Resp 4 - Airways Function Flashcards
Why are cartilage rings slightly offset relative to each other?
it gives greater tensile strength
Which cells produce mucus?
Goblet cells
How much mucus is produced a day?
10mL
What is coughed up mucus called, when infection present?
Sputum
What are the 7 different cell types in the airway?
- Lining cells
- Contractile cells
- Secretory cells
- Connective tissue
- Neuroendocrine
- Vascular cells
- Immune cells - come and go depending on health
Explain how goblet cells secrete mucus.
- Mucin granules move to the apical surface and fuse with it
- Little pore forms - water enters through the pore
- Concentrated mucus diluted and expands rapidly
- More and more mucus pops out of the goblet cell
The functional units are called acini. What do mucous acini and serous acini do?
(Submucosal Glands also secrete salt and water)
Mucous acini secrete mucus
Serous acini secrete antibacterials (watery mucus).
Serous acini is distal to the mucus acini
Describe the structure of cilia
Structure:
- 9+2 arrangement
- They have rods within them
- They have apical hooks (to engage with the mucus).
Approximately 200 cilia per ciliated cell
Describe the pattern of beating of cilia.
“Metachronal rhythm”
One field of cilia beats, then the next, then the one after that etc. While field 2/3 are beating, the first field is on its backstroke.
Metachronal rhythm allows cilia to move mucus sequentially along.
What are the functions of airway epithelium?
- Secretion of mucin, water and electrolytes.
- Mucociliary clearance
- Physical barrier vs inhaled insult
- Produces regulatory and inflammatory mediators
Give examples of regulatory and inflammatory mediators produced by the airways.
- NO (by NOS)
- CO
- Arachidonic acid metabolites
- Chemokines
- Cytokines
- Proteases
Where does NOS reside in the airways?
In the epithelium - lots of NO produced here.
NO may control beating of the cilia, giving NO donors to ciliated cells causes faster ciliary beating.
What are the functions of airway smooth muscle?
Control:
- Structure (hypertrophy, proliferation - e.g. during asthma). Hypertrophy may increase contractile force of the muscle. Marked increase in mediator secretion (e.g. cytokines)
- Tone
- Secretions.
How is airway smooth muscle involved in secretory functions?
- In response to inflammation/cytokines, NOS upregulated.
- Prostaglandins upregulated.
- Chemokines (+ cytokines + adhesion molecules) recruits inflammatory cells.
Smooth muscle therefore involved in the inflammatory process.
How much of the total CO goes to airway vasculature? (i.e. trachea-broncial circulation)
1-5%
Blood flow through the tracheo-bronchial circulation is among the highest to any tissue.
Name 2 sites from where the bronchial arteries can arise.
- Aorta
2. Intercostal arteries
How does blood return from the tracheal circulation?
Via the systemic veins
How does blood return form the bronchial circulation?
Via systemic and bronchial circulation and it goes to both sides of the heart
What is present in the sub epithelial microvascular network?
Massive plexus - contains lots of arteries, veins and capillaries
What are the functions of the tracheo-bronchial circulation?
- Gas exchange between airway tissues and blood
- Warming of inspired air
- Humidification of inspired air
- Clears inflammatory mediators
- Clears inhaled drugs
- Supplies inflammatory cells to airway tissue and lumen
- Supplies airway tissues and lumen with proteinaceous plasma
Describe plasma exudation
- Plasma leaks out of post capillary venules
- Post capillary venules have endothelial cells that can contract
- When endothelial cells contract, they form a gap - plasma leaks through this gap
- Endothelial cells are innervated by sensory nerves (but actually perform a motor function).
What happens to plasma exudation during asthma?
Histamines and platelet activating factor are produced.
This causes the sensory nerves to become activated and exaggerates the plasma exudation process.
Name 4 things which control airway function
- Nerves
- Regulatory and inflammatory mechanisms (histamine/arachidonic metabolites/cytokines/chemokines)
- Proteinases
- Reactive gas species (e.g. NO)
How is bronchoconstriction brought about in the airway?
- Peanut swallowed
- Parasympathetic (cholinergic) nerve are the most important. Through a cholinergic reflex (mediated by a central system), bronchoconstriction occurs.
What is unique about humans compared to other animals?
We don’t have a sympathetic pathway for bronchodilation
How do humans bronchodilate?
- We either rely on adrenaline (relaxes airways)
2. Or we have our own neuronal pathway linked to NO production (via NOS). NO stimulates airway opening
Describe the outcomes of the cholinergic mechanisms the airways.
Airway smooth muscle contracts in response to acetylcholine
- Cholinergic reflex contracts smooth muscle.
- Causes mucus secretion
- (Little bit of vasodilation).
Inflammatory cells produce more than one mediator. Mediators do more than one thing.
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Name 3 conditions involving a loss of airway control.
What abnormalities are they associated with?
- Asthma
- COPD
- Cystic Fibrosis
Abnormal airway inflammation and obstruction
What is airway remodelling?
Airway changes in structure over a long period of time
Define asthma
Clinical syndrome characterised by increased airway responsiveness to a variety of stimuli.
(leading to airway obstruction)
What does airway inflammation lead to?
Remodelling
Describe airway inflammation in asthma
- Airway lumen blocked by a mucus plug which contains lots of eosinophils (very aggressive). Eosinophils infiltrate to submucosa.
- Epithelial fragility
- Thickening of basement membrane
- Blood vessels become prominent
Describe bronchoconstriction in asthma
- Epithelium is folded - smooth muscle contracted and airway has shut down.
- Mucus plug blocks lumen
- Mucus usually is ok, but with bronchoconstriction it can block airways.
What causes goblet cell exocytosis?
ATP
