Respiratory Diseases

Question 1

Diseases of the lung can be

Answer 1

1. Infectious
2. Non-infectious
   Non-neoplastic
   Neoplastic

Question 2

Anatomy of the lung

Answer 2

2 lungs: left and right
Each lung has multiple lobes
Right - 3 lobes
Left - 2 lobes
A lot of holes - spongey cross-section

Question 3

Function of the lung

Answer 3

Oxygenation of blood
Removal of waste products (CO2)
Requires ventilation and perfusion
Ventilation: movement of air
Perfusion: movement of blood

Question 4

Air pathway and anatomy

Answer 4

Trachea -> Bronchi -> Bronchioles
Series of branching tubes; respiratory tree with 23 generations

Question 5

Bronchioles and trachea composition

Answer 5

No smooth muscle or cartilage in bronchi and trachea
Thin strands of smooth muscle with epithelial lining; 1 mm in diameter

Question 6

Structure of the lung

Answer 6

Airways, acini and secondary lobules, vasculature, lymphatics, pleura.
Airways: Trachea -> bronchi -> bronchioles (including terminal bronchioles and respiratory bronchioles)
Acini: Basic units of gas exchange supplied by a single terminal bronchiole (“Terminal respiratory unit”).
Acini include: Respiratory bronchioles, distal alveolar ducts, alveolar sacs (interstitial septum/alveolar wall lines all)
Alveolar sacs are lined by type 1 and type 2 pneumocytes.
Type 2 cells are the progenitor cells for type 1 cells and produce surfactant.

Question 7

Alveolar wall

Answer 7

Alveolar wall: Gas transfer takes place across the alveolar-capillary membrane. The alveolar-capillary membrane consists of:
a) Capillary endothelium
b) Basement membrane and surrounding interstitial tissue
c) Alveolar epithelium (type 1 and 2 pneumocytes).
Gas bypasses all of these membrane components
Lines the terminal respiratory unit

Question 8

Gas exchange

Answer 8

Requires
Ventilation: Gas movement from nose and mouth through large airways (trachea, bronchi, bronchioles) to lung parenchyma (alveoli), where gas exchange occurs
Perfusion:
Two systems of vessels:
Pulmonary: Deoxygenated blood is carried by the pulmonary artery from the right side of the heart to the lungs
The intimate contact between air in the alveoli and blood in the pulmonary capillaries allows gas exchange to occur
Oxygenated blood returns through the pulmonary vein to the left atrium
Bronchial: Oxygenated blood from the descending aorta and intercoastal arteries supplies lung parenchyma

Interference of either of these processes results in respiratory failure

Question 9

Respiratory failure

Answer 9

Inability to maintain normal oxygen saturation of blood and to remove CO2 from blood entering the lungs.
Could be due to:
Decreased ventilation
Decreased perfusion
Ventilation/perfusion imbalance

Question 10

How are injuries to the lung mediated?

Answer 10

Air - lungs are exposed to 10k L of air/day
Common mechanism of injury
**Most injuries occur due to something which is inhaled
Inhaled injurious agents can be
1. Infectious
Virus
Bacteria
Fungi
2. Non-infectious
Toxic gases
Cigarette smoke/particles
Inorganic particles
Organic particles
Blood
Bloodborne injurious agents can be:
1. Infectious
2. Non-infectious
Drugs - amiodarone (for heart arrhythmia), bleomycin (for cancer)
Autoimmune diseases (antibodies attack lungs)

Question 11

Mechanism of defence for inhaled injurious

Answer 11

Nasal clearance - cough or sneeze
Tracheobronchial clearance by muco-ciliary “blanket” (ciliated epithelium)
Mucus is very sticky
Injurious agents are stuck here
Cilia sweep toward trachea
Clears smaller particles to be coughed up/swallowed
Alveolar clearance by macrophage system/immune system

Question 12

Pulmonary infections

Answer 12

More frequent than infections of other organs
Account for the largest number of workdays lost
Most are upper respiratory tract infections caused by viruses

Question 13

Pneumonia

Answer 13

Inflammation of the lung secondary to infection
Caused by bacteria, viruses, fungi, protozoa, rickettsia, and others
Most commonly caused by aspiration of organisms that colonize the oropharynx and less commonly by inhalation of infected aerosols, hematogenous dissemination and direct inoculation

Question 14

Organisms enter the lung by

Answer 14

Aspiration:
Oral cavity infectious organisms (or in the stomach) gets misplaced
Gains access to lung
Inhalation:
Organism is in the environment
We breathe it in (COVID)
Blood:
Organism gains access to the blood - carried to the lung, where it establishes a secondary infection
Direct inoculation:
Trauma, stabbings, lung is penetrated by an object that is contaminated by bacteria/fungi
Once an organism enters the lung, neutrophils will proliferate in the acinus

Question 15

Factors which determine if infection will occur depend on

Answer 15

1. Dose and virulence of the organisms
   A lot of organism/high virulence results in infection
2. Host susceptibility - pneumonia will occur if:
   i) Defense mechanisms are impaired
   ii) Impaired resistance (immunocompromised)

Question 16

Examples of impaired host defenses

Answer 16

1) Loss or suppression of the cough reflex
Coma, anaesthetic
We lose the cough reflex and the sneeze reflex
No eating or drinking before operations
This empties the stomach and prevents stomach contents from being aspirated into the lung
2) Injury to mucociliary apparatus
Cigarette smoking, inhalation of corrosive gases or hot gases, viral diseases
People with burns die - inhaled hot gases -> destroy mucociliary apparatus
Spanish flu - secondary bacterial infections occur after viral infection
3) Interference with alveolar macrophages
Alcoholism, malnutrition, diabetes (decreased function of macrophages)
4) Accumulation of fluid or secretions in alveoli
Pulmonary edema, cystic fibrosis
CF - thick mucus, overgrowth of bacteria -> bacterial pneumonia