resp 2 lectures Flashcards by Mark Sunarich

Trachea and bronchi have ciliated epithelial cells, goblet cells, submucosal glands
- number distribution throughout airways?
- functions?
- issue?

Numerous in
trachea and bronchi; progressively fewer in distal airways
Function: clearance of mucus containing trapped particles
Vulnerable to injury

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Bronchioles: Club Cell
- what is it?
- function?

non-ciliated cells in bronchiolar epithelium
Function:
> Stem cell for regeneration
> Metabolism and detoxification
> Quell inflammatory responses

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Causes of Airway Injury

Some viruses injure both bronchiolar and alveolar epithelium (=bronchointerstitial pneumonia)
Allergic or idiopathic inflammatory disease:
> Asthma in horses (aka heaves), cats
> Canine chronic bronchitis
Chronic irritants & oxidants:
> tobacco smoke, dust, inhaled chemicals, …
Toxic: Club cells metabolize chemicals, eg. 3-methylindole

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Viruses that cause airway injury
& predispose to bacterial pneumonia
- cattle and sheep

BHV-1
BRSV
PIV3
Corona

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Viruses that cause airway injury
& predispose to bacterial pneumonia
- swine

Influenza

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Viruses that cause airway injury
& predispose to bacterial pneumonia
- horse

Influenza
EHV-1
EHV-4

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Viruses that cause airway injury
& predispose to bacterial pneumonia
- dogs

Distemper
CPIV
CAV-2
Coronavirus
Influenza

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Viruses that cause airway injury
& predispose to bacterial pneumonia
- cats

FHV-1
Calici

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Non-infectious inflammation of
small airways

Asthma/heaves: cats, horses
Canine chronic bronchitis
Human asthma & COPD

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Acute effects of airway disease

Failure of mucociliary clearance > bacterial pneumonia
Airway obstruction due to:
> smooth muscle contraction (bronchoconstriction), triggered by inflammatory mediators such as leukotrienes, other eicosanoids, or cytokines
> inflammation and edema of the airway wall
> exudates and necrotic cells within the lumen

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Airway Injury: Effects on Lung Function

decreased alveolar ventilation > hypoxemia hypercapnea
increased expiratory effort & work of breathing
> airways collapse, air gets trapped in lung

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Airway Injury: Bronchitis, Bronchiolitis and Bronchiolar Necrosis
- sequelae

– Repair
– Bronchiolitis fibrosa obliterans
– Chronic bronchiolitis: metaplasia, neoplasia

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Repair of Bronchiolar Injury
What if healing is delayed by extensive damage, or ongoing necrosis?

Club cells proliferate & repopulate airway epithelium
Differentiation into ciliated cells
<><><>
Healing delayed: fibrosis, which can permanently affect the function of the lung

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Bronchiolitis fibrosa obliterans
Obliterative bronchiolitis
- what is this?

Erosion of epithelium
Exudation of fibrin and leukocytes into lumen
Infiltration of fibroblasts
“Organization” by fibrosis

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Sequelae to Chronic Irritation, Inflammation, or Necrosis of the Airways

Ciliated epithelium is sensitive to injury
* Mucous metaplasia: protective adaptation
* Squamous metaplasia: protective adaptation
* Neoplastic transformation

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Airway Injury:
Bronchitis, Bronchiolitis and Bronchiolar Necrosis
- cause
- acute effects
- sequelae

Causes:
* Viruses
* Chronic irritants
* Allergic
* Toxic
<><><>
Acute effects:
* Failure of mucociliary clearance
* Obstruction to airflow by exudate, edema, and bronchoconstriction
* Failure of alveolar ventilation…
<><><><>
Sequelae:
* Repair
* Bronchiolitis obliterans
* Mucous or squamous metaplasia
* Neoplastic transformation

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type 1 vs 2 pneumocytes

Type I Pneumocytes
* Gas exchange
* Susceptible to injury
<><><><>
Type II Pneumocytes
* Stem cell for regeneration
* Production of surfactant lipid & protein
* Metabolism and detoxification

Blood-air interface:
- components
- functions

*Type I pneumocyte
*Basement membrane
*Endothelium
<><><>
*Critical for efficient gas exchange, esp O2
*Effects on compliance

Causes of Interstitial Lung Disease

Injury to Alveolar Epithelium or Endothelium
<><><><>
* Viruses often injure alveolar and bronchiolar epithelium (bronchointerstitial pneumonia)
* Sepsis & SIRS: damage to endothelium
* Toxic agents
> Direct-acting toxins: chlorine gas, ammonia, sulfur dioxide, nitrogen dioxide (silos)
> Toxins which are converted by type II pneumocytes to reactive intermediates: 3-methylindole, paraquat
* Idiopathic

The Evolution of Interstitial Lung Injury
- acute and chronic

Resembles Normal Wound Healing
<><><><>
* Acute
> Edema & hyaline membranes: fibrin and necrotic debris, due to alveolar epithelial injury

Subacute to chronic
> Proliferation of type II pneumocytes: a necessary but dysfunctional step in repair
> Interstitial fibrosis: a permanent impediment to lung function

Determinants of pulmonary fibrosis?

Following an acute one-time injury, type II pneumocytes eventually differentiate into type I pneumocytes, and lung function returns to normal. In less favorable circumstances, type II pneumocytes persist and interstitial fibrosis may develop.
<><><><>
The balance between epithelial repair (optimal) and repair by fibrosis (a permanent barrier to gas exchange) depends on persistence of the stimulus and extent of injury (and perhaps also the adequacy of the repair process). Chronic persistent stimuli (such as ongoing exposure to irritant chemicals, persistent virus infections, dusts particles, or hypersensitivity) are more likely to cause fibrosis than one-time insults (such as viral infection). Similarly, chronic inflammatory responses may heal by fibrosis. Finally, with severe damage, fibrosis may develop before the tissue has time to heal.

Alveolar Injury: Effects on Lung Function

Obstructs oxygen exchange > hypoxemia
Reduced lung compliance > increased work of breathing
Reduced lung volume

Bronchointerstitial Pneumonia
- definition
- cause

Definition: concurrent injury to bronchiolar and alveolar epithelium
Cause: viral, toxic

Acute Respiratory Distress Syndrome and Acute Interstitial Lung Injury
- definition
- lesions
- causes, in dogs

ARDS= clinical definition:
“acute onset, severe hypoxemia, without evidence of heart failure”
<><><><>
Many cases of ARDS have lesions of interstitial lung disease
<><><><>
Dogs: most are idiopathic—clinical investigation is important!
Systemic inflammatory diseases: endotoxemia, DIC, pancreatitis
Trauma, strangulation
Aspiration of sterile gastric acid
Toxins: paraquat, oxygen, chlorine gas—bleach
Bacterial pneumonia (not an interstitial lung disease)

Clinical term: Acute respiratory distress syndrome - corresponds to what pathologic term?

Pathologic term: Interstitial lung disease

Chronic interstitial lung diseases in dogs and cats - frequency - signs - lesions - who is affected

* Rare * Chronic progressive dyspnea * Fibrosis, proliferation of type II pneumocytes * Cats, Westies, Dalmatians & others

Pneumoconiosis - what is this?

lung's reaction inhaling certain dusts - a rare cause of interstitial lung disease in domestic animals

Cor Pulmonale - what is this? causes?

- Right heart failure 2ry to lung disease - Lung disease > ⇧ Resistance to blood flow through lungs > Right heart failure <><><><> * High altitude disease * Chronic airway obstruction (eg. asthma) * Pulmonary vascular disease (incl. reverse PDA) * Chronic interstitial lung disease

Hydrothorax cause, clinical signs

- Hydrothorax appears as clear, low-protein fluid in the chest, and is most commonly the result of right- or left-sided heart failure. - the simple presence of fluid leaves less room in the chest for lungs to expand. The physical presence of the fluid causes the atelectasis.

Chylothorax : milky lymph fluid - causes?

* Idiopathic * increases Venous pressure: heart failure, neoplasia * Intrathoracic masses: neoplasia, granulomas *Thoracic duct injury <><><><> The major causes are: * Heart failure. Increased central venous pressure prevents drainage of lymph from the thoracic duct into the vena cava. * Lung lobe torsion. * Many cases are idiopathic. * Uncommonly due to obstruction of the thoracic duct by tumours, or other masses, or rarely due to traumatic rupture of thoracic duct.

PLEURITIS - causes

Inflammation of the pleural cavity usually represents bacterial infection, and the bacteria can arrive in the pleural space by three routes: * External penetrating injury: cat bite wounds, penetrating injury, plant awn migration in dogs, etc. Cellulitis of the neck such as from penetrating injury to the pharynx from foreign bodies can spread by gravity into the pleural cavity. * Extension from bacterial pneumonia or rupture of a lung abscess. This is the common cause of pleuritis in adult horses. Careful inspection reveals consolidation of the underlying lung tissue. * Hematogenous spread: bacteremia, such as in neonates with omphalitis or failure of passive transfer, or feedlot cattle with pleuritis caused by Histophilus somni. Feline infectious peritonitis usually induces peritoneal lesions, but some cats present with pleural effusion.

FIP lung / thoracic lesions

- Peritonitis, nephritis and lymphadenitis are common manifestations, but some cats with FIP have pleuritis with or without lesions in other tissues. - In all cats with pleural FIP, dry or wet form, tiny raised white granulomas are present on the pleural surface of the lung. - In the wet form, cloudy, protein-rich fluid fills the pleural cavity. This exudate is difficult to grossly distinguish from bacterial pleuritis, but granulomas on the pleural surface suggest a diagnosis of FIP.

Pneumothorax - cuases

*Penetrating injury *Ruptured pulmonary bulla

Lung parasites of... cats

* Aelurostrongylus abstrusus * Paragonimus kellicotti

Lung parasites of...dogs

* Toxocara canis larval migration * Oslerus osleri * Crenosoma vulpis * Angiostrongylus vasorum

major lung parasites of cattle, goats and sheep, horses

* Cattle: Dictyocaulus viviparus * Goats and Sheep: Muellerius capillaris, ... * Horses: Dictyocaulus arnfieldii

Aelurostrongylus abstrusus - hosts - significnace - lesions - similar parasite in sheep?

Cat lung parasite (Metastrongyle) * Snail or slug intermediate host * Usually incidental * Subpleural nodules in caudal lung containing microscopic parasites <><><><> Muellerius sp. in sheep is similar

neoplasia of the pleura - what do we see?

* Implantation of tumours * Primary pleural tumours: mesothelioma (rare)

Paragonimus kellicotti (trematode) - hosts - lung lesions - significance?

cats * Crayfish intermediate, or meat of paratenic host * Adult flukes in cyst-like nodule in lung * Inflammatory reaction to eggs <><><><> - usually just an incidental finding - eggs can cause inflammatroy reaction - if cyst ruptures, can result in pneumothorax and respiratory distress

Muellerius capillaris, hosts and lesions

- tiny pale or red nodules, more severe disease in goats than sheep - fairly common

Dictyocaulus viviparus - hosts, lesions

cattle - worms live in caudal bronchi - make sure you cut there on PM! Don’t just stop at tracheal bifurcation - management for a cattle herd is much different than for eg. viral lung diseases - not super common in Ontario but it is out there

which of the common lung parasites are microscopic

Toxocara canis Muellerius Aelurostrongylus