Respiratory Gas Exchange

Question 1

What process do gases move down their concentration gradients?

Answer 1

Diffusion

Question 2

What is partial pressure?

Answer 2

The pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own

Question 3

Sum of the partial pressures or tensions of a gas must be equal what?

Answer 3

Total pressure

Question 4

What is atmospheric pressure (at sea level)?

Answer 4

760 mmHg (barometric pressure)

Question 5

How do you calculate the partial pressure of a gas?

Answer 5

Partial pressure of gas (Pgas) = Fraction of gas (Fgas) in mixture x barometric pressure

Question 6

Oxygen makes up 21% of the total gases in air. What is the partial pressure of oxygen at the mouth?

Answer 6

PO2 = 0.21 x 760 = 159 mmHg (at mouth)

Question 7

What is the water vapour partial pressure at body temperature?

Answer 7

47 mmHg

Question 8

Oxygen makes up 21% of total gases in the air. What is the partial pressure of oxygen in the trachea? (water vapour partial pressure at body temp = 47 mmHg)

Answer 8

PO2 = 0.21 x (760-47) = 150 mmHg in trachea

Question 9

Describe the pattern of branching in the respiratory tree

Answer 9

Airways branch into smaller and more numerous bronchioles before terminating to a group of alveoli.
Each division results in an increase in number, a decrease in diameter, and an increase in surface area

Question 10

What are the components of the conducting airways?

Answer 10

Bronchi containing cartilage and non-respiratory bronchioles
Everything from the trachea to the bronchioles
Does not participate in gas exchange

Question 11

What is ‘anatomic dead space’?

Answer 11

The total volume of the conducting airways from the nose/mouth to the level of the terminal bronchioles. Fills with inspired air at the end of each inspiration but is exhaled unchanged. Does not participate in gas exchange.

Question 12

What volume of air is in the conducting airways?

Answer 12

150ml (30% of average breath)

Question 13

What are the respiratory airways?

Answer 13

Bronchioles with alveoli where gas exchange occurs (from terminal bronchioles to alveoli)

Question 14

What volume of air is held in the respiratory airways?

Answer 14

~2,500ml

Question 15

What is the respiratory unit?

Answer 15

The basic physiological unit of the lung consisting of respiratory bronchioles, alveolar ducts and alveoli

Question 16

How many alveolar sacs are present in an adult?

Answer 16

~300-400 million

Question 17

What shape are alveoli?

Answer 17

Polygonal

Question 18

What is the diameter of an alveoli?

Answer 18

~250 micrometres

Question 19

What types of epithelial cells are found in alveoli?

Answer 19

Type 1 and type 2 epithelial cells

Question 20

Which type of epithelial cells occupy 97% of surface area of alveoli?

Answer 20

Type 1 epithelial cells

Question 21

Which epithelial cells are the primary site of gas exchange?

Answer 21

Type 1 epithelial cells

Question 22

Which type of epithelial cell occupies 3% of surface area of alveoli?

Answer 22

Type 2 epithelial cells

Question 23

What do type 2 epithelial cells do?

Answer 23

Produce pulmonary surfactant - reduces surface tension

Question 24

What does surfactant allow the lung to do?

Answer 24

Important for normal lung function

Allows lung to expand and have elastic properties

Question 25

What is often the cause of death in premature babies ~23 weeks?

Answer 25

Lungs are unable to produce surfactant Breathing is very laboured, lungs can't expand Epithelial lining can get irritated and come away from the lung

Question 26

What is the function of alveolar macrophages?

Answer 26

Removal of debris

Question 27

Which characteristics make alveoli perfectly designed for gas exchange?

Answer 27

- Large surface area (100m^2) - Very thin walls (0.5 micrometers) - Good diffusion characteristics

Question 28

The lung has 2 separate blood supplies. What are these termed?

Answer 28

Pulmonary circulation | Bronchial circulation

Question 29

Describe the pulmonary circulation

Answer 29

Brings deoxygenated blood from the heart to the lungs and oxygenated blood from the lungs to the heart, and then rest of the body Pulmonary artery brings deoxygenated blood to lungs, pulmonary vein carries oxygenated blood to heart

Question 30

Describe the bronchial circulation

Answer 30

Bronchial circulation is part of the systemic circulation carrying oxygenated blood to support the tissues of the lungs Not to do with gas exchange

Question 31

What is the total blood volume in the pulmonary circulation?

Answer 31

500ml (10% total)

Question 32

How much blood is in the alveolar-capillary network at rest?

Answer 32

75ml

Question 33

During exercise, how much blood is in the alveolar-capillary network?

Answer 33

150-200ml | Involves recruitment of new capillaries secondary to an increase in pressure and flow

Question 34

Describe arteries in the alveolar capillary network

Answer 34

Thin walled, highly compliant, large diameter, low resistance (compared to systemic circulation)

Question 35

Where does gas exchange occur?

Answer 35

Respiratory airways | Through dense mesh-like network of capillaries and alveoli

Question 36

What is the distance between alveoli and red blood cells, and what is the distance composed of?

Answer 36

1-2 micrometres: type 1 alveolar epithelial cell, capillary endothelial cell and basement membrane

Question 37

How long does it take for a RBC to pass through capillaries?

Answer 37

Less than 1 second | Sufficient time for CO2 and O2 in gas exchange

Question 38

Describe the movement of oxygen in the pulmonary circuit in terms of pressure gradients

Answer 38

Oxygen moves from an area of high concentration (100 mmHg) in alveoli to an area of low concentration (40 mmHg) in blood vessel

Question 39

Describe the movement of carbon dioxide in the pulmonary circuit in terms of pressure gradients

Answer 39

Carbon dioxide moves from an area of high (45 mmHg) concentration in the blood vessel to an area of low (40 mmHg) concentration in the alveolar sac

Question 40

Similar volumes of oxygen and carbon dioxide move each minute. Why is the pressure gradient for oxygen much bigger than that of carbon dioxide?

Answer 40

Carbon dioxide is more diffusible

Question 41

Pulmonary circulation carries large volumes of blood at ___ pressures

Answer 41

Low

Question 42

Pulmonary circulation brings ____________ blood from right ventricle to alveolar-capillary network where gas exchange occurs

Answer 42

Deoxygenated