The respiratory system

What are the 2 portions of the respiratory tract

1. air conducting portion

2. respiratory portion

what is included in the upper respiratory tract

• nasal cavities

• nasopharynx

• larynx

what is included in the lower respiratory tract

• trachea

• bronchi

• bronchioles

• respiratory bronchioles

• alveolar ducts

• alveolar sacs

• alveoli

what kind of cells do we find in the air conducting portion?

• epithelial lining, with supporting tissues: cartilage, smooth muscle, elastic fibres

What kind of cells do we find in the respiratory portion and why?

• simple squamous epithelia + v. scarce loose connective tissue

• why? - for optimal gas exchange and diffusion

Outline the structure of respiratory epithelium

• brush cells

• basal cells

• ciliated cells

• goblet cells

• neuroendocrine cells

respiratory epithelium = ciliated, pseudostratified columnar epithelium

What 3 regions do we find in the nasal cavity

1. cutaneous region = nasal vestibule

2. respiratory region

3. olfactory region

what cells do we find in the cutaneous region

• stratified squamous epithelium

what cells do we find in the respiratory region

• ciliated, pseudostratified columnar epithelium

• = respiratory epithelium

what cells do we find in the olfactory region (general)

• olfactory epithelium

what is the structure of the nasal cavity

• paired chambers separated by a bony and cartilaginous septum

What is this a section of and what can we identify?

transverse section of the nasal cavity

• orange arrow = maxillary bone

• middle = midline septum

• blue arrows = conchae (dorsal and ventral)

• b = bone (maxilla)

• d = dorsal conchae

• oc = oral cavity

• s = septum

• v = ventral conchae

How can we refer to the conchae in chickens?

• turbinates

what does the nasopharynx connect?

• nasal cavities to the larynx

what makes up most of the structure of the nasopharynx

• respiratory epithelium

• stratified squamous epithelium caudodorsally along the soft palate

what does the submucosa contain in the nasopharynx and what does it form?

• glands

• lymph nodules

• pharyngeal tonsil

what is the larynx

• air passageway b/w oropharynx and trachea

what is the larynx formed from

• cartilage plates

• it’s a tubular region

what is the function of the larynx

• producing sounds - vocal folds

what makes up most of the larynx

• respiratory epithelium

What can we identify in this section and what is it a section of?

• cartilage (left arrow)

• goblet cells

• submucosa with blood vessels (RBCs in birds can be nucleated!)

• chicken URT

what is the funciton of the trachea

• air tube for air conduction and conditioning of inspired air

what are the 4 layers of the trachea?

1. mucosa (w. respiratory epithelium)

2. submucosa

3. cartilaginous layer

4. adventitia

What is the function of the cartilaginous layer

• keeps lumen open, cartilage and smooth muscle

What structure is this and what has been identified

• trachea

• cartilage rings (top)

• skeletal muscle running alongside the trachea

• respiratory epithelium

What are the layers we can identify here?

• blue = adventitia

• then cartilage

• then submucosa

• mucosa

• epithelium

• lumen

Why may the adventita appear much larger in a slide sample?

• held together by weak connective links b/w cells

• stretches

When do the bronchi form?

• when the bifurcates into 2 main bronchi

what do we see in the bronchi structure that’s not in the trachea

• an additional layer of smooth muscle = muscularis

• found b/w mucosa and submucosa

how do we get from the trachea to the alveoli?

• trachea → bronchi → bronchioles → alveoli

what happens to the respiratory epithelium as we mov more distally down the bronchioles?

• simple columnar

• simple cuboidal

• still ciliated!

How do the bronchi become bronchioles?

• bronchi → intrapulmonary bronchi → terminal bronchioles

What cell type do we only see in the bronchioles?

• epithelium with Clara/Club cells

What kind of cell are Clara/club cells

• bronchiolar exocrine cells

What can we find here?

• respiratory pleura

• bronchi

• bronchioles

• alveoli

what structures are ‘conducting’ in the airway?

• trachea

• extrapulmonary bronchi

• intrapulmonary bronchi

What are the transitional structures in the respiratory tract?

• respiratory bronchiole

• primary, secondary and tertiary bronchioles

What are the sites of exchange in the airway tract?

• alveolar duct

• alveolar sac that contain alveoli

What are respiratory bronchioles

• continuation of a terminal bronchiole, interrupted by thin-walled outpocketings = alveoli

what occurs in the respiratory bronchioles

• air conduction and gas exchange

• = transitional

what cells make up bronchioles

• simple cuboidal

what cells make up alveoli?

• simple squamous

how does the amount of resp. bronchioles vary among species?

• carnivores>>herbivores

• absent in humans and small rodents

what is the function of alveoli

• site of gas exchange b/w air and blood

what is the structure of alveolar ducts?

• elongated airways that are lined by alveoli only

what is the structure of alveolar sacs

• spaces surrounded by clusters of alveoli

what is the alveolar septum

• septal wall

• tissue b/w adjacent alveolar air spaces

What are the 3 types of cells we find in alveolar epithelium

1. Type 1 cell

2. Type 2 cells

3. Brush cell (rare)

Outline type 1 alveolar cells

• type 1 pneumocytes

• v. thin, squamous cell, 95% of alveolar surface lining

Outline type 2 alveolar cells

• type 2 pneumocyte

• cuboidal cell

• secretes surfactant

• covers ~5% alveolar surface

what are the 5 opacities in radiographs?

• gas = anechoic = black

• fat = dark grey

• soft tissue/fluid = lighter grey

• white = bone/mineral

• bright white = metal

What are each of the letters

A = aorta

B = caudal vena cava

C = trachea

D = crura of diaphragm

E = crura of diphragm

F = cardiac silhouette

G = lung

H = liver

the red outline = normal bronchiole presence in a radiograph

Where are the lobes in a DV radiograph

Working in a clock:

1-2 = left cranial

2-3 = left craniocaudal

3-4 = left caudal

4-5 = accessory

7-8 = right caudal

8-9 = right middle

9-11 = right cranial

why is knowing about the accessory lung lobe useful?

• can be surgically removed

what’s in the lung structures wise which we can see

• bronchi

• alveoli

• interstitial tissue

• blood vessels

Are these normal? Should we refer for these?

• yes, blue = bronchi - gas filled tube, soft tissue wall

• yellow = blood vessel - soft tissue wall, fluid filled (same opacitites)

what is the white on abnormal radiographs coming from

• usually something that’s already there

• fluid

• tumour etc

what are the 4 patterns of abnormal lungs on radiographs

• bronchial

• interstitial: diffuse or nodular

• alveolar

• vascular

what do normal bronchi look like on a radiograph?

• we can see the walls or larger ones (usually towards the middle of the image)

• they exist right tot he periphery of the lung lobes - we just can’t see them b/c they’re smaller and thinner walled

what do we see on a lung radiograph that indicates something wrong with bronchi, why and what may be wrong with them?

• bronchi look like donuts if cut transversely or train tracks if cut longitudinally

• we see bronchi more clearly in the periphery

why = wall becomes mineralised (opacity is more white) and therefore easier to see/wall becomes thicker and is easier to see

What do bronchial patterns look like on radiographs and what could a cause be

• bronchi are more prominent due to thick/mineral opacity

• bronchitis

Outline interstitial patterns:

1. what does it look like normally

2. what does it look like when abnormal

3. what are the 2 kinds and how do they differ in appearance?

1. don’t appreciate it

2. we see it - thickened e.g. haemorrhage or frank nodules

3. diffuse = unstructured nodular = soft tissue mass (be careful to not mistake for vessels)

What are the 2 lung patterns present here

1. interstitial - nodular

2. alveolar (RHS)

what are key features of an unstructured/diffuse interstitial pattern

• can still see soft tissue

• air still where it should be (bronchi and alveoli)

• can see cardiac silhouette

Outline alveolar lung pattern:

1. what is normal

2. what is abnormal

3. what do we see if abnormal

4. what would the fluid be?

5. what can’t we see compared to interstitial lung pattern

1. alveoli filled with air = anechoic = gas opacity

2. fluid filled or collapsed (soft tissue) but air still in bronchi

3. soft tissue/fluid opacity, air in bronchi b/c bronchi are currently fine. may be focal/diffuse depending on the case

4. could be anything e.g. blood/pus/oedema/other

5. can’t see soft tissue opacities - border obliteration of the heart

Outline vascular pattern:

1. what’s normal

2. what’s abnormal

3. where do we find veins

4. what should the diameter of the cranial lobar artery and vein be?

1. can see pulmonary vessels therefore soft tissue opacity

2. bigger/smaller

3. ventral and central

4. same diameter as proximal 1/3 of 4th rib

what should the diameter of the arteries and veins be the same as and at which rib?

• 9th rib - at the point when they cross this rib

When we have a vascular lung pattern what does it mean when:

1. vessels are enlarged

2. if they’re smaller

1. too much circulation - fluid overload - left to right shunt

2. too little circulation e.g. hypovolaemia - R → L shunt

   • lungs look less white - seeing vessels is normal, if they’re small it will be less white, more black on the radiograph

Outline the pleura:

1. what’s normal?

2. what’s abnormal?

1. pleura surrounds lungs but can’t be appreciated on the normal radiograph. Lungs occupy entire space - we can see vessels all the way to the periphery

2. lungs are pulled back from the edge due to contents (air/fluid/mass) in the pleura and heart may appear elevated

What’s wrong here?

• gap beneath lung in right lateral recumbency due to fluid

• collapsed lung on the DV view - tissue opacity = what’s left of the lung

What’s wrong here?

• increased opacity (orange)

• cardiac silhouette elevated (green)

• decreased opacity (red)

• vessels aren’t visible in the area of decreased opacity, lungs aren’t there. Gas opacity in the pleural space - lungs unable to expand in with the gas therefore increased opacity

What do these radiographs show?

• pleural effusion

• can’t see cardiac silhouette, lungs are floating in something, fluid in the pleural space

what is the mediastinum, what parts are there to it?

• a ‘gap’ b/w the lung lobes in which we find the heart, oesophagus and trachea. It’s not a structure, just a space w/in the thorax.

• has a cranial and caudal part

Is this a normal mediastinum?

• no

• it’s wider than normal, in the cranial mediastinum

• soft tissue/fluid opacity that’s pushed the trachea upwards (in right radiograph with the radiopaque areas, that shows the trachea being pushed upwards)

Is this a normal radiograph?

• no

• can’t see diaphragm, no cardiac outline, poor lung definition…why?

  • diaphragm has collapsed and the abdominal contents are in the thorax