PROCEDURE - Upper airways
1.
PRE-WORK
(before lab) review
the upper airway
bony architecture of the human skull from your atlas or a skull in the lab.
(Figure723)
(Netter011)
(Netter013)
(Netter015)
(Netter078)
(Netter090)
Anterior nasal orifices - These are the triangular shaped openings leading into the nasal cavity.
Looking into the nose of a skull you may be able to observe posteriorly wide round openings leading from the cavity into the nasopharynx.
Nasal Septum - The septum is partly bone (posterior third) and partly cartilage (anterior two thirds) separating the nasal cavities into left and right. The septum spans from the ethmoid bone superiorly to the vomer bone and hard palate inferiorly.
In a dry skull, the septal cartilage is absent and only the posterior bony septum is observed.
Hard palate - The maxilla and palatine bones contribute the flat sheet of bone forming the hard palate. The hard palate separates the nasal cavities (superiorly) from the oral cavity (inferiorly)
Hyoid bone - This bone is a C shaped bone located inferior to the mandible and posterior to the tip of the chin (the mental protuberance).
Unlike most bones, the hyoid bone has no joints and is only distantly articulated to other structures by muscle/ligament connections serving as an important fulcrum on which the muscles can act.
Thyroid cartilage - The thyroid cartilage is just superior to the cricoid cartilage. At the anterior midline the thyroid cartilage forms a distinct bump, the laryngeal prominence (or Adam's apple).
Cricoid cartilage - The cricoid cartilage is signet-ring shaped, has a broad posterior lamina and a narrower anterior arch, and is located approximately at the level of C6.
The cricoid cartilage is the only continuous ring of cartilage in the airways, the thyroid cartilage (roughly V shape) and tracheal cartilages (C-shape) are all discontinuous posteriorly with the gap spanned by muscle tissue.
Much of this dissection session is to be performed on the sagittally sectioned hemi-head. The hemi-head is present in your translucent organ storage box under the table. At the end of the lab the hemi-head is to be placed back into the biohazard bag and then into the translucent organs storage container under the table.
Where specifically directed in the instructions below, steps are performed on the intact donor.
PROCEDURE - Nasal cavity
2. On the hemi-head, examine the nasal cavity and if the head
has an intact nasal septum remove the septum with bone cutters or heavy scissors
(Figure724) (Netter045) (Netter077)
(Photo7154)
Use bone cutters or forceps to break away parts of the septum bony-cartilaginous framework to completely remove the septum. It is usually easiest to start at the anterior septum and work posteriorly.
The septum is formed by the perpendicular plate of the ethmoid bone, the vomer bone, and the septal cartilage which are covered by a highly vascularized respiratory mucosa.
Nasal regions are supplied by multiple major vascular territories. Supply to the nose arises from superficial face via angular artery branches, deep face from maxillary artery branches, and intracranial via ophthalmic artery branches.
Thus, when damaged in a 'nose bleed' both ends of a damaged artery are perfused and disproportional volumes of blood emerge from small breaks.
3. Examine the hemi-head medial (cut) surface and observe the
location of the nasal cavity and the three divisions
of the pharynx.
(Figure729) (Netter077) (NetterBP044)
(Photo7155)
Nasal cavity: The nasal cavities are airspaces in the mid-head between the orbit (laterosuperiorly) and the oral cavity (inferiorly).
Nasopharynx: The nasopharynx lies posterior to the nasal cavity and superior to the soft palate.
Oropharynx: The oropharynx lies posterior to the oral cavity (tongue) between the soft palate superiorly and the epiglottis inferiorly.
Laryngopharynx: The laryngopharynx extends from the epiglottis to the lower border of the cricoid cartilage. This area may not be fully present on the hemihead depending on the location of the transverse cut or slight deviation from the midline on the hemisection cut.
The pharynx, particularly the oropharynx, is a common region of 'pipe' shared by both the digestive system and the respiratory system. Foods/liquids must traverse the oral cavity, oropharynx, and in the laryngopharynx be directed into the esophagus. Air typically passes through the nasal passages, nasopharynx, oropharynx, and in the laryngopharynx to be directed into the trachea (although when needing large volumes of air during physical exertion, inspiration through the oral cavity is utilized).
Since it is a shared region, a series of muscles with precise movements are needed to ensure foods/liquids pass into the esophagus and not the trachea.
The pharynx is also a high risk region for invasive micro-organisms and has an abundant lymphoid tissue defense system (i.e. the tonsils). The tonsils are arranged in a rough annular ring (Waldeyer's tonsillar ring) spanning the nasopharynx and oropharynx. Some of the tonsils are too small to see unless inflamed, but we will examine their approximate locations later in the lab.
4. Observe the lateral wall of the nasal cavity and
identify from superior to inferior.
(Figure725) (Netter043)
(Photo7155)
Roof of the nasal cavity - this is formed by the nasal bone, cribriform plate, and parts of the sphenoid bone.
Sphenoethmoidal recess - the space between the superior concha and the roof of the nasal cavity.
All conchae have considerable variability between individuals. The superior concha is the most variable, ranging from a barely detectable bump to a fully formed ridge. Conchae are also referred to as turbinates. The terms are interchangeable and you may come across either depending on the source.
Superior concha - The most superior of the conchae, which are narrow bone shelves that extend medially and curl downwards into the nasal airway.
Superior meatus - the space immediately inferolateral to the superior concha.
Middle concha - The middle bony shelf, typically larger than the superior concha (usually as long as the little finger).
Middle meatus - the space inferolateral to the middle concha.
Inferior concha - the largest and most inferior of the bony shelves. This can be as long as 5-6cm length.
Inferior meatus - the space inferolateral to the inferior concha.
Hard palate (floor of the nasal cavity) - The hard palate of the mouth also forms the floor of the nasal cavity.
5. Identify the frontal sinus.
(Figure725) (Netter043)
(Netter051)
(Photo7155)
In some individuals, or if the sagittal cut is off center from the midline, the frontal sinus may be covered by thin bone or mucoperiosteum. If that is present, break through the wall so you can observe the sinus.
6. Identify the sphenoid sinus posterior to the superior
concha.
(Figure725) (Netter043)
(Netter051)
(Photo7155)
In some individuals, or if the sagittal cut is off center from the midline, the sphenoid sinus may be covered by thin bone or a sheet of mucoperiosteum (respiratory epithelium and connective tissue). If either is present, break through the tissue so you can observe the sinus.
Note that the roof of the sphenoid sinus is the floor of the hypophyseal fossa holding the pituitary gland.
A common approach to pituitary surgery (e.g. a transsphenoidal hypophysectomy) uses a nasal approach through the sphenoid sinus. This is an effective technique for the removal of pituitary tumors with minimal morbidity and hospital stay
7. Using scissors cut away the middle concha and observe
the structures in the middle meatus.
(Figure726) (Netter043) (Photo7097) (Photo7098)
Hiatus semilunaris - On the lateral wall of the meatus is a curved fissure, the hiatus semilunaris.
Ethmoid bulla - Superior to the hiatus semilunaris is a bulge in the wall of the nasal cavity, the ethmoid bulla. The openings to the ethmoidal sinus are via numerous small openings, typically too small to visualize.
Opening to the frontal sinus - Towards the anterior end of the hiatus semilunaris is the opening to the frontal sinus. Insert a probe into the opening and up towards the frontal sinus (or from the sinus towards the nose) to confirm the connection between the structures.
Opening to the maxillary sinus - Inferiorly along the hiatus semilunaris is the opening of the maxillary sinus, the largest of the paranasal air sinuses. Insert a probe into the opening and observe that the maxillary sinus is large (the probe can enter 2-3cm before encountering the lateral wall of the sinus).
8. Using scissors cut away the inferior concha and observe
the structures in the inferior meatus.
(Figure726)
(Netter043) (Photo7098)
Nasolacrimal duct - Near the anterior limit of the inferior concha is the opening for the nasolacrimal duct. This duct carries tears from the eye to the nasal cavity. It is typically small and not observable.
9. Carefully break through the lateral wall of the middle
meatus around the
opening to the maxillary sinus in order to remove the medial wall (i.e. completely open into the sinus).
(Figure727) (Netter051)
Note that the lateral wall of the middle meatus is the medial wall of the maxillary sinus.
10. Insert a probe into the sinus and feel/observe the extent of the
superior, posterior, and inferior walls.
(Netter049)
(NetterBP022)
(Netter063)
There is commonly a small ridge or 'line' visible along the superior wall of the maxillary sinus. This is formed by the infraorbital nerve traveling within the bone of the roof of the maxillary sinus (which is the floor of the orbit).
The superior wall of the maxillary sinus is the floor of the orbit, the posterior wall forms the anterior limit of the infratemporal region, and the inferior wall lies above the maxillary teeth.
11. Break into the roof of the maxillary sinus around the
infraorbital nerve to reveal
the infraorbital branch of the maxillary (V2) nerve and accompanying artery.
(Figure728)
Infraorbital nerve - The infraorbital nerve is the continuation of the maxillary (V2) nerve as it passes out through the infraorbital foramen.
Superior alveolar nerve branches arise from the infraorbital nerve and descend to innervate the superior teeth. These are named anatomically (e.g. the most anterior branch would be the 'anterior superior alveolar nerve' while the most posterior the 'posterior superior alveolar nerve', etc.). We will not dissect these.
The infraorbital nerve also gives rise to processes heading in and out of the pterygopalatine ganglion located behind the bone of the posterolateral wall of the maxillary sinus. The pterygopalatine ganglion is the largest of the parasympathetic ganglia of the head and supplies the lacrimal gland, and mucosal glands of the nasal, pharynx and palate.
Inflammation of this ganglia during upper respiratory tract infections involving the sinuses is partly responsible for the array of symptoms including mucus production, tense feeling behind the eye along with redness and lacrimal secretions. The pterygopalatine ganglia is sometimes referred to as 'the ganglia of hay fever' in recognition of the suite of symptoms the ganglion generates.
PROCEDURE - Nasopharynx
12. Examine the hemi-head
and observe the region immediately posterior to the nasal cavity.
(Figure729a) (Netter077)
(Photo7155)
This region is defined as the nasopharynx. It is the region of the airway that lies posterior to the nasal cavity but superior to the soft palate.
13. Examine the most superoposterior point of the
nasopharynx (just inferior to the sphenoid sinus) for the location of the
adenoid tonsils.
(Figure729) (Netter077)
(Photo7156)
This location houses the adenoid tonsils in the mucosa wall (sometimes called the nasopharyngeal tonsils to demarcate their location). These are rarely discernable as a distinct structure and appear just as a soft mound or thickening of the mucosal wall. Although you will not see the tonsils themselves, be aware of their presence at this location.
The adenoids are the least likely to exhibit significant inflammatory enlargement, however when that occurs they can enlarge considerably and block the flow of air through the nasal passages.
Additional individual lymphoid follicles visible only with a microscope are common through the nasal and oral regions, collectively these individual follicles are part of the mucosal associated lymphoid tissue (MALT).
14. Observe the lateral wall of the nasopharynx and
identify the pharyngeal orifice of the pharyngotympanic
tube (also known as the Eustachian tube).
(Figure725) (Netter043)
(Photo7156)
The cartilaginous portion of the Eustachian tube forms a bulge/elevation under the mucous membrane, the torus tubarius.
The Eustachian tube extends from the middle ear to the lateral wall of the nasopharynx, allowing equalization between the middle ear and ambient atmospheric pressure.
15. Follow the cut edge of the soft palate posteriorly
where it ends as the uvula.
(Netter043)
(Photo7156)
The uvula is a conical projection from the posterior edge of the soft palate comprised of muscle, connective tissue and some mucus glands.
16. Inferior to the uvula and superior to the hyoid bone is
the region defined as the oropharynx.
(Figure729a) (Netter072)
(Photo7060a)
This region is a shared space for food as well as for air intake either through the oral or nasal cavities.
This region was examined in detail in the Digestion and Hormones course and you can refer to the oral cavity lectures/labs to refresh your memory.
CLINICAL EXERCISE - Tracheostomy
17. The open tracheostomy procedure is one of the oldest described surgical interventions. It involves the creation of an opening in the anterior neck to establish an alternative airway into the trachea.
In this clinical exercise, you will perform a tracheostomy on your donor in a mock intervention. For the steps to take:
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PROCEDURE - Larynx
The following steps are all to be performed on the intact donor and excised donor lungs present in the translucent organ storage box below the table.
18. On the anterior side of the larynx of the donor
palpate for the thyroid and cricoid cartilages.
(Netter078)
(Netter090)
(Photo7021)
The thyroid cartilage has a prominent point, the laryngeal prominence, at the midline and lateroposteriorly directed cartilage lamina.
Both males and females have a laryngeal prominence at the midline, however in males this is typically more prominent.
19. Insert blunt point scissors into the
tracheostomy hole you made and cut through the cricoid & thyroid cartilage working
superiorly along the midline until the cartilages are transected.
(Figure785)
In some individuals with thick cartilage, or partial ossification, you may need to use your bone cutters to break the ossified cartilage followed by the scissors to free any residual soft tissue.
20. Continue the incision superiorly through
the thyrohyoid membrane to the level of the hyoid bone.
(Figure785)
Do not cut through the hyoid bone itself as that region is to be preserved for later MS1 student study.
21. Insert blunt point scissors into the cricothyrotomy hole and continue the opening inferiorly through the cricoid
cartilage, tracheal rings, and isthmus of the thyroid gland stopping
approximately at the level of the clavicles.
(Figure785a)
22. With forceps or a Weitlaner retractor spread the incision reflecting the
thyroid cartilage lamina laterally till you can see into the opening.
(Figure785b)
(Netter077)
(Netter078)
(Photo7092)
Vestibule - The vestibule extends from the laryngeal inlet to the first set of paired folds (vestibular folds), essentially the region of the airway directly superior to the folds.
Vestibular folds (false vocal cords) - There are the first set of folds encountered when proceeding inferiorly into the larynx (located just superior to the true vocal folds). The vestibular folds are infoldings of mucous membrane over a band of fibrous tissue. These are non-motile and primarily serve to protect the vocal folds from food and liquids.
Ventricle - The lateral out-pocketing (space) between the vestibular folds and the vocal folds is known as the ventricle.
Vocal folds (true vocal folds) - These are twin infoldings of mucous membrane inferior to the vestibular folds. The vocal folds are formed by coverings over the vocalis muscle and thus, can be vibrated to form vocalizations.
Glottis - This is an older term you may come across defined as the opening between the vocal folds (the rima glottidis).
Infraglottic cavity - The infraglottic cavity is the area below the vocal folds. It is continuous inferiorly with the lumen of the trachea.
23. Slide your finger, or a probe, into the piriform recess, a small space
inside the larynx lateral to the cricoid cartilage.
(Netter078) (Netter079)
(Photo7092)
(Netter079)
(Photo7091)
These are paired spaces, so there is one on the left side and one on the right site. Closure of the airway with the epiglottis during swallowing directs food through the piriform recesses into the esophagus.
These are a common location for foreign objects, particularly sharp objects such as fishbones, to become lodged 'in the throat' causing respiratory obstruction.
Blows to the back combined with abdominal thrusts (known as the Heimlich maneuver) is one of the most effective methods of treating acute airway obstruction by a swallowed object. The current methodology is 5 back blows followed by 5 abdominal thrusts (for the unconscious patient chest thrusts are recommended) repeated until advanced medical support arrives.
PROCEDURE - Lung
24. Using fingers explore the right and left pleural
cavities with your hand.
(Netter202) (Netter204)
(Photo2027)
Push your hand deep and posterior along the lateral side of the rib cage and feel how deep/inferior the costodiaphragmatic recess is along the lateral and posterior aspect of the thorax.
This arrangement is formed by the posterior diaphragm attachment being more inferior than the anterior diaphragm attachment to the costal margin. Thus, the diaphragm has a posteriorly sloped dome-like shape.
Move your hand to the most superior point in the pleural cavity on each side and observe how the cavity extends into the neck. The plural cavity (and lungs) extends approximately an inch superior to the thoracic inlet and houses the apex of the lung. Thus, any injury just superior to the clavicle has a risk of lung penetration at the apex.
For review of the different pleura/spaces refer to Figure214 which shows the thorax and a sagittal cross-section and Figure215 which shows the thorax and a transverse cross-section.
In the living, the parietal and visceral pleura layers are directly pressed against each other with only a thin sheen of fluid to lubricate movement. Thus, the 'space' of the cavity is extremely small (just the fluid gap between two opposed membranes). However, in patients with lung collapse, air or fluid pathologically accumulates creating a large gap that may need aspiration (via needle or tube) to remove the pathological material.
During inspiration lung tissue moves down into the costodiaphragmatic recess. During expiration lung tissue moves out of the recess and only a thin sheen of fluid is present there between the pleura.
There is also a costomediastinal recess, although this is not as important as the costodiaphragmatic recess during breathing.
25. Palpate the trachea inferiorly from the larynx and
observe that it is medial to the carotid arteries then passes posterior to the
arch of the aorta.
(Netter210)
(Netter211)
Deep to the arch of the aorta the trachea divides at the carina (an internal ridge of cartilage not visible from the outside) into the left and right main stem bronchi entering the hilum of the lungs.
Observe the cut surfaces of the bronchi on the left and right sides of the mediastinum with plates of cartilage present in the walls of the bronchi.
The hilum of the lungs contains the large main stem bronchi, pulmonary arteries, and pulmonary veins. Smaller structures include the bronchial arteries (supplying oxygenated blood to the bronchi and pulmonary arteries) and numerous lymph nodes.
26. Examine the surface features of the left lung.
(Figure216) (Netter205)
(iPhoto2001)
The left lung has two lobes, superior and inferior, which are separated by the oblique (major) fissure. The oblique fissure starts high on the back and proceeds anterior and inferiorly.
Thus, the bulk of the superior lobe is anterior and the bulk of the inferior lobe posterior to the root of the lung.
Identify the apex (most superior point of the lung) which extends into the root of the neck.
Identify the lingula, which is a small projection of the superior lobe at the most anterior/inferior point. The lingula varies in size and extent between individuals.
On the mediastinal surface of the lung, anterior and inferior to the root of the lung, is a large depression (the cardiac impression) produced by the heart.
Observe posterior from the cardiac impression that the descending aorta presses a vertical furrow just posterior to the root of the lung. The aortic arch presses a curved furrow in the lung superior to the root (the aortic impression).
27. Examine the root of the left lung (hilus) through which all of
the vessels and nerves enter the lungs.
(Figure216) (Netter205)
(iPhoto2001)
Identify the left main stem bronchus, which is posterior and towards the midpoint of the root of the lung. However, if the cut was distal to the division into lobular bronchi you may see more than one bronchi. To aid identification, us a probe or finger to feel the bronchus. Bronchi contain small plates of stiff cartilage.
Examine for branches of the pulmonary artery, which enters the left lung at the superior region of the hilum. However, as noted above if the cut is partly into the lung the pulmonary artery will already be branched into multiple lobar arteries and not a single superior position artery. The pulmonary artery branches run close to the bronchi, as artery branches follow bronchi branches all the way down to the alveolar (microscopic) level.
The pulmonary veins are hard to distinguish readily from the arteries. They typically have a thinner wall and are not closely associated with bronchi.
Look for the bronchial arteries that supply blood to the bronchi. As they supply blood to the bronchial tree they are usually immediately adjacent to the bronchus and are quite small at approximately 1-2mm in diameter.
It is also common to find blackened lymph nodes associated with the root of the lung. Loosen the tissue at the root of the lung with a probe or forceps to look for blackened deposits.
At the inferior border of the root of the lung, the anterior and posterior pleural surfaces come together to form a fold, the left pulmonary ligament, which extends down to just above the diaphragm. This has no significant function and is a remnant of how the pleura folded during development.
28. Examine the surface features of the right lung.
(Figure217) (Netter205)
(iPhoto2001)
The right lung has three lobes, superior, middle and inferior. The horizontal (minor) fissure separates the superior lobe from the middle/inferior lobes, and the oblique (major) fissure separates the inferior lobe from the middle/superior.
Thus, the bulk of the superior lobe is anterior, the bulk of the inferior lobe posterior to the root of the lung, and the middle lobe is almost entirely anterior to the root of the lung.
Identify the apex (most superior point of the lung) which extends into the root of the neck.
The right lung does not have a lingula.
Impressions in the right lung are less distinct than those in the left, but you may observe a vertical furrow posterior to the root of the lung where the esophagus presses and another impression superior to the root where the azygos vein forms a furrow.
29. Examine the root of the lung (hilus) through which all of
the vessels and nerves enter the lungs.
(Figure217) (Netter205)
(iPhoto2001)
The right main stem bronchus divides early sending the right superior branch, the eparterial bronchus, to the upper lobe (thus, it is likely your cut through the root of the lung will have occurred after this initial division leaving multiple segmental bronchi airway passages on your cut surface at the superior part of the root of the lung).
In the right lung, the pulmonary artery typically lies between the pulmonary veins and main stem bronchus. As with the left lung, the pulmonary artery branches closely associate with the bronchi down to the individual alveoli.
The pulmonary veins are hard to distinguish readily from the arteries. They typically have a thinner wall and are not closely associated with bronchi.
Look for the small bronchial artery that supplies blood to the bronchi. As it supplies blood to the bronchial tree, it is usually located immediately adjacent to the bronchus.
If you didn't find blackened lymph nodes in the left lung, investigate the root of this lung to find an example.
At the inferior border of the root of the lung, the anterior and posterior pleural surfaces come together to form a fold, the right pulmonary ligament, that extends down to just above the diaphragm similar to that of the left lung. This ligament also has limited clinical significance.
30. Insert the nozzle of the bulb aspirator into one of the bronchi and squeeze the bulb to inflate/deflate several times.
This should selectively inflate (ventilate) one of the lobes or segments of the lung.
If the lung segment does not inflate check that the nozzle is firmly pressed against the bronchial tissue so as to make an airtight junction. If there is extensive clotted blood in the lung segment chosen this may impede inflation, in which case select a different lobar/segmental bronchi to ventilate.
31. On both lungs, dissect away tissue surrounding a
bronchus, so that you can follow that bronchus to observe the segmental branching of the
bronchus and associated pulmonary artery.
(Figure218)
(Netter208)
(Photo2034)
The mainstem bronchus divides into lobar bronchi which, as the name implies, are the supply branches to each of the lobes. These lobar branches divide into segmental branches.
Segmental bronchi enter the different bronchopulmonary segments. There are typically 10 segments in the right lung and 8 ing the left lung (though there is some variability, particularly in the left lung). It is not feasible to identify them specifically in the lab.
You do not need to know the names/organization of lung segments in anatomy (Netter209), but we want you to appreciate their existence as the segmental organization of the lung is critical in pulmonary surgery procedures.
32. When your dissections for the day are finished complete the steps below.
Place the lungs back into the biohazard bag and return the organs as well as hemihead to the translucent organ box with the digestive organs.
When repacking the organ box, ensure that the tray with digestive organs is on the bottom of the box so as not to crush any of the organs under the tray.
As the bags may leak, always keep bagged organs on top of the dissection table or inside the organ storage boxes under the table. Do not place the bags on the floor or on chairs.
CHECKLIST
Skeletal Structures
Sinuses
Frontal sinus
Sphenoid sinus
Ethmoid sinuses
Maxillary sinus
Nasal septum
Cribriform plate
Hard palate
Nasal cartilage
Concha
Superior concha
Middle concha
Inferior concha
Hiatus semilunaris
Larynx
Cricoid cartilage
Thyroid cartilage
Epiglottis
Soft Structures
Spaces
Sphenoethmoidal recess
Superior meatus
Middle meatus
Opening into the frontal sinus
Opening into the maxillary sinus
Ethmoid bulla (opening of ethmoidal air cells)
Inferior meatus
Nasopharynx
Opening into the
Eustachian tube
Oropharynx
Soft palate
Uvula
Pharynx
Larynx
Epiglottis
Vestibule
Vestibular (false vocal) folds
Ventricle
Vocal (true vocal) folds
Costodiaphragmatic recess
Left Lung
Superior lobe
Inferior lobe
Oblique (major) fissure
Apex
Lingula
Cardiac impression
Aortic
impression
Bronchus
Pulmonary vein
Pulmonary artery
Lymph nodes
Bronchial artery
Right Lung
Superior lobe
Middle lobe
Inferior lobe
Horizontal
(minor) fissure
Oblique (major) fissure
Apex
Bronchus
Pulmonary vein
Pulmonary artery
Lymph nodes
Bronchial artery