Lung Cell Biology

Question 1

Give the structure of the lungs from the trachea to the alveolar sacs

Answer 1

1. Trachea
2. Bronchi
3. Bronchioles
4. Terminal bronchioles
5. Respiratory bronchioles
6. Alveolar ducts
7. Alveolar sacs

Question 2

What can the SA of the lungs be compared to

Answer 2

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

Question 3

What is the function of the lung epithelium

Answer 3

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)

Question 4

How does COPD affect the epithelium

Answer 4

Fewer ciliated cells - mucous cant be cleared efficiently

More goblet cells which release a lot of mucous

Question 5

Describe the goblet cells

Answer 5

More found in large airways than small airways
1/5 of epithelial cells
Synthesise and secrete mucus

Question 6

How does smoking affect the goblet cells

Answer 6

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

Question 7

Describe the ciliated cells of the lung

Answer 7

60-80% of epithelial cells

Cilia beat metasynchronously

Question 8

How does smoking affect the ciliated cells

Answer 8

Ciliated cells severely depleted
Cilia beat asynchronously 
Found in the bronchioles
Unable to transport thickened mucus
Leads to respiratory infection and bronchitis

Question 9

How does COPD affect the ciliated cells

Answer 9

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.

Question 10

Describe the difference in mucous coverage in the lungs

Answer 10

Thin sol phase that overlays cells

Thick gel phase at the air interface

Question 11

What does the mucous contain

Answer 11

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

Question 12

Describe Club/clara cells

Answer 12

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

Question 13

How does smoking affect the Clara cells

Answer 13

Low number of club cells

Question 14

Describe the different types of epithelial cells

Answer 14

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

Question 15

What is the function of type II pneumocystis

Answer 15

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

Question 16

Describe the macrophages found in the lungs

Answer 16

No ciliated cells
Phagocytic that engulf deposited particles
Migration to the mucociliary layer in the upper airways once “fill”

Question 17

Describe stromal cells/ myofibroblasts

Answer 17

Makes ECM (cement for the lungs)
Collagen and elastin to give elasticity and compliance
Divide to repair

Question 18

What does abnormal repair by the stromal cells include

Answer 18

Type II cell proliferation
Stromal cell proliferation
Connective tissue synthesis by underlying fibroblasts

Question 19

What is the effect of alveolar fibrosis

Answer 19

Type II try to repair but cannot differentiate into type I
Increased fibroblasts
Increased collagen deposition

Question 20

What is the effect of smoking on the fibroblasts/ stromal cells

Answer 20

Apoptosis and necrosis of the epithelium
Blocking of repair
No transdifferentiation

Question 21

What is the effect of smoking on the immune cells of the lungs

Answer 21

Increased number of inflammatory cells, macrophages and neutrophils up to 10 fold

Question 22

What are the functions of alveolar macrophages (includes neutrophils)

Answer 22

Phagocytosis
Release proteins for antimicrobial defence
Synthesise antioxidants e.g. glutathione
Xenobiotic metabolism

Question 23

Where are the alveolar macrophages found

Answer 23

Lower respiratory tract and throughout the airways

Neutrophils are more abundant

Question 24

Describe the polymorphonuclear neutrophils

Answer 24

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

Question 25

Describe COPD

Answer 25

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.

Question 26

Describe chronic bronchitis

Answer 26

Large/central airways affected, copious mucus production for three months of the year.
Airways obstructed by mucus and thickened mucosal cell layer.

Question 27

Describe small airways disease

Answer 27

The small airways become blocked/obstructed due to mucus secretion and stenosis/narrowing of airway wall due to fibrosis.

Question 28

Describe emphysema

Answer 28

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