Upper Airway and digestive tract Flashcards
Describe the basic structure of the nasal cavity
The smaller anterior regions of the cavities are enclosed by the external nose, whereas the larger posterior regions are more central within the skull. The anterior apertures of the nasal cavities are the nares, which open onto the inferior surface of the nose. The posterior apertures are the choanae, which open into the nasopharynx.
The nasal cavities are separated:
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from each other by a midline nasal septum,
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from the oral cavity below by the hard palate, and
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from the cranial cavity above by parts of the frontal, ethmoid, and sphenoid bones.
Lateral to the nasal cavities are the orbits.
Each nasal cavity has a floor, roof, medial wall, and lateral wall
What is important to remember about the nasal cavity
Drians into the cranial cavity (venous)- can transfer infections from the outside world into the cranial cavity,
Summarise the structure of the nasal cavity
Upper part of respiratory tract Anterior & posterior regions Contain conchae Warm and humidify air, help trap pathogens Meatus (meatuses) in between
What type of epithelium lines the conchae
Respiratory Epithelium
It increases the surface area for warming and humidifying the inspired air (conchae are also referred to as turbinate bones)
Conchae= bone + epithelium
Turbinate = bone
What are the key structures of the lateral wall of the nasal cavity
The lateral wall is characterized by three curved shelves of bone (conchae), which are one above the other and project medially and inferiorly across the nasal cavity (Fig. 8.226B). The medial, anterior, and posterior margins of the conchae are free.
The conchae divide each nasal cavity into four air channels (Fig. 8.226C,D):
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an inferior nasal meatus between the inferior concha and the nasal floor,
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a middle nasal meatus between the inferior and middle concha,
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a superior nasal meatus between the middle and superior concha, and
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a spheno-ethmoidal recess between the superior concha and the nasal roof.
These conchae increase the surface area of contact between tissues of the lateral wall and the respired air.
Which sinus drains into the sphenoethmoidal recess
the sphenoidal sinus
Name two important openings into the lateral wall of the nasal cavity
The openings of the paranasal sinuses, which are extensions of the nasal cavity that erode into the surrounding bones during childhood and early adulthood, are on the lateral wall and roof of the nasal cavities (Fig. 8.227). In addition, the lateral wall also contains the opening of the nasolacrimal duct, which drains tears from the eye into the nasal cavity.
What are the 3 regions of the nasal cavity
Each nasal cavity consists of three general regions—the nasal vestibule, the respiratory region, and the olfactory region (Fig. 8.228):
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The nasal vestibule is a small dilated space just internal to the naris that is lined by skin and contains hair follicles.
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The respiratory region is the largest part of the nasal cavity, has a rich neurovascular supply, and is lined by respiratory epithelium composed mainly of ciliated and mucous cells.
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The olfactory region is small, is at the apex of each nasal cavity, is lined by olfactory epithelium, and contains the olfactory receptors.
Summarise the innervation of the nasal cavity
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Olfaction is carried by the olfactory nerve [I].
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General sensation is carried by the trigeminal nerve [V], the anterior region by the ophthalmic nerve [V1], and the posterior region by the maxillary nerve [V2].
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All glands are innervated by parasympathetic fibers in the facial nerve [VII] (greater petrosal nerve), which join branches of the maxillary nerve [V2] in the pterygopalatine fossa.
Sympathetic fibers are ultimately derived from the T1 spinal cord level. They synapse mainly in the superior cervical sympathetic ganglion, and postganglionic fibers reach the nasal cavities along blood vessels, or by joining branches of the maxillary nerve [V2] in the pterygopalatine fossa.- innervate vascular smooth muscle
Which bones contribute to the skeletal framework of the nasal cavity
Bones that contribute to the skeletal framework of the nasal cavities include:
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the unpaired ethmoid, sphenoid, frontal, and vomer bones, and
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the paired nasal, maxillary, palatine, and lacrimal bones and inferior conchae.
Of all the bones associated with the nasal cavities, the ethmoid is a key element.
Describe the key features of the ethmoid bone
The single ethmoid bone is one of the most complex bones in the skull. It contributes to the roof, lateral wall, and medial wall of both nasal cavities, and contains the ethmoidal cells (ethmoidal sinuses).
The ethmoid bone is cuboidal in overall shape (Fig. 8.229A) and is composed of two rectangular box-shaped ethmoidal labyrinths, one on each side, united superiorly across the midline by a perforated sheet of bone (the cribriform plate). A second sheet of bone (the perpendicular plate) descends vertically in the median sagittal plane from the cribriform plate to form part of the nasal septum.
Describe the medial wall of the nasal cavity
The medial wall of each nasal cavity is the mucosa-covered surface of the thin nasal septum, which is oriented vertically in the median sagittal plane and separates the right and left nasal cavities from each other.
The nasal septum (Fig. 8.232) consists of:
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the septal nasal cartilage anteriorly,
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posteriorly, mainly the vomer and the perpendicular plate of the ethmoid bone,
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small contributions by the nasal bones where they meet in the midline, and the nasal spine of the frontal bone, and
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contributions by the nasal crests of the maxillary and palatine bones, rostrum of the sphenoid bone, and the incisor crest of the maxilla.
Describe the consequences of a deviated nasal septum
The nasal septum is typically situated in the midline; however, septal deviation to one side or the other is not uncommon, and in many cases is secondary to direct trauma. Extreme septal deviation can produce nasal occlusion. The deviation can be corrected surgically.
Describe the floor of the nasal cavity
The floor of each nasal cavity (Fig. 8.233) is smooth, concave, and much wider than the roof. It consists of:
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soft tissues of the external nose, and
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the upper surface of the palatine process of the maxilla and the horizontal plate of the palatine bone, which together form the hard palate.
The naris opens anteriorly into the floor, and the superior aperture of the incisive canal is deep to the mucosa immediately lateral to the nasal septum near the front of the hard palate.
Describe the roof of the nasal cavity
The roof of the nasal cavity is narrow and is highest in central regions where it is formed by the cribriform plate of the ethmoid bone
Anterior to the cribriform plate the roof slopes inferiorly to the nares and is formed by:
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the nasal spine of the frontal bone and the nasal bones, and
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the lateral processes of the septal cartilage and major alar cartilages of the external nose.
Posteriorly, the roof of each cavity slopes inferiorly to the choana and is formed by:
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the anterior surface of the sphenoid bone,
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the ala of the vomer and adjacent sphenoidal process of the palatine bone, and
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the vaginal process of the medial plate of the pterygoid process.
Describe the lateral wall of the nasal cavity
The lateral wall of each nasal cavity is complex and is formed by bone, cartilage, and soft tissues.
Bony support for the lateral wall (Fig. 8.235A) is provided by:
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the ethmoidal labyrinth, superior concha, middle concha and uncinate process,
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the perpendicular plate of the palatine bone,
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the medial pterygoid plate of the sphenoid bone,
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the medial surfaces of the lacrimal bones and maxillae, and
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the inferior concha.
What is the semilunar hiatus
Inferior to the ethmoidal bulla is a curved gutter (the semilunar hiatus), which is formed by the mucosa covering the lateral wall as it spans a defect in the bony wall between the ethmoidal bulla above and the uncinate process below.
The anterior end of the semilunar hiatus forms a channel (the ethmoidal infundibulum), which curves upward and continues as the frontonasal duct through the anterior part of the ethmoidal labyrinth to open into the frontal sinus.
Describe the sphenopalatine foramen
One of the most important routes by which nerves and vessels enter and leave the nasal cavity is the sphenopalatine foramen in the posterolateral wall of the superior nasal meatus. This foramen is just superior to the attachment of the posterior end of the middle nasal concha and is formed by the sphenopalatine notch in the palatine bone and the body of the sphenoid bone.
The sphenopalatine foramen is a route of communication between the nasal cavity and the pterygopalatine fossa. Major structures passing through the foramen are:
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the sphenopalatine branch of the maxillary artery,
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the nasopalatine branch of the maxillary nerve [V2], and
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superior nasal branches of the maxillary nerve [V2].
Describe the foramen cecum
In addition, there is a connection in some individuals between nasal veins and the superior sagittal sinus of the cranial cavity through a prominent foramen (the foramen cecum) in the midline between the crista galli and frontal bone.
Describe the arteries of the nasal cavity
Arteries that supply the nasal cavity include vessels that originate from both the internal and external carotid arteries (Fig. 8.239):
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Vessels that originate from branches of the external carotid artery include the sphenopalatine, greater palatine, superior labial, and lateral nasal arteries.
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Vessels that originate from branches of the internal carotid artery are the anterior and posterior ethmoidal arteries
Significant anastomoses- clinically relevant in nose bleeds
Describe the venous drainage of the nasal cavity
Veins draining the nasal cavities generally follow the arteries (Fig. 8.240):
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Veins that pass with branches that ultimately originate from the maxillary artery drain into the pterygoid plexus of veins in the infratemporal fossa.
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Veins from anterior regions of the nasal cavities join the facial vein.
In some individuals, an additional nasal vein passes superiorly through a midline aperture (the foramen cecum), in the frontal bone anterior to the crista galli, and joins with the anterior end of the superior sagittal sinus. Because this nasal vein connects an intracranial venous sinus with extracranial veins, it is classified as an emissary vein. Emissary veins in general are routes by which infections can track from peripheral regions into the cranial cavity.
Veins that accompany the anterior and posterior ethmoidal arteries are tributaries of the superior ophthalmic vein, which is one of the largest emissary veins and drains into the cavernous sinus on either side of the hypophyseal fossa.
Summarise the paranasal sinuses
There are four paranasal air sinuses—the ethmoidal cells, and the sphenoidal, maxillary, and frontal sinuses (Fig. 8.231A,B). Each is named according to the bone in which it is found.
The paranasal sinuses develop as outgrowths from the nasal cavities and erode into the surrounding bones. All of the paranasal sinuses:
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are lined by respiratory mucosa, which is ciliated and mucus secreting,
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open into the nasal cavities, and
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are innervated by branches of the trigeminal nerve [V].
Describe the role of sinuses in the skull
It makes the skull lighter
Acts as a crumple one for the brain
Increases projection of the voice - role in resonation
Describe the frontal sinuses
The frontal sinuses, one on each side, are variable in size and are the most superior of the sinuses (Fig. 8.231A–C). Each is triangular in shape and is in the part of the frontal bone under the forehead. The base of each triangular sinus is oriented vertically in the bone at the midline above the bridge of the nose and the apex is laterally approximately one-third of the way along the upper margin of the orbit.
Each frontal sinus drains onto the lateral wall of the middle meatus via the frontonasal duct, which penetrates the ethmoidal labyrinth and continues as the ethmoidal infundibulum at the front end of the semilunar hiatus.
The frontal sinuses are innervated by branches of the supra-orbital nerve from the ophthalmic nerve [V1]. Their blood supply is from branches of the anterior ethmoidal arteries.
Describe the ethmoidal air cells
The ethmoidal cells on each side fill the ethmoidal labyrinth (Fig. 8.231A,B). Each cluster of cells is separated from the orbit by the thin orbital plate of the ethmoidal labyrinth, and from the nasal cavity by the medial wall of the ethmoidal labyrinth.
The ethmoidal cells are formed by a variable number of individual air chambers, which are divided into anterior, middle, and posterior ethmoidal cells based on the location of their apertures on the lateral wall of the nasal cavity:
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The anterior ethmoidal cells open into the ethmoidal infundibulum or the frontonasal duct.
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The middle ethmoidal cells open onto the ethmoidal bulla, or onto the lateral wall just above this structure.
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The posterior ethmoidal cells open onto the lateral wall of the superior nasal meatus.
Describe the blood supply and innervation of the ethmoidal air cells
Because the ethmoidal cells often erode into bones beyond the boundaries of the ethmoidal labyrinth, their walls may be completed by the frontal, maxillary, lacrimal, sphenoid, and palatine bones.
The ethmoidal cells are innervated by:
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the anterior and posterior ethmoidal branches of the nasociliary nerve from the ophthalmic nerve [V1], and
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the maxillary nerve [V2] via orbital branches from the pterygopalatine ganglion.
The ethmoidal cells receive their blood supply through branches of the anterior and posterior ethmoidal arteries.
Describe the maxillary sinus and its drainage
The maxillary sinuses, one on each side, are the largest of the paranasal sinuses and completely fill the bodies of the maxillae (Fig. 8.231A,B). Each is pyramidal in shape with the apex directed laterally and the base deep to the lateral wall of the adjacent nasal cavity. The medial wall or base of the maxillary sinus is formed by the maxilla, and by parts of the inferior concha and palatine bone that overlie the maxillary hiatus.
The opening of the maxillary sinus is near the top of the base, in the center of the semilunar hiatus, which grooves the lateral wall of the middle nasal meatus.
Describe the structural relationships, innervation and blood supply of the maxillary sinus
Relationships of the maxillary sinus are as follows:
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The superolateral surface (roof) is related above to the orbit.
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The anterolateral surface is related below to the roots of the upper molar and premolar teeth and in front to the face.
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The posterior wall is related behind to the infratemporal fossa.
The maxillary sinuses are innervated by infra-orbital and alveolar branches of the maxillary nerve [V2], and receive their blood through branches from the infra-orbital and superior alveolar branches of the maxillary arteries.
Describe the sphenoidal sinuses
The sphenoidal sinuses, one on either side within the body of the sphenoid, open into the roof of the nasal cavity via apertures on the posterior wall of the spheno-ethmoidal recess (Fig. 8.231C,D). The apertures are high on the anterior walls of the sphenoid sinuses.
The sphenoidal sinuses are related:
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above to the cranial cavity, particularly to the pituitary gland and to the optic chiasm,
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laterally, to the cranial cavity, particularly to the cavernous sinuses, and
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below and in front, to the nasal cavities.
Describe the clinical relevance, blood supply and innervation of the sphenoidal sinuses
Because only thin shelves of bone separate the sphenoidal sinuses from the nasal cavities below and hypophyseal fossa above, the pituitary gland can be surgically approached through the roof of the nasal cavities by passing first through the anteroinferior aspect of the sphenoid bone and into the sphenoidal sinuses and then through the top of the sphenoid bone into the hypophyseal fossa.
Innervation of the sphenoidal sinuses is provided by:
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the posterior ethmoidal branch of the ophthalmic nerve [V1], and
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the maxillary nerve [V2] via orbital branches from the pterygopalatine ganglion.
The sphenoidal sinuses are supplied by branches of the pharyngeal arteries from the maxillary arteries.
Describe the clinical relevance of the structural relationships of the different sinuses
- Roots of upper teeth and the maxillary sinus – root infections can form fistulas into the maxillary sinus and cause infection.
- Mastoid air cells and middle ear – mastoid air cells can become eroded by infection and the erode through tegmen tympani into the cranium and cause infection to the brain.
- Sphenoid sinus and pituitary gland – trans-sphenoidal surgery to access the pituitary gland
Describe the mastoid air cells
They are small sinuses within the mastoid part of the temporal bone
The mastoid air cells communicate with the middle ear via the aditus ad antrum and the mastoid antrum
This is a possible route for infection of the middle ear
Describe mastoiditis
Infection within the mastoid antrum and mastoid cells is usually secondary to infection in the middle ear. The mastoid cells provide an excellent culture medium for infection. Infection of the bone (osteomyelitis) may also develop, spreading into the middle cranial fossa.
Drainage of the pus within the mastoid air cells is necessary and there are numerous approaches for doing this. When undertaking this type of surgery, it is extremely important that care is taken not to damage the mastoid wall of the middle ear to prevent injury to the facial nerve [VII]. Any breach of the inner table of the cranial vault may allow bacteria to enter the cranial cavity and meningitis will ensue.
Summarise the larynx
Hollow structure Composed of: Cartilages Membrane Muscles
Acts as a:
Valve
Sound producer
Describe the structural relationships of the larynx
The cavity of the larynx is continuous below with the trachea, and above opens into the pharynx immediately posterior and slightly inferior to the tongue and the posterior opening (oropharyngeal isthmus) of the oral cavity
What does the larynx consist of
The larynx is both a valve (or sphincter) to close the lower respiratory tract, and an instrument to produce sound. It is composed of:
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three large unpaired cartilages (cricoid, thyroid, and epiglottis),
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three pairs of smaller cartilages (arytenoid, corniculate, and cuneiform), and
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a fibro-elastic membrane and numerous intrinsic muscles.
The larynx is suspended from the hyoid bone above and attached to the trachea below by membranes and ligaments. It is highly mobile in the neck and can be moved up and down and forward and backward by the action of extrinsic muscles that attach either to the larynx itself or to the hyoid bone.
During swallowing, the dramatic upward and forward movements of the larynx facilitate closing the laryngeal inlet and opening the esophagus.
Motor and sensory innervation of the larynx is provided by the vagus nerve [X].
Summarise the cricoid cartilage
The cricoid cartilage is the most inferior of the laryngeal cartilages and completely encircles the airway (Fig. 8.206). It is shaped like a signet ring with a broad lamina of cricoid cartilage posterior to the airway and a much narrower arch of cricoid cartilage circling anteriorly.
