Respiratory Physiology

Question 1

Main anatomical divisions of the respiratory tract.

Answer 1

Key points:

• conducting zone
• transitional and respiratory zones
• acinus

Question 2

How do the epithelial cell types change as one progresses through the airways within the lung?

Answer 2

Columnar –> cuboidal –> squamous
More cilia ———————– less to no cilia

Question 3

Which pneumocyte type is responsible for secretion of surfactant?

Answer 3

Type II

Question 4

What is the thickness of the thickest portion of the blood-gas barrier?

Answer 4

3 micrometers

Question 5

What collagen type makes up the pulmonary epithelial barrier?

Answer 5

Type IV

Question 6

Fick’s law

Answer 6

Diffusion of gas through a tissue is proportional to surface area and partial pressures of gas on either side but inversely proportional to thickness of the membrane that diffusion must occur across.

D = directly proportional to the solubility of gas but inversely proportional to its molecular weight.

Question 7

Define the following:

• Tidal volume
• Vital capacity
• Residual volume
• Functional residual capacity
• Total ventillation
• Alveolar ventillation

Answer 7

• Tidal volume = the volume inspired during normal respiration
• Vital capacity = the amount of air that can be inhaled/exhaled during maximal inhalation/exhalation
• Residual volume = air left in the lunds following maximal inhalation/exhalation
• Functional residual capacity = the volume remaining in the lungs after normal expiration.
• Total ventillation = the total volume of air leaving the lung per minute

Question 8

What is the normal ratio of pulmonary capillary perfusion to air flow?

Answer 8

Normally it is equal giving a V/Q ratio of 1.

Question 9

How can alveolar ventillation be estimated clinically?

Answer 9

Using ETCO₂:

All expired CO₂ should come from the alveolus and therefore CO₂ concentration is inversely proportional to alveolar ventillation.

Question 10

How does air move through the different parts of the lung?

Answer 10

In the conducting airways it is by convection/bulk flow. In the respiratory zone diffusion of gas becomes much more important.

Question 11

Compare anatomic dead space vs. physiologic dead space

Answer 11

Anatomic = the physical space that is not ventillated in the lung

Physiologic = the proportion of the lung that is not being ventillated.

This should be relatively equal in health.

Question 12

What is the difference in how fast CO2 and O2 can diffuse?

Answer 12

CO2 diffuses 20x faster due to its higher solubility.

Question 13

Define a diffusion limited gas vs. perfusion limited (give examples)

Answer 13

Diffusion Limited

This refers to a gas that is rapidly taken up by haemoglobin therefore the partial pressure in the blood never rises to opose diffusion. So other properties of fick’s law come in to play e.g. membrane thickenss. An example is carbon monoxide as it binds rapidly and strongly to haemoglobin.

Perfusion Limited

This is where the partial pressures will equate so the the gas needs to be cleared from that area of the capillary to achieve further transfer of the gas into the blood. An example is NO.

O₂ has properties of both of these. Initially diffusion limiting is the only issue as the oxygen binds to haemoglobin. Once fully bound (about 1/3 of the way through the capillary) it becomes a perfusion limited gas.

Question 14

How does NO form in the capillary to allow vasodilation?

Answer 14

L-arginine is synthesised to NO by endothelial nitrogen oxide synthase (eNOS).

Question 15

How is fluid cleared from the alveolar space in a normally functioning lung?

Answer 15

Via the Na/KATPase on the epithelial cells.

Question 16

What are the four mechanisms of hypoxaemia?

Answer 16

Hypoventillation

Diffusion impairment

Shunt

V/Q mismatch

Question 17

Why will a patient with V/Q mismatch (or shunt) hyperventillate but not increase their PaO2?

Answer 17

The hyperventillation occurs due to the chemoreceptor response to increased CO2 levels in the circulation. Therefore, ventillatory drive increases and the alveoli that are functional will blow off the CO2.

Question 18

What is the normal adult haemoglobin variant?

Answer 18

Haemoglobin A

Question 19

What product of red blood cell metabolism is produced in greater amounts during conditions of chronic hypoxaemia?

Answer 19

2,3-diphosphoglycerate - this shifts the HbO2 curve to the right.

Question 20

What is the result of shifting the HbO2 curve to the right?

Answer 20

Oxygen binds less strongly to haemoglobin and so is offloaded in greater amounts in the tissues. However, it is then harder to saturate the haemoglobin under conditions of lower oxygen tension.

Question 21

What is the result of carbon monoxide on the HbO2 curve?

Answer 21

Shifts to the left making it harder for haemoglobin to offload its oxygen.

Question 22

What is the haldane effect?

Answer 22

That H+ binds more readily to Hb in deoxygenated blood.

Question 23

What are the three forms in which Co2 can be carried in the blood?

Answer 23

1. Dissolved
2. As HCO3
3. Carboxyhaemoglobin

Question 24

What is the action of the external and internal intercostal muscles?

Answer 24

External = pull the ribs up and out

Internal = Pul the ribs down and inwards

Question 25

What is the main component of surfactant?

Answer 25

Dipalmitoyl phosphatidylcholine

Question 26

Which airways present the most airway resistance?

Answer 26

The medium sized bronchi

Question 27

Which nerve acts as the effector for respiration?

Answer 27

The phrenic nerve.

Question 28

What is the mechanism by which central chemoreceptors affect ventillation?

Answer 28

They detect changes in blood PCo2 indirectly by responding to changes in H+ concentration in the CSF. This concentration is a result of the diffusion of Co2 into the CSF.

Question 29

Where are the central chemoreceptors located?

Answer 29

In the ventral medulla.

Question 30

Where are peripheral chemoreceptors located?

Answer 30

Carotid and aortic bodies

Question 31

What do the peripheral chemoreceptors detect, which is the most important?

Answer 31

• O2 (has most profound effect)
• CO2
• pH (carotid bodies only in humans)

Question 32

Hering-Breuer inflation reflex

Answer 32

Slowing of respiration with increased airway stretch.

Question 33

Cheyne-Stokes respitation

Answer 33

Phenomenon where in chronic hypoxaemia patients have 10-20s apnoic pauses and then suddently hyperventillate for a similar period of time.

Question 34

Law of laplace and relevance to respiratory physiology.

Answer 34

One can see that with a sphere of decreasing radius inward pressure increases markedly. Also, with decreased surface tension the pressure is reduced (which is what surfactant does).

Question 35

Pouiselle’s law and its relevance to respiratory physiology

Answer 35

Can be used to look at flow rates, pressure and resistance during laminar flow. It can also be re-arranged to tell you about resistance. The most important point is that decreasing airway diameter causes a marked increase in resistance.

Question 36

Reynaulds number (and calculation) that results in turbulant flow

Answer 36

> 2000