week 1 - functional histology of the respiratory system Flashcards
what does the respiratory system contain?
mucous membrane and serous membrane
what does the mucous membrane line?
conducting portion of the respiratory tract, bears mucus-secreting cells (goblet cells)
what is the conducting portion of the respiratory tract?
nasal cavity, pharynx, larynx, trachea, primary bronchi, secondary bronchi, bronchioles, terminal bronchioles (branches 1-16)
what does the serous membrane contain?
outer parietal and inner visceral serosa (with air in between the 2 - like lubricating fluid of pleural cavity)
what does the serous membrane line?
the pleural sacs which envelope each lung
why are lungs shiny?
covered by moist pleura
what is the respiratory portion of the respiratory system?
respiratory bronchioles (branches 17-23), alveolar ducts, alveoli
which sections of the respiratory system are extrapulmonary?
nasal cavity, pharynx, larynx, trachea, primary bronchi
which sections of the respiratory system are intrapulmonary?
secondary bronchi, bronchioles, terminal bronchioles, respiratory bronchioles, alveolar ducts, alveoli
what happens as you go from nasal cavity all the way to alveoli?
the walls of the passageways become thinner as their lumens decrease in diameter
which structures (from outermost) have the same type of epithelium?
nasal cavity, pharynx, larynx, trachea, primary bronchi, secondary bronchi, bronchioles
what is the type of epithelium within the nasal cavity, pharynx, larynx, trachea, primary bronchi, secondary bronchi, bronchioles?
pseudostratified epithelium (goblet cells), with cilia and goblet cells (trap dirt) - lines the airways from the nasal cavity to the largest bronchioles
what type of epithelium comes after pseudostratified epithelium in the respiratory tract?
simple columnar epithelium with cilia and Clara cells (NO goblet cells)
what does simple columnar epithelium line in the respiratory tract?
terminal bronchioles (end of conducting portion)
what type of epithelium lines the beginning of the respiratory portion?
simple cuboidal epithelium with Clara cells and few sparsely scattered cilia
what does simple cuboidal epithelium line in the respiratory portion?
respiratory bronchioles and alveolar ducts
what comes after simple cuboidal epithelium in the respiratory portion?
simple squamous type 1 (gas exchange), some type 2
what does type 1 simple squamous line?
alveoli
where is the olfactory mucosa? function?
posterior superior region of each nasal fossa - allows us to smell
what is the order of the different pharynx from nasal cavity down?
nasopharynx –> oropharynx –> laryngopharynx
what are the different components of the nasal cavities?
non-olfactory regions & olfactory regions
what lies the olfactory regions?
particularly thick (tall) pseudostratified columnar epithelium, withOUT goblet cell (no mucus), has microbilli
what lies the non-olfactory regions?
pseudostratified ciliated epithelium
mucous glands & venous sinuses in lamina propria
what is the function of the non-olfactory regions of the nasal cavities? how does it achieve this?
venous plexus swells every 20-30 mins, alternating air flow from side to side, preventing overdrying of the nasal cavity
allows arterial blood flow to warm inspired air (rich blood flow)
how is patency of non-olfactory region of nasal cavity maintained?
by surrounding cartilage or bone
aside from tall pseudostratified epithelium, what type of cells does the olfactory region contain?
olfactory cells (bipolar neurones - 1 dendrite extends to the surface to form a swelling from which non-motile cilia extend parallel with the surface - increase SA & respond to odours)
describe the lamina propria (middle mucosa) of the olfactory region
lamina propria blends with submucosa (layer above mucosa)
has serous glands to flush odorants from the epithelial surface
how do olfactory nerves form?
axons of olfactory cells join each other to form an olfactory nerve
what does the larynx contain?
false vocal cord, ventricle (between the 2), true vocal cord
what contributes to the resonance of the voice?
the ventricles with the ventricular folds
what are the ventricular folds of the larynx lined by?
psuedostratified epithelium with mucous glands and numerous lymph nodules
what is each vocal cord of the larynx lined by?
stratified squamous epithelium
what does each vocal cord of the larynx contain?
- a vocal ligament (large bundle of elastic fibres, running front to back)
- a vocalis muscle (bundle of skeletal muscle)
what do the vocal cords help with?
stop foreign objects from reaching the lungs
they close to build up pressure when coughing is required
how big is the trachea?
10cm long, 2.5cm wide
what does the trachea divide into? where?
2 primary bronchi in the mid-thorax
how does the histology of primary bronchi differ from trachea?
primary bronchi’s hyaline cartilage rings and spiral muscle completely encircle the lumen
where is foreign body more likely to lodge? (left or right bronchus?) why?
right bronchus
path of right bronchus more vertical than left
how many lobes does each lung have?
3 on right (superior, middle, inferior)
2 on left (superior & inferior)
what happens to the C-shaped cartilaginous tracheal ring with ageing?
transformed in part to bone
what does the fibroelastic membrane (close to oesophagus - half moon crescent) contain?
trachealis muscle
what do secretions form the epithelium and submucosal glands (submucosa) of the trachea and bronchi contain?
mucins, water, serum proteins, lysozyme (destroys bacteria), antiproteases (inactive bacterial enzymes)
lymphocytes contribute immunoglobulins (IgA)
what is not present in cystic fibrosis sufferers?
CFTR ion channel molecule
what happens in cystic fibrosis sufferes?
Cl- transport across membrane compromised
in respiratory tract, water doesn’t leave the epithelium in sufficient quantities to adequately hydrate secreted mucus (lack of osmosis)
mucus becomes viscous & less readily moved into oropharynx for swallowing - pulmonary infections can occur
how does the histology of secondary & tertiary bronchi differ from primary bronchi?
similar except cartilages arranged as irregular crescent plates or islands, rather than rings
how is the blood supply to the bronchioles and alveoli?
pulmonary artery & vein
bronchial artery to terminal & respiratory bronchioles
capillary plexus @ alveoli
lymphs
histology of bronchiole
bronchiole has no cartilage or glands
surrounding alveoli keep the lumen open
blood supply to bronchiole & bronchus
pulmonary arteries carry deoxygenated blood (larger)
bronchial arteries carry oxygenated blood
histology of bronchus
small diameter with cartilage reduced to small islands
glands in submucosa
why can absence of cartilage in walls of bronchioles be problematic?
it allows the passages to constrict and almost close down when smooth muscle contraction becomes excessive
what happens in asthma?
bronchoconstriction (lack of cartilage in walls of bronchioles) can become excessive in asthma & cause more difficulty with expiration than inspiration
why is expiration more difficult than inspiration?
during expiration the bronchial walls are no longer held open by the surrounding alveoli
when do Clara cells appear?
when bronchioles get smaller, goblet cells give way to Clara cells, interspersed between ciliated cuboidal cells (respiratory bronchioles & alveolar ducts)
what is the function of Clara cells?
secrete a surfactant lipoprotein, which prevents the walls sticking together during expiration
also secrete abundant Clara cell protein (CC16)
what is the importance of CC16 - Clara cell protein?
- a measurable marker in bronchoalveolar lavage fluid (if lowered, then lung damage)
- a measurable marker in serum (if raised, then leakage across air-blood barrier)
why is it important not to have goblet cells in terminal bronchioles?
to prevent individuals from drowning in their own mucus in these very narrow airways
describe the passageways opening onto alveoli of: terminal bronchioles respiratory bronchioles alveolar ducts alveolar sacs, alveoli
TB: no alveolar openings
RB: bronchiole wall opens onto some alveoli
AD: duct wall has lots of openings onto alveoli
AS: composite air space onto which many alveoli open
what can alveoli open into?
a respiratory bronchiole
an alveolar duct
an alveolar sac
another alveolus (via alveolar pore)
when do new alveoli stop developing?
up to 8 years old
what do alveolar walls have?
abundant capillaries
supported by a basketwork of elastic & reticular fibres
a covering composed mainly of type 1 pneumocytes
a scattering of intervening type 2 pneumocytes
how close do alveoli lie to blood streaming in capillaries?
0.2 micro meter (um)
what do type 1 cells do? how much of alveoli are composed of type 1 cells?
type 1 cells (squamous pneumocytes) cover 90% surface area for gas exchange with capillaries
what do type 2 cells do? cover how much of alveoli?
type 2 cells (cuboidal pneumocytes) cover 10% of SA and produce surfactant
what else line alveolar surface aside from type 1 squamous pneumocytes & type 2 cuboidal?
numerous macrophages - phagocytose particles
what is emphysema? how can it occur?
destruction of alveolar walls and permanent enlargement of air spaces which can result from smoking or alpha 1-antitrypsin deficiency (misfolding proteins not secreted, can’t control lung tissue from self destruction)
what do alveolar walls normally do? what happens in emphysema? hallmark sign?
alveolar walls normally hold bronchioles open - allowing air to leave lungs on exhalation
when alveolar walls damaged, bronchioles collapse - difficult to empty air in lungs
hallmark sign: pursed-lip breathing
what happens in pneumonia?
inflammation of the lung caused by bacteria lung consolidates (tough) as the alveoli fill with inflammatory cells
what is the most common causative bacterium of pneumonia?
Streptococcus pneumoniae
