1. DEFENCE AGAINST INFECTIOUS DISEASE
The human body has structures and processes that resist the continuous threat of invasion by pathogens.
Topic 6.3
IB Biology
Miss Werba

2. TOPIC 6 – HUMAN PHYSIOLOGY
6.1
DIGESTION & ABSORPTION
6.2
THE BLOOD SYSTEM
6.3
DEFENCE AGAINST INFECTIOUS DISEASE
6.4
GAS ECHANGE
6.5
NEURONS & SYNAPSES
6.6
HORMONES, HOMEOSTASIS & REPRODUCTION
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3. THINGS TO COVER U.1 U.2 U.3 U.4 U.5 U.6 U.7 U.8 Statement Guidance
The skin and mucous membranes form a primary defence against pathogens that cause infectious disease.
U.2
Cuts in the skin are sealed by blood clotting.
U.3
Clotting factors are released from platelets.
U.4
The cascade results in the rapid conversion of fibrinogen to fibrin by thrombin.
U.5
Ingestion of pathogens by phagocytic white blood cells gives non-specific immunity to diseases.
Subgroups of phagocyte not required.
U.6
Production of antibodies by lymphocytes in response to particular pathogens gives specific immunity.
Subgroups of lymphocyte are not required but students should be aware that some lymphocytes act as memory cells and can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered.
U.7
Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells.
U.8
Viruses lack a metabolism and cannot therefore be treated with antibiotics. Some strains of bacteria have evolved with genes that confer resistance to antibiotics and some strains of bacteria have multiple resistance.
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4. THINGS TO COVER A.1 A.2 A.3 Statement Guidance NOS 4.8
Causes and consequences of blood clot formation in coronary arteries.
A.2
Florey and Chain’s experiments to test penicillin on bacterial infections in mice.
A.3
Effects of HIV on the immune system and methods of transmission.
The effects of HIV on the immune system should be limited to a reduction in the number of active lymphocytes and a loss of the ability to produce antibodies, leading to the development of AIDS.
NOS
4.8
Risks associated with scientific research—Florey and Chain’s tests on the safety of penicillin would not be compliant with current protocol on testing.
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5. PATHOGENS
U.1
Any organism or virus that can cause infectious disease is called a pathogen.
Most pathogens only infect one species.
The Ebola virus and HIV have appeared to cross the species barrier from wild animals to humans.
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6. THE IMMUNE RESPONSE
The immune response is how your body recognizes and defends itself against the presence of a pathogen.
The human immune system is composed of three major parts that work together to keep out or neutralize pathogens:
physical barriers,
the innate immune system, and
the adaptive immune system
These are our “three lines of defence”.
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7. FIRST LINE OF DEFENCE: Physical barriers
U.1
The physical barriers to infection include:
intact skin and
mucous membranes
Both host natural flora and fauna which compete with pathogens
Both have lysozyme enzymes present to break down pathogens
Both have a pH that is unfavourable to pathogens
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8. FIRST LINE OF DEFENCE: Physical barriers
U.1
Skin:
Protects external structures (outer body areas)
Is a continuous, (hopefully) unbroken layer
Is dry – discourages growth/reproduction of pathogens
Has several layers of keratinized (hardened) cells
Contains biochemical defence agents sebaceous glands secrete chemicals which inhibit the growth of some bacteria
The skin also releases acidic secretions to lower pH and prevent bacteria from growing
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9. FIRST LINE OF DEFENCE: Physical barriers
U.1
Mucous membranes:
Protect internal structures (externally accessible cavities and tubes, such as trachea, vagina and urethra)
Contains cells that release fluids to wash away pathogens (mucus, tears, saliva, etc.)
Contains biochemical defence agents secretions contain lysozyme, which can destroy cell walls and cause cell lysis
May be ciliated to aid in the removal of pathogens
Is sticky - traps pathogens
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10. FIRST LINE OF DEFENCE: Physical barriers
U.1
Intact skin
Intact mucosa
Acidic skin secretions
Keratinised
Mucous
Nasal hairs
Cilia
Gastric juice
Acidic vaginal secretions
Digestive enzymes in saliva & tears
Urine
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11. FIRST LINE OF DEFENCE: Physical barriers
U.1
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12. What happens when they make it past the 1st line???
THE IMMUNE RESPONSE
U.2
What happens when they make it past the 1st line???
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13. SECOND LINE OF DEFENCE: Innate immune system
The innate immune response has two features:
non-specific  cannot differentiate between microbes
non-adaptive  produces the same response every time (no memory)
Both the blood and lymphatic systems support the immune response.
The blood system produces the body’s leucocytes (white blood cells) and transports them to the sites of infection in the blood.
Lymph also contains leucocytes and comes from the drainage of fluid from the blood stream and surrounding tissues.
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14. SECOND LINE OF DEFENCE: Innate immune system
Cellular defences
Systemic & Chemical defences
Phagocytes
Natural Killer cells
Blood clotting
Inflammation
Antimicrobial proteins - interferons - cytokines - complement
Fever
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15. THE IMMUNE RESPONSE
U.2
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16. SECOND LINE OF DEFENCE: Innate immune system
Phagocytosis
Macrophages (phagocytic leucocytes) ingest pathogens
Phagocytes circulate in blood but can enter the body tissues in response to infection.
They concentrate at sites of infection in response to the release of chemicals from the damaged cells.
They detect pathogens and engulf them (by endocytosis or more specifically, phagocytosis)
Membrane forms around pathogen to form a vesicle
Lysosomes digest contents of vesicles
Macrophages are assisted by antibodies attached to pathogens.
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17. SECOND LINE OF DEFENCE: Innate immune system
U.2 – U.4
Blood clotting
Blood clotting involves a chain of biochemical reactions.
Allows us to seal wounds and prevent excess blood loss.
Blood clotting involves platelets (fragments of much larger cells)
Platelets contain granules filled with chemicals that act in the clotting process, including:
Serotonin
Ca2+ ions
Enzymes
ADP
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18. SECOND LINE OF DEFENCE: Innate immune system
U.2 – U.4
Blood clotting
A blood clot consists of a plug of platelets within a network of insoluble fibrin fibres.
The fibrin fibres become entangled and create a mesh in which red blood cells become trapped, blocking blood flow.
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19. SECOND LINE OF DEFENCE: Innate immune system
U.2 – U.4
Platelets
Damaged blood vessels. Exposure to air.
stimulates
Prothrombin in plasma
Clotting factors released from platelets
stimulates
Thrombin
stimulates
Soluble fibrinogen circulating in plasma
Insoluble fibrin fibres
+ RBCs
CLOT
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20. SECOND LINE OF DEFENCE: Innate immune system
Blood clotting
cf. Topic 6.2
An embolism is an obstruction in a blood vessel that gets stuck while traveling through the bloodstream.
The obstruction is usually a blood clot but it can also be air, fat, tumour tissue, or other foreign matter.
An obstruction in a coronary artery can reduce or block blood flow to the heart muscle, which can lead to a heart attack.
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21. SECOND LINE OF DEFENCE: Innate immune system
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22. What happens when they make it past the 2nd line???
THE IMMUNE RESPONSE
U.5
What happens when they make it past the 2nd line???
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23. THIRD LINE OF DEFENCE: Adaptive immune system
Cellular defences
Chemical defences
Antigen-presenting cells (APC)
B cells
Plasma cells
Helper T (TH) cells
Cytotoxic T (TC) cells
Suppressor T (TS) cells
Delayed hypersensitivity T (TDH) cells
Memory cells
Antibodies (immunoglobulins)
Cytokines
Complement
Antigens
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24. THIRD LINE OF DEFENCE: Adaptive immune system
Antigen:
a substance or molecule that is recognised by the body as foreign and causes an immune response (ie. antibody formation)
Antibody:
a protein that recognizes an antigen
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25. THIRD LINE OF DEFENCE: Adaptive immune system
The adaptive immune response has two features:
specific  can differentiate between specific microbes and respond accordingly
adaptive  it can produce a heightened response upon re-exposure (it has memory)
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26. THIRD LINE OF DEFENCE: Adaptive immune system
The immune system can differentiate between ‘self’ and 'non-self’ cells due to the presence of MHC marker proteins.
Macrophages possess MHC class II markers, which present foreign substances to the adaptive immune system.
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27. THIRD LINE OF DEFENCE: Adaptive immune system
Antigen presentation:
When macrophages engulf a pathogen and destroy it (via the lysosome), they present antigen fragments on their surface with their MHC class II molecules.
This allows cells of the adaptive immune system (lymphocytes) to generate a specific response against that particular antigen.
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28. THIRD LINE OF DEFENCE: Adaptive immune system
Antibody production:
Antibodies are produced by B lymphocytes.
The antibodies that are produced are specific for that antigen.
The antigen is presented to the B cell by an antigen presenting cell (APC) or Helper T (TH) cell
The lymphocyte capable of thwarting this antigen-bearing cell will divide many times, forming a clone.
Once selected, this clone will expand, allowing a lot of the antibody to be produced to neutralise the infection.
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29. THIRD LINE OF DEFENCE: Adaptive immune system
Antibody production:
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30. THIRD LINE OF DEFENCE: Adaptive immune system
Antibodies act in different ways:
Opsonisation
Makes a pathogen more recognisable to phagocytes
Neutralisation of viruses
Binding to a virus to prevent it from entering a host cell
Neutralisation of toxins
Binds to pathogen toxins preventing them from causing damage
Agglutination
Clumping the pathogens together to prevent them from entering cells
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31. THIRD LINE OF DEFENCE: Adaptive immune system
Immune memory :
Some of the B lymphocytes capable of thwarting this antigen differentiate to form memory B cells.
These memory cells can quickly reproduce to form a clone of plasma cells if a pathogen carrying a specific antigen is re-encountered.
The memory cells can remain dormant for many years, providing the basis for immunity.
Helper T (TH) cells also produce memory cells.
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32. Macrophage Helper T cell B cell
U.6
Macrophage
ingests pathogen
presents antigen on surface via MHCII
Helper T cell
corresponds to specific antigen
releases antigen
divides to form memory cells
releases cytokines
releases cytokines
divides to form active TH cells
IMMUNITY
B cell
corresponds to specific antigen
presents antigen on surface via antibody
divides to form memory cells
IMMUNITY
divides to form plasma cells
SECRETE ANTIBODIES
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33. THIRD LINE OF DEFENCE: Adaptive immune system
Antibody production:
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35. ANTIBIOTICS
U.7
U.8
Antibiotics inhibit specific chemicals or metabolic pathways found in bacteria.
eg. cell protein synthesis or cell wall formation
This is why antibiotics are effective against prokaryotic cells but not viruses or eukaryotic cells.
Viruses are intra-cellular parasites and lack a metabolism. Therefore, they cannot therefore be treated with antibiotics.
Some strains of bacteria have evolved with genes that confer resistance to specific antibiotics and some strains of bacteria have multiple resistance.
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36.
23 min

37. ANTIBIOTICS
A.2
Alexander Fleming accidentally discovered penicillin in
Howard Florey and Ernst Chain later extracted enough penicillin to test penicillin on bacterial infections in mice.
Animal trials (1938):
injected the mice with the penicillin to test its toxicity
then they injected mice with a haemolytic streptococci bacteria
they gave half the mice penicillin and the rest all died
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38. ANTIBIOTICS Human trial 1:
toxicity trial run on a cancer patient was attempted
patient had a bad reaction to the treatment, which was later shown to be due to impurities in the sample.
Human trial 2 (1941):
patient had a bacterial infection in a wound
patient given a purified penicillin preparation and showed immediate signs of improvement
insufficient penicillin was available to continue his treatment and he later died
Further trials were later conducted and large scale production of antibiotics began in America.
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39. There are risks associated with scientific research.
RISKS OF RESEARCH
NOS 4.8
There are risks associated with scientific research.
Florey and Chain’s tests on the safety of penicillin would not be compliant with current protocol on testing.
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40. EFFECTS OF HIV HIV: Human Immunodeficiency Virus
It reduces the number of active lymphocytes that are involved in antibody production.
This results in a loss of the ability to produce antibodies.
As a result, the infected person is more likely to develop a disease.
These diseases are called opportunistic diseases and are the major cause of death of people with HIV and AIDS.
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41. EFFECTS OF HIV AIDS: Acquired Immune Deficiency Syndrome
AIDS is caused by HIV
AIDS is not a disease – but a collection of symptoms and/or opportunistic diseases that develops over the course of the HIV infection.
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42. TRANSMISSION OF HIV
A.3
HIV is transmitted through blood, sexual contact, body fluids, placenta, childbirth or breastfeeding.
Blood and semen contain the highest concentration of HIV
Transmission rates are uneven around the world.
Transmission risk increases depending on society’s traditions, beliefs, behaviour.
Condoms or other latex barriers only protection against transmission through sexual contact.
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43. DEFENCE AGAINST INFECTIOUS DISEASE
Q1.
Which of the following statements about antibodies is correct?
Antibodies are polypeptides.
Antibodies are produced by the bone marrow.
Antibodies are pathogenic foreign substances.
Antibodies kill bacteria but not viruses.
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44. DEFENCE AGAINST INFECTIOUS DISEASE
Q2. Describe how phagocytic leucocytes may act as a defence against disease. [4] Q3. Outline the cause and transmission of HIV and AIDS. [5]
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