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Block 3 > Role of haemoglobin in oxygen delivery to tissue > Flashcards

Role of haemoglobin in oxygen delivery to tissue Flashcards

1
Q

Describe oxygen delivery system to tissues

A

Oxygen diffuses into from blood to tissues to cells via oxygen pressure gradient.

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2
Q

Pressure of arterial PO2

A

100 mmHg

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3
Q

Pressure of interstitial fluid PO2

A

40 mmHg

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4
Q

Pressure of intercellular PO2

A

25 mmHg

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5
Q

Haemoglobin carries?

A

15 mL of oxygen per gram

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6
Q

Describe haemoglobin function

A
  • Hb increases blood oxygen carrying capacity by 60x

- Without Hb, not enough oxygen can dissolve in blood.

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7
Q

What is haemoglobin?

A

Metalloprotein that binds to oxygen

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8
Q

_____ of blood oxygen is bound to Hb

A

98.5%

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9
Q

Composition of haemoglobin?

A

Made of 4 polypeptide chains alpha-gamma-beta, each with heme group (iron molecule in a porphyrin group)

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10
Q

How many iron molecules are bound to each oxygen molecule?

A

Each iron molecule can reversibly bind to one oxygen molecule (4 per haemoglobin)

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11
Q

Haemoglobin A (Hb A) is?

A

Adult haemoglobin with 2 alpha-chains and 2 beta-chains

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12
Q

Haemoglobin F (Hb F) is?

A

Fetal Hb with 2 alpha-chains and 2 gamma-chains; higher oxygen binding affinity; replaced by Hb A at 6 months.

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13
Q

Define “cooperative binding”

A

When one molecule of oxygen binds to haemoglobin, the conformation changes to R state and Hb affinity for more oxygen increases.

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14
Q

T state of haemoglobin?

A

T state = Deoxygenated state; tense; low affinity for oxygen

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15
Q

R state of haemoglobin?

A

R state = oxygenated state; relaxed; high affinity for oxygen

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16
Q

Cooperative binding explains?

A

Explains the oxygen-haemoglobin dissociation curve

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17
Q

Hb carrying capacity is dependent on?

A

Depends on surrounding PO2 of blood.

18
Q

Describe the flat curve at PO2 > 70 mm Hg

A

Increasing or decreasing PO2 has little effect (e.g. breathing high [O2] air or high altitude)

19
Q

Describe steep curve at PO2 < 50 mmHg

A

Small change in PO2 has large effect on binding.

  • This is a range of PO2 of capillaries
  • Venous capillary blood is about 75% saturated.
  • Unbinding from Hb allows more Oxygen to diffuse into tissues.
20
Q

Factors that affect oxygen-haemoglobin curve: lower binding affinity

A
  • Bohr effect: increase in partial pressure of carbon dioxide, lower pH (increase acidity)
  • Increase temperature
  • Increase 2,3-biphosphoglycerate (BPG)
21
Q

What is BPG (2,3-Biphosphoglycerate)?

A

BPG = component of RBC; increased levels of BPG in chronic hypoxia (reduce oxygen)

22
Q

Lower binding affinity allows for?

A

Allows more oxygen to unload at same partial pressure of oxygen.

Occurs when oxygen is needed in tissue - i.e. in sites with increased metabolic activity

23
Q

Hb F has higher affinity which?

A

Shifts O2-Hb curve left.

24
Q

Polycythaemia is when?

A

Hb = 20

25
Q

Normal blood O2-Hb level

A

Hb = 15

26
Q

Anaemia blood O2-Hb level

A

Hb = 10

27
Q

Carbon monoxide poisoning happens by?

A
  • CO binds at oxygen binding site of Hb

- CO-induced hypoxia does NOT cause breathlessness

28
Q

Describe the steps in CO binding at oxygen binding site of Hb

A
  • Binds with 200x higher affinity
  • PCO2 that is 1/200 PO2 will bind with 50% of Hb sites
  • Blood PO2 will be normal but Oxygen content of blood will be very low
29
Q

CO-induced hypoxia does NOT cause breathlessness because?

A
  • PCO2 levels triggers chemoreceptors but PCO2 are normal (CO2 binds to different site of Hb)
  • PO2 levels of blood have minor chemoreceptor role, but PO2 levels are normal.
30
Q

Define hypoxia

A

Diminished supply of oxygen below metabolic requirements

31
Q

Hypoxic hypoxia

A

Failure of oxygen to reach blood in lungs

32
Q

Stagnant hypoxia

A

Failure to transport sufficient oxygen due to inadequate blood flow

33
Q

Anaemic hypoxia

A

Oxygen carrying capacity of blood inadequate

34
Q

Histotoxic hypoxia

A

Failure of tissues to utilize oxygen

35
Q

Carbon dioxide is transported in 3 forms:

A
  • Dissolved CO2 (proportional to PCO2) - 10%
  • Carbamino haemoglobin (HbCO2) - 20%
  • Bicarbonate ions (HCO3) - 70%
36
Q

Carbaminohaemoglobin (HbCO2)

A
  • Different binding site than oxygen

- CO2 has higher affinity for reduced Hb (i.e. after unloading of oxygen) - Haldane effect

37
Q

Bicarbonate ions (HCO3)

A
  • Conversion accelerated by carbonic anhydrase in RBC
  • Following reaction occurs inside RBC: CO2 + H2O H2CO3 H+ + HCO3-
  • HCO3 easily diffused through RBC membrane
  • H+ cannot diffuse out and accumulates inside RBC
  • H+ has higher affinity for reduced Hb (i.e. after unloading of oxygen) - Haldane effect
  • Hb is very effective buffer by reducing free H+ (i.e. increase pH)
38
Q

What does Bohr effect and Haldane effect work to?

A

They work to facilitate oxygen release, and carbon dioxide and hydrogen ion uptake in tissues.

39
Q

Bohr effect

A

pH decrease or CO2 increase shift Hb-O2 dissociation curve right

40
Q

Haldane effect

A

Removal of oxygen from Hb increases the affinity for CO2 and H+

Block 3 (9 decks)

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