Lung Cell Biology Flashcards
Give the structure of the lungs from the trachea to the alveolar sacs
- Trachea
- Bronchi
- Bronchioles
- Terminal bronchioles
- Respiratory bronchioles
- Alveolar ducts
- Alveolar sacs
What can the SA of the lungs be compared to
SA of the lung is similar to that of the tennis court.
A glass of wine on a tennis court can be compared to the surfactant present on the epithelium
What is the function of the lung epithelium
Forms a continuous barrier, isolating external environment from the host
Produces secretions to facilitate clearance, via mucociliary action and protect underlying cells and maintain reduced surface tension
Metabolises foreign and host-derived compounds
Releases mediators
Triggers lung repair process (regeneration)
How does COPD affect the epithelium
Fewer ciliated cells - mucous cant be cleared efficiently
More goblet cells which release a lot of mucous
Describe the goblet cells
More found in large airways than small airways
1/5 of epithelial cells
Synthesise and secrete mucus
How does smoking affect the goblet cells
Cell number doubles at least
Secretions increase
More viscoelastic
Modified gel phase traps cigarette smoke particles but will trap microorganisms to enhance chance of infection
Describe the ciliated cells of the lung
60-80% of epithelial cells
Cilia beat metasynchronously
How does smoking affect the ciliated cells
Ciliated cells severely depleted Cilia beat asynchronously Found in the bronchioles Unable to transport thickened mucus Leads to respiratory infection and bronchitis
How does COPD affect the ciliated cells
There is extensive damage.
Fibrosis occurs in an attempt to heal tissue. When this occurs around a collapsed airway, the damage cannot be reversed.
Lots of inflammatory cells exist in the route.
Describe the difference in mucous coverage in the lungs
Thin sol phase that overlays cells
Thick gel phase at the air interface
What does the mucous contain
Mucin proteins, proteoglycans and GAGs
Viscoelasticity
Serum-derived proteins e.g. albumin, alpha1 antitrypsin
Combats microorganisms and phagocytes
Antiproteinases from epithelial cells e.g. secretory leucoprotease inhibitor
Combats microorganisms and phagocytes
Antioxidants e.g. uric acid, ascorbic acid , glutathione
combats inhaled oxidants e.g. ozone, cigarette smoke
Describe Club/clara cells
20% of the epithelial cells
Increase proportionally distally (bronchi and bronchioles rich)
Role is xenobiotic metabolism i.e. metabolismof foreign compounds deposited by inhalation - detoxification
Repair of damaged epithelium
How does smoking affect the Clara cells
Low number of club cells
Describe the different types of epithelial cells
Type I - flat thing cell for facilitating gas exchange and solute transport
Type II - secretory cell of surfactant. Ratio of I to II is 1:2
Type I cells cover 95% of the alveolar surface while the remaining 5% is type II
What is the function of type II pneumocystis
Synthesise and secrete phospholipid-rich surface active material, pulmonary surfactant that prevents lung collapse on expiration. Surfactant is stored in the lamellar bodies
Immunological functions and detoxification
Synthesise and secrete anti-proteases
Precursor of alveolar epithelial type I cells. Divide and differentiate to replace damaged type I cells
Describe the macrophages found in the lungs
No ciliated cells
Phagocytic that engulf deposited particles
Migration to the mucociliary layer in the upper airways once “fill”
Describe stromal cells/ myofibroblasts
Makes ECM (cement for the lungs)
Collagen and elastin to give elasticity and compliance
Divide to repair
What does abnormal repair by the stromal cells include
Type II cell proliferation
Stromal cell proliferation
Connective tissue synthesis by underlying fibroblasts
What is the effect of alveolar fibrosis
Type II try to repair but cannot differentiate into type I
Increased fibroblasts
Increased collagen deposition
What is the effect of smoking on the fibroblasts/ stromal cells
Apoptosis and necrosis of the epithelium
Blocking of repair
No transdifferentiation
What is the effect of smoking on the immune cells of the lungs
Increased number of inflammatory cells, macrophages and neutrophils up to 10 fold
What are the functions of alveolar macrophages (includes neutrophils)
Phagocytosis
Release proteins for antimicrobial defence
Synthesise antioxidants e.g. glutathione
Xenobiotic metabolism
Where are the alveolar macrophages found
Lower respiratory tract and throughout the airways
Neutrophils are more abundant
Describe the polymorphonuclear neutrophils
Only around 5% of LRT phagocytes
Higher proportion in conducting/large airways
Stores high levels of potent proteases in granules and released on activation
Release very potent oxidative molecules such as hydroxyl anions during activation
Describe COPD
Affects 15-20% of smokers.
Mixture of Bronchitis, Small airways disease, Emphysema.
May exist together, but also separately. Usually takes many years to develop and become clinically important.
Describe chronic bronchitis
Large/central airways affected, copious mucus production for three months of the year.
Airways obstructed by mucus and thickened mucosal cell layer.
Describe small airways disease
The small airways become blocked/obstructed due to mucus secretion and stenosis/narrowing of airway wall due to fibrosis.
Describe emphysema
Destruction of the respiratory tissue (especially the respiratory bronchioles of smokers) by proteolytic enzymes leads to loss of connective tissue scaffold, basement membrane “cement” and normal cell organisation. Loss of surface area and elastic recoil. Loss of vascular tissue. Gas exchange severely compromised. Affects fewer, about 10% of smokers
