Transcript Respiratory Anatomy-Histology Correlate

Respiratory
Anatomy-Histology Correlate
By: Michael Lu, Class of ‘07
NOTE:
- Visceral pleura is in direct contact with
the lungs, while parietal pleura is
everything else.
- 4 sections of parietal pleura: cupola,
costal, diaphragmatic, and mediastinal.
- Surface projections of parietal pleura:
Landmark
Inferior border of lung
Pleural reflection
Midclavicular
6th rib
8th rib
Midaxillary
8th rib
10th rib
Scapular
10th rib
12th rib
- Potential spaces of the costomediastinal
and costodiaphragmatic recesses, where
there is no lung tissue.
- The right lung contains 3 lobes –
superior, middle, and inferior – separated
by horizontal and oblique fissures.
- The left lung only contains superior and
inferior lobes. In addition, the cardiac
notch is an indent in the superior lobe,
forming the lingula that wraps around the
apex of the heart.
- Review the locations of the great vessels –
aorta, pulmonary trunk, pulmonary arteries
and veins, superior and inferior vena cava,
azygos vein, thoracic duct, etc.
- With the lungs removed, we see a better
view of the mediastinum. Notice on both
sides the phrenic nerves passing anterior
to the root of the lungs, vagus nerves
passing posterior, and the sympathetic
trunk running along the vertebrae. In the
thorax, the sympathetic trunk gives off both
white and grey rami communicantes
posteriorly and the greater splanchnic
nerve anteriorly.
- Note the left vagus nerve giving off the
recurrent laryngeal nerve wrapping under
the aortic arch. The arch of the aorta is also
attached to the left pulmonary artery via the
ligamentum arteriosum.
- Note on the right side the azygos vein
running posteriorly and draining into the
vena cava.
- Note on the left side the thoracic duct
that drains all the lymph in the body below
the diaphragm and on the left side above
the diaphragm.
- Note the relative locations of the
pulmonary arteries and veins and bronchi,
and the differences between the right and
left sides. These will be looked more closely
in the next slide.
NOTE:
- The left lung contains 2 lobes – an upper
and a lower lobe – separated by an oblique
fissure. The right lung contains 3 lobes – an
upper, a middle, and a lower lobe –
separated by transverse and oblique
fissures. The corresponding segments are
detailed in the next slide.
- Both lungs have grooves for the
subclavian arteries, brachiocephalic veins,
1st rib, esophagus, and cardiac impression.
The left lung has a groove for the aorta,
while the right lung has one for the azygos
vein.
- Since the apex of the heart is situated left
of midline, the left lung also has a cardiac
notch and lingula that wraps around the
apex.
- The reflection of the parietal pleura
forming the pulmonary ligament.
- On both sides, the bronchus is
posterior and the pulmonary veins are
anterior and inferior.
- On the left side, the pulmonary arteries
are the most superior, even above the
bronchus.
- On the right side, the pulmonary
arteries lie anterior to the bronchus.
Right lung
Left lung
SUPERIOR LOBE
Apical, anterior, and posterior segments
Apicoposterior, anterior, superior lingular,
and inferior lingular segments
MIDDLE LOBE
Medial and lateral segments
N/A
INFERIOR LOBE
Superior, medial basal, lateral basal,
anterior basal, and posterior basal segments
Superior, medial basal, lateral basal,
anterior basal, and posterior basal segments
- The respiratory system is divided into the conducting portion and the respiratory portion. The conducting
portion includes the nasal cavities, pharynx, larynx, trachea, and bronchi; the respiratory system starts from the
first branches of the respiratory bronchioles, alveolar ducts, and alveoli. The conducting portion warms, humidifies,
and cleans the air as it passes down to the respiratory portion for actual gas exchange.
- As shown above, the conducting portion is characterized by pseudostratified columnar epithelium with cilia,
goblet cells, gland tissue, and hyaline cartilage. The respiratory portion begins with the first branches of the
respiratory bronchioles; essentially where hyaline cartilage ends and there is abundant smooth muscle, elastic
fibers, reticular fibers, and epithelium transition from cuboidal to simple squamous.
- We will start at the beginning of the respiratory tract
and work our way down.
- Pay attention to the superior, middle, and inferior
nasal conchae and meatuses. The following histology
slides will show the abundance of blood vessels near
the surface to warm the air, and ciliated cells along the
epithelium to clean it. In addition, the conchae and
meatuses create turbulence within the nasal cavity to
slow down the inspired air and to help warm and
humidify it.
- Note the various sinuses and their openings: frontal
sinus, sphenoidal sinus, maxillary sinus, ethmoidal
cells, ethmoidal bulla, semilunar hiatus, frontonasal
duct, and nasolacrimal duct.
- Nasal concha and its mucosa are shown
in the histological slides here.
- The top panel emphasizes the warming
function of the nasal mucosa. The large
number of dilated veins transfer heat from
the blood to the inspired air. This
appearance of thin-walled veins
immediately adjacent to the mucosa is
typical of the nasal walls and cavity.
- The lower panel is a close-up of the nasal
mucosa. Note the respiratory epithelium,
which is mainly composed of
pseudostratified, ciliated columnar
epithelium with goblet cells. The other
structures include mixed muco-serous
glands, nerves, normal arteries and veins,
and thin-walled dilated veins.
- The goblet cells and glands provide mucus
to humidify the inspired air and trap dust,
particles, and bacteria.
- The ciliated cells beat and help to clear the
nasal cavity of these foreign particles and
mucus and clean the inspired air.
- The olfactory mucosa is located at the
superior part of the nasal cavity. Respiratory
epithelium lines the remainder of the walls
of the nasal cavity.
- Olfactory epithelium:
- thicker than respiratory epithelium
- Bowman’s glands, which are pure
serous glands, are found below the
epithelial surface
- abundant nerve fibers originating
from olfactory receptor cells
converge and give rise to the olfactory
tract, providing the special sense of
smell
- absence of goblet cells
- Respiratory epithelium:
- thinner than olfactory epithelium
- many mucus-secreting glands
- no nerve fibers
- abundance of goblet cells
- After the nose and nasal cavity, the air
travels down the pharynx, which is divided
into the nasopharynx, oropharynx, and
laryngopharynx.
- In the side panel, the pharyngeal mucosa
is detailed – note the non-keratinized
stratified squamous epithelium,
connective tissue, mucous glands, and
underlying elastic layer.
- Note the following: nasal septum, hard
and soft palate, hyoid bone, epiglottis,
thyroid cartilage, cricoid cartilage, vocal
fold, thyroid gland, pharyngeal and
lingual tonsils, pharyngeal constrictor
muscles, and retropharyngeal space.
- The pharynx connects the nasal and oral cavities
superiorly with the larynx and esophagus inferiorly. It
sorts food, water, and air to arrive at their destinations.
- In the pharynx, the paths of food and air cross. Food
travels from the mouth (anterior) to the esophagus
(posterior). Air travels from the choanae (posterior) to
the trachea (anterior).
- The pharynx contains 2 layers of muscles – outer
circular and inner longitudinal.
- The outer circular muscles include the superior,
middle, and inferior pharyngeal constrictor
muscles. One easy landmark to identify them is the tip
of the greater horn of the hyoid bone, to which the
middle pharyngeal constrictor attaches. The 3 muscles
contract serially to push a bolus down the esophagus.
- The inner longitudinal muscles include the
stylopharyngeus, salpingopharyngeus, and
palatopharyngeus muscles, which elevate and widen
the pharynx to accommodate a bolus when swallowing.
- The levator veli palatini and tensor veli palatini (not
shown here) muscles elevate the soft palate to seal off
the nasopharynx when swallowing. The epiglottis
closes off the larynx and trachea.
- The interior fascia is the pharyngobasilar fascia, an
area which does not have any muscle tissue.
- The pharyngeal mucosa is covered by nonkeratinized stratified squamous epithelium, with an
underlying dense layer of elastic tissue (blue brackets).
- The larynx connects the nasopharynx with the
trachea. It specializes in voice production. Note the
abundance of cartilages – 3 paired and 3 unpaired.
- The thyroid cartilage is the largest cartilage but does
not continue posteriorly. Anteriorly, it forms the
laryngeal prominence (Adam’s apple) with the
superior thyroid notch.
- The cricoid cartilage is the only complete ring of
cartilage in the larynx.
- The epiglottis protects the airway when swallowing.
- The 3 paired arytenoid, corniculate, and cuneiform
(not shown here) cartilages participate in voice
production.
- The intrinsic muscles of the larynx play a crucial
role in voice production.
- Cricothyroid muscles – tense the vocal folds to
control pitch.
- Posterior cricoarytenoid muscles – the ONLY
abductors of vocal folds.
- Lateral cricoaryteniod muscles – adduct vocal folds.
- Transverse arytenoid muscle – adducts vocal folds.
- Thyroarytenoid muscles – relaxes vocal folds.
- Vocalis muscles – contraction affects frequency of
vibrations and controls pitch.
- The vagus nerve is the major motor innervation, via
the superior and inferior laryngeal nerves and
recurrent laryngeal nerves.
-The panel on the left shows the relative positions of the true vocal
cords (vocal fold) and false vocal folds (ventricular or
vestibular folds). The panel below shows a magnified view, with
the true vocal cord closer to the cricoid cartilage and the false vocal
fold near the thyroid cartilage.
- The true vocal cords contain underlying skeletal muscle called the
vocalis muscles. Under the false vocal folds, the connective tissue
is filled with glands that secrete mostly mucus.
- The vocal cord is covered by stratified squamous nonkeratinized epithelium.
- The false vocal cord is covered by respiratory epithelium.
- As we continue down the respiratory tract, we enter
the trachea. Shown on the left panel is the trachea and
the major bronchi, which branch into segmental bronchi
and determine the bronchopulmonary segments.
- Histological slides of the trachea are shown below.
The bottom left panel exhibits the characteristic Cshaped rings of hyaline cartilage (C). The rings are
joined posteriorly by bands of smooth muscle known as
trachealis muscle (T). Tracheal mucosa (M) and some
strands of longitudinal muscle (L) are also shown.
- The trachea is lined with respiratory epithelium
sitting on a thick basement membrane. The elastic layer
contains many longitudinally oriented elastic fibers. The
submucosa contains loose connective tissue and mixed
muco-serous glands.
-Continuing down the respiratory tract, the
trachea bifurcates into two main or primary
bronchi. Within the tracheal bifurcation is a
keel-shaped cartilage known as the carina.
- The right main bronchus is wider, shorter,
and runs more vertically than the left main
bronchus. The left main bronchus is longer
and passes inferior to the arch of the aorta
and anterior to the esophagus and thoracic
aorta.
- The main bronchi later divide into
segmental bronchi. A characteristic
component that allows us to identify bronchi
is the presence of cartilage that appear as
chips and not semi-circular as in the
trachea.
- Bronchi are lined with the pseudostratified
ciliated columnar epithelium (respiratory
epithelium) with glands within the
submucosa.
- Note the presence of bronchial arteries,
which are distinct from pulmonary arteries
and veins. This will be explained in a later
slide.
- The bronchi further separate into
bronchioles. The defining feature of a
bronchiole versus a bronchus is the
absence of cartilage.
- Notice the abundance of smooth muscle
within the bronchiole wall. The epithelium is
frequently folded due to contraction of the
smooth muscle.
- The epithelium goes through a transition
from the pseudostratified ciliated columnar
respiratory epithelium to cuboidal ciliated
epithelium, as shown magnified in the
lower panel.
- The lower panel also compares the
relative size of the bronchiole to a typical
pulmonary artery.
- There are progressively fewer goblet cells.
They are replaced by Clara cells. Within
the magnified inset of the lower panel, the
Clara cells are cuboidal but do not have
cilia. They secrete a more watery substance
than mucus and the fluid continues to
moisten, warm, and clean the air.
- Terminal bronchioles are the smallest and
last branches of the conducting portion and
ciliated respiratory epithelium is replaced by
non-ciliated and ciliated cuboidal cells.
- Terminal bronchioles continue as respiratory
bronchioles, which then open into alveolar ducts and
individual alveoli.
- This is the respiratory portion of the respiratory
system, where the actual gas exchange occurs.
- Note the walls are composed of squamous
epithelium, containing both type I and II pneumocytes.
Type I pneumocytes or alveolar cells are very thin and
provide support to the alveoli. The type II
pneumocytes synthesize and secrete surfactant –
reducing surface tension and allowing the alveoli to
remain open.
- The arrows in the lower right panel indicate
pulmonary macrophages in the alveoli, but not within
the walls.
-There are two different circulations within
the lung.
- The low pressure, high volume
circulation flows to the lungs from the right
heart in order to be oxygenated. The
pulmonary arteries and veins are both
thin-walled vessels in this circulation.
- The high pressure, small volume
circulation provides oxygenated blood
primarily from the left heart and aorta to the
conducting portion of the respiratory
system. It includes the bronchial arteries
that have thicker walls to carry the high
pressure blood flow.
- There are 4 layers that exist between the
blood and inspired air in the blood-air
barrier:
- 1) capillary endothelium (continuous, no
fenestrations)
- 2) fused basal lamina
- 3) alveolar epithelium (type I pneumocyte)
- 4) surfactant
- Note the proximity of the red blood cell to
the inhaled air within the alveoli.