Flashcards in Inflammation 4 Deck (17):
WHY IS THE LUNG VULNERABLE TO AIRBORNE INFECTION?
Huge area of alveoli acting as interface between inspired air and respiratory system. (Equine lung surface is ~2000m2)
Large volume of air is continuously entering the lungs.
There is a high concentration of noxious elements in the air.
THE LUNGS ARE VULNERABLE TO BLOOD BORNE MICROBES/TOXINS/EMBOLI
Because the entire output of the right heart enters the lungs.
9% of total lung volume is in the lungs.
The pulmonary capillary bed is the largest in the body. eg. Humans have 2400km of capillaries, 1ml of blood occupies ~16km of capillary bed.
IMPORTANT FEATURES OF BRONCHI
Supported by cartilage.
Efficient mucocilliary defences.
IMPORTANT FEATURES OF BRONCHIOLES
Transition zone between conducting airways and gas exchange.
Diminished mucociliary defences.
No supporting cartilage.
Clara cells are metabolically active, producing reactive metabolites.
Alveolar macrophages and neutrophils accumulate, and can release damaging oxidative free radicals.
IMPORTANT FEATURES OF ALVEOLI
Delicate, thin walled.
Comprised of vascular endothelium (capillary)
Fused basal lamina
TYPE I PNEUMOCYTES- Provide support, holding alveoli together.
TYPE II PNEUMOCYTES- Produce surfactant. Also principal cells of repair in case of Type I cell damage.
PORES OF KOHN- Permit passage of bacteria and exudates between alveoli. Interalveolar connections.
Oxygen passes from alveolus to blood, CO2 passes from blood to alveolus for expiration.
NORMAL RESPIRATORY TRACT FLORA.
SEEN IN THE UPPER RESPIRATORY TRACT ONLY.
Nasal cavity, pharynx, larynx.
Can cause disease if it enters the lower tract. The lower tract is essentially sterile.
M. haemolytica in cattle.
P. multocida in cats, cattle, pigs.
B. bronchiseptica in dogs, pigs.
Can be BRONCHOPNEUMONIA
GRANULOMATOUS PNEUMONIA (TB, parasitic pneumonia)
Commonest in domestic species.
Initiates in (terminal) bronchi and extends in to surrounding parenchyma. Can involve ALL airways.
Caused by inhaled organisms- BACTERIA, MYCOPLASMA/VIRUSES (with secondary bacteria), ASPIRATED FOOD/GASTRIC CONTENTS.
Caused by- bland aspiration. (non toxic material in lungs)
-P. multocida/B. bronchiseptica/A. pyogenes/Streptococcus/E. coli
-Parainfluenza 3/Respiratory Syncytial Virus/distemper.
Purulent/mucopurulent exudate with many neutrophils.
Can be patchy, confluent, or affect whole lobes.
Bronchioles and alveoli are packed with cells- neutrophils, macrophages.
Dilated, congested alveolar walls (microscopy)
Can be seen in combination with suppurative bronchopneumonia. (fibrinosuppurative)
Caused by- irritant aspiration (toxic)
-M. haemolytica/A. pleuropneumoniae
Exudate contains FIBRIN, neutrophils, necrotic debris. Causes oedema.
Rapid spread within and between lobules, often seen affecting large confluent areas, whole lobes.
Fibrinous adhesions on lung and pleural surface can be seen.
ACUTE FIBRINOUS BRONCHOPNEUMONIA IN CALVES
Caused by Mannheimia haemolytica colonising lower respiratory tract.
-Lysis of alveolar macrophages and neutrophils.
-Release of lysosomal contents
-Tissue necrosis and fibrinous bronchopneumonia
-Extensive fibrin deposits in interlobular septa.
POSSIBLE SEQUELAE TO ACUTE BRONCHOPNEUMONIA
-Progression to chronic pneumonia- BALT hyperplasia, bronchiolar goblet cell metaplasia, fibrosis.
Caused by Mycoplasma infection, leads to peribronchial 'cuffs' forming, due to massive hyperplasia of BALT.
The bronchioles are 'squished' by BALT.
Form of bronchopneumonia.
ALVEOLAR COLLAPSE AND RESOLUTION
Seen in enzootic pneumonia (eg. Mycoplasmal infection in pigs, cuffing pneumonia)
Alveolar collapse is seen due to peribronchial cuffing by hyperplastic BALT.
This is then CONSOLIDATED by movement of (inflammatory) cells and fluid in to the alveoli.
Can be INTERSTITIAL- larval migration
BRONCHITIS- intrabronchial adult worms
GRANULOMATOUS- aberrant parasites, dead larvae or eggs.
Sheep lungworm. Very commonly seen; does not cause clinical disease, but is a public health issue.
NON IMMUNE ANIMALS- young animals. Puffy, coalescing lesions are seen, commonly on the caudal lung.
Adult worms and larvae can be seen on microscopy.
IMMUNE ANIMALS- LEAD SHOT LESIONS. Granulomatous inflammation walls off degenerate larvae.