Lung Structure and Function
AQA
Biology and Disease.
3.1.4 The lungs of a mammal act as an interface with
the environment. Lung function may be affected by
pathogens and by factors relating to lifestyle.
Lung function
• The gross structure of the human gas exchange
system limited to the alveoli, bronchioles,
bronchi, trachea and lungs.
• The essential features of the alveolar epithelium
as a surface over which gas exchange takes place.
• The mechanism of breathing.
• Pulmonary ventilation as the product of tidal
volume and ventilation rate.
• The exchange of gases in the lungs.
Recap.
• The course of infection, symptoms and
transmission of pulmonary tuberculosis.
• The effects of fibrosis, asthma and
emphysema on lung function
The biological basis of lung disease.
Candidates should be able to
• explain the symptoms of diseases and conditions
affecting the lungs in terms of gas exchange and
respiration
• interpret data relating to the effects of pollution
and smoking on the incidence of lung disease
• analyse and interpret data associated with
specific risk factors and the incidence of lung
disease
• recognise correlations and causal relationships.
The gross structure of the human gas exchange
system limited to the alveoli, bronchioles,
bronchi, trachea and lungs.
Label the diagram below.
•
•
•
•
•
•
Larynx
Trachea
Bronchi (singular is bronchus).
Bronchioles
Lung
Alveoli (singular is Alveolus).
The essential features of the alveolar epithelium as a
surface over which gas exchange takes place.
• Goblet cells are part of Psudostratified
Ciliated Columnar Epithelium and secrete
mucin.
• Mucin forms mucus (glycoproteins and
carbohydrates) which is sticky to trap inhaled
particles smaller than 5-10um.
• Cilia beating can carry particles upwards at a
rate of 1cm per minute. These can then be
swallowed into the acid bath of the stomach.
The essential features of the alveolar epithelium
as a surface over which gas exchange takes
place.
• Phagocytic macrophages (giant cells) patrol the
surfaces of the airways. Phagocytes engulf and
destroy micro-organisms.
• Smooth muscle in the bronchioles allows the
increased diameter during exercise through
muscle relaxation. This permits more oxygen to
reach the alveoli and more carbon dioxide to be
removed.
• Each alveolus contains elastic (elastin) fibres that
assist in the elastic recoil needed for exhalation.
1. CO2 rich air is exhaled.
2. O2 rich air is inhaled.
3. Large no. alveoli, alveoli have a large
a.
surface area.
4. Very thin squamous epithelial cells.
5. Slow movement of red blood cells
b.
6. Red blood cells flatten against capillary
wall.
7. Capillaries bring in oxygen depleted blood.c.
8. Capillaries remove oxygen rich blood.
9. Thin capillary wall.
d.
10. Red blood cells have a large surface area.
11. Cavity (lumen) within alveolus provides
air space.
Maintains steep
concentration
gradient.
Provides enormous
surface area.
Short diffusion
distance.
Increases time for
diffusion.
The essential features of the alveolar epithelium as a
surface over which gas exchange takes place.
12. Surface is moist.
13. Surfactants are secreted.
13. Phagocytes (macrophages)
present.
14. Supporting tissue contains
elastin.
15. Air is warmed so more kinetic
energy provides faster random
molecular movement.
Deoxygenated blood supplied in
the pulmonary artery from the
right ventricle of the heart so
is under low pressure.
• Gas diffuses through tissues in
solution.
• Reduce surface tension.
• Keep alveolar surfaces clean
and free of bacteria.
• Enables elastic recoil forcing
air out of alveoli.
• Reduced speed of blood flow.
Fick’s Law
Rate of diffusion =
Surface area of exchange x Difference in concentration
Thickness of exchange surface.
Relate these to tissue changes caused by ;
Asthma, Fibrosis and Emphysema.
The mechanism of breathing.
Inspiration (Inhale)
Forced Expiration (Exhale)
External intercostal muscles Internal intercostal muscles
contract (external relax).
contract (internal relax).
Diaphragm contracts (flattens).Diaphragm relaxes (dome
shaped).
Elastin fibres stretch.
Elastin fibres recoil*.
Rib cage moves up and out. Rib cage moves down and in.
Pressure drops within the lung Pressure increases around the
tissue and alveoli.
lung tissue and alveoli.
Air is drawn in.
Air is forced out.
* Sufficient for passive breathing.
Measurements of breathing.
• Spirometer attached to a data-logger. This
creates traces of the breathing volumes and
air flow rates.
• Lung capacity bags.
• Peak flow meters (rate of air movement).
• Relative composition of gases (not at St.
David’s!).
Pulmonary ventilation as the product
of tidal volume and ventilation rate.
Pulmonary ventilation as the product of tidal
volume and ventilation rate.
Vital capacity =
tidal volume + inspiratory reserve
volume + expiratory reserve
volume.
= 0.6 + 1.4+2 = 4 L
Ventilation rate at rest = 1 full
breath in 5 seconds.
60/5= 12
12 x 1 = 12 breaths per minute.
Pulmonary ventilation =
Tidal volume x rate
= 0.6 x 12 = 7.2 L/min.
How else could these units be
presented?
The exchange of gases in the lungs.
Pie Chart to show the Partial Pressures of
Atmospheric Gases at Sea Level.
0.97
21, 21%
Nitrogen
Oxygen
Carbon dioxide
78%
Others
Explain the differences in air
composition between the three
samples.
Plot to show the relative difference in gas samples during breathing.
25
% composition of air
20
15
Oxygen
Carbon dioxide
10
5
0
Inhaled Air
Alveolar Air
Exhaled Air
Explain the
differences in air
composition
between the three
samples.
Alveolar air
has oxygen
removed and
carbon dioxide
added.
• Exhaled air has been mixed
with residual air within the
air passages (bronchioles,
bronchi and trachea) so is
closer to atmospheric air in
composition than that in
the alveolar lumen.
Summary
• Lung function
• The gross structure of the human gas exchange
system limited to the alveoli, bronchioles,
bronchi, trachea and lungs.
• The essential features of the alveolar epithelium
as a surface over which gas exchange takes place.
• The mechanism of breathing.
• Pulmonary ventilation as the product of tidal
volume and ventilation rate.
• The exchange of gases in the lungs.