6.4 Gas Exchange

Question 1

Ventilation

Answer 1

Ventilation is the exchange of gases between the lungs and
the atmosphere (achieved by the physical act of breathing)
These gases are integral to the process of cell respiration
* Oxygen is an input, carbon dioxide is a by-product
Ventilation maintains the concentration gradient necessary
for passive diffusion (O2 = into lungs, CO2 = out of lungs)
Ventilation rates will change with exercise and can be
measured via spirometry (measures amount / rate of air)

Question 2

Lung Structure

Answer 2

larynx
rib
intercostal
muscles
trachea
bronchiole
bronchus
alveolus
lung
diaphragm

Question 3

Mechanism of Breathing

Answer 3

Breathing utilises antagonistic sets of respiratory muscles in
order to facilitate the passage of air (inhalation / exhalation)
* Muscles change lung volume to create negative pressure
* Negative pressure is equalised by air from atmosphere
* Air flows in / out according to the volume of the thorax

Question 4

Mechanism of breathing: Inhalation

Answer 4

Inhalation
* Diaphragm muscles contract (diaphragm flattens)
* External intercostal muscles pull ribs up (outwards)
* This increases the volume of the thoracic cavity
* Pressure in lungs decreases below atmospheric pressure
* Air flows into the lungs in order to equalise the pressure

Question 5

Mechanism of Breathing: Exhalation

Answer 5

Exhalation
* Diaphragm muscles relax (diaphragm curves upwards)
* Internal intercostal muscles pull the ribs down (inwards)
* Abdominal muscles contract to push diaphragm upwards
* This decreases the volume of the thoracic cavity
* Pressure in lungs increases above atmospheric pressure
* Air flows out of the lungs to equalise the pressure

Question 6

Pneumocytes

Answer 6

Pneumocytes (alveolar cells) line the alveoli and comprise
the majority of the inner surface of the lungs
Type I pneumocytes:
* Involved in gas exchange between alveoli and capillaries
* Are extremely thin (minimises gas diffusion distances)
Type II pneumocytes:
* Responsible for the secretion of pulmonary surfactant
* This creates a moist surface that reduces surface tension
(prevents sides of alveoli from adhering to each other)

Question 7

Lung Disorders

Answer 7

Lung Cancer
Cancer is uncontrolled cell proliferation, leading to tumors
* Lungs possess a rich blood supply (for gas exchange),
increasing the chances of metastasis (spread of cancer)
There are many factors that contribute to lung cancer:
* Intrinsic: Genetics, age, certain diseases / infections
* Extrinsic: Smoking, asbestos, radiation exposure
Emphysema
Emphysema is the abnormal enlargement of the alveoli
* These form air spaces and lower the overall surface area
Emphysema is most commonly caused by smoking
* Chemicals in the cigarettes damage the alveoli
* Phagocytes release elastase as part of immune response
* Elastase destroys the elastic fibres in the alveolar walls
* Huge air spaces (pulmonary bullae) develop in the lungs