Respiratory 6 - Lung cell biology Flashcards
How many generations of gas exchange units are there?
23
What proportion of epithelial cells are goblet cells?
1/5
Describe the role of Type II cells.
Produce SURFACTANT (so that lung does not collapse at low pressure on exhalation)
Also synthesise and secrete antiproteases
Make up 5% of alveolar surface
Precursor for Type 1 pneumocytes
What is the role of Type I epithelial cells?
Gas exchange takes place through them
What is the role of Type I epithelial cells?
Gas exchange takes place through them
What do endosomes do in the lung cells?
They transfer solutes accross the blood-gas barrier.
What are caveolae?
“little caves” - indentations in endothelial/epithelial cells where excoytosis happens - communication.
Where is surfactant stored in epithelial type II cells?
In lamellar bodies
How do surfactants look like and how do they work?
They are secreted as swirls. Then unravels to form a layer over the epithelium. Can form 9 layers for example.
Unused surfactant is stored in “the corners” of the alveolus as tubular myelin.
What is surfactant made of?
10% protein - contains protein used in spreading and activity of surfactant
90% lipid, of which 90% is phospholipid. This enable polarisation at the apical surface.
What are the 3 main structuresof pulmonary vasculature?
- muscular
- partially muscular (terminal bronchiole)
- non muscular (respiratory bronchioles)
What happens to alveoli in someone with COPD (emphysema)?
No solid fill, holes appearing - loss of respiratory surface
What happens in fibrosis?
The lungs attempt to repair but leads to scar tissue formation = fibrosis.
Lungs become solid
Type II cells multiply to repair damaged alveolar epithelium but also produce too much surfactant and stimulate fibroblast production of connective tissue (collagen deposit).
gas exchange = impossible
How does oedema impair gas exchange (IV endotoxin)?
Oedema will form in between capillary and epithelial cell which takes away surface gas exchange.
How do goblet cells and mucus change in smokers?
Goblet cells INCREASE in number
Secretions INCREASE in quantity
Secretions are THICKER
What is the structure of mucus?
A thin sol phase overlays the cells
A thick gel phase is at the mucus-air interface
What does mucus contain?
Mucin protein, proeoglycans, GAGs - give viscoelasticity
Serum derived proteins - albumin + alpha-1 antitrypsin + alpha-1 proteinase inhibitor
There are also antiproteases that have been secreted by the epithelia.
Anti-oxidants
What proportion of epithelial cells are ciliated cells?
80%
How do ciliated cells change in smokers?
Ciliated cell are severely depleted
Beat asynchronously
Ciliated cells found in bronchioles (though reduced in airways)
Unable to transport thickened mucus - smoker’s cough
Give two characteristics of small airways.
< 2 mm in diameter
NOT cartilaginous
What are clara cells?
Non-ciliated secretory epithelia found in the large, central and small airways and bronchi and bronchioles
How are clara cells distributed throughout the respiratory system?
They increase in proportion distally
What is the major role of clara cells?
Xenobiotic metabolism (ie drug metabolism)
What are the two classes of enzymes produced by clara cells and what do they do?
Phase 1 and Phase 2 - they are meant to be involved in metabolising foreign substances but they are also implicated in oncogenesis.
Phase 1 enzymes convert procarcinogens to carcinogens
Phase 2 enzymes conjugate the carcinogens to make them inactive
Clara cells also produce antiproteases and lyoszyme.
What are the diseases in COPD?
bronchitis + emphysema + small airways disease
What do stromal fibroblasts do?
- make ECM
- make collagen and elastin to give alveolus elasticity and compliance
- divide to repair
How do numbers of macrophages and neutrophils change in smokers and during infection?
Increase 5-10 fold
Neutrophils become more predominant than macrophage
What do alveolar macrophages do and what proportion of total phagocytic cells in a normal lung consist of macrophages?
70% of total phagocytic cells in normal lung
