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Respiratory Physiology > Pulmonary Blood Flow, Gas Exchange and Transport > Flashcards

Pulmonary Blood Flow, Gas Exchange and Transport Flashcards

1
Q

Bronchial circulation

A
  • Bronchial arteries arise from thoracic aorta

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

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2
Q

Pulmonary circulation

A
  • 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)
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3
Q

Dalton’s Law

A

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

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4
Q

Charles’ Law

A

Volume occupied by gas is directly related to the absolute temperature

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5
Q

Henry’s Law

A

Volume of gas dissolved in liquid is determined by:

  • Pressure of gas
  • Solubility of gas in liquid
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6
Q

Difference between partial pressure and gas content

A

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

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7
Q

Diffusion

A

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

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8
Q

Alveolar PO2

A

100 mmHg

13.3 kPa

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9
Q

Alveolar PCO2

A

40 mmHg

5.3 kPa

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10
Q

Arterial PO2

A

100 mmHg

  1. 3 kPa
    - determined by diffusion
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11
Q

Arterial PCO2

A

40 mmHg

5.3 kPa

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12
Q

Venous PO2

A

40 mmHg

5.3 kPa

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13
Q

Venous PCO2

A

46 mmHg

6.2 kPa

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14
Q

4 factors affecting gas exchange

A

Directly proportional to:

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

Indirectly proportional to:
4. Thickness of the membrane

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15
Q

Oxygen diffusion

A

Large partial pressure gradient (100->40)

Low solubility

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16
Q

Carbon dioxide diffusion

A

Small partial pressure gradient (46->40)

High solubility so faster than oxygen

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17
Q

Thickness of the membrane

A
  • Type I pneumocytes (simple squamous epithelium)

- Alveolar macrophages ingest foreign material in alveoli

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18
Q

Oxygen demand of resting tissues

A

250 ml/min

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19
Q

Oxygen carrying capacity of plasma

A

3 ml/min

- 15ml/min to tissues

20
Q

Oxygen carrying capacity of haemoglobin

A

200 ml/min

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

21
Q

Haemoglobin

A
  • Co-operatively binds 4 molecules of oxygen
  • 1.34ml oxygen per gram
  • 92% HbA
  • 8% HbA2, HbF and glycosylated Hb
22
Q

Determinant of oxygen saturation of haemoglobin

A

Partial pressure of oxygen in arterial blood (plasma)

  • 0.25s (0.75s transmit time)
  • Haemoglobin sequesters oxygen from plasma maintaining the partial pressure gradient
23
Q

Oxyhaemoglobin dissociation curve

A

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

24
Q

PO2 of 100mmHg (normal systemic arterial PO2)

A

Haemoglobin is almost 100% saturated

25
Q

PO2 of 60mmHg

A

Haemoglobin is 90% saturated

26
Q

PO2 of 40mmHg (normal venous PO2)

A

Haemoglobin is 75% saturated

27
Q

Causes of anaemia

A

Compromised oxygen-carrying capacity of blood

  • Iron deficiency
  • Haemorrhage
  • B12 deficiency
28
Q

PaO2 in anaemic patient

A

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

29
Q

Decreased haemoglobin affinity for oxygen

A
  1. Decreased pH
  2. Increased PCO2
  3. Increased temperature
  4. Added 2,3-DPG
30
Q

Increased haemoglobin affinity for oxygen

A
  1. Increased pH
  2. Decreased PCO2
  3. Decreased temperature
  4. No 2,3-DPG
31
Q

2,3-DPG: Production and Function

A
  • By erythrocytes
  • In situations associated with inadequate oxygen supply
  • It helps maintain oxygen unloading in tissues
32
Q

Foetal haemoglobin

A

Greater affinity for oxygen that HbA

- Necessary for extracting maternal blood

33
Q

Myoglobin (protein in oxidative muscle fibres) haemoglobin

A

Greater affinity for oxygen than HbA (and HbF)

34
Q

Carbon dioxide transport: tissues to blood

A
  • 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)
35
Q

Carbon dioxide transport: pulmonary capillaries

A
  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
36
Q

Ventilation

A

Air getting to alveoli (L/min)

37
Q

Perfusion

A

Local blood flow (L/min)

38
Q

Distribution of pulmonary circulation: 2 factors

A
  • Hydrostatic (blood) pressure

- Alveolar pressure

39
Q

Lung base: high blood flow

A
  • Arterial pressure exceeds alveolar pressure

- Vascular resistance is low

40
Q

Lung apex: low blood flow

A
  • Alveolar pressure exceeds arterial pressure

- Vascular resistance is high (compression of arterioles)

41
Q

Surface anatomy where ventilation and perfusion are matched

A

Rib 3

42
Q

Ventilation < Perfusion

A

“shunt”

  • Pulmonary vasoconstriction (divert to better ventilated areas)
  • Mild bronchodilation (increased PCO2)
43
Q

Ventilation > Perfusion

A

“Alveolar dead space” - alveoli are ventilated but not perfused.

  • Pulmonary vasodilation
  • Bronchoconstriction (decreased PCO2)
44
Q

Anatomical dead space

A

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

45
Q

Physiological dead space

A

Alveolar dead space + anatomical dead space

Respiratory Physiology (5 decks)

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