Diseases of the lung parenchyma Flashcards
Compare type 1 and type 2 alveolar cells
Type 1:
- Flattened pneumocytes, fragile
- Have to act as the minimal barrier to gas exchange
- Terminally differentiated and can’t replicate
Type 2:
- Square shaped
- Release surfactant
- Replicate and differentiate into type 1 pneumocytes
- important for repair
Which species has a poor degree of collateral ventilation?
Cattle
What separates alveolar lobules, what is the function of this?
Septa - fibrous walls
– prevent collateral ventilation, but also prevent spread of infectious disease
Describe how the septa is different in:
- Cattle, pigs, sheep
- Horses
- Carnivores, rodents
- Thick complete septa
- Incomplete, thick septa
- No distinct septa
Give 3 examples of congenital abnormalities of the lung parenchyma
- Congenital melanosis: black pigment
- Agenesis of one or more of the lung lobes: failure to form
- Ectopic lung tissue outside of the thoracic cavity
What 2 abnormalities can occur due to problems with lung inflation?
- Atelectasis
- Emphysema
What is atelectasis?
Incomplete distention of the lung
What are the causes of atelectesis?
- complete internal obstruction of the airway
- external compression of the airway or lung
- pneumothorax
- defective surfactant production
- recumbency in LAs
Define emphysema
Excessive inflation of the lung
What are the causes of emphysema?
- forced respiratory effort e.g. pneumonia
- obstructive airway disease
How does emphysema change the structure of the lung tissue, how does this affect gas exchange?
Over inflated alveolar walls break down creating larger airspaces + less area for gas exchange
What are the 3 main functional consequences of alveolar emphysema?
- loss of lung elasticity (early airway collapse, increased dead space)
- loss of pulmonary capillaries (reduced alveolar perfusion)
- fibrosis of remaining alveolar walls (inhibits gas exchange and reduced compliance)
Define pulmonary oedema
Fluid present in the airways
What are some consequences of pulmonary oedema?
- Dyspnoea, tachypnoea: rapid, but difficult breathing
- Hypoxia, cyanosis
- Cough: moist and productive
Pulmonary oedema will only occur if…?
- There is damage to the alveolar epithelium
- Increased interstitial fluid volume
What can cause damage to the alveolar epithelium?
Infectious agents
Toxins
Irritants
How can pulmonary oedema appear grossly in the lung tissue?
Lungs heavy
Interlobular septa expanded
Lungs “wet” + ooze fluid (frothy)
How would pulmonary oedema appear histologically?
Eosinophilic homogenous material (fluid) diffusely present throughout alveoli
Normal pulmonary interstitial fluid is balanced by?
Hydrostatic pressure
Capillary permeability
Osmotic pressure
What are some causes of increased hydrostatic pressure?
- inflammation
- passive congestion (heart failure)
- circulatory overload
What are some causes of increased capillary permeability?
- endothelial damage by toxins or infectious agents
- shock
- inflammation
What are some causes of reduced capillary osmotic pressure?
Hypoproteineamia – level of plasma proteins is relatively low
What are some causes of reduced drainage of interstitial fluid (lymphatics)?
Blockage of lymphatics by inflammation or tumours
What are the different types of emboli?
- Thromboemboli
- Tumour cells: metastases
- Fat
- Air
What is a thromboemboli?
Fragments of a blood clot that pass through the blood stream and get lodged
What makes the lung a good site for embolism?
- Fine capillary network
- Good blood supply
Define infarction
Death of tissue resulting from a failure of blood supply
How does the body react to sterile thromboemboli?
- Fibrinolytic breakdown of the thrombus if it is small
- Fibrotic scarring if extensive
How does the body react to infected thromboemboli?
- Vasculitis (inflamed vessels), secondary thrombosis
- Abscess
What are some common sources of infected thromboemboli?
- Heart bacterial endocarditis
- Joint infections
- Liver abscesses
Describe how liver abscesses occur in LAs
Focal area of infected material surrounded by a fibrous wall
- LAs on a cereal diet have increased acidity of the rumen which decreases motility
- Bacterial formation on the rumen wall occurs causing ulcers
- Bacteria invade the ulcer and pass through the rumen to the hepatic portal vein => liver
Hepatic abscesses can cause thrombosis in which major vessel?
Vena cava
What are some causes of pulmonary haemorrhage
- pulmonary thromboembolism
- trauma
- infection
- abscesses
- tumours
- exercise induced e.g. racehorses
Name the four morphologically distinct types of pneumonia
- Bronchopneumonia
- Interstitial pneumonia
- Embolic pneumonia
- Granulomatous pneumonia
What are the 3 common causes of bronchopneumonia?
- Bacteria
- Aspiration of food/GI contents
- Viruses
What is the route of entry and distribution of bronchopneumonia in the lung?
Inhalation
Cranioventral
Why is the distribution of bronchopneumonia in a cranioventral fashion?
- Greater deposition of particles and organisms
- Gravitational affects and airflow
Describe the pathogenesis of bronchopneumonia
- Inhaled pathogen causes injury at bronchiole-alveolar junction
- Loss of epithelium, blood vessels become hyperaemic (dilate)
- inflammatory response
- Filling of alveoli and bronchioles with exudate, cells and debris
- inflammation and infection spreads to adjacent parts of the lungs through interlobar septae
Describe the inflammation response of bronchopneumonia
Exudation of fluid + plasma proteins through spaces between epithelial cells
Recruitment of alveolar Macrophages + immigration of neutrophils
How might bronchopneumonia appear grossly on the lung?
Firm
Dark pink to red-grey
Collapsed
How does exudate change as the severity of bronchopneumonia increases?
Suppurative (pus = neutrophils predominantly) can become fibrinous – not black and white, continuous. Confined to lobules
Fibrinous – more damaging to tissues and vessels as it spreads. Spreads rapidly between lobules.
Name some causes of fibrinous bronchopneumonia
- Bacterial e.g. Mannheimia haemolytica in cattle
- Inhalation of a highly irritant materia
Describe the pathogenesis of Mannheimiosis
- Caused by Mannheimia haemolytica bacteria
- Recently weaned and assembled suckled calves
- Stress, viral infections, + other factors impair respiratory defence mechanisms
- Bacteria colonise LRT
- Leucotoxin production damages WBCs
- Lysis of alveolar macrophages and neutrophils
- Release of WBC lysosomal contents
- Acute damage to bvs leads to fibrinous bronchopneumonia (+ toxaemia)
