resp 2 Flashcards
what is the main cause of TB
mycobacterium tuberculosis
what is tb
bacterial infection into alveoli
chronic inflammatiory response due to factors in bacterial wall
infection can be asymptomatic
what are the factors that predict the outcome of TB
number of organisms ingested (bacterial load)
immune response - malnutrition, infancy, old age, poor-underpriveleged, overcrowded environments, co-morbidities, immunosuppressive therapy or drug-dependent
admin of appropriate antibiotics
what determines the disease pattern for TB
primary infection = first exposure to bacteria
secondary infection: previously exposed individual
can go from primary -> secondary -> milliary
or primary -> primary progressive -> miliary
what are the stages of primary TB development
exposure to myobacterium tuberculosis alveolar macrophage endocytosis t lymphocyte hypersensitivity cell-mediated immune response granuloma formation
describe stage 1 of TB = exposure to m. tuberculosis
uninfected person inhales infected aerosols
bacili avoid standard defence mechanisms and move into lung alveoli
describe stage 2 TB = alveolar macrophage endocytosis
Macs engulf but cant degrade m.tb because of cell wall lipids
mtb remains within macphag
no lysosome fusion => no antigen processing
bacilli replicate slowly within macs every 16-20 hrs
some macs carry bacilli to regional lymph nodes
can disseminate by blood = ghon complex => legions
describe 3rd stage of TB = T lymphocyte hypersensitivity
macs degrade some bacteria = present antigen to T lymphs =>
takes 3 weeks for T helper response hypersensitivity reaction
describe the 4th step primary TB development = cell mediated immune response
Th1 cells => interferon gamma => activate macs to become bactericidal = inc conc of lytic enzymes + stim formation of phagolysosome
now act macs can contain infection
describe 5th stage primary TB development = granuloma formation
T helper cells = forming granuloma + caseous necrosis
epitheliod macs form giant cells
also secrete TNF to recruit more monoccytes
what are the main features of granuloma formation in primary TB
- central area of caseous necrosis
- surrounded by act macs
- giant cells
- lymphocytes
- fibroblasts
describe the 6th stage of primary TB = healed or latent lesions
healed lesion = immune response destroys bacteria => scar tissue
latent lesion = mtb adapt to env by changing their metabolism = slow down replication inc cell wall thickness, enter dormant state and can be reactivated
describe the pathogenesis of primary tb, focusing on ghon complex
- ghon focus = granuloma in periphery of lung w/organisms
- lymph node involvement for help from lymphocytes
- altogether = ghon complex
describe the pathogenesis of progressive primary TB
high bac load/inc bac virulence/immunosuppression
-local progression = lesion enlarges, large areas of caseous necrosis causing cavities, expand to lower lobe
dissemination disease = miliary TB
what is miliary TB
prganisms drain through lymphs to venous blood and circulate back to lungs via pulmonary arteries
describe the pathogenesis (2 steps) of secondary TB
reactivation of dormant disease from old granuloma
reinfection = newly acquired bacs
what do you see in path pots for secondary TB
destruction of lung with cavitations
apcial lesions bc high o2 content at apex
little lymph invovlement bc pre-existing hypersensitivity. -> prompt infmam response that partition infection
t-cell mediated immune response is familiar with TB antigens -> tissue necrosis and production of cavities
what are the outcomes of secondary TB
can be asymptomatic
symptoms from cystokines and ac macs (malaise, fever)
progressive pulm involvement -> purulent sputum
cured with prolonged antibiotics except for resistant strains
best outcome = calcification of apical TB be collagen deposition around granuloma
what outcomes can occur in secondary TB if there are problems with the legions
apcial lesion can enlarge until tissue is destryoed
- lesions erodes BV =miliary spread, haemoptysis (gonnac ough blood)
- lesion erodes bronchi = tuberculous bronchopreumonia
- lesion invades pleura = pleuritic pain, tuberculous empyema (caseous necrosis within pleural cavity)
what is tuberculous bronchopenumonia
outcome of bronchi erosion bc of legion expansion
infected lymph node erodes into bronchus
living bacilli pass down bronchi and bronchioles )gravity)
infection spreads -> granulomatous lesions -> galloping consumptions = fatal
