Lung cell biology

Question 1

What are the external insults to the lungs

Answer 1

Smoking, pollution

Question 2

What is the effect of tobacco on the lungs

Answer 2

COPD- puts holes in the lung- can lead to emphysema

Question 3

What are the knock on effects of things that affect the airways

Answer 3

May have knock on effects on the CVS- systemic effects

Question 4

What can respiratory bronchioles have

Answer 4

Alveoli

Question 5

Describe the shape of the lungs

Answer 5

The lungs have a funnel shape, the respiratory bronchioles and alveoli have the largest surface area

Question 6

What happens to the cross-sectional area of the lungs

Answer 6

Cross sectional area of the lung: increases peripherally, with respiratory bronchioles and alveoli occupying the largest surface area (extends to up to 23 generations)
10^4cm^2 at airway generation 23

Question 7

Describe the surface area of the lungs relative to the lung lining liquid

Answer 7

surface area of lungs equal to the area of a tennis court, but lining liquid volume equal to a wine glass

Question 8

Describe lung surfactant

Answer 8

Phospholipid rich substance in the alveoli- prevents the alveoli from collapsing
Produced by type 2 pneumocytes
Prevents alveolar collapse (by giving them stability)
Increases lung compliance by reducing surface tension of alveolar lining fluid
Prevents transudation of fluid in alveoli.

Question 9

What happens in babies delivered before the 24th week

Answer 9

No surfactant- thus they need respiratory support to keep the lungs open and to perform gas exchange

Question 10

What happens to gas exchange in COPD

Answer 10

Lungs rot away, see holes- less gas exchange

Question 11

Describe the basic functions of the respiratory epithelium

Answer 11

• Forms a continuous barrier, isolating external environment from host
• Produces secretions to facilitate clearance, via mucociliary escalator, and protect underlying cells as well as maintain reduced surface tension (alveolae)- secretions can protect the lung from external insults
• Metabolises foreign and host-derived compounds •Releases mediators
• Triggers lung repair processes

Question 12

What is key to remember about mediators

Answer 12

they are important- but can go out of control in disease

Question 13

What does the epithelium need to be able to do

Answer 13

Regenerate itself

Question 14

Describe goblet cells

Answer 14

§ Found in the large, central and small airways.

§ Make up 20% or 1/5th of the epithelium.

§ Synthesise and secrete mucous.

Question 15

What is different about goblet cells in smokers

Answer 15

In smokers -
* goblet cell number at least doubles * secretions increase
* secretions are more viscoelastic
Modified gel phase traps cigarette smoke particles but also traps and harbours microorganisms, enhancing chances of infection (frequent bronchitis)

Question 16

What happens to mucous production in patients with COPD

Answer 16

Increased goblet cell numbers (goblet cell hyperplasia) & increased mucus secretion
Cigarette smoke causes hyperplasia and hypertrophy of mucous-secreting glands of the large cartilaginous airways.
Hyperplasia of the goblet cells occurs at the expense of cilia
Mucous gland hypertrophy is express as gland:wall ratio and Reid index, normally <0.4

Question 17

Describe ciliated cells

Answer 17

Large, central and small airways
* Normally ~60-80% of epithelial cells
* Cilia beat metasynchronously -
Imagine a field of corn with wind blowing to form “flow waves”

Question 18

What is different about ciliated cells in smokers

Answer 18

• ciliated cells are severely depleted
• cilia beat asynchronously
• ciliated cells found in bronchioles
• cilia unable to transport thickened mucus
  Reduced mucus clearance leading to respiratory infection and bronchitis. Airways obstructed by mucus secretions.
   Reduced mucous clearance leading to respiratory infection and bronchitis.
  o Metaplasia to form ciliated cells in the bronchioles.

Question 19

Describe the roles of the alveolar walls

Answer 19

intact walls hold airways open (elastic walls)
Alveolar attachemts (septa) creates tensile forces on the airways (positive pressure upon exhalation to prevent collapse)

Question 20

What is the diameter of small, bronchiolar airways

Answer 20

2mm

Question 21

What happens to the small, bronchiolar airways in COPD

Answer 21

in COPD fibrosis and destroyed alveoli lead to collapsed airways - walls disrupted due to inflammatory cell proteinases and mechanisms - irrevocable damage; stenosis can occur, preventing gas exchange distal to the closure

Question 22

What is the consequences of this damage to the bronchiolar airways in COPD

Answer 22

In COPD, the small airways collapse to <2mm diameter due to decreased elasticity and destruction of peri-bronchiolar support. This leads to: mucous becoming trapped, airway narrowing, cell breakdown by enzymes and inflammatory cells (this reduces peripheral gas exchange). BE AWARE OF STENOSIS OF THE SMALL AIRWAYS.

Question 23

What causes alveolar destruction (emphysema) in COPD

Answer 23

Cigarette smoke and other inhaled noxious particles cause inflammatory cell activation within the lung, inducing these cells to release inflammatory mediators and proteases
In COPD, smoking induces the release of neutrophil elastase, which destroys alveolar attachments. As the distal airways are held open by alveolar septa, destruction of alveoli causes the airways to collapse, resulting in airway obstruction.
Decreased elasticity of supporting sturcture
Destruction of peribronchiolar support
Plugging, inflammatory narrowing and plugging of small airways

Question 24

Why does fibrosis occur

Answer 24

In an attempt to repair damage
when this happens in a collapsed airway- cannot repair
lots of inflammatory cells- play a role in small lung cell disease

Question 25

Summarise the causes of small airway obstruction

Answer 25

More secretions, more glandular tissue, loss of elasticity, intraluminal mucus plugs, mucosal oedema, Sm hypertrophy and peribronchial fibrosis Obstruction, increasing resistance to air flow. Mismathc in V:Q- impairing gas exchange

Question 26

Describe club (Clara) cells

Answer 26

non-ciliated secretory bronchiolar epithelial cells; replace damaged epithelium; contain secretory granules for xenobiotic metabolism - detoxifying enzymes present; enriched in bronchiolar regions; lower in smokers.  Found in the large, central, small, bronchi and bronchiole airways – increase proportionally distally (more later on).  Major role is xenobiotic metabolism. ~ 20% of epithelial cells

Question 27

Describe ciliated bronchiolar epithelium

Answer 27

BRONCHIOLAR CILIATED CELLS – increased in smokers and COPD | Beat synchronously to move mucus up to epiglottis and clear trapped debris, cells etc

Question 28

What does smoking cause in susceptible subjects (i.e those with COPD)

Answer 28

many holes form in the alveoli | Emphysematous alveoli in COPD

Question 29

Summarise COPD

Answer 29

COPD = bronchitis + emphysema + small airways disease. Affects 10-20% smokers.

Question 30

Describe alveoli

Answer 30

An alveolus is a blind-ending terminal sac of respiratory tract. Most gaseous exchange occurs in the alveoli. because alveoli are so numerous, they provide the majority of lung volume and surface area the majority of alveoli open into alveolar sacs. Communication between adjacent alveoli is possible through perforations in the alveoli wall called pores of Kohn. The alveoli are lined with type 1 and 2 pneuomocytes which sit on the basement membrane Type 1- structural Type 2- produce surfactant

Question 31

Summarise the alveolar unit

Answer 31

 In smokers, holes appear in alveoli which reduce surface area of the lungs (elastic tissue loss).  Alveolar walls consist of: o Type 1 Epithelial Cells. o Type 2 Epithelial Cells – Cover 5% of the surface BUT much smaller so NUMBER RATIO is T2:T1 = 2:1. o Stromal fibroblasts – make ECM and divide to repair. o Alveolar macrophages. o Capillary endothelium. See diagram!

Question 32

Describe type 1 pneumocytes

Answer 32

TYPE I EPITHELIAL CELL COVERS 95% ALVEOLAR SURFACE To aid gaseous diffusion, they are very thin; they contain flattened nuclei and few mitochondria- cells are joined by tight junctions.  Large cells: ~80m.

Question 33

Describe type 2 pneumocytes

Answer 33

Surfactant producing cells containing rounded nuclei, their cytoplasm is rich in mitochondria and ER, and microvilli exist on their exposed surface. TYPE II CELLS SYNTHESISE AND RELEASE SURFACTANT TO PREVENT ALVEOLAR COLLAPSE ON EXPIRATION

Question 34

Describe the shape of type 2 pneumocytes

Answer 34

 Cuboidal shaped at ~10microm and positioned in the corners of the alveoli.

Question 35

Where are type 2 pneumocytes found

Answer 35

Epithelial type II cells containing lamellar bosies which store surfactant prior to release onto the air-liquid interface (AL). These cells sit in the corners of the alveoli, and embedded in the interstitium with the apices facing the air. when lung stretches, surfactant is released to replace that which has been used

Question 36

What is the ratio of type 2: type 1 cells

Answer 36

 T2:T1 ratio of NUMBERS = 2:1. |  T2:T1 ratio of AREA = 5:95.

Question 37

Summarise type 2 epithelial cells

Answer 37

Repair/progenitor cells Precursor of type I cells Secrete surfactant Cover 5% of the alveolar surface

Question 38

Describe stroll cells in the alveoli

Answer 38

Make extracellular matrix – the lung’s cement Collagen, elastin, to give elasticity and compliance Divide to repair [produce interstitial fibrosis if too much deposited - lungs solidify and cannot breathe]

Question 39

Describe alveolar macrophages

Answer 39

Derived from circulating blood monocytes lie on alveolar surface or on alveolar septal tissue phagocytose foreign material and bacteria replace cilia in alveoli migrate to airways along mucociliary escalator or through lymphatic drainage system.

Question 40

What enzymes are released by Clara cells

Answer 40

 Contain 2 types of enzymes and other: o Phase 1 enzymes – Cytochrome p450 oxidases.  These metabolise foreign compounds but also can activate pro-carcinogens to carcinogens. o Phase 2 enzymes – Glutathione S-transferase.  Neutralise BPDE (pro-carcinogens). o Other: anti-proteinases and lysozyme.

Question 41

Describe the alveolar epithelial-endothelial barrier

Answer 41

very thin, hence why diffusion rapid

Question 42

Describe alveolar fibrosis

Answer 42

 Classic emphysema = centre-lobular ( pathology starts in acinus- here particles reach)  Pathway = infection  chronic damage (T1 cell death)  alveolar fibrosis (repair mechanism). o Results in increased T2 cells, collagen deposition and fibroblasts (make ECM and connective tissue).

Question 43

Describe normal repair

Answer 43

 NORMAL repair = T1 cell death triggers growth factor release to increase T2 proliferation and differentiation into type 1 cells

Question 44

Describe abnormal repair

Answer 44

 ABNORMAL repair = excess tissue breakdown  elevated growth factor release  fibrotic effect (irreversible).

Question 45

What are the effects of growth factors in fibrosis

Answer 45

Type II cell proliferation, Stromal cell proliferation, Connective tissue synthesis

Question 46

What happens in alveolar fibrosis

Answer 46

type 2 cells divide in idiopathic or interstitial fibrosis- but they don't differentiate- severely affecting gas exchange Cross talk in both directions with fibroblasts: myofibroblasts induce TII cells to cause fibroblasts to proliferate and release ECM, before fibroblasts cause TII cells to remain as TII not convert to TI copious amounts of connective tissue

Question 47

Describe how the alveolar epithelium can orchestrate repair

Answer 47

Conversion to T1 cells- re-epithelialisation Conversion to myofibroblasts- more fibrosis- undesirable in excess MYOFIBROBLASTS CAN TURN TO T2- unsure of mechanism

Question 48

How does smoking damage this repair process

Answer 48

 Smoking BLOCKS proliferation and differentiation of T2 into T1 cells. It also blocks communication of T2 cells to myofibroblasts. More necrosis and apoptosis of T1 and T2 cells no repair- formation of holes in lung- alveolar damage seen in COPD

Question 49

What are the secretory cells of the epithelia

Answer 49

goblet, type 2 cells, club cells

Question 50

What functions do these secretory cells have in common

Answer 50

•Secretory epithelial cells have many things in common. •Secrete protective lining layer to trap deposited particles – surfactant and mucus •Synthesise and release antioxidants eg glutathione, superoxide dismutase, •Synthesise and secrete antiproteinases – eg secretory leukoproteinase inhibitor (SLPI)- back up alpha 1 anti-trypsin •Release lysosyme •Carry out xenobiotic metabolism (eg process and detoxify foreign compounds such as carcinogens in cigarette smoke) •Contain cytochrome P450, phase I & II enzymes- lung second to liver in its ability to metabolise xenobiotics

Question 51

What do all smokers have

Answer 51

Alveolar inflammaiton- increased number of inflammatory cells (macrophages) not all macrophages are involved in phagocytosis increased neutrophils if infection

Question 52

What are the roles of neutrophils and macrophages in the lungs

Answer 52

Phagocytosis Antimicrobial defence Synthesise antioxidants eg glutathione Xenobiotic metabolism

Question 53

Quantify the changes in the numbers of neutrophils and macrophages in smokers

Answer 53

Increase by up to 10-fold in smokers

Question 54

Describe the proportions of macrophages and neutrophils in the respiratory units

Answer 54

Respiratory units – Mainly macrophages (approx 90%);- no cilia, they remove the particles Neutrophils up to 10% (may increase to 30% in smokers with respiratory infection) percentages only go up if infection reaches alveoli

Question 55

Describe the proportions of macrophages and neutrophils in the airways

Answer 55

Airways – Macrophage:neutrophil ratio:- 70%:30% in non-smokers 30%:70% in COPD Still lots of macrophages, but neutrophils have increased by a higher degree increase due to presence of bacteria, as they are not being cleared by the mucociliary escalator

Question 56

What enzymes are released by neutrophils and macrophages

Answer 56

``` SERINE PROTEINASES eg neutrophil elastase (NE) METTALLOPROTEINASES eg MMP9; Zn/metal at reactive site) lead to alveolar inflammation ```

Question 57

What are the substrates for these enzymes

Answer 57

Substrates: proteins; connective tissue, elastin, collagen Activate other proteinases (eg NE degrades and activates MMP), Inactivates antiproteases (eg MMP degrades and inactivates alpha-1 antitrypsin) Activate cytokines/chemokines and other pro-inflammatory mediators Will lose lung tissue if more proteinases than antiproteinases

Question 58

What are the roles of oxidants secreted by neutrophils and macrophages

Answer 58

oxidants Generate highly reactive peroxides Interact with proteins and lipids Inactivate alpha-1 antitrypsin Fragment connective tissue

Question 59

Describe the roles of mediators released by macrophages and neutrophils

Answer 59

Chemoattractants/cytokines (eg IL8) attract more inflammatory cells during infection or after toxicant or microbial deposition/inhalation Growth factors and proteases trigger growth and repair by other cells eg epithelium, stromal fibroblasts

Question 60

Summarise the roles of these mediators

Answer 60

cytokines attract more inflammatory cells during infection and growth factors trigger growth and repair

Question 61

What are the roles of phase 1 and 2 enzymes

Answer 61

These enzymes are involved in xenobiotic metabolism, ie metabolism of foreign compounds deposited by inhalation found in club cells, type 2 cells and macrophages

Question 62

Describe what happens to pro carcinogens

Answer 62

found in cigarette smoke and are converted to active compounds in lungs by phase I enzymes, before phase II enzymes make them water soluble metabolites that are excreted; if overloaded then DNA binding and mutation occurs (no metabolism)- adduct formation, no repair, mutation

Question 63

Describe Alpha 1- antitrypsin

Answer 63

inhibits neutrophil elastase, preventing emphysema | no inhibitor, lungs rot rapidly

Question 64

Summarise the effects of smoking

Answer 64

 Smoking BLOCKS proliferation and differentiation of T2 into T1 cells. It also blocks communication of T2 cells to fibroblasts.  Macrophage and neutrophil numbers increase up to 10-fold. o Macrophage: Neutrophil ratio = 70:30 but REVERSES in COPD (in UPPER airways). o Secrete proteases, metalloproteinases (e.g. MMP9)  alveolar inflammation. o Secrete anti-microbial oxidants and mediators such as growth factors.  Smoking contains pro-carcinogens which get inadvertently activated by phase 1 enzymes from Clara cells. o Normally, phase 2 enzymes can metabolise these pro-carcinogens but they may be inactivated by smoking.

Question 65

Summarise alveolar macrophages

Answer 65

 Form ~70% of phagocytic cells in the lungs.  Increase 5-10 fold in a smoker’s lungs.  Secretes chemokines for chemotaxis of inflammatory/immune cells.  Secrete proteases to digest foreign bacteria.  Secrete oxidants and anti-oxidants.

Question 66

Summarise neutrophils

Answer 66

 Form ~5% of phagocytic cells in the lungs.  Increase 5-10 fold in smoker’s lungs and proportionally (up to 30% of phagocytic cells).  Higher proportion in conducting/large airways.  Stores high levels of potent proteases.  Releases very potent oxidative molecules such as hydroxyl anions during activation.