lecture 4: structure and function of the airways Flashcards
what are the basic functions of the airways?
- conduit to conduct oxygen to the alveoli and the co2 out of the lungs
- they are needed to facilitate mechanical stability
- control calibre
- protect and clean mucus
what is the basic anatomy of the airways and lungs?
- the branching of the lungs is called dichotomous branching
- the c rings of the bronchi and trachea are slightly offset from eachother to give greater tensile strength
** what is the organisation of the airways?
- the c rings are not complete
- the c rings are offset
- below the cartilage there is a layer of smooth muscle
- submucosal glands are embedded
how doe the cilia beat?
- metasynchronously
how much mucus is made a day ?
what cells make the mucus ?
how do the goblet cells secrete their mucus?
10mL
goblet and submucosal glands
- mucin granules come to the apical surface and fuse with it
- a little pore forms and water goes through the pore
- the concentrated mucus expands rapidly
- then the mucus pops out
- a massive amount of mucin comes out of a tiny granule
***what is the function of the airways epithelia?
- secretion of mucin, water and electrolytes
- movement of mucus by cilia
- physical barrier against inhaled insult
- production of regulatory and inflammatory mediators
NO
CO
chemokines
cytokines
***what is the arrangement of the airway submucosal glands?
- functioning areas are called acini
- they secrete mucus out of the collecting duct
- the mucus moves to the collecting duct
- the cilia waft the mucus
- there are serous glands that are peripheral to the mucus cells
- the serous cells make watery mucus
- the watery secretions from the serous cells flush over the mucus secretions
- the glands also secrete water and antibacterials ect.
what is the function of airway submucosal glands?
- mucous cells secrete the mucus
- serous cells secrete anti bacterials
- glands also secrete water and salts
what is the structure of cillary?
Each individual cilia displays a ‘9+2’ relationship with 9 filaments around 2 central filaments.
The rods then slide over each other to simulate movement.
200 cilia per cell.
how do the cilia beat?
metachronal rhythm
like a wave
cilia waft the mucous up the respiratory tract using the apical hooks
what is the smooth muscle function in the airway?
regulates
tone
secretion
structure
what happens to the smooth muscle function during respiratory disease?
With respiratory disease, more inflammation and smooth muscle hypertrophy/proliferation which increases contractile forces of smooth muscle meaning more secretions are made
furthermore
in response to cytokines NOS is up regulated
- in response to chemokines inflammatory cells are recruited
- the COX enzymes produce more prostaglandins
what does the tracheo bronchial circulation do?
- takes 1-5% of cardiac output
- blood flow to the airway mucosa
- very rich in blood so you get direct gas exchange
- contributes to the warming and humidification of inspired air
- clears the inflammatory mediators and inhaled drugs
- Supplies airway tissue and lumen with inflammatory cells and proteinaceous plasma
***what is the mechanism of plasma exudation in the airways
- When the endothelial cells contract, they pull away from each other and form a gap which plasma leaks from
- This system can become exaggerated in disease
- endothelial cells are served by sensory nerves
- so in something like asthma these sensory nerves might become activated and therefore causing the plasma exudation process
what are the control systems of airways function?
- the nerves are PNS and SNS
- the regulatory mechanisms are
- histamines
- cytokines and chemokines
- Arachidonic Metabolites.
- proteinases
- reactive gas species
NO is important
what are the most important nerves for the innervation of the airways?
- via the vagus nerve
- cholinergic nerves are the most important pathways
- the cholinergic reflex can trigger bronchoconstriction
why are the nervous innervation of humans different to other animals?
- most animals have PNS pathways causing constriction and SNS = relaxation
- humans have constriction via PNS nerves
- dilation via the adrenaline from adrenal gland and NO in the nervous pathway
epidemiology of respiratory disease?
asthma - 5%
COPD - 4th leading cause of death
cystic fibrosis - autosomal recessive
what is asthma?
- airways obstruction over short periods of time
- A clinical SYNDROME characterised by an increased airway responsiveness to various stimuli
eosinophils are a major player and act fast to form mucous plugs made of eosinophils
the mucous plug combined with bronchoconstriction can cause full obstruction of breathing
what is the histology of asthma?
epithelial fragility, thickening of the basement membrane and prominent blood vessels.
**what is the pathophysiology of asthma?
- PAF causes plasma exudation.
- ATP causes goblet cell exocytosis.
- Epithelial fragility exposes sensory nerves which mean the airway becomes more sensitive – this sets up a CENTRAL CHOLINERGIC REFLEX to be more sensitive.
- This reflex stimulates bronchoconstriction and secretion of mucous.
- Repeated stimuli cause hypertrophy of SMCs and proliferation of goblet cells.
what is NOS expression in the human airway epithelium?
- there is a lot of NOS in the epithelium
- (nitric oxide synthase)
- so a lot of NO gets produced
- NO helps to control the beats of the cilia
why is the cholinergic response very important?
- causes bronchoconstriction
- contracts smooth muscle
- also causes the secretion of mucus
- eg when a peanut comes down the cholinergic reflex happens
humans use adrenaline to dilate the airway
