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.

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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. CO 2 rich air is exhaled.

2. O 2 rich air is inhaled.

3. Large no. alveoli, alveoli have a large surface area.

4. Very thin squamous epithelial cells.

a.

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.

10. Red blood cells have a large surface area. d.

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.

• • • • • 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.

Deoxygenated blood supplied in the pulmonary artery from the right ventricle of the heart so is under low pressure.

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 contract (internal relax).

Internal intercostal muscles contract (external relax).

Diaphragm contracts (flattens).

Diaphragm relaxes (dome shaped).

Elastin fibres stretch.

Elastin fibres recoil*.

Rib cage moves up and out.

Pressure drops within the lung tissue and alveoli.

Rib cage moves down and in.

Pressure increases around the 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 Others 78%

20 15 10 5 0 25

Explain the differences in air composition between the three samples.

Plot to show the relative difference in gas samples during breathing.

Oxygen Carbon dioxide 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.