The upper respiratory passageways: Comparative anatomy and structural/functional considerations

How do the nasal passageways modify and regulate the volume of inspired air?

Respiratory pathway (blue)

• Warms the air- rich blood supply

• Moistens the air- glandular secretions -mucus

• Cleanses the air- mucus and cilia

• Regulates airflow- blood vessel congestion or constriction

Olfactory pathway (red)

• Runs alongside the respiratory pathway and is responsible for detecting smells.

What are respiratory passages lined by?

‘respiratory’ epithelium

• EXCEPT for ethmoidal (and middle) conchae and the vomeronasal gland

What is the histological classification of respiratory epithelium?

Histological classification: Pseudostratified columnar ciliated epithelium with goblet cells

• 5:1 ratio (plus other cell types described)

• Note: Smoking increases mucus-producing goblet cells and reduces ciliated cells, which weakens mucociliary clearance and makes it easier for infections and inflammation to develop

How does the respiratory epithelium have an ‘air conditioning function’?

Goblet cells produce a mucus sheet

• Produced by goblet cells and sub- mucosal glands

• Moistens air

• Traps particulate matter

Cilia

• Motile- beat in concert

• Mucus and trapped particulate is wafted towards pharynx where it is swallowed or expectorated

Submucosa is also highly vascular (bvs)

• Warms the incoming air

• Acts like an erectile tissue

• Congestion- disrupts airflow

• Vasoconstriction- allows increased airflow during exercise

Describe the cellular structure of the olfactory epithelium.

• What structures have this type of tissue?

Present in ethmoidal conchae and vomeronasal organ.

Olfactory receptor cells (green)

• Bipolar neurons - apical pole carries a non motile cilia with specific odorant binding receptors

• Unite to form an olfactory nerve which passes through the cribriform plate to terminate in olfactory bulb

Bowmans gland (purple)

• secretion solubilizes incoming odorants and washes away excess

Supporting cells (red)

• Provide metabolic and physical support to olfactory cells

Basal cells (blue)

• stem cells- can differentiate and replace olfactory receptor cells

Why are dogs able to perceive more odours than humans?

• Dogs possess up to 300m olfactory receptors in their noses, compared to about 6m in humans.

• The part of a dog's brain that is devoted to analysing smells is, proportionally speaking, 40 times greater than ours.

• Dogs' noses also function quite differently than our own- shape & spacing of nostrils, separation of airflow into different pathways, comma shaped

What are some unique palpable landmarks specific to bovine skulls?

Naso-incisive notch

Facial tuberosity

How do large ruminant nasal cavities differ from carnivores?

• Conchae - Less complex compared to the carnivore. Dorsal, ventral, and ethmoidal conchae (middle v. small)-

• Dorsal & Ventral conchae

• Rostral section -scrolled

• Caudal section -forms a sinus

What are conchae?

Conchae are not the nasal cavities themselves, but rather bony structures (turbinates) that project into the nasal cavities

How do the frontal sinuses appear in large ruminants?

• Frontal sinuses are extensive in adult

• Give rise to adult head conformation

• Each frontal sinus consists of Rostral & Caudal compartments

• Invasion of cornual process @ 6 months (has implications for dehorning & fracture)

  • extending into horns, base of horn has extension of the frontal sinus

• Drainage :

• Poor; drain directly into nasal cavity via Ethmoidal meatuses, worse when mucosa inflamed

What is the implication of the frontal sinuses in slaughter and euthanasia of large ruminants?

• Frontal sinuses protect the cranial cavity

• Landmarks for euthanasia

Describe the main features of the maxillary sinuses in large ruminants.

• Large sinus of major clinical importance

• Roots of the upper cheek teeth project into the ventral floor (Sinus enlarges with age, increasing dental association)

• Extends medially to form the palatine sinus and caudally to form the lacrimal bulla, which protrudes into the orbit

• Communicates with the nasal cavity via the nasomaxillary opening*, positioned dorsal to the main sinus compartment

• Clinical significance: sinus infections are difficult to drain because the drainage opening* is high (dorsal) relative to the sinus floor

Describe main features of the Nasopharynx in large ruminants.

• Partial division of nasopharynx by the pharyngeal septum:

• Auditory openings

• Pharyngeal tonsil

• On the caudal edge of the Pharyngeal septum

• Tubal tonsil

• Close to the entrance of each auditory tube

What parasites may affect the frontal sinuses in small ruminants?

Oestrus ovis: Adult Sheep nasal fly/or sheep gad fly; nose bot (larval stage)

What is the main function of the rostral plate in the pig?

• Rostral bone

- Strengthens the snout region

Snout rings stop rooting

Describe the main features of the sinuses in the Porcine.

Frontal and maxillary sinuses are extensive in the adult

• Frontal sinuses

• Excavates entire dorsal surface of the skull

• Cranial cavity 5cm below skull

• Difficult to stun reliably and humanely by mechanical bolt, stunning preferred

• Maxillary sinus also extensive

What is the name of the diverticulum present in the Porcine?

• What problems can this structure pose?

Nasopharynx pharyngeal diverticulum

• Function: supports nasopharyngeal tonsil; can cause problems for tubing piglets