Topic 6.4

Question 1

Ventilation

Answer 1

• Fresh air is pumped into the alveoli
• Stale air is removed

Question 2

What is the purpose of ventilation

Answer 2

• Maintain the concnetration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries

Question 3

Explain the role of concentration gradient in the procuess of gas exchange

Answer 3

• Gases diffuse between alveoli and capillaries only if a concentration gradient exist
• The air in the alveolus has a higher oxygen concentration
• The air in blood has a higher carbon dioxide concentration

Question 4

Type I pneumocytes

Answer 4

• Extremely thin alveolar cells that are adapted to carry out gas exchange
• Epithelium of alveolus
• Thin, enable gas exchange

Question 5

Type II pneumocytes

Answer 5

• Rounded cells that occupy little space of alveolar surface area
• Secrete a fluid which coats the inner surface of the alveoli

Question 6

Annotate the following diagram of an alveolus

Answer 6

Refer to picture

Question 7

Outline the purpose of the solution secreted by Type I penumocytes

Answer 7

• This moisture allows oxygen in the alveolus to dissolve and diffuse into the capillaries
• The fluid provides an area from which carbon dioxide can evaporate into the air and be exhaled
• Contains a pulmonary surfactant
• Reduces surface tension and prevents the water from causing the sides of the alveoli to adhere when the air is exhaled from the lungs (prevent collapse of the lung)

Question 8

Annotate the following diagram of a lung

Answer 8

Refer to picture

Question 9

Trachea

Answer 9

• Rings of cartilage in its wall to keep it open even when air pressure inside is low or pressure in surrounding tissues is high
• Divides to form two bronchi, leading to two lungs

Question 10

Bronchioles

Answer 10

• Tree-like structure of narrower airways that bronchi divide into
• Smooth muscle fibres in their walls, allowing the width of these airways to vary

Question 11

Where does gas exchange occur

Answer 11

Alveoli

Question 12

Describe muscle contraction during inspiration

Answer 12

• Diaphragm moves downwards and flattens
• Ribcage moves upwards and outwards
• Cause the pressure inside the thorax to drop below atmospheric pressure
• Air is drawn into the lungs from the atmosphere

Question 13

Describe muscle contraction during expiration

Answer 13

• Diaphragm moves upwards and become more domed
• Ribcage moves downwards and inwards
• Cause the pressue inside the thorax to increase
• Air is pushed out

Question 14

Describe the antagonistic muscle pairs in respiration

Answer 14

• When diaphragm contracts, abdomen wall muscles relaxes
• When external intercostal muscles contract, internal intercostal muscles relax

Question 15

Outline the five causes of lung cancer

Answer 15

• Tobacco smoke contains mutagenic chemicals and increase the incidence of lung cancer
• Passive smoking (non-smokers inhale tobacco smoke exhaled by smokers)
• Air pollution (diesel exhaust fumes, nitrogen oxides, smoke from burning coal, wood, or other organic matter)
• Radon gas (radioactive gas that leaks out of certain rocks and accumulates in badly ventilated buildings)
• Asbestos, silica and some other solids if dust or other particles of them are inhaled (construction sites or quarries, mines or factories)

Question 16

Outline the consequences of lung cancer

Answer 16

• Difficulties with breathing
• Persistent coughing
• Coughing up blood
• Chest pain
• Loss of appetite
• Weight loss
• General fatigue

Question 17

Emphysema

Answer 17

• Thin-walled alveoli is replaced by larger air sacs with much thicker walls
• Total suface area for gas exchange is reduced
• Distance over which diffusion of gases occurs is increased
• Gas exchange is less effective

Question 18

Outline the function of phagocytes inside alveoli

Answer 18

• Prevent lung infections by engulfing bacteria
• Produce elastase, a protein-digesting enzyme, to kill them inside the vesicles formed by endocytosis

Question 19

Alpha 1-antitrypsin (A1 AT)

Answer 19

• Enzyme inhibitor that prevents elastase and other proteases from digesting lung tissue
• In smokers, the number of phagocytes in the lungs increase and they produce more elastase

Question 20

Outline the consequences of emphysema

Answer 20

• Low oxygen saturation in the blood
• Higher than normal carbon dioxide concentration
• Patient lacks energy, shortness of breath, laboured ventilation

Question 21

Outline the possible causes of emphysema

Answer 21

• While the molecular mechanisms involved are not fully understood, there is evidence that cancer is a cause
• Cigarette smoke contains chemical irritants that damage the alveolar walls
• The damage to lung tissue leads to the recruitment of phagocytes to the region, which produce an enzyme called elastase
• This elastase, released as part of an inflammatory response, breaks down the elastic fibres in the alveolar wall
• Elastase activity can be usually be blocked by an enzyme inhibitor (α-1-antitrypsin), but not when elastase concentrations are increased
• A small proportion of emphysema cases are due to a hereditary deficiency in this enzyme inhibitor due to a gene mutation