Respiratory structure and function

Question 1

How do oxygen and carbon dioxide move between air and blood?

Answer 1

Simple diffusion (high to low partial pressure)

Question 2

Define Fick’s law of diffusion.

Answer 2

The amount of gas that moves across a sheet of tissue is proportional to the area of the sheet, but inversely proportional to the thickness.

Question 3

What is the area of the blood-gas barrier?

Answer 3

50-100 squared metres

Question 4

How many alveoli are there in the human lungs?

Answer 4

About 500 million

Question 5

What is the average size of alveoli?

Answer 5

About 1/3rd a mm each in diameter

Question 6

Tha trachea divides into?

Answer 6

Left and right main bronchi

Question 7

The left and right bronchi divide into?

Answer 7

Lobar and then segmental bronchi

Question 8

What are the smallest airways without alveoli?

Answer 8

Terminal bronchioles

Question 9

Which airways make up the conducting airways?

Answer 9

Trachea to terminal bronchioles

Question 10

What is the function of the conducting airways?

Answer 10

To lead inspired air to the gas exchanging regions of the lung.

Question 11

What happens to cartilage in the airways as you move down the respiratory tree?

Answer 11

Larger proximal airways have a lot of cartilage in their walls; ths decreases as airways progress distally.

As cartilage decreases, smooth muscle increases = very small distal airways are composed mainly of smooth muscle.

Question 12

What is the anatomic dead space?

Answer 12

A group of airway structures that do not take part in gas exchange as they do not have alveoli (bronchi down to terminal bronchioles).

Question 13

What does the term ‘dead space’ refer to?

Answer 13

Areas of the lung that receive ventilation but no blood flow.

Question 14

What is the normal volume of the anatomical dead space?

Answer 14

150mls

Question 15

How is the partial pressure of a gas found?

Answer 15

Multiply its concentration by the total pressure (barometric pressure)

E.G 0.21 (21% O2 in atmosphere) x 760 (barometric pressure of oxygen).

0.21 x 760 = 159mmHg

Question 16

What is the partial pressure of O2 at sea level?

Answer 16

159mmHg

Question 17

What is the water vapour pressure of the upper airways?

Answer 17

47mmHg

**Must be subtracted from the total gas pressure in order to get an accurate partial pressure in the airways.

Therefore, partial pressure of O2 in the upper airways is:

0.21 x (760-47) = 149mmHg

Question 18

What is the actual shape of the alveoli?

Answer 18

They are polyhedral.

Question 19

How thin can the blood-gas barrier be in alveoli?

Answer 19

Sometimes about 0.3 micrometres in some places.

Question 20

Describe the diffusion path from the alveolar gas to the interior of the erythrocyte.

Answer 20

Surfactant
Alveolar epithelium
Interstitium
Capillary endothelium
Plasma
Red cell membrane

Question 21

The terminal bronchioles divide into?

Answer 21

Respiratory bronchioles

Question 22

What do respiratory bronchioles have that terminal bronchioles do not have?

Answer 22

Occasional alveoli budding from their walls

Question 23

What comes after respiratory bronchioles?

Answer 23

Alveolar ducts

Question 24

What are the alveolar ducts completely lined with?

Answer 24

Alveoli

Question 25

What is the respiratory zone?

Answer 25

The alveolated region of the lunge where gas exchange occurs.

Question 26

The portion of lung distal to the terminal bronchiole forms an anatomical unit called the?

Answer 26

Acinus

Question 27

What is the distance from the terminal bronchiole to the most distal alveolus?

Answer 27

A few mm

Question 28

What is the volume of the respiratory zone during rest?

Answer 28

2-3 litres **Respiratory zone makes up most of the volume of the lung.

Question 29

What are the holes in the walls of the alveoli called?

Answer 29

Pores of Kohn

Question 30

Where do pulmonary capillaries run?

Answer 30

In the walls of the alveoli

Question 31

What happens during inspiration?

Answer 31

Volume of thoracic cavity increases; -Diaphragm contracts and moves downwards -Intercostal muscles contract which raises the ribs (bucket handle) and increases the cross sectional area of the thorax

Question 32

Inspired air flows down to the terminal bronchioles by what method?

Answer 32

Bulk flow (after terminal bronchioles, forwards velocity of the gas becomes small because of the cross-sectional area of the airways becomes so big)

Question 33

What becomes the dominant mechanism of ventilation in the respiratory zone after the termination of bulk flow?

Answer 33

Diffusion of gas within the airways.

Question 34

During diffusion in the alveoli, why are concentration differences within the acinus essentially abolished within seconds?

Answer 34

Because the rate of diffusion of gas molecules is so rapid and the distances to be covered so short.

Question 35

Why does inhaled dust commonly settle in the terminal bronchioles?

Answer 35

Because this is where the velocity of gas falls rapidly.

Question 36

What happens to the lung during resting breathing?

Answer 36

It returns passively to its pre-inspiratory volume due to it's elasticity.

Question 37

A normal breath of 500ml requires a distending pressure of what?

Answer 37

Less than 3cm water **The lungs are remarkably easy to distend

Question 38

During normal inspiration, an air flow rate of 1L/ second requires a pressure drop along the airways of what?

Answer 38

Less than 2cm water **Pressure required to move gas through the airways is VERY small

Question 39

The airways are divided into what 2 zones?

Answer 39

Conducting zone and respiratory zone.

Question 40

Volume of anatomic dead space?

Answer 40

150ml

Question 41

Volume of the alveolar region?

Answer 41

2.5-3L

Question 42

Gas movement in the alveoli is chiefly by?

Answer 42

Diffusion

Question 43

According to Weibel, the conducting zone is made up of how many generations of division?

Answer 43

The first 16 generations make up the conducting zone.

Question 44

According to Weibel, the last 7 zones (generations of airways) make up what?

Answer 44

Respiratory zone (or transitional zone) **These are generations 17-23

Question 45

Where do the terminal bronchioles become the respiratory bronchioles according to Weibel?

Answer 45

Between zone 16 and 17.

Question 46

What is the gross series of pulmonary blood flow?

Answer 46

Pulmonary artery Capillaries Pulmonary veins

Question 47

Where do arteries run in the lung?

Answer 47

Travel with bronchi and flow down the centres of the lobules.

Question 47

Where do veins flow in the lung?

Answer 47

Veins move to pass between lobules (at the periphery of the lung)

Question 48

Where do the capillaries form a dense network?

Answer 48

In the walls of the alveoli.

Question 49

What is the diameter of a capillary segment in the alveoli?

Answer 49

7 - 10 micrometres **This is JUST large enough for a red blood cell

Question 50

Why is the arrangement of capillaries in the alveolar walls so efficient for gas-exchange?

Answer 50

Because the lengths of capillary segments are so short that the dense network forms forms an almost continuous sheet of blood.

Question 51

Why can capillaries easily leak plasma and sometimes red blood cells into the alveolar spaces?

Answer 51

The blood-gas barrier is so thin = capillaries are easily damaged. Increasing pressure in capillaries to high levels or inflating lungs to high volumes = can raise wall stress of capillaries = ultrastructural changes occur that cause leakage.

Question 52

What receives the whole output of the right heart?

Answer 52

Pulmonary artery (and subsequently the lungs)

Question 53

What is the mean arterial pressure of the pulmonary artery?

Answer 53

15mmHg **Incredibly low due to the very small resistance of the pulmonary circuit.

Question 54

A mean pulmonary arterial pressure of 15mmHg allows for a blood flow rate of what through the pulmonary artery?

Answer 54

6L per minute

Question 55

What is the thickness of the blood-gas interface?

Answer 55

0.2-0.3 micrometres

Question 56

What is the surface area of the blood-gas interface?

Answer 56

50-100m squared

Question 57

How many alveoli are there in the human lung?

Answer 57

500 million

Question 58

The blood-gas interface is so thin that large increases in capillary pressure can cause what?

Answer 58

Damage to the barrier.

Question 59

How long does each red blood cell spend in the capillary network?

Answer 59

0.75s

Question 60

How many alveoli will a red blood cell traverse in the 0.75s it spends in the alveolar capillary network?

Answer 60

2-3

Question 61

What is the blood supply for the conducting airways?

Answer 61

The bronchial circulation (additional blood system to the alveolar capillary network)

Question 62

Can the lung function without bronchial circulation.

Answer 62

Yes (for example, after lung transplants the bronchial circulation is disrupted)

Question 63

In the bronchial circulation, where is blood carried away to?

Answer 63

Some to pulmonary veins Some enters systemic circulation

Question 64

What is the diameter of capillaries in the alveolar wall?

Answer 64

7-10 micrometres

Question 65

What is the thickness of the capillary walls in the alveoli?

Answer 65

Less than 0.3 micrometres

Question 66

How long does blood spend in the alveolar capillaries?

Answer 66

About 0.75s

Question 67

What does surfactant do?

Answer 67

Lowers the surface tension of the alveoli, preventing them from collapsing in. **Surfactant massively increases the stability of the alveoli.

Question 68

Large particles in air are filtered out by what part of the airway?

Answer 68

The nose

Question 69

Small particles in air that deposit in the conducting airways are removed how?

Answer 69

Muco-ciliary escalator that sweeps debris up to the epiglottis where it is swallowed.

Question 70

How are particles that are deposited in the alveoli removed?

Answer 70

Macrophages and then via lymphatics or blood flow.

Question 71

What type of flow takes air from the atmosphere to the terminal bronchioles?

Answer 71

Bulk flow, also known as convective flow.