- diaphragm, intercostal muscles,
elastic tissue in lungs
- means by which air is moved in
and out of lungs continuously
- nose, pharynx, larynx, trachea,
bronchi, bronchioles, terminal
- warm/cool, humidify, filter &
conduct incoming air to
- lined with respiratory epithelium
-respiratory bronchioles, alveolar
ducts, alveolar sacs, alveoli
-site of exchange of O2 and CO2
between blood and alveoli
3 DIVISIONS OF RESPIRATORY SYSTEM
NASAL CAVITY & PARANASAL AIR SINUSES
- Respiratory area is lined with pseudostratified
ciliated columnar epithelium with goblet cells
and is highly vascularized
- Olfactory area (roof of nasal cavity and superior concha) is lined with olfactory
epithelium – specialized bipolar (sensory) neurons with sustentacular
(supporting) cells and basal cells (stem cells)
SAGITTAL VIEW CORONAL VIEW
CELLS OF RESPIRATORY EPITHELIUM
•Ciliated cells – most abundant, tall with basal nuclei, lots of
mitochondria to provide ATP for ciliary beating of mucus
and its’ trapped particulate matter.
•Goblet cells - ~30% of cells, have narrow basal stem
containing nucleus and most organelles and apical theca
containing mucinogen which becomes hydrated to form
•Basal cells – ~30% of cells, lie on basal lamina, do not reach
apical surface. Undifferentiated stem cells that will give rise
to other cell types.
•Brush cells - ~3% of cells, narrow columnar cells with tall
microvilli. Thought to have sensory receptors on basal
surfaces and act as sensory receptors.
•DNES cells -~3% of cells – have numerous small granules in
their basal cytoplasm whose contents act on other cells of the
•Olfactory cells – bipolar neurones, apical dendrite ends in olfactory vesicle
from which non-motile cilia with receptors for odiferous substances arise. When
a threshold level of receptors are occupied an action potential is generated and
transmitted to the olfactory bulb via axon which passes through cribiform plate
to synapse in olfactory bulb.
•Sustentacular cells – tall columnar cells with microvilli. Provide physical
support, nourishment and electrical insulation for olfactory cells.
•Basal cells – stem cells to replace olfactory and sustentacular cells.
•Bowman’s glands – provide serous fluid to refresh olfactory cilia.
serves only as an air
passageway. It is lined with
The OROPHARYNX and
serve as passageways for
both air and food. They are
lined with stratified
squamous epithelium (for
The muscular wall of the entire pharynx consists of skeletal muscle
All cartilages hyaline except
Vocal ligaments are elastic
Larynx, 69b (H&E)
Stratified squamous non-keratinized
epithelium of vocal fold
Pseudostratified ciliated columnar
epithelium of vestibular fold and ventricle
CONDUCTING & RESPIRATORY
PORTIONS OF THE RESPIRATORY TREE
•Mucosa lined with respiratory epithelium which continuously
propels mucus and debris towards the larynx
•Seromucous glands in submucosa help produce mucus ‘sheets’
•16-20 C-shaped rings of hyaline cartilage prevent the trachea
from collapsing. Closed posteriorly by trachealis (smooth) muscle
- allows oesophagus to expand anteriorly when swallowing.
into right and
•Primary bronchi run obliquely in the mediastinum, enter lung
where they subdivide into secondary and tertiary bronchi
•Mucosa and submucosa similar to trachea. Inc. smooth muscle &
elastic fibers in lamina propria. Mixed glands in submucosa.
•Plates of hyaline cartilage encircle bronchus and prevent collapse.
Lung, 72a (H&E) – bronchi and bronchioles
WALL OF A BRONCHUS
Blood vessels and glands
by fine elastic fibers)
Bronchus (cartilage &
smooth muscle in wall)
Bronchiole ( no
cartilage, just smooth
muscle in wall)
(alveoli off walls)
CELLS LINING BRONCHIOLES
Clara (bronchiolar) cells – columnar cells with domed
apices and short blunt microvilli. Apical cytoplasm filled
with secretory granules containing surfactant-like
material that reduces surface tension and faciliates
patency of bronchioles. Cells also degrade inhaled toxins.
As tubes become smaller, resp. epithelium
becomes lower with fewer goblet and
ciliated cells. Terminal bronchioles are
lined with simple cuboidal epithelium.
Proportion of smooth muscle increases
allowing for constriction (para.) and
dilation (symp.) of airways.
Respiratory bronchioles – first structures in respiratory zone,
alveoli arise from their walls, terminate in alveolar ducts
Alveolar ducts – linear arrangements of alveoli, lined with
type I cells, isolated regions of smooth muscle cells in lamina
propria between adjacent alveoli, lead to alveolar sacs
RESPIRATORY REGION OF THE LUNG
Type II cells
Dust cell (macrophage)
Type I cell
~ 250 million alveoli in lungs provide 140m2
of surface area for
CELLS OF ALVEOLAR WALLS
•Type I cells (squamous alveolar cells) - highly attenuated, cover
97% of surface area of alveolus, organelles grouped around
nucleus so most cytoplasm virtually free of organelles. Joined to
other type I and type II cells by tight junctions to prevent leakage
of fluid into air space. Basement membrane fuses with that of
endothelial cell to minimise thickness of respiratory membrane.
•Type II cells (septal cells) – account for 60% of alveolar cells but
only 3% of surface area. Cytoplasm filled with lamellar bodies
which contain surfactant that lowers alveolar surface tension.
They divide to form new Type II and type I cells.
•Alveolar macrophages (dust cells) – derived from monocytes,
found in alveolar septa, migrate between type I cells to enter
lumen of alveolus, phagocytose dust and bacteria and migrate to
bronchioles where ciliary action carries them to the pharynx to be
swallowed. Over 2 million dust cells are cleared per hr.
ALVEOLI & INTERALVEOLAR SEPTUM
Alveolar pores connect adjacent alveoli – allow for equalization
of pressure and alternate routes for blocked passages
Type II cell Type I cell
THE BLOOD-AIR BARRIER
•Type I cell
Barrier is extremely
(15 times thinner than a
piece of paper) to
Type I cell