Structure and function of airways Flashcards
What is dichotomous branching?
2 branches emerging from one
Why are the cartilages c shaped in the trachea?
To allow the oesophagus to pass without being affected
Why are the cartilages not stacked neatly?
More tensile strength
What are functions of the airways?
- conduit pipes to oxygen and carbon dioxide
- mechanical stability of airways controlled by cartilage
- smooth muscle control air flow
- protection and cleansing of air
What are some of the structures in the airway?
- airway lumen
- cartilage
- ciliated cells
- goblet cells
- mucus
- blood vessels
- submucosal glands (embedded in smooth muscle so when muscle contracts, mucus is squeezed out)
- smooth muscle
What are the different cells types in the airways?
- lining cells
- contractile cells
- secretory cells
- connective tissue
- neuroendocrine cells
- vascular cells
- immune cells
Give examples of lining cells
ciliated, intermediate, brush and basal
Give and example of a contractile cell
smooth muscle cells
Give examples of secretory cells
goblet (epithelial), mucous, serous (glands)
Give examples of connective cells
fibroblasts, interstitial cells
Give examples of neuroendocrine cells
nerves, ganglia, neuroepithelial bodies
Give examples of vascular cells
endothelial, pericyte and plasma cells
What are mucin granules?
They contain highly condensed form of mucin (found in mucus). The granules are found in goblet cells
What happens to mucin when it is released out of the goblet cells?
It expands as it absorbs water
What are submucosal glands?
They secrete mucus
What is the structure of a submucosal gland?
The serous cells are peripheral to the mucus cells. The serous cells produce watery mucus that has lysozymes. These secretions go over the mucus and wash into collecting duct. The glands also secrete water, salt and enzymes.
What is the structure of cilia?
They have rods within them with apical hooks.
If the cilia is cut transversely, there are 9 rods outside to 2 inside.
The rods slide over each other which uses lots of energy. There are 200 per cell.
What is the pattern of cilia beating?
Metachronal rhythm - one field beats then the one behind it and etc. The one that beat first is in backstroke waiting to beat again. Allows subsquential movement. Becuase cilia movement isn’t in sync, mucus can be moved.
How is mucus found on top of cilia?
Mucus is found in flakes over cilia, not a complete layer
Which regulatory and inflammatory mediators are produced by airway epithelium?
- NO
- CO
- Arachidonic acid
- Chemokines
- Cytokines
- Proteases
What is known about NOS expression in epithelium? Why is it found in these amounts?
There are lots of NOS in epithelium so lots of NO is produced. It could be important in controlling cilia beating as without it cilia beats much faster
What is airway tone?
How relaxed or contracted their airway is - affected by inflammation
When airways are inflamed, what happens to smooth muscle cells?
- Hypertrophy and proliferation of SMCs
- Increased contractile force so more secretion of mediators too (SMCs produce some secretions too) such as cytokines
- So function and phenotype change
How do the airways react to cytokines?
- NOS upregulation
- COX enzymes make more prostaglandins
- chemokines recruit other inflammatory cells
What are the features of the tracheo-bronchial circulation - where does blood return, where do the vessels come from?
- 1-5% of CO
- Highest profusion
- bronchial arteries arise from many places on aorta, intercostal arteries etc.
- blood returns from tracheal circulation via systemic veins
- blood returns from bronchial circulation to both sides of heart via broncial and pulmonary veins
What are the functions of the tracheo-bronchial circulation?
- good gas exchange
- warming and humidification of inspired air
- clears inflammatory mediators and inhaled drugs
- supplies airway tissue and lumen with inflammatory cells and proteinaceous plasma
Why does plasma leak out of post capillary venules?
They have contractile endothelial cells. When they contract, they pull apart and a gap forms through which plasma leaks.
What type of innervation causes endothelial cell contraction?
Sensory nerves with motor function supply the endothelial cells to allow contraction
When might plasma exudation go out of control and why?
In inflammation or disease plasma exudation can go out of control as histamine and platelet activating factors are made that active sensory nerves
Which things control the airway?
HINT: substances, molecules etc.
- nerves
- inflammatory and regulatory mediators ( histamine, cytokines and arachidonic metabolites like prostaglandins)
- proteinases
- reactive gas species like superoxide anion and NO
What would happen if food entered the airway?
cholinergic nerves (parasympathetic) - message to central system and cholinergic reflex causes bronchoconstriction
Which 2 pathways are used to relax the airways?
Other animals use the parasympathetic pathway to relax but in humans adrenaline is used - causes airway relaxation. A neuronal pathway is used - produces NO which opens the airways
Why can inflammatory cells have various different effects?
Inflammatory cells produce many mediators so can have various consequences
What are some respiratory diseases affecting the airways?
asthma - 5% of pop
COPD - 4th most common cause of death in UK, USA
CF
What is airway remodelling?
airway changes in structure over a long period of time
What is asthma and why is it reversible?
Syndrome characterised by increased airway responsiveness to a variety of stimuli- leads to airway obstruction. Obstruction is
reversible because adrenaline causes the airways to reopen. Airway inflammation leads to remodelling.
What are the symptoms of asthma?
dyspnoea, wheezing and cough
What is the histopathology of airways in a person with asthma?
Lumen blocked by mucus plugs with lots of eosinophils. Epithelial becomes fragile, BM thickens and blood vessels become prominent. In submucosa, eosinophil infiltration
What happens to the airway in a person who died of asthma?
- epithelium becomes folded as smooth muscle contracts
- lumen is blocked by mucus plug
What is the pathophysiological schema of asthma?
- PAF causes plasma exudation
- ATP causes goblet cell exocytosis
- epithelial fragility exposes the sensory nerves - more responsive to mediators
- Leads to a central cholinergic reflex - causes SM contraction and shutting down of the airways, and mucus secretion
- Hypertrophy of the smooth muscle and the glands
- Increase in the number of goblet cells - chemical mediators released
- Mast cells mediators cause bronchoconstriction, mucus secretion etc.
