Respiratory Physiology I

Question 1

What is internal respiration?

Answer 1

The intracellular mechanisms which consume oxygen and produce carbon dioxide as a waste product.

(food + oxygen –> energy + carbon dioxide).

Question 2

What is external respiration?

Answer 2

The sequence of events that lead to oxygen and carbon dioxide being exchanged between the external environment and the cells of the body.

Question 3

Summarise the four steps of external respiration.

Answer 3

1. Ventilation - gas exchange between the atmosphere and alveoli.
2. Exchange of oxygen/carbon dioxide between air in the alveoli and pulmonary blood.
3. Transport of oxygen and carbon dioxide in the blood to the tissues.
4. Exchange of oxygen between the blood and tissues.

Question 4

What body systems are involved in external respiration?

Answer 4

Respiratory, cardiovascular, haematology and nervous systems.

Question 5

What is ventilation?

Answer 5

The mechanical process of moving air between the atmosphere and the alveolar sacs.

Question 6

What is Boyle’s Law? (Proper description + what this actually means)

Answer 6

At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas.

Essentially, as the volume of a gas increases, the pressure it exerts decreases.

Question 7

Summarise how the pressure gradient between the alveoli and atmosphere is created during inspiration.

Answer 7

1. The thorax and lungs expand as a result of contraction of inspiratory muscles. (Lowering the pressure according to Boyle’s Law).
2. The pressure inside the lungs is then lower than atmospheric pressure.
3. Air can flow down this pressure gradient into the alveoli.

Question 8

What are the two forces holding the thoracic wall and the lungs in close opposition?

Answer 8

1. The intrapleural fluid cohesiveness - water molecules are attracted to each other, puling the pleural membranes together.
2. The negative intrapleural pressure - creates transmural pressure gradient across lung and chest wall, thus lungs expand outwards and chest squeezes inwards.

Question 9

Describe the relationship between the pressures in the alveoli, pleural cavity, and atmosphere before inspiration occurs under the following headings.

1. The alveolar pressure.
2. The atmospheric pressure.
3. The pressure within the pleural cavity.

Answer 9

1. The alveolar pressure is equal to atmospheric pressure, 760 mmHg.
2. The atmospheric pressure is 760 mmHg, and is equal to the alveolar pressure.
3. The pressure within the pleural cavity (756 mmHg) is less than the pressure in the alveoli, as well as the atmospheric pressure

Question 10

Is inspiration an active or passive process?

Answer 10

Active, thus depending on muscle contraction.

Question 11

In what direction is the volume of the thorax is increased when the diaphragm contracts to flatten out its dome shape?

Answer 11

Vertically.

Question 12

Describe the nerve supply of the diaphragm.

Answer 12

Phrenic nerve - from cervical 3, 4 and 5 vertebral levels.

“C3, 4 and 5 keep the diaphragm alive!”

Question 13

What intercostal muscles contract during normal inspiration and what does this do?

Answer 13

External intercostals.

Lifts the ribs and moves out the sternum (“bucket handle mechanism”).

Increases the volume of the thorax in the AP direction.

Question 14

Is normal expiration an active or passive process?

Answer 14

Passive, brought about by relaxation of muscles which were contracted during inspiration.

Question 15

Summarise how air is expelled from the lungs during normal expiration in terms of pressure gradients and how these are created.

Answer 15

1. The chest wall and lungs recoil to their pre-inspiratory size due to their elastic properties.
2. This increases intra-alveolar pressure such that it exceeds atmospheric pressure. (Smaller volume so pressure increased - Boyle’s Law).
3. Air then follows the negative pressure gradient created between the alveoli and the atmosphere until an equilibrium is reached once again.

Question 16

What happens to both the intra-alveolar and intrapleural pressures initially during inspiration?

Answer 16

The pressures both decrease.

Question 17

What happens to the intra-alveolar pressure as the end of an inspiration is approached? Does the same thing happen to the intrapleural pressure?

Answer 17

The pressure increases back to atmospheric, as the gradient will be equilibraited by air entering the lungs.

The intrapleural pressure continues to decrease until inspiration is complete.

Question 18

What happens to the intra-alveolar and intrapleural pressures initially during expiration?

Answer 18

The pressures both increase.

Question 19

What happens to the intra-alveolar pressure as the end of expiration is approached? Does the same thing happen to the intrapleural pressure?

Answer 19

The pressure decreases back to atmospheric, as the pressure gradient be equilibriated by air leaving the lungs.

The intrapleural pressure continues to increase until expiration is complete, as it decreases further than intra-alveolar pressure during inspiration.

Question 20

What is pneumothorax?

Answer 20

Air in the pleural space.

Question 21

How can a pneumothorax arise?

Answer 21

It can be spontaneous, traumatic, or iatrogenic.

Question 22

How does a pneumothorax lead to lung collapse?

Answer 22

It abolishes the transmural pressure gradient.

Question 23

What are the symptoms of pneumothorax?

Answer 23

Small pneumothorax can be asymptomatic.

However, where they exist, symptoms include shortness of breath and chest pain.

Question 24

What typical signs can be observed upon examination of a patient presenting with pneumothorax?

Answer 24

Hyper-resonance upon percussion over the affected area.

Decreased or absent breath sounds when the affected area is auscultated.

Question 25

What are the two factors which cause lung recoil during expiration?

Answer 25

1. Elastic connective tissue in the lungs causing the lungs to bounce back into shape. 2. Alveolar surface tension.

Question 26

Describe what causes alveolar surface tension and the force produced as a result of this.

Answer 26

Caused by attraction between water molecules at the liquid-air interface. It produces a force which resists the stretching of the lungs.

Question 27

What would happen if alveoli were lined with water alone? (i.e. the absence of pulmonary surfactant.)

Answer 27

The surface tension would be too strong, resulting in alveolar collapse.

Question 28

What is pulmonary surfactant made up of and what cells secrete it?

Answer 28

It is a complex mixture of lipids and proteins. Secreted by type II alveolar cells.

Question 29

What is the Law of LaPlace and what does this mean in terms of alveoli?

Answer 29

LaPlace's Law - P = 2T/r, where P is the inward directed collapsing pressure, T is the surface tension, and r is the radius of the "bubble". In terms of alveoli, this means that smaller alveoli (smaller radius) have a higher tendency to collapse.

Question 30

What does pulmonary surfactant do and how does it achieve this?

Answer 30

Lowers alveolar surface tension. It does this by interspersing between water molecules lining the alveoli.

Question 31

Does pulmonary surfactant lower the surface tension of smaller or larger alveoli more?

Answer 31

It lowers smaller alveoli surface tension more, preventing their collapse. (Remember LaPlace's Law: P = 2T/r.)

Question 32

What causes "respiratory distress syndrome of the newborn"?

Answer 32

Premature babies not producing enough pulmonary surfactant (as usually not synthesised till later in gestation).

Question 33

What would be observed in a baby with respiratory distress syndrome of the newborn? What is the reason behind this?

Answer 33

Strenuous respiratory efforts. Baby is attempting to overcome the high surface tension to adequately inflate the lungs.

Question 34

Describe how alveolar interdependence arises.

Answer 34

If one alveolus starts to collapse, surrounding alveoli are stretched and recoil. This exerts expanding forces on the collapsing alveolus, opening it.

Question 35

What are the three forces keeping the lungs open?

Answer 35

1. Transmural pressure gradient. 2. Pulmonary surfactant. 3. Alveolar interdependence.

Question 36

What are the two forces which promote alveolar collapse?

Answer 36

1. Elasticity of stretched lung connective tissue. | 2. Alveolar surface tension.