6.4 gas exchange

Gas Exchange Topic 6.4

• 6.3 Gas Exchange• Ventilation maintains concentration gradients of oxygen and carbon

dioxide between air in alveoli and blood flowing in adjacent capillaries.

• Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange.

• Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other by reducing surface tension.

• Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.

• Muscle contractions cause the pressure changes inside the thorax that force air in and out of the lungs to ventilate them.

• Different muscles are required for inspiration and expiration because muscles only do work when they contract.

Applications: •Causes and consequences of lung cancer•Causes and consequences of emphysema.•External and internal intercostal muscles, and diaphragm and abdominal muscles as examples of antagonistic muscle action.•Skill: Monitoring of ventilation in humans at rest and after mild and vigorous exercise. (Practical 6)Guidance:•Ventilation can either be monitored by simple observation and simple apparatus or by data logging with a spirometer or chest belt and pressure meter. Ventilation rate and tidal volume should be measured, but the terms vital capacity and residual volume are not expected.•Students should be able to draw a diagram to show the structure of an alveolus and an adjacent capillary.

Alveoli• Microscopic sacs at the terminal ends of the

bronchioles• Site of gas exchange in the lungs• Consist of two cell types:– The Type I pneumocytes are extremely thin alveolar

cells that are adapted to carry out gas exchange.– Type II pneumocytes secrete a solution containing

surfactant that creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other by reducing surface tension.

The Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out

gas exchange.Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other by reducing surface tension

Effects of Emphysema:Emphysema is a chronic lung disease. The large number of small alveoli are replaced by a small number of much larger much less elastic air spaces. These have much smaller surface area and so there is much less gas exchange.

Symptoms are breathlessness and forced breathing it is a type of COPD and untreated can lead can be fatal.

What causes Emphysema?1.Constant inflammation that occurs to our lungs will cause infection.2.Phagocytes remove bacteria and numbers increase.3.Phagocytes release the protein digesting enzyme elastase on their way to reach lungs from capillaries.4.That enzyme destroys elastin in the walls of the alveoli.5.The air spaces are bigger and less elastic.

Contributory factors:•Cigarette smoking•Air pollution•Gender; men are more likely to develop emphysema than women•People’s age; older age is a risk factor for emphysema•Genetic factors