PATH 201 - LECTURE 12

what is the pulmonary defence mechanism around larger microrganisms

• trapped in the mucocilliary blanket that lines the nose and the upper respiratory tract and transported by cilliary action to the back of the throat where it is swaller

what is the pulmonary defence mechanism around smaller microrganisms

• smaller than 5 micrometres are carried in to the alveoli where they are phagoyctosed by leukocytes

what are the mechanisms by which microorganisms evade pulmonary defenses

• attachment and entry into epithelial cells in the lower respiratory tract

• release of toxins that impair cilia

• resistance to killing following phagocytosis

what are some examples of upper respiratory tract infections

sore throat, tonsilitis, pharyngitis, laryngitis, sinusitis and the common cold

are upper respiratory infections caused by virus or bacteria

mostly virus

what is pneumonia

infection of the lung tissue

when does pneumonia occur

• when hosts immune system is compromised

• when local defence mechanism of the lung is compromised

what are some examples of compromised local defences of the lungs

• loss or suppression of the cough reflex

• impaired ciliary function

• thick mucus

• impaired phagocytic activity

• pulmonary congestion the edema

• upper respiratory infection

what are the anatomical classifications of pneumonia

• lobar

• bronchopneumonia

describe lobar pneumonia

• when an entire lobe is infected

describe bronchopneumonia

• when infection starts in bronchi and bronchioles and spreads to adjacent lung tissue in a patchy way

• not confined to one lob or lung

when is it useful to classify pneumonia by etiological agent

• it can determine treatment

what are some examples of pneumonia classified by clincal setting

• community acquired pneumonia

• hospital acquired

• aspiration pneumonia

what is the most common causative organism of community acquired bacterial pneumonia

streptococcus pneumoniae

does bacterial pneumonia present as lobar or bronchi

mostly lobar

but can be both

what are the 4 stages of lobar pneumonia

congestion

red hepatizatin

grey hepatization

resolution

over what duration does the first stage of lobar pneumonia occur

• day 1

describe the congestion phase of pneumonia

• dilated and congested capillaries in the alveoli wall

• fibrin rich fluid exudate in the alveolar spaces

over what duration does the second stage of pneumonia occur

days 2-4

describe the red hepatization phase of pneumonia

• fibrinous exudate, neutrophils and some RBCs in the alveolar spaces

• capillaries in the alveolar wall still congested

over what druation does the 3rd stage of lobar pneumonia occur

• day 5-8

describe the grey hepatization phase of lobar pneumonia

• Fibrinous exudate in the alveolar space now has macrophages and few neutrophils

• macrophages contain hemosiderin

• alveolar wall congestion has subsided

what is hemosiderin

brown haemoglobin derived pigment from phagocytosis of red blood cells

Describe the fourth stage of lobar pneumonia

resolution - enzymatic digestion of the exudate occurs, followed by expectoration and phagocytosis by macrophages

what is occuring here

stage 1 of lobar pneumonia - congestion

what is occuring here

• stage 2 red hepatization

• nuetrophuls are the cells with the dark purple stained nuclei

what is occuring here

stage 3 of pneumonia - grey hepatization

what is occuring here

bronchopneumonia

• inflammation is patchy and surrounding the bronchi

what are common complications of bacterial pneumonia

• pleural effusion

• emphysema

• lung abscess

• respiratory and circulatory failure

what is pleural effusion

• fluid accumulation between the lung and ribcage in the pleural space

what is lung abscess

necrotic area in the lung

what kind of pneumonia do viruses produce

atypical pneumonia

what is atypical pneumonia

• inflammaotry exudate is in the alveolar walls rather than inside the alveolar spaces

• composed primarily of mononuclear cells such as lymphocutes, macrophages and plasma cells (instead of neutrophils)

what bacteria can lead to atypical pneumoia

• mycoplasma pneumoniae

• chlamydophila pneumoniae

whats this

viral/atypical pneumoniae

whats this

complication of viral pneumoniae where hylaine membranes are lining the alvoeli and causing acute resperitaoty distress syndrome

gas exchange cannot occur

what causes tubercolosis

• myobacterium tubercolosis

how is tb transmitted

cough sneeze laugh sing

can people wiht latent TB or extrapulmonary TB transmit the infection

no

describe mycobacterium tubercolosis

• aerobic bacillus with a lipid capsule

describe how myobacterium tubercolosis can be visualised

• not visible under gram stain

• visualised by ziehl-neelsen stain - pink

what happens after the initial tubercolosis infection

• mycobaterial antigen enter the hilar lymph nodes and presented to T cells which differentiate into TH1 cells

• TH1 cells produce IFN-y which activates macrophages

• macrophages secrete TNF which leads to monocyte and macrophage recruitment

• activated macrophages become epitheliod cells

• epitheliod cells, monocytes and lymphocyte form TB granulomas

what is a TB granuloma

• infection cant be cleared and so they develop a granuloma to contain it

what are giant cells

fusion of mutliple macrophages creates giant cells

what is caseous necrotic core of TB granuloma

• centre is cheesy and necrotic

• collateral tissue damage as a result of the immuen response and cytokine release

what is granuloma surroudned by

• fibrosis

• which is an attempt at healing

what r all the arrows

what are all the arrows

what is the gohn focus

• area of primary infection in the lung that develops granulomas

what is the ghon complex

• hilar lymph nodes that were involved in the first infection that develop granulomas + ghons focus

• together make the ghon complex

what are the red and white arrows

red arrow is the ghon focus

white arrows are the hilar lymph nodes involved in the intial infection that also develop granulomas

what are the possible outcomes after primary infection

• immunity against TB

• latent TB

• progressive TB

describe immunity against TB as a possible outcome of the primary infection

• TH1 response leads to killing of the organism

• ghon complex heals by fibrosis

• fibrosis followed by calcification

• the pateint will then have acquired immunity against TB

describe latent TB as a possible outcome of TB

• the organism may remain dormant within the intial ghon focus or in the extrapulmonary sites

• it can get reactivated when the hosts immunity drops

describe progressive primary TB as a possible outcome of the primary infection

• in immunosurpressed people the infection progresses and the immune resposne results in extemsive necrosis and damage

what is miliary TB

• during progressive primary TB

• spread of the organism can lead to TB granulmoas in multiple organs

scattered millet seed like granulomas

milliary tb

what is the result of reactivation of TB

• reactivate or reinfection results in rapid mobilisation of a vigorous immune reaction

• large necrotic granulomas with lots of fibrosis around them form

where do secondary lesions due to secondary TB form

• in the apical parts of the lungs where oxygen tension is the highest bc mycobacterium tubercolosis is an aerobic organism

what is chronic fibrocaseous TB

• secondary TB

• called that due to the massive areas of central caseous necrosis surrounded by fibrsos

what is cavitary TB

• secondary TB - extensive tissue destruction destroys adjacent bronchial walls

• patient will then cough up bacteria laden caseous material which leaves cavities - therefore cavitary TB

does secondary TB lead to miliary TB

yes it can but not as common as it is with primary TB

what are the arrows pointing to

The left arrow is TB lesions with extensive caseation and fibrosis - fibrocaseous TB

The right arrow is the apical cavity created after coughing up caseous necrotic matieral - cavitary TB

how is TB defintively diagnosed

• identifying M. tubercolosis in a clincal sample using Z-N stain or PCR

what are some observations that are used in the diagnosis of TB

• cough, sputum, night fever sweat

• granulomas

• chest x ray

• mantoux test/interferon gamma release assay

what is the treatment for active TB

2-phase treatment

1. intensive phase: bacteriocidal

2. confirmation phase: sterilization

describe intensive phase treatment

4 drugs given for 2 months

describe confirmation phase

2 drugs given for 4 months

Describe the treatment against latent disease

• patient under 40 - 1 drug 9 months or 2 drugs 4 months