step in the reactions in the clotting process?
A
The last step of this cascade of reactions is the conversion of fibrinogen, a soluble and inactive clotting factor in blood, to insoluble fibrin.
14
Q
What enzyme catalyses the conversion of fibrinogen to insoluble fibrin?
A
- This reaction is catalysed by an enzyme called thrombin, which itself had to be activated by the cascade of reactions.
- The result is a network of fibers that traps red blood cells and platelets to form a scab.
15
Q
Image showing fibrin trapping red blood cells and the beginning of a scab
A
16
Q
What happens when a blood clot forms in a coronary artery
A
- Clots can form in the coronary arteries and block the flow of blood.
- Such a clot is called a thrombus , and if it happens in the coronary arteries, it is called a coronary thrombus.
17
Q
Define a thrombus
A
A blood clot that forms in a vessel and remains in the place where it was formed.
18
Q
Diagram of a coronary thrombus and the effect on the heart
A
19
Q
Explain how atherosclerosis works
A
- Atherosclerosis narrows the lumen of arteries and slows down blood flow; thus increasing the chance of a clot blocking a coronary artery.
- This will lead to certain parts of the heart not receiving any oxygen and nutrients, causing that part of the heart to die, resulting in a heart attack.
- When a blood clot reduces the amount of blood reaching the heart muscles rather than stopping it completely, it causes angina or chest pain due to heart muscles not getting enough oxygen-rich blood.
20
Q
When does thrombosis of coronary arteries or formation of a clot within the coronary artery start?
A
- When the fatty deposit (plaque) in artery walls ruptures the lining of the vessel.
- The clot that began at the site of the rupture can grow larger with time and completely block the artery.
21
Q
What other factors can increase the risk of blood clot formation?
A
Smoking, obesity, hypertension (=high blood pressure), and diabetes.
22
Q
The network that forms the basis of a scab is ___
A
Fibrin
23
Q
An initial event in the process of scab formation is the ___
A
Activation of thrombin
The platelets release clotting factors to activate thrombin, which in turn catalyzes the conversion of fibrinogen into fibrin.
24
Q
How can a blood clot cause a heart attack?
A
A blood clot in a coronary artery prevents oxygen and nutrients from reaching the heart muscle.
25
What is the name of a clot that forms in the arteries that supply the heart muscle, and remains there?
A coronary thrombus
26
Despite our body's primary defense systems – the skin and mucous membranes – ___
Pathogens can enter our bodies and cause disease.
27
What happens when pathogens enter the human body and cause disease?
When this happens, the body's second line of defense by the immune system is activated.
28
What two sections can the immune system be subdivided into?
- The non-specific immune system involving phagocytes.
- The specific immune system made up of lymphocytes and antibodies.
29
The blood cells that have an immune function are called ___
White blood cells (or leukocytes).
30
How many types of leukocytes are there?
There are five types of leukocytes, but for our purposes, we will discuss only two.
31
What is the first type of leukocyte (white blood cell)?
Macrophages (phagocytes)
32
Explain how macrophages work
- Macrophages are often called phagocytes because one of their main functions is phagocytosis.
- These cells engulf a pathogen that has entered the body and is found in the lymph nodes or the blood.
- Once inside the phagocyte, enzymes secreted by the lysosome will digest the pathogen.
33
Diagram showing a phagocyte engulfing and digesting bacteria
34
Give an example of how phagocytes are involved in non-specific immunity
- Phagocytes can squeeze past the leaky endothelial cells of the capillaries and invade the tissue where an infection has occurred, for example, in a small wound in your skin.
- This is an example of non-specific immunity to diseases as the phagocytes can respond equally well to a variety of organisms.
35
Define a pathogen
A disease-causing virus or microorganism.
36
Give examples of pathogens
Viruses, bacteria, protozoans, prions, and fungi.
37
Give an overview of how the specific immune system works
- The specific immune system recognizes proteins and other molecules on the surface of pathogens as foreign.
- Any molecule that enters the body and triggers an immune response is called an antigen.
- The immune system usually responds by producing antibodies
38
Diagram of an antibody
39
The type of white blood cell responsible for specific immune responses is called a ___
Lymphocyte
40
Give an example of a type of lymphocyte
- A B lymphocyte, or a B cell.
- There is an amazing diversity of B cells in the body; they have the capability to recognize millions of different antigens through receptors on their surfaces.
- These receptors are essentially an antibody attached to its cell surface as an integral protein so that the antigen binding site points outwards.
41
What is an antibody?
A protein molecule made by lymphocytes with a specific structure and the function of recognising antigens.
42
What happens when a B cell encounters an antigen?
- A complex set of actions takes place to initiate destruction of that antigen.
- Firstly, the B cell divides repeatedly through mitosis to create many copies of the B cell that can recognise the antigen.
- This process is called clonal selection: 'clonal' comes from the fact that mitosis exactly duplicates, or clones, the B cells, and 'selection' comes from the idea that only one type of B cell, the one matching the antigen, has been 'chosen' to divide.
43
What can B cells become? (clonal selection)
- Most of these B cells become plasma cells which make and secrete large quantities of the antibody to circulate in the blood.
- Some of the B cells become memory cells: a long-lived pool of cells capable of responding quickly to the same antigen in case you encounter it again.
44
What are the two ways in which antibodies produced plasma cells work?
- They can bind to the antigen, which allows phagocytes to recognise and then destroy the pathogen.
- They can bind to proteins in the coat of a virus, which will prevent the virus from entering other (human) cells.
45
What happens once an infection has been overcome?
- The number of plasma cells that produce these specific antibodies will decrease.
- However, the memory cells remain in the bloodstream and lymph nodes for a long period of time so that if the same pathogen invades the body again, the response will be much faster.
- This antibody production in response to an infection is called specific immunity.
- This is the reason you only get chicken pox once, and the reason that vaccines work.
46
Explain how some lymphocytes can act as memory cells
Some lymphocytes activated by an infection act as memory cells and can quickly reproduce to form a clone of plasma cells if a pathogen carrying the specific antigen is encountered again.
47
Diagram showing antibody production by B lymphocytes
48
What is an antigen?
An antigen is any molecule or entity that enters the body and triggers an immune response. It is often found on the surface of a pathogen.
49
What is an antibody?
An antibody is a large protein with variable regions produced by your own body that will bind to an antigen.
50
What is the difference between a leukocyte and a lymphocyte?
- A leukocyte is any type of white blood cell.
- A lymphocyte is a particular type of white blood cell that produces antibodies.
51
An antigen associates with which part of an antibody?
Variable regions composed of heavy chains and light chains combined.
52
What is the sequence of events that describes the destruction of pathogens in body tissues by phagocytes?
-Chemical recognition, amoeboid motion (extension of pseudopodia), endocytosis, enzymatic digestion.
-For a phagocyte to engulf a pathogen, first of all, there is chemical recognition. This is followed by the amoeboid movement (accomplished by protrusion of cytoplasm of the cell) to form pseudopodia. Next, the pathogen is taken inside the phagocyte by endocytosis for enzymatic digestion.
53
What is the function of the lymphocytes called memory cells?
Remain in the body long term to react to a specific antigen if it is encountered again.
54
What is a T lymphocyte or T cell?
-A type of lymphocyte called a T lymphocyte, or a T cell, is important in helping B cells complete their function of making antibodies.
55
Diagram of the central role of a T helper cell (one particular type of T cell)
In this diagram, APC stands for a special type of white blood cell ( Antigen Presenting Cell)
.
56
What is APC?
- A special type of white blood cell (Antigen Presenting Cell), that traps the antigen and presents it to the T helper cell.
- Once the antigen has been recognized by the T helper cell, the immune system is activated to fight against the antigen.
- It triggers the production of antibodies and activates macrophages and killer T cells, which will engulf and destroy the antigen.
57
What is HIV?
HIV, or human immunodeficiency virus, infects and stops T helper cells from functioning.
58
Explain how HIV stops T helper cells from functioning
- The infected T helper cells are destroyed, leading to a reduced number in the body.
- Since T helper cells are needed to activate B cells to produce antibodies, infection with HIV causes a loss in the ability to produce antibodies, which can lead to the development of AIDS (acquired immune deficiency syndrome).
59
What does HIV cause an overall reduction of?
Active lymphocytes in the body, including both T and B cells: activated T cells decrease as infected T helper cells are destroyed and activated B cells decrease because there are fewer T helper cells to cause their activation.
60
Diagram of human immunodeficiency virus
61
Describe the structure of HIV
- HIV is a retrovirus that has RNA as its genetic material.
- Once HIV infects a cell through the proteins on the surface of its envelope, it makes a DNA copy from its RNA, with the help of an enzyme called reverse transcriptase.
- The cDNA that is produced is inserted into the host cell's genome.
62
How can HIV be treated?
These days, the infection can be slowed down, or even stopped, with the use of antiviral drugs specifically targeting reverse transcriptase activity.
63
Diagram showing the early symptoms a person can develop when infected with HIV
64
Examples of early HIV symptoms
- Cough with phlegm
- Shortness of breath
- High heart rate
- Muscular fatigue
- Low blood pressure
- Nausea and vomiting
65
What happens when HIV is untreated?
-It will develop into AIDS.
66
What is AIDS?
A range of diseases normally only seen in severely immuno-suppressed patients, for example, fungal pneumonia and Kaposi sarcoma, which is a form of skin cancer.
67
How can HIV be transmitted?
- Sexual intercourse
- Transfusion of infected blood
- Sharing of needles by drug users
- From mother to child during pregnancy, birth, or breastfeeding.
- HIV cannot be transmitted through ordinary day-to-day contact such as shaking hands, hugging and kissing, or via sharing food, drink, or personal items.
68
Anti-retroviral drugs that combat HIV infection target ___
Reverse transcriptase of the virus so that it does not reproduce as quickly in the body
69
What is an antibiotic?
Any substance produced by a microorganism (usually fungi) that can inhibit the growth of other microorganisms.
70
In what concentration are antibiotics most effective and what problems are there with this nowadays?
- Normally, antibiotics require low concentrations to be effective.
- Unfortunately, with their uncontrolled use in hospitals and agriculture, resistance has become widespread, and routinely effective concentrations must now be increased to higher dosages.
71
Why can antibiotics be used to treat bacterial infections in humans and animals?
- Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells.
- Thus, antibiotics can be used to treat bacterial infections in humans and animals (because they are eukaryotes) without harming their body cells.
72
Explain how antibiotics work
- Antibiotics do not have an effect on human cellular processes.
- The drugs target bacterial cell wall and membrane formation, ribosome function or DNA replication, transcription, and translation.
- None of these may directly kill the bacteria, but they will slow down or stop the growth and prevent cellular division.
73
Image of a population of bacteria that exhibits variety in its ability to resist different antibiotics.
Each different antibiotic is contained in white paper dots that have been placed on the petri dish.
Cream-colored areas show bacterial growth, but the clear circles around the paper dots show areas where bacteria cannot grow.
This image also shows that bacterial species may show resistance to more than one antibiotic.
74
Explain the relationship between antibiotics and fungi (reword?)
- Most antibiotics are isolated from (saprotrophic) fungi.
- Fungi and bacteria can compete for the same food resources, so fungi often secrete antibiotics to inhibit the growth of the competing bacteria.
75
Give an example of an antibiotic
Penicillin
76
Are viruses affected by antibiotics?
- No
- Viruses are not living and do not have their own metabolic processes.
- Viruses infect living cells and make use of (or abuse) the cell's own metabolic processes to spread the viral infection.
77
Explain how resistance to new antibiotics develops
- Natural selection favors the spread of resistance.
- Thus, if a mutation causing resistance to an antibiotic occurs in a bacterium, after several generations a strain of bacteria will evolve with genes that confer resistance to that antibiotic.
- Such a scenario must have occurred many times among different types of bacteria.
- But, the biggest problem arises when bacteria exchange genes coding for antibiotic resistance and develop resistance to several antibiotics.
78
When can resistance against antibiotics be particularly dangerous?
- It is not so bad when resistance to only one antibiotic has been developed, but there are currently several strains of bacteria that have become resistant to all known antibiotics.
- Infection with such a strain can be lethal.
- Some diseases, once widespread and untreatable, including tuberculosis and sexually transmitted diseases, such as gonorrhea and chlamydia, are making a comeback due to the strains of bacteria that cause these diseases to be resistant to antibiotics.
- This is likely to affect the lives of millions of people.
79
How have strains of bacteria evolved differently in their response to antibiotics?
- Some strains of bacteria have evolved with genes that grant resistance to (one or few) antibiotics.
- However, some strains of bacteria have multiple resistance making them very difficult to treat.
80
Diagram showing the possible effects of a chlamydia infection
81
The percentage of bacteria showing antibiotic resistance in Neisseria gonorrhoeae and other species of disease-causing bacteria has risen considerably in the past few years.
What has caused this increase?
When an antibiotic is used, only bacteria that are resistant to it survive and these bacteria pass on resistance to their offspring and other strains.
82
Viruses cannot be treated with antibiotics because ___
They do not have a metabolism of their own.
83
Why is resistance to antibiotics a problem?
Bacteria can exchange genes for antibiotic resistance, thereby gaining resistance they didn't have.
84
When and by whom was penicillin discovered?
1928
Alexander Fleming
85
What needed to be done after the discovery of penicillin in 1928?
- Testing needed to be done to ascertain if this molecule would be effective in fighting human infections.
- Howard Florey and Ernst Chain began on this project in the early 1930s.
86
Give an overview of how Florey and Chain used mice to test penicillin
- Florey and Chain infected eight mice with Streptococcus.
- This bacterium causes pneumonia in mice.
- Eight mice were kept under identical conditions, but four of the eight were given an injection of penicillin.
- The four mice that were not treated with penicillin died within 24 hours, but the treated mice stayed alive.
87
What does the result of Florey and Chain's experiment show?
This experiment does not prove a causal relationship but gives a very strong indication that penicillin may have played a role in the recovery of the mice
88
How did Florey and Chain test penicillin on humans?
- Florey and Chain proceeded to test penicillin on very sick patients with infections.
- Most survived, and the commercial production of the drug in the 1940s allowed testing on more and more patients; eventually confirming it as a very effective weapon against infections.
- These days there are very strict protocols and regulations for the testing of new drugs on humans.
- What Florey and Chain did in the 1930s and 1940s would not be allowed today.
89
Describe the regulations in place for testing drugs
- Many nations have their own regulating body, but the standards of the US Food and Drug Administration are considered to be among the most strict.
- These include pre-clinical studies on individual cells and two mammalian species to investigate toxicity before any human trials begin.
- Clinical trials on humans should begin with testing on healthy subjects to further investigate any possible problems (such as possible side effects, and how quickly the drug is metabolized and excreted from the body) before sick patients receive the drug.
90
What did Florey and Chain test through their experiments on mice?
Whether penicillin was effective in treating bacterial infection.
91
What was the conclusion reached by Florey and Chain's experiments?
Penicillin can be used to treat bacterial infections.
92
Why would Florey and Chain's tests of penicillin not be allowed to proceed in the same way today?
There are strict controls on carrying out testing on humans.
93
Which of the following processes in bacteria can be interrupted by antibiotics?
I. cell wall formation
II. aerobic respiration
III. ribosome function
IV. DNA replication
V. plasmid copying
I, III and IV
94
Which is the correct sequence of events when your skin is cut?
I: Thrombin is produced.
II: Fibrinogen is converted into fibrin.
III: Platelets release clotting factors.
III → I → II
95
Which molecules enter the body and trigger an immune response?
Antigens
96
Which enzyme found in HIV allows a DNA copy of the viral RNA to be produced within the host cell?
Reverse transcriptase
97
Describe the structure of antibodies
Antibodies are made up of four polypeptide chains, two heavy and two light chains.
