L13 Tuberculosis

Question 1

Bacterium responsible for most TB cases

Answer 1

Mycobacterium tuberculosis

Question 2

How is TB transmitted and is it acute or chronic

Answer 2

water droplets inhaled into alveoli

chronic

Question 3

What factors will influence the outcome of TB

Answer 3

number and type of organism
immune response (malnutrition, age, immunosuppression etc)
administration of appropriate antibiotics

Question 4

What two things does the pattern of disease depend upon

Answer 4

primary: first exposure to bacteria
OR
secondary: previously exposed individual

Question 5

5 basic stages to primary TB

Answer 5

1. exposure to MTB
2. alveolar macrophage endocytosis
3. T lymphocyte hypersensitivity
4. cell-mediated immune response
5. granuloma formation

Question 6

What happens with macrophages trying to phagocytose bacteria?

Answer 6

can’t degrade
MTB has special wall lipids which prevents a phagosome from forming
no phagosome = no antigen processing
bacilli replicate slowly within macrophages every 16-24 hrs
some macrophages to lymph nodes then blood stream
bacteria continue to proliferate in alveoli (primary site) and lymph nodes = Ghon complex

Question 7

What is a Ghon complex

Answer 7

alveoli and lymph node involvement

Question 8

What is a Ghon focus

Answer 8

only alveoli

Question 9

How does T lymphocyte hypersensitivity occur

Answer 9

some bacteria degraded
present antigen to T lymphocytes (approx. 3 weeks) for T-helper cell response
hypersensitivity reaction activated

Question 10

What happens with the cell-mediated immune response

Answer 10

Th1 cells produce interferon gamma
IFN gamma activates macrophages to become epithelioid macrophages
now MTB can be destroyed if good enough

Question 11

What cytokine prompts macrophages to become epithelioid macrophages

Answer 11

interferon gamma

Question 12

Steps in formation of granuloma

Answer 12

T helper cells form granuloma with caseous necrosis
epithelioid macrophages come together to form giant cells
TNF secreted and more monocytes recruited

Question 13

What are the 5 layers of a granuloma

Answer 13

caseous necrosis
epithelioid macrophages
giant cells 
lymphocytes
fibroblasts

Question 14

What does the course of the disease depend upon

Answer 14

whether patient is sensitized to organism

Question 15

What are latent TB lesions

Answer 15

MTB adapt by changing metabolism

• slow down active replication
• increase cell wall thickness
• “dormant” state that can be reactivated

Question 16

What do 10% of primary TB patients usually develop

Answer 16

progressive primary TB = dissemination disease (military TB, small spots of infection which can spread to other organs)

Question 17

Type of lesion in primary TB

Answer 17

peripheral

Question 18

Type of lesion in secondary TB

Answer 18

apical

Question 19

How can secondary TB develop

Answer 19

reactivation
reinfection

HAS TO BE AFTER HAVING PRIMARY

Question 20

How can secondary TB be characterized

Answer 20

apical lesions in apex of lungs in area with higher oxygen content
little lymph node involvement
T- cell mediated response is familiar = tissue necrosis and cavitation (ie nuclear bombing site of infection)

Question 21

What is secondary TB treated with

Answer 21

prolonged antibiotics

Question 22

What are the symptoms of secondary TB

Answer 22

malaise, anorexia, weight loss, fever
purulent sputum (green)
erosion of cavities into airways
blood in sputum (haemoptysis)
pleuritic pain

Question 23

What will the best case of secondary TB result in

Answer 23

calcification of apical lesions

Question 24

What is the worst case scenario with secondary TB

Answer 24

lesion erodes blood vessels, bronchi, pleura