Pulmonary Blood Flow, Gas Exchange and Transport

Question 1

Bronchial circulation

Answer 1

• Bronchial arteries arise from thoracic aorta

- Nutritive (airway smooth muscle, nerves and lung tissue)

Question 2

Pulmonary circulation

Answer 2

• Pulmonary artery carries entire CO from RV and supplies dense capillary network around alveoli
• Pulmonary vein returns oxygenated blood to the LA of the heart
• High flow, low pressure (25/8mmHg)

Question 3

Dalton’s Law

Answer 3

Sum of pressures of individual gases = total pressure of gas mixture

Question 4

Charles’ Law

Answer 4

Volume occupied by gas is directly related to the absolute temperature

Question 5

Henry’s Law

Answer 5

Volume of gas dissolved in liquid is determined by:

• Pressure of gas
• Solubility of gas in liquid

Question 6

Difference between partial pressure and gas content

Answer 6

Partial pressure of a gas is related to the concentration of that gas in the gas content

Question 7

Diffusion

Answer 7

Air diffuses across a permeable membrane down partial pressure gradient until equilibrium is reached

Question 8

Alveolar PO2

Answer 8

100 mmHg

13.3 kPa

Question 9

Alveolar PCO2

Answer 9

40 mmHg

5.3 kPa

Question 10

Arterial PO2

Answer 10

100 mmHg

13. 3 kPa
    - determined by diffusion

Question 11

Arterial PCO2

Answer 11

40 mmHg

5.3 kPa

Question 12

Venous PO2

Answer 12

40 mmHg

5.3 kPa

Question 13

Venous PCO2

Answer 13

46 mmHg

6.2 kPa

Question 14

4 factors affecting gas exchange

Answer 14

Directly proportional to:

1. Partial pressure gradient
2. Gas solubility
3. Available surface area

Indirectly proportional to:
4. Thickness of the membrane

Question 15

Oxygen diffusion

Answer 15

Large partial pressure gradient (100->40)

Low solubility

Question 16

Carbon dioxide diffusion

Answer 16

Small partial pressure gradient (46->40)

High solubility so faster than oxygen

Question 17

Thickness of the membrane

Answer 17

• Type I pneumocytes (simple squamous epithelium)

- Alveolar macrophages ingest foreign material in alveoli

Question 18

Oxygen demand of resting tissues

Answer 18

250 ml/min

Question 19

Oxygen carrying capacity of plasma

Answer 19

3 ml/min

- 15ml/min to tissues

Question 20

Oxygen carrying capacity of haemoglobin

Answer 20

200 ml/min

- 1000ml/min to tissues (only 25% is extracted)

Question 21

Haemoglobin

Answer 21

• Co-operatively binds 4 molecules of oxygen
• 1.34ml oxygen per gram
• 92% HbA
• 8% HbA2, HbF and glycosylated Hb

Question 22

Determinant of oxygen saturation of haemoglobin

Answer 22

Partial pressure of oxygen in arterial blood (plasma)

• 0.25s (0.75s transmit time)
• Haemoglobin sequesters oxygen from plasma maintaining the partial pressure gradient

Question 23

Oxyhaemoglobin dissociation curve

Answer 23

Curve that plots the proportion of haemoglobin in its saturated form against the partial pressure of oxygen

Question 24

PO2 of 100mmHg (normal systemic arterial PO2)

Answer 24

Haemoglobin is almost 100% saturated

Question 25

PO2 of 60mmHg

Answer 25

Haemoglobin is 90% saturated

Question 26

PO2 of 40mmHg (normal venous PO2)

Answer 26

Haemoglobin is 75% saturated

Question 27

Causes of anaemia

Answer 27

Compromised oxygen-carrying capacity of blood - Iron deficiency - Haemorrhage - B12 deficiency

Question 28

PaO2 in anaemic patient

Answer 28

Normal (roughly 100%), despite total blood oxygen low

Question 29

Decreased haemoglobin affinity for oxygen

Answer 29

1. Decreased pH 2. Increased PCO2 3. Increased temperature 4. Added 2,3-DPG

Question 30

Increased haemoglobin affinity for oxygen

Answer 30

1. Increased pH 2. Decreased PCO2 3. Decreased temperature 4. No 2,3-DPG

Question 31

2,3-DPG: Production and Function

Answer 31

- By erythrocytes - In situations associated with inadequate oxygen supply - It helps maintain oxygen unloading in tissues

Question 32

Foetal haemoglobin

Answer 32

Greater affinity for oxygen that HbA | - Necessary for extracting maternal blood

Question 33

Myoglobin (protein in oxidative muscle fibres) haemoglobin

Answer 33

Greater affinity for oxygen than HbA (and HbF)

Question 34

Carbon dioxide transport: tissues to blood

Answer 34

- 7% in plasma - 23% combines with deoxyhaemoglobin to form carbamino compounds 1. 70% combines with water (+carbonic anhydrase) in RBC to form carbonic anhydrase 2. Carbonic anhydrase dissociates to bicarbonate and H+ 3. Bicarbonate moves out of RBC (chloride shift)

Question 35

Carbon dioxide transport: pulmonary capillaries

Answer 35

1. Bicarbonate moves into RBC in exchange for Cl- 2. Bicarbonate + H+ combine forming carbonic acid 3. Carbonic acid dissociates 4. CO2 moves down its partial pressure gradient from blood to alveoli

Question 36

Ventilation

Answer 36

Air getting to alveoli (L/min)

Question 37

Perfusion

Answer 37

Local blood flow (L/min)

Question 38

Distribution of pulmonary circulation: 2 factors

Answer 38

- Hydrostatic (blood) pressure | - Alveolar pressure

Question 39

Lung base: high blood flow

Answer 39

- Arterial pressure exceeds alveolar pressure | - Vascular resistance is low

Question 40

Lung apex: low blood flow

Answer 40

- Alveolar pressure exceeds arterial pressure | - Vascular resistance is high (compression of arterioles)

Question 41

Surface anatomy where ventilation and perfusion are matched

Answer 41

Rib 3

Question 42

Ventilation < Perfusion

Answer 42

"shunt" - Pulmonary vasoconstriction (divert to better ventilated areas) - Mild bronchodilation (increased PCO2)

Question 43

Ventilation > Perfusion

Answer 43

"Alveolar dead space" - alveoli are ventilated but not perfused. - Pulmonary vasodilation - Bronchoconstriction (decreased PCO2)

Question 44

Anatomical dead space

Answer 44

Air in conducting zone of respiratory tract unable to participate in gas exchange

Question 45

Physiological dead space

Answer 45

Alveolar dead space + anatomical dead space