Topic 6.3: Defense Against Infectious Disease Flashcards Preview

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Flashcards in Topic 6.3: Defense Against Infectious Disease Deck (43):
1

What is the first line of defense against infectious disease?

The first line of defence against infectious disease are the surface barriers that prevent the entry of pathogens into the body

These surface barriers include both the intact skin and mucous membranes

2

Why is the skin protective against infectious disease?

Protects external structures when intact (outer body areas)
Consists of a dry, thick and tough region composed predominantly of dead surface cells
Contains biochemical defence agents (sebaceous glands secrete chemicals and enzymes which inhibit microbial growth on skin)
The skin also secretes lactic acid and fatty acids to lower the pH (skin pH is roughly ~ 5.6 – 6.4 depending on body region)

3

Why is the mucous membrane protective against infectious disease?

Protects internal structures (i.e. externally accessible cavities and tubes – such as the trachea, oesophagus and urethra)
Consists of a thin region of living surface cells that release fluids to wash away pathogens (mucus, saliva, tears, etc.)
Contains biochemical defence agents (secretions contain lysozyme which can destroy cell walls and cause cell lysis)
Mucous membranes may be ciliated to aid in the removal of pathogens (along with physical actions such as coughing / sneezing)

4

Define clotting

Clotting (haemostasis) is the mechanism by which broken blood vessels are repaired when damaged

Clotting functions to prevent blood loss from the body and limit pathogenic access to the bloodstream when the skin is broken

5

What are the two key components of a blood clot?

platelets and insoluble fibrin strands

6

What happens with platelets to form a blood clot?

Platelets undergo a structural change when activated to form a sticky plug at the damaged region (primary haemostasis)

7

What happens with fibrin strands to form a blood clot?

Fibrin strands form an insoluble mesh of fibres that trap blood cells at the site of damage (secondary haemostasis)

8

Define coagulation cascade

The process by which blood clots are formed involves a complex set of reactions collectively called the coagulation cascade

9

What is the first step of the coagulation cascade?

Clotting factors cause platelets to become sticky and adhere to the damaged region to form a solid plug
These factors also initiate localised vasoconstriction to reduce blood flow through the damaged region

10

After Clotting factors cause platelets to become sticky and adhere to the damaged region to form a solid plug, what is the next step of the coagulation cascade?

Additionally, clotting factors trigger the conversion of the inactive zymogen prothrombin into the activated enzyme thrombin

11

After Additionally, clotting factors trigger the conversion of the inactive zymogen prothrombin into the activated enzyme thrombin, what is the next step of the coagulation cascade?

Thrombin in turn catalyses the conversion of the soluble plasma protein fibrinogen into an insolube fibrous form called fibrin

12

After Thrombin in turn catalyses the conversion of the soluble plasma protein fibrinogen into an insolube fibrous form called fibrin, what is the next step of the coagulation cascade?

The fibrin strands form a mesh of fibres around the platelet plug and traps blood cells to form a temporary clot

13

After The fibrin strands form a mesh of fibres around the platelet plug and traps blood cells to form a temporary clot, what is the last step of the coagulation cascade?

When the damaged region is completely repaired, an enzyme (plasmin) is activated to dissolve the clot

14

Define coronary thrombosis

Coronary thrombosis is the formation of a clot within the blood vessels that supply and sustain the heart tissue (coronary arteries)

Occlusion of a coronary artery by a blood clot may lead to an acute myocardial infarction (heart attack)

15

What is the first step to how atherosclerosis develops?

Atheromas (fatty deposits) develop in the arteries and significantly reduce the diameter of the lumen (stenosis)

16

After Atheromas (fatty deposits) develop in the arteries and significantly reduce the diameter of the lumen (stenosis), what is the next step to how atherosclerosis develops?

The restricted blood flow increases pressure in the artery, leading to damage to the arterial wall (from shear stress)

17

After The restricted blood flow increases pressure in the artery, leading to damage to the arterial wall (from shear stress), what is the next step to how atherosclerosis develops?

The damaged region is repaired with fibrous tissue which significantly reduces the elasticity of the vessel wall

18

After The damaged region is repaired with fibrous tissue which significantly reduces the elasticity of the vessel wall, what is the next step to how atherosclerosis develops?

As the smooth lining of the artery is progressively degraded, lesions form called atherosclerotic plaques

19

After As the smooth lining of the artery is progressively degraded, lesions form called atherosclerotic plaques, what is the next step to how atherosclerosis develops?

If the plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow

20

After If the plaque ruptures, blood clotting is triggered, forming a thrombus that restricts blood flow, what is the last step to how atherosclerosis develops?

If the thrombus is dislodged it becomes an embolus and can cause a blockage in a smaller arteriole

21

What is the second line of defense against infectious disease?

The second line of defence against infectious disease is the innate immune system, which is non-specific in its response

A principle component of this line of defence are phagocytic white blood cells that engulf and digest foreign bodies
Other components of the innate immune system include inflammation, fever and antimicrobial chemicals (complement proteins)

22

Define phagocytosis

Phagocytosis is the process by which solid materials (such as pathogens) are ingested by a cell (i.e. cell ‘eating’ via endocytosis)

23

What is the first step of phagocytosis?

Phagocytic leukocytes circulate in the blood and move into the body tissue (extravasation) in response to infection

24

After Phagocytic leukocytes circulate in the blood and move into the body tissue (extravasation) in response to infection, what is the next step of phagocytosis?

Damaged tissues release chemicals (e.g. histamine) which draw white blood cells to the site of infection (via chemotaxis)

25

After Damaged tissues release chemicals (e.g. histamine) which draw white blood cells to the site of infection (via chemotaxis), what is the next step of phagocytosis?

Pathogens are engulfed when cellular extensions (pseudopodia) surround the pathogen and then fuse to form an internal vesicle

26

After Pathogens are engulfed when cellular extensions (pseudopodia) surround the pathogen and then fuse to form an internal vesicle, what is the next step of phagocytosis?

The vesicle is then fused to a lysosome (forming a phagolysosome) and the pathogen is digested

27

After The vesicle is then fused to a lysosome (forming a phagolysosome) and the pathogen is digested, what is the last step of phagocytosis?

Pathogen fragments (antigens) may be presented on the surface of the phagocyte in order to stimulate the third line of defence

28

What is the third line of defense against infectious disease?

The third line of defence against infectious disease is the adaptive immune system, which is specific in its response

It can differentiate between particular pathogens and target a response that is specific to a given pathogen
It can respond rapidly upon re-exposure to a specific pathogen, preventing symptoms from developing (immunological memory)

29

What are B lymphocytes?

B lymphocytes (B cells) are antibody-producing cells that recognise and target a particular pathogen fragment (antigen)

30

What are helper T lymphocytes?

Helper T lymphocytes (TH cells) are regulator cells that release chemicals (cytokines) to activate specific B lymphocytes

31

What is the first step of developing memory B cells?

When phagocytic leukocytes engulf a pathogen, some will present the digested fragments (antigens) on their surface

These antigen-presenting cells (dendritic cells) migrate to the lymph nodes and activate specific helper T lymphocytes

32

After These antigen-presenting cells (dendritic cells) migrate to the lymph nodes and activate specific helper T lymphocytes, what is the next step of developing memory B cells?

The helper T cells then release cytokines to activate the particular B cell capable of producing antibodies specific to the antigen

33

After The helper T cells then release cytokines to activate the particular B cell capable of producing antibodies specific to the antigen, what is the next step of developing memory B cells?

The activated B cell will divide and differentiate to form short-lived plasma cells that produce high amounts of specific antibody

34

After The activated B cell will divide and differentiate to form short-lived plasma cells that produce high amounts of specific antibody, what is the next step of developing memory B cells?

Antibodies will target their specific antigen, enhancing the capacity of the immune system to recognise and destroy the pathogen

35

After Antibodies will target their specific antigen, enhancing the capacity of the immune system to recognise and destroy the pathogen, what is the last step of developing memory B cells?

A small proportion of activated B cell (and activated TH cell) will develop into memory cells to provide long-lasting immunity

36

Define antigen

Antigen: An antigen is a substance that the body recognises as foreign and that will elicit an immune response

37

Define antibody

Antibody: An antibody is a protein produced by B lymphocytes (and plasma cells) that is specific to a given antigen

38

Define antibiotics

Antibiotics are compounds that kill or inhibit the growth of microbes (specifically bacteria) by targeting prokaryotic metabolism

39

Why don't antibiotics work on viruses?

Viruses do not possess a metabolism (they are not alive) and instead take over the cellular machinery of infected host cells

40

Define HIV

The Human Immunodeficiency Virus (HIV) is a retrovirus that infects helper T cells, disabling the body’s adaptive immune system

41

Explain the effects of HIV

HIV specifically targets the helper T lymphocytes which regulate the adaptive immune system
Following infection, the virus undergoes a period of inactivity (clinical latency) during which infected helper T cells reproduce
Eventually, the virus becomes active again and begins to spread, destroying the T lymphocytes in the process (lysogenic cycle)
With a reduction in the number of helper T cells, antibodies are unable to be produced, resulting in a lowered immunity
The body becomes susceptible to opportunistic infections, eventually resulting in death if the condition is not managed

42

How is HIV Transmitted?

HIV is transmitted through the exchange of body fluids (including unprotected sex, blood transfusions, breastfeeding, etc.)
The risk of exposure to HIV through sexual contact can be minimised by using latex protection (i.e. condoms)
A small minority of people are immune to HIV infection (they lack the CD4+ receptor on TH cells that HIV requires for docking)
HIV is a global issue, but is particularly prevalent in poorer nations with poor education and health systems

43

Define pathogen

A pathogen is a disease causing agent that disrupts the normal physiology of the infected organism

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