Lecture13 microscopic structure of the respiratory

1. Lecture 13Lecture 13 ESS_2nd semesterESS_2nd semester
Microscopic structure of the respiratory
system
Nasal cavity, larynx, and trachea
Histology of the lung and blood-air barrier
Outline of development of respiratory passages
and the lung

2. the respiratory system (RS) includes
lungs and
a system of tubes
that links the sites of gas exchange with the external environment
Main functions of the RS are:
oxygenation of blood by way of inspired air
elimination of carbon dioxide (a toxic by-product of body metabolism) by
way of expired air
excretion of water and volatile substances, such as alcohol etc,
besides mentioned functions, RS takes part in some specialized functions as
are
phonation
smell
filtration of inspired air

3. Respiratory system consists of 2 principal parts:
1. conducting portion (respiratory passages)
that involves
extrapulmonary one - nasal cavity,
nasopharynx, larynx, trachea and primary
bronchi
intrapulmonary one – bronchial tree
(bronchi, bronchioles, and terminal bronchioles)
2. respiration portion consisting of:
respiratory bronchioles
alveolar ducts and alveoli
A wall of respiratory passages
is rigid and prevents collapse lumen of the conducting
portion
is composed of 3 layers
 mucosa - covers the luminal surface and consists of
pseudostratified ciliated columnar epithelium
with mucous goblet cells and thin lamina propria
 fibrocartilaginous layer - supports the walls,
being composed of hyaline, and elastic cartilages
and bundles of smooth muscle tissue (caudally and
dorsally)
 adventitia - loosely connects both previous layers
with surroundings
is composed of loose connective tissue with blood
vessels and nerve bundles

5. Nasal cavity
- is divided by a midline nasal septum
into right and left part - nasal fossae,
- both fossae communicates with the
exterior through the nares (nostrils),
with the nasopharynx through the
posterior nares
each nasal cavity comprises
• vestibule
• respiratory portion (area) and
• olfactory portion (area)
Vestibule
- narrow zone in which the epidermis from external surface of the nose is replaced by
nonkeratinized pseudostratified columnar epithelium
around the inner surface of the nares are large sebaceous and sweat glands bound to thick
and short hair called vibrissae
they filter out large particles from the inspired air

6. Respiratory area (portion)
- is lined with pseudostratified ciliated columnar epithelium with goblet cells
- a lamina propria containing seromucous glands
it grows deeply together with the periosteum or perichondrium of bone or cartilage
three bony shelf-like projections called conchae protrude into both nasal fossae from the lateral wall of the
nasal septum
the superior concha belongs to the olfactory portion
the middle and inferior conchae contain a rich vascular plexus (mainly in inferior conchae) that serves to warm
of inspired air (conditioning of the inspired air) – (They also produce turbulence of the air so that the contact
surface with mucosa becomes greater and thereby increasing the humidity!)
Olfactory area (portion)
occupies the roof of each nasal fossa (regio olfactoria)it is lined with olfactory mucosa that contains the
receptors for the sense of smell (sensory cells-unipolar!)
cells are modified bipolar neurons–they have dilated apex with nonmotile cilia and axon (BOWMANS
GLANDS)

7. Paranasal sinuses
are air-filled cavities within the bones of the skull (maxillary, frontal, ethmoid and
sphenoid), which communicate through small openings with the nasal cavities
they are lined with the same but thinner mucosa (periost + lamina propria +
epithelium) as the respiratory portion of nasal fossae
The nasopharynx
is upper part of the pharynx which
- anteriorly is open into the nasal cavity through posterior nares,choana!
- posteriorly and laterally is surrounded by the muscular tissue
- caudally is continued with the oropharynx and larynx
the epithelium of the pharynx is pseudostratified ciliated columnar with goblet cells
small glands (mucous, serous and mixed) and accumulations of lymphatic tissue
(pharyngeal tonsil - posteriorly, tubal tonsils - laterally) are in the lamina propria
the middle layer of the pharynx is of muscular character being formed by bundles of
the striated muscles

8. Larynx C3-C6
is an irregular tube connecting pharynx and trachea
the skeleton of the organ is formed large hyaline
(thyroid, cricoid, and most of the arytaenoid) and small
elastic (epiglottis, cuneiform and corniculate) cartilages
that are bound together by ligaments + membranes.
striated skeletal muscles insert to the surface of
cartilages and provide to move against each other
inner surface is covered by the mucosa consisting of
dense connective tissue with seromucous glands and
the islets of lymphatic tissue
except two sites, the entire larynx is lined with
pseudostratified ciliated columnar epithelium with
goblet cells
below the aditus, the mucosa forms 2 pairs of folds that
extend into the lumen of the larynx
the upper pair constitutes the false vocal cords,
covered by typical pseudostratified columnar epithelium;
the lower pair of folds constitutes true vocal cords
that are covered by stratified squamous epithelium
bbetween folds the sinus and saccule of the
larynx a small slit-like diverticulum of
laryngeal cavity is located on each side

9. True vocal cords:
- stratified squamous epithelium,
- lamina propria (loose fibroconnective tissue),
- ligamentum vocale (elastic connective tissue),
- musculus thyreoarytaenoideus (cross-striated muscle tissue
lying in plica vocalis outer to ligamentum)
False vocal cords:
- pseudostratified ciliated columnar epithelium + goblet cells
- lamina propria of mucosa with mixed glands
the shape of the opening between the vocal cords (the glottis) varies with
breathing and phonation

10. The epiglottis
closes aditus into the larynx

basic tissue of the organ is elastic
cartilage
it is covered with a mucous coat:
stratified squamous epithelium is
on its lingual aspect
while
pseudostratified columnar
epithelium is on the laryngeal
surface
the mucosa contains mixed serous
and mucous glands

11. Trachea
is a tube about 10-12 cm long, 2-2.5 cm in
diameter
Mucosa: (inner side)
- pseudostratified ciliated columnar epithelium +
goblet cells
- lamina propria mucosae (thin layer of connective
tissue (with elastic fibers,
it contains islets of lymphatic tissue)
Submucosa: layer of loose connective tissue with
small mixed glands
Fibrocartilaginous layer: C-shaped hyaline
cartilages (l6-20) + (annular lig.) , posteriorly free
ends are connected by ligaments (X, Y-shaped),
musculus trachealis is present in posterior part of
the tracheal wall
Adventitia: loose connective tissue with blood
vessels and nerves
it connects the trachea with surrounding structures
similar structure as trachea show the primary or
extrapulmonary bronchi

12. Lungs (Lat. pulmo, Greek pneumón)
are located in the pleural cavity lined by
parietal pleura, which is to come over the
lungas the visceral pleura (mesothelium
+ thin layer of dense connective tissue) at
the hilum of each lung
the pleural cavity contains a small amount
of watery, serous fluid
The bronchial tree
primary bronchi (extrapulmonary) enter the
right and left lung
they divide in secondary bronchi (3 in the
right, 2 in the left that supply pulmonary
lobes
secondary or lobar bronchi divide into
tertiary bronchi supplying broncho-
pulmonary segments (anatomical units
of the structure)
the tertiary bronchi repeatedly divide, at
minimal 10 times, so that small bronchi of
12 orders arise
these are called bronchioles and conduct
air into pulmonary lobules

13. bronchioles are the last of intrapulmonary bronchi that contain cartilage in their wall
in general, the structure of primary bronchi is similar to the trachea
proceeding toward the respiratory portion, a simplification of histologic
organization of both epithelium and underlying lamina propria is
observed
it must be emphasized that the simplification is gradual, and no abrupt transition
can be observed between the bronchi and bronchioles
Pulmonary lobule
the unit of structure of the lung is called the pulmonary lobule
there is a part of the lung parenchyma of pyramidal shape (apex of the pyramid is
directed toward the hilum of the lung)
at the apex; bronchiole and the branch of pulmonary artery enter the lobule
the branches of pulmonary vein (with oxygenate blood) run in the connective tissue
of interlobular septa, which delineate adjacent lobules
interlobular septa contain also lymphatic vessels

14. Pulmonary lobule
air is conducted to it by
bronchiole
each bronchioles divides into
5 - 7 terminal bronchioles
each terminal bronchiole
subdivides into 2 or more
respiratory bronchioles
that are sites of transition between
the conducting and respiratory
portions of RS
respiratory bronchioles pass
into
alveolar ducts and sacs
and these into
alveoli

16. ALVEOLIALVEOLI (alveoli pulmonum)
- have diameter 100 – 300 mm
- number of alveoli is cca 300 -
500 millions
- they occupy surface area of 80 - 120
m
2
- are polyhedral or hexagonal and
separated by a thin interalveolar septae
- the septum consists of interstitium
(connective tissue with elastic and
reticular fibers and different cell types
(fibroblasts, mono- and lymphocytes,
alveolar macrophages) and blood
capillaries
- both sides of septae are covered with
respiratory epithelium on basal lamina
- interalveolar pores occur in the wall
of alveoli and are important for
collateral circulation

17. Respiratory epithelium
the type I alveolar cells or membranous pneumocyte s - flattened, with micropino-
cytotic vesicles near basal and apical surfaces and thin processes (20–25 nm), cells cover cca
97 % of the alveolar surface
the type II alveolar cells or granular pneumocytes - cuboidal cells with secretory
granules in the cytoplasm; they contain phospholipid-
protein and are secreted on the surface of
epithelium as monomolecular film "lining
complex" (surfactant) that is primarily
composed of dipalmitoyl lecithin
the layer of surfactant (about 30 nm thick)
prevents from atelectasis (alveolar collapse)
lamina basalis

19. Alveolar macrophages:
occur within the alveoli or in the septae
cells are movable and able to phagocyte inspired particles of dust etc.
they form a part of phagocyte macrophages system

20. Blood-air barrier consists of:
1- respiratory epithelium with
surfactant on the surface,
2- the basal laminae of closely
apposed alveolar and endothelial
cells,
3- endothelial cells of blood
capillaries of continuous type
the total thickness of these
layers varies from 0.1 to 1.5
mm
insufficient surfactant production
causes difficulty in expanding
alveoli and injury of the
respiratory epithelium in
premature new-borns
the disease - respiratory
distress syndrome
glucocorticoids stimulate the synthesis
of surfactant and are used in
treatment of the Respiratory Distress
Syndrome (RDS).

21. TRACHEA
pseudostratified ciliated columnar ep. with
goblet cells
^
right - PRIMARY BRONCHI - left
(the same epithelium)
^
3 - SECONDARY BRONCHI - 2
(LOBAR)
LOBES
(the same epithelium)
^
l0 - TERTIARY BRONCHI - 8
(SEGMENTAL)
(the same epithelium)
SEGMENTS
^
BRONCHIOLES (of 12 order)
(ciliated columnar ep.) 1 mm in diameter
PULMONARY LOBULES
^
^^
TERMINAL BRONCHIOLES
(simple ciliated columnar - cuboidal ep.) 0.5 mm
in diameter
lamina propria is composed largely of smooth
muscle and elastic fibers
^
RESPIRATORY BRONCHIOLES
(cuboidal- squamous ep.)<0.3 mm in diameter,
wall is interrupted by more or less numerous
alveoli where gas exchange occurs
smooth muscle and elastic connective tissue lie
beneath the epithelium
^
ALVEOLAR DUCTS
is a part of tree whose wall protrude in individual
alveoli
A.d. open into atria that communicate with
alveolar sacs (2 or more of which arise from each
atrium
^
ALVEOLAR SACS AND ALVEOLI
respiratory ep. with two cell types
The bronchial treeThe bronchial tree

22. Pleura
pleura parietalis
pleura visceralis
is composed of simple squamous epithelium (mesothelium) and thin layer of connective tussue ( 1 mm)

Blood supply of the lungs
two blood circulations are distinguished in the lungs: functional and nutritive ones
Functional circulation: truncus pulmonalis < into right and left pulmonary artery < their branches
(follow respir. tree) < capillary network around alveoli > venules (collect the blood rich in
oxygen) > venules and veins in interlobular connective tissue (septa) > vv. pulmonales
Nutritive circulation: bronchial arteries (the branches of aorta or intercostal arteries) - follow the bronchi,
run in interlobular connective tissue and in pleura - return through vv. pulmonales into the heart

23. Outline of development of respiratory passages and the
lung
the low part of respiratory system (from larynx downstairs) develops as an
outgrowth of the ventral wall of the foregut
as the wall of entire gut is lined by the endoderm the epithelial lining of conducting
as well as respiratory portions is of endodermal origin
the cartilaginous and muscular components of the trachea and lungs derive
from the mesenchyma (from the splanchnic mesoderm)

initial stage of development
is called as the respiratory
diverticulum
it occurs in the caudal end
of the ventral wall of the
pharynx when the embryo
is aged 26 to 27 days

24. the diverticulum then expands in caudal direction and it becomes separated
from the foregut by the development of two longitudinal
esophagotracheal ridges (folds)
the ridges subsequently fuse to form a septum–esophagotracheal
septum
the foregut is divided in
a dorsal portion, the esophagus, and a ventral portion, the trachea and lung bud
the site where the trachea communicates with the pharynx is called laryngeal
Orifice, between 5
th
and 6
th
pharyngeal arches.

25. 4. The FOURTH – SIXTH.
Cartilage – cartilages of larynx and trachea.
Mesenchyme – cricothyroid, levator veli palatini, constrictors of pharynx,
intrisic muscle from larynx.
The 4th aortic arch – has the ultimate fate different on the left and right
sides, On the left it forms a part of the arch of the aorta between the left
common carotid artery and the left subclavian vein. On the right side the
proximal segment of the right subclavian artery.
The 5th aortic arch - is transient and soon obliterates.
The 6th aortic arch – transform into pulmonary artery (their branches)
Branchial nerves – Superior laryngeal branch of the vagus, recurrent
laryngeal branch of the vagus.

26. a lung bud soon divides into two knob-like bronchial buds
early in the fifth week, each bronchial bud enlarges to form a primitive
primary bronchus
concurrently, the primary bronchi subdivide into secondary bronchi (on
the right 3, on the left 2) that will supply future lobes
each secondary bronchus subsequently undergoes dichotomous branching;
the branches are called the tertiary or segmental bronchi (supply
bronchopulmonary segments) - 10 in the right, 8 or 9 in the left (7th week)
The 24 weeks, about 17 orders of branches have formed and the
respiratory
bronchioles are present

27. with subsequent growth in caudal and lateral directions, the lung buds
penetrate into primitive pleural cavities
the mesoderm, which covers the outside of the lung, develops into the
visceral pleura
the somatic mesoderm layer, covering the body wall from the inside,
becomes the parietal pleura
the space between the parietal and visceral pleura is the pleural cavity

28. during development of the lungs, the endodermal lining thins so that the barrier
between the blood vessels in the mesenchyma and the air that will fill the lungs at
birth is as slight as possible (BLOOD-AIR BARRIER)
this continuous process is conventionally divided up into four general periods that
overlap because differentiation is usually more advanced in the cranial part of the
lungs than caudally
periods:
Pseudoglandular period - lungs somewhat resemble of a gland, at the
end; all major elements of the organ have formed except those involved with
gas exchange (respiratory bronchioles and alveoli)
endoderm cells are cuboidal

29. Canalicular period - vascularization begins and the respiratory bronchioles
are developed, at the ends of some respiratory bronchioles thin-walled
terminal sacs may be seen
survival of the fetus is unlikely at this time
Terminal sac period = primitive alveoli period - the development of
terminal sacs continues, capillaries come into close contact with the
epithelium of primitive alveoli, type I alveolar epithelial cells are already
differentiate, production of pulmonary surfactant begins
after 28 weeks survival of the fetus is possible

30. Alveolar period - is characterized by differentiation of terminal sacs into
the future alveolar ducts

31. Malformations of the respiratory system
 Lung agenesis - lung buds fail to form, unilateral or bilateral, survival is
possible in unilateral form (compensation by the remaining lung)
bilateral agenesis is fatal
 Respiratory distress syndrome - inadequate production of surfactant
in premature babies
the lungs may therefore collapse and the endoderm cell surface may be
damaged
 Tracheo-esophageal fistula - situation when the trachea and gut were
to come into contact -
it is commonnly associated with esophageal atresia - blind ending of the
gut - incidence is 1 per 3,000 - 4,500 births

32. clinical finds:
the new-born baby will gag as its saliva enters its lungs and shows signs of respiratory distress
milk may be regurgitated on feeding
when the child cries, its abdomen may become distended as air is drawn into the stomach