Gross and Microscopic Anatomy of the Upper Airway Flashcards
Upper respiratory tract
Nasal cavity, nasopharynx, oropharynx, upper laryngopharynx (larynx).
Lower respiratory tract
- Larynx
- Trachea
- Brocnchi; and
- The rest of the respirtaory tree located in the lungs
Functions of the respiratory system
- Gas exchange
- Humidifying and warming air
- Filtering air
- Voice production
- Olfaction
- Immune functions
- Minor endocrine role
- Involved in regulation of blood pH
- H20 + CO2 <–> H2CO3 <–> H+ + HCO3
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- H20 + CO2 <–> H2CO3 <–> H+ + HCO3
Conducting zone
- Nasal cavity
- Pharynx
- Larynx
- Trachea
- Bronchi
- Bronchioles
Respiratory zone
- Respiratory bronchioles, alveolar ducts and sacs, alveoli
External nose
Composed of bone and cartilage (cartilage missing on skulls).
- Openings (nostrils (nares = 1)) lead into nasal cavity.
The nasal cavity
The nasal cavity is located between the nares anteriorly and the choane posteriorly where the passage becomes the nasopharynx.
The first part of the nasal cavity is divided into a respiratory region where air is warmed and humidified and mucus captures dust particles and an olfactor region superiorly, the part of the nasal cavity involved in smell.
Lateral nasal wall
Three conchae/turbinates (superior, middle and inferior) are bony projections from the lateral wall of the nasal cavity (note the small size of the superior concha - can be hard to identify).
Space underneath concha
termed ‘meatus’.
Superior, meatus, middle meatus and inferior meatus in the nasal wall.
Function of conchae
Increase the surface area of respirtory epithelium and cause turbulent flow of inspired air, aiding warming, humidification and removal of dust particles.
Bones of lateral nasal wall
Middle and superior concha are processes of the ethmoid bone and the inferior nasal concha is a separate bone. Other bones of the lateral wall include the; nasla, macilla, lacrimal, ethmoid, palatine and sphenoid.
Roof, floor of nasal cavity
The nasal cavity is separated superiorly form the brain by frontal, ethmoid, sphenoid bones and inferiorly it is separated fromt he oral cavity by the hard palate (maxilla and palatine bones).
Choanae
Posteriorly, the nasal cavity is continuous with nasopharynx at teh choanae.
Nasal septum
Separates the nasal cavity at the midline, bone include the vomer and perpendicular plate of ethmoid. Note that the anterior part of the nasal septum is cartilaginous.
Histology of the vestibule of the nasal cavity.
Lined with stratified squamous epithelium (keratinised –> non-keratinised) and also contains thick hairs for filtering large particles.
Histology of the respiratory region of the nasal cavity
Thick mucosa (epithelium + underlying CT) for warming and humidifying inspired air. Mucus captures particles and cilia move mucus posteriorly into nasopharynx where it is usually swallowed.
Epithelium is pseudostratified columnar, ciliated with goblet cells and the underlying CT (lamino propria) has abundant blood vessels and seromucous glands (not always obvious).
Types of glands in the nasal cavity
Mucous glands (and goblet cells) secrete mucus to trap small inhaled particles.
Serous glands secrete watery secretion to help humidify inspired air, large, thin-walled venules warm inspired air.
What is the lamina propria of the nasal cavity continuous with?
Periosteum or perichondrium.
What cell types of present in respiratory epithelium?
- Ciliated columnar cells
- Goblet cells
- Small granule cells (Kulchitsky cells): enteroendocrine cells
- Basal cells: divide and differentiate into other cell types
- Brush cells: may transduce general sensation or chemosensory.
Olfactory region of nasal cavity.
About 10cm2
Superior part of the nasal cavity
Composed of pseudostratified, ciliated columnar epithelium with olfactor receptor neurons.
How do you differentiate between olfactory and respiratory epithelium in the nasal cavity?
NO goblet cells and the nuclei appear more organised in olfactor epithelium compared to respiratory epithelium.
Cells of olfactory epithelium
- Olfactor cells: bipolar neurons
- Supporting (sustentacular) cells: provide mechanical and metabolic support for olfactor cells, nuclei located more apically.
- Basal cells: stem cells tor eplace olfactor and supporting cells, nuclei are located more basally.
- Brush cells: general sensory cells (other than olfaction)
Bowman’s glands
Olfactor glands.
Branched tubuloalveolar seorus glands. Secretions function to continue trap then wash away adorants.
Olfactory receptor neurons
Bipolar neurons (1 dendrite, 1 axon) with a dendrit knob bearing (probably) non-motile cilia (up to 200um long). Odorant receptors are located on the cilia.
Unlike most nerve cells, olfactor neurons are replaced throughout life (lifespan 1-2 months) from basal cells located in the basal region of the olfactory epithelium.
What is the pathway of the olfactor cell axons and nerves?
Axons travel from the olfactory cell body to the olfactory nerve (CNI) then to the CNS. Olfactor nerved pass through cribiform plate of ethmoid bone, synapse in olfactor bulb (part of CNS)
Paranasal air sinuses
Outgrowths of nasal cavity, expand into surrounding skull bones during childhood.
- Frontal
- Sphenoid
- Maxillary
- Ethmoid ‘air cells’
Paranasal air sinus histology
Lined by repiratory mucosa (fewer glands and goblet cells and usually thinner compared to the rest of the nasal cavity).
Sphenoid sinus
Opens into sphenoethmoidal recess posterior to superior concha.
Frontal sinus
OPen via nasofrontal duct into semilunar hiatus of middle meatus.
Maxillary sinus
Opens into semilunar hiatus of middle meatus.
Ethmoid air cells (sinuses)
Open into middle meatus and superior meatus.
Nasolacrimal duct
(tears from eyes) opens into inferior meatus.
Drainage of paranasal air sinuses
Most sinuses drain under the effect of gravity when in the upright position. However, the opening of maxillary sinus is located at the top of the sinus so it drains bestw hen you lie on your side.
General sensory innvervation of nasal cavity
Trigeminal nerve (CNV) mostly maxillary division (CN V2), also ophthalmic division (CV V1) - pain, temperature, touch etc.
General blood supply of nasal cavity
Arteries from the external carotid, mostly from maxillary artery, also from ophthamic artery and facial artery.
Pharynx
- Nasopharynx: (respiratory epithelium), conveys air.
- Oropharynx: (stratified squamous), conveys air and food.
- Laryngopharynx: (stratified squamous), conveys air and food.
Abrasion of food takes priority over warming and humidifying air.
Nasopharynx
Contains pharyngeal tonsil (adenoids when enlarged) and opening of pharyngotympanic (auditory, Eustachian) tube.
Pharyngotyympanic tube.
Auditory tube/Eustachian tube.
Runs from the nasopharynx to middle ear (tympanic cavity). and allows equalisation of air pressure across the tympanic membrane. It is also a potential route of spread of infection from nasal cavity to middle ear (especially in young children as they have shorter narrower tubes and they are not good at clearing mucous).
Oropharynx
Located posterior to the fauces (junction of oral cavity and oropharynx), contains the palatine tonsils. A passage for air and food.
Lingual tonsils location
Posterior 1/3 of teh tongue.
Waldeyers ring
A ring of lymphoid tissue surrounding the openings of the oropharynx. Composed of pharyngeal, palatine and lingual tonsils which together act as an immune gateway for the respiratory and alimentary tract.
Soft palate
Contains skeletal muscles that can depress and narrow soft palate. Acts to separate the oropharynx from oral cavity (breathe and chew at same time). During swallowing the soft palate can be elevated to separate the nasopharynx from the oropharynx so food travels down into the oesophagus and not upward into the nasopharynx
Function of the larynx
- The larynx is a conduit for air moving beteern the URT and LRT.
- Prevents food and liquid from entering into the LRT during swallowing.
- Voice production (phonataion). The vocal cords vibrate as air moves past to produce sound (note tongue, teeth, lips, palate etc also important in voice production).
Anatomy of the larynx
The larynx opens off the laryngopharynx which runs from the epiglottis superiorly to the cricoid cartilage inferiorly. Superiorly the larynx is attached to hyoid bone by the thyrohyoid ligament (membrane). Inferiorly teh larynx is continuous with the trachea. The larynx is located at vertebral levels C3-C6.
Relationship of the oeseophagus, laryngopharynx and trachea.
The laryngopharynx gives rise to both the larynx and oeseophagus. In the neck, the oeseophagus is anteiror to the cervical spine with the trachea located anteiror to the oeseophagus.
Cartilages of the larynx
The larynx has 9 cartilages.
- Unpaired cartilages: thyroid, cricoid, epiglottic.
- Paired caritlages: arytenoid, corniculate and cuneiform.
Anteriorly only the thyroid and cricoid caritlages are visible; the thyroid cartilage produces the laryngeal prominence (Adam’s apple).
Thyroid cartilage
The thyroid cartilage has the following features:
- Superior horn (cornu)
- Inferior horn
- Lamina
- Superior thyroid notch
Cricoid caritlage
Feature sof the cricoid include:
- Lamina
- Arch
Arytenoid cartilages
Sit on the cricoid caritlage posteriorly, features include:
- Apex superiorly
- Vocal process anteriorly
- Muscular process laterally
Corniculate caritlages
Sit on the apex of the arytenoid caritlages.
Cuneform caritlages
Sit in the ary-epiglottic folds (very small and are unattached to the other cartilages).
Histology of the caritalages of the larynx
Hyaline cartilage (similar to trachea) except for epiglottis which is elastic cartilage. The hyaline cartilages often ossify with older age.
Histology of the walls of the larynx
Mostly lined by respirtaory epithelium: pseudostratified ciliated columnar with goblet cells with areas of higher abrasion lined by nonkeratinised stratified squamous epithelium.
Areas of high abrasion include the lingual surface of the epiglottis (food passes over this surface) and the edge of the true vocal cord (air vibrating over the surface)
Histology of the epiglottis
- Elastic cartilage.
- The lingual surface of the epiglottis has stratified squamous epithelium
- The pharyngeal surface is respiratory epithelium.
- Note the presence of multiple seromucous glands.
Vocal and vestibular folds
Are fold of mucous membrane, containing ligaments attached to arytenoid and thyroid cartilages.
Space between them is the ventricle (a space).
Vestibular fold
- False vocal cord.
- Superior to vocal fold.
- Vestibular fold probably has a protective function.
Have a core of (sero) mucous glands, CT and lymph nodules. They are lined by pseudostratified ciliated columnar epithelium.
Vocal fold
- True vocal cord.
- Involved in voice production.
The vocal folds are mucous membrane overlying the vocal ligament, vocalis muscle, and vocal process of arytenoid caritlage. It is lined bya stratified squamous epithelium.
- Vestibular fold (false vocal cord)
- Vocal fold (true vocal cord)
- Rima glottis
Subdivisions of the larynx
Internal spaces
- Vestibule (supraglottic cavity) - from aditus (inlet) to vestibular folds
- Ventricle - between vestibular and vocal folds.
- Infraglottic (subglottic) cavity - below vocal folds to the start of the trachea.
Rima glottis
The space between the vocal folds.
The rima glottis as abducted during breathing and adducted during phonation (vibrate), holding breath and valsalva manoeuvre.
The resting position of the cords is open - for respiration.
The glottis
Refers to the vocal folds + rima glottis.
Muscles involved in abduction/adduction of vocal folds.
The arytenoid caritlages can slide medially/laterally and rotate to adduct/abduct the vocal folds.
- Abduction: posterior cricoarytenoids.
- Adduction: lateral cricoarytenoids and transverse arytenoids.
What are the functions of the muscles of the larynx?
- Abduct/adduct vocal folds
- Adjust length and tension of vocal folds
- Narrowing of laryngeal opening
Muscles of the larynx involved in adjusting length and tension of vocal folds.
- Cricothyroid: lengethens (increases tension on) vocal folds
- Vocalis: adjusts tension on vocal folds, varies length that vibrates.
- Thyroarytenoid: shortens (decreases tension on) vocal folds.
Muscles involved in narrowing of laryngeal opening
The oblique arytenoid, aryepiglottic, thyroepiglottic mm narrow larygeal inlet, adduct aryepiglottic folds and pull apiglottis posteriorly.
Phonation (vocalisation)
- Lateral cricoarytenoids and transverse arytenoid adduct vocal cords.
- Pitch can be altered by adjusting tension on cords:
- Vocalis
- Thyroarytenoid
- Cricothyroid
Or by raising/lowering larynx and pharynx (suprahyoid, infrahyoid muscles).
Swallowing
- Soft palate elevates to close off nasopharynx.
- Pharynx and larynx elevate, larynx moves anteriorly which open laryngopharynx (suprahyoid mm).
- The larynx is protected by the contraction of muscles at laryngeal inlet, adduction of the aryepiglottic folds and the posterior movement of the epiglottis.
Innervation of muscles of larynx
All supplied by vagus n (CN X), mostly via recurrent (inferior) laryngeal nerve.
Exception: cricothyroid via superior laryngeal n.
Sensory innervation of larynx
Vagus (CN X) via:
- Superior laryngeal nerve above vocal fold (vestibule, ventricle)
- Recurrent (inferior) laryngeal nerve below vocal fold (infraglottic cavity)
Lymphatics of the larynx
Lymphatic drainage to deep cervical nodes along internal jugular vein.
Blood supply of larynx
- Superior laryngeal a from superior thyroid a from external carotid a
- Inferior laryngeal a from inferior thyroid a from thyrocervical trunk from subclavian a
