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The respiratory system
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Comprises lungs and branches to connect site of gas exchange with external
environment
o Air moved by ventilation mechanism involving thoracic cage,
intercostals muscles, diaphragm, elasticity of lung tissue
Anatomically divided
o Upper respiratory tract
o Lower respiratory tract
Functionally divided
o Conducting portion (nasal cavities, nasopharynx, larynx, trachea,
bronchi, bronchioles, terminal bronchioles)
 Passage of air to and from the lungs
 Condition the air (cleaning, moistening and warming)
o Respiratory portion (respiratory bronchioles, alveolar ducts, alveoli)
 Gas exchange

Taken from Mescher, Junqueira’s Basic Histology: Text and Atlas, Twelfth Edition
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com, Pulmonary Microanatomy, taken from
https://www
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com/notes/note/n/g-pulmonary-microanatomy/deck/6270302

Clinical note
Immotile cilia syndrome
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Immotility of cilia and flagella; sometimes also dynein deficiency
Causes male infertility and chronic respiratory tract infections (both sexes)

Smoking
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Some sections of epithelial lining from nasal cavity to larynx are stratified
squamous – in regions subject to direct airflow or physical abrasion e
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oropharynx, epiglottis, vocal folds
o Provides protection from wear and tear
In smokers, proportion of goblet cells to ciliated cells increases to clear the
particulate and gaseous pollutants (e
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CO2, SO2)
o Provides rapid clearance
o BUT reduced cilia means decreased movement of mucus layer congestion

Nasal cavities
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Two components to each nasal cavity
o External vestibule
o Internal nasal cavity (fossa)
External vestibule
o Skin enters nostrils (nares) – sweat glands, sebaceous glands and
vibrissae (hairs) to filter out particulate matter
o Epithelium loses keratinized nature as it gets further into the vestibule
and transition to respiratory epithelium
Nasal cavity
o Cavernous chambers within the skull separated by osseous nasal
septum
o Conchae: three bony, shelf like projections extending from lateral wall
of each nostril (six in total)
 Superior conchae covered with olfactory epithelium
 Middle and inferior covered with respiratory epithelium
o Narrow passage between conchae known as the meatus
 Increases surface area of the mucous layer for moistening the
incoming air and reduces turbulence
 Located below each conchae
o Swell bodies: large venous plexuses in the lamina propria of conchae
 Become engorged with blood every 30 mins, causing distension
of the mucosa; airflow is blocked via this nostril so directed via
other nostril; allows mucosa to recover from dehydration

Rich vascular system
 Meshed latticework of vessels next to underlying periosteum,
with branches extending toward the surface
 Blood flows posteroanterially, i
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opposite direction to inspired
air, allowing it to be warmed quickly
Eustachian tube and sinuses connect into conchae
Sinuses lined with respiratory epithelia
Frontal sinus is located in the frontal bone of the skull; has small connecting
tube and drains into middle meatus
Ethmoid sinuses are located inferior to the frontal sinuses in the ethmoid bone
o Anterior drains into middle meatus
o Middle and posterior drain into superior meatus
Sphenoid sinus located close to the pituitary in sphenoid bone; drains into
sphenothmoidal recess located above superior conchae
Maxillary sinuses located in the maxillary bone; drain into middle meatus
o Drains out of the top, out of the ostium (hole in bone) - so only drains
when full (ostium is lower in other sinuses)
o Largest sinus and most likely to get infected
Function of sinuses
o Lighten skull
o Phonation
o Crumple zone
Sinuses innervated by trigeminal nerve (cranial nerve 5)
o Three main branches – ophthalmic, maxillary, mandibular
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Taken from apsubiology
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apsubiology
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htm

Clinical note
Swell bodies
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Allergic reactions and inflammation can cause abnormal enlargement in
both nostrils; restricted blood flow

Nosebleeds
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Numerous thin-walled venules located close to epithelial surface –
common occurrence

Smell (olfaction)
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Olfactory epithelium: specialised region of mucous membrane covering
superior conchae
It is pseudostratified, columnar epithelium comprising three cell types:
o Basal cells
 Small cells located at basal surface, don’t extend to apical
 Stem cells for other cell types
o Supporting cells
 Columnar cells with broad, cylindrical apexes and narrow bases
 Microvilli submerged in fluid layer
 Supportive role not thoroughly understood; have numerous ion
channels so may maintain the microenvironment
o Olfactory neurons
 Bipolar neurons throughout olfactory epithelium
 Nuclei lie between those of the supporting cells and the basal
cells
 Apical dendritic end has a knoblike swelling containing basal
bodies, from which emerge long non-motile cilia – large surface
area for membrane chemoreceptors
 Receptors respond to odiferous substances - AP generated
along basal axon to pass through the lamina propria and
cribiform plate
 Synapse with olfactory bulb, pass along olfactory tract to the
brain (cranial nerve 1)
Lamina propria of olfactory epithelium has large serous glands (Glands of
Bowman) which produce a flow of fluid surrounding the olfactory cilia,
facilitating access of new odiferous substances

Taken from Mescher, Junqueira’s Basic Histology: Text and Atlas, Twelfth Edition
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g
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g
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com, Head Anatomy, available at
http://www
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com/medical-atlas
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Mescher
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Twelfth Edition

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