Nasal Cavities Flashcards
Identify the features of the external nares of different species and explain their role in airway resistance
Identify the main features of the external nares
Nostrils
Nasal Vestibule
What are nostrils?
They are the actual meatus surrounded by hairless skin. This skin can be highly modified depending on species
The meatus/nostrils are surrounded by nasal cartilage dorsally and ventrally
What are the nasal vestibule?
The opening of the nasal cavity, and contains the opening of the nasolacrimal duct which is visible just inside of the ventral surface
Outline the species differences of the external nares with regards to cattle
Nostrils surrounded by smooth hairless nasolabial plate:
Stratified cornified epithelium
Serous glands create moisture
Nasolabial glands
Outline the species differences of the external nares with regards to Equidae
No ventral nasal cartilage
Incomplete cartilaginous ring:
Distensible nostrils
Alar cartilages (plate and horn):
Form comma shaped nostrils.
Ventral ‘true’ nostril
Dorsal ‘false’ nostril
Skin lined diverticulum
Within nasoincisive notch
Outline the species differences of the external nares with regards to Carnivordae
Nasal plate:
Divided by median groove (philtrum)
Secretions from lateral nasal gland
Outline the species differences of the external nares with regards to Suidae
Small nostrils on snout
Highly sensitive
Contains the os rostrale
Outline the species differences of the external nares with regards to Aves
Slit like openings.
Not diving birds eg gannet
Operculum:
Overhanging bony flap
Wide communication between nasal cavity and pharynx:
Choana
Provide an overview of nasal cavity function
Conduction and preparation inspired of air:
Moisten air
Warm air
Filters particles
Mucus traps particles -> swallowed
Air flow resistance
Heat exchangers for cooling the brain:
Cooled venous blood passes via the rete mirabalis and cools the arterial blood going to the brain
Olfaction:
Caudal regions of the turbinates covered by olfactory epithelium
Defense mechanisms
Provide an overview of nasal cavity structure
Extends from nostrils to cribriform plate of ethmoid bone:
Divided by nasal septum
Further divided into nasal meatuses by nasal conchae:
Which further increase nasal surface area
Highly vascular structure
List the key landmarks bordering the nasal cavity
Dorsally and laterally:
facial bones.
Ventrally:
hard palate.
Rostrally:
nostrils (external nares).
Caudally:
pharynx / ethmoid bone.
Define the term conchae
Turbinate bones which project into the nasal cavity and form scrolls and are covered by nasal mucus. They are coiled to increase SA. 3 divisions:
Dorsal
Including the alar fold (small cartilaginous structure at the rostral end of the nasal cavity)
Ventral
Only turbinate which leads to the pharynx
Ethmoidal
Attached to the ethmoidal plate
Rich in sensory nerve endings as it is responsible for sense of smell
Define the term turbinates
Delicate Scrolls which can be split into three groups:
Ectoturibinates
In frontal sinus
6 in dogs; 20-30 in horses
Endotubinates In nasal cavity 5-6 #1 & #2 form dorsa; and middle conchae Attach to cribriform plate caudally Maxilloturbinates In nasal cavity Paired Attached to medial wall of maxilla Forms the ventral concha
Ethmoturbinates in collective term for ecto- and endoturbinates
Define the term meatus
Dorsal nasal meatus
The passage between the roof of the nasal cavity and the dorsal nasal concha.
Middle nasal meatus
Between the dorsal and ventral conchae, it communicates with the paranasal sinuses.
Ventral nasal meatus
Main pathway for airflow leading to the pharynx, positioned between ventral nasal concha and
floor of the nasal cavity.
Runs into common
Common nasal meatus
What is the cribriform plate?
A part of the ethmoid bone
Outline the species differences of the nasal cavity with regards to Equidae
Endoturbinates: part of ethmoidal bone which provides support for dorsal (1st endoturbinate) and middle (2nd endoturbinates) conchae
Simple Structure
4 nasal meatus
Dorsal meatus
to olfactory mucosa
Middle meatus
to paranasal sinuses
Ventral meatus
to the pharynx
Common meatus
to the pharynx
Outline the species differences of the nasal cavity with regards to Bovidae
Very small middle meatus
Outline the histology of nasal mucosa
Nasal cavity can be split into three separate regions;
Vestibular
Respiritory
Olfactory
Describe the histology of the vestibular region of the nasal mucosa
Lined by subcutaneous mucus which is composed of stratified squamous epithelium
Describe the histology of the respiratory region of the nasal mucosa
Lined by respiritory mucus which is composed of epithelium and lamina propria.
The epithelium consists of pseudostratified ciliated columnar cells, with goblet cells embedded.
The laminar propria contains many blood vessels and seromucous glands
Outline the functions of the respiratory epithelium
- Regulation of air flow by erectile tissue
- Cleaning (cilia)
- Humidification (evaporator)
- Warming (variable blood perfusion)
- Protecting reflexes (sneeze reflex).
3) and 4) are important for cooling the brain and for saving water from expiratory air in some species e.g. Camels, kangaroos.
Describe the overall structure of the olfactory region of the nasal mucosa
Lined by olfactory mucosa composed of olfactory epithelium
Overall structure:
The ethmoturbinates extend rostrally from the ethmoid bone
Covered with respiratory epithelium
Also contains olfactory sensory neurones
Sniffing alters the normal airflow to bring the air into contact with the ethmoturbinates
Describe the microstructure (histology) of the olfactory region of the nasal mucosa
Tall pseudostratified ciliated columnar appearance of olfactory epithelium
Composed of:
Olfactory receptor cells
Olfactory cells are bipolar neurones
Cell body embedded within the middle of the stratum
Apical portion extends as thin dendritic processes, which terminated as a swelling known
as the olfactory bulb. This bulb gives rise to non-motile cilia like structures which detects
chemicals
Basal portion is where a single non myelinated axon penetrates the basement membrane
and joins with other axons forming bundles in the lamina propria
The axons group into bundles which penetrate the cribriform plate and enter the
olfactory lobe of the brain through the Olfactory N (CN I)
Olfactory neurones continuously renewed due to the presence of neural stem cells in the
basal layer
Supporting cells
Basal cells
What is the vomeronasal organ
Vomeronasal Organ
Accessory olfactory sense organ. Can be known as the Jacobson’s Organ
Contained within hard palate:
-paired, blind ending ducts originating from the incisive ducts, which connect nasal and oral
cavities
-Unique chemoreceptors distinct from other olfactory organs:
-May play a role in pheromone detection
-Lip curling (Flehmen)
Outline the transitions of the nasal mucous membranes
Vestibule:
Transition from integument (Skin) to mucous membrane
b: Nasal cavity:
respiratory epithelium
c: caudodorsal part of the ethmoidal conchae:
olfactory epithelium
Explain the path of airflow along the nasal chambers
Inhaled air is warmed and humidified by the rostral portions of the nasal mucosa, and the mucosa itself is cooled by this interaction. At exercise or with high ambient temperature, dilatation of blood vessels that comprise the rich vascular supply to the nasal mucosa enhances heat and moisture exchange
Explain how the nasal chamber provide resistance to airflow
Resistance = length / radius^4
Resistance to flow also affected by changes in direction
Horses are obligate nasal breathers:
Very hard for them to mouth-breathe
Flow aided by:
Ram air into nostrils
Straighter head-neck-thorax alignment
Compromise flow v air preparation:
Turbinates necessary hindrance
Horses have less complex turbinates to reduce resistance
