Role of haemoglobin in oxygen delivery to tissue

Question 1

Describe oxygen delivery system to tissues

Answer 1

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

Question 2

Pressure of arterial PO2

Answer 2

100 mmHg

Question 3

Pressure of interstitial fluid PO2

Answer 3

40 mmHg

Question 4

Pressure of intercellular PO2

Answer 4

25 mmHg

Question 5

Haemoglobin carries?

Answer 5

15 mL of oxygen per gram

Question 6

Describe haemoglobin function

Answer 6

• Hb increases blood oxygen carrying capacity by 60x

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

Question 7

What is haemoglobin?

Answer 7

Metalloprotein that binds to oxygen

Question 8

_____ of blood oxygen is bound to Hb

Answer 8

98.5%

Question 9

Composition of haemoglobin?

Answer 9

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

Question 10

How many iron molecules are bound to each oxygen molecule?

Answer 10

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

Question 11

Haemoglobin A (Hb A) is?

Answer 11

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

Question 12

Haemoglobin F (Hb F) is?

Answer 12

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

Question 13

Define “cooperative binding”

Answer 13

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

Question 14

T state of haemoglobin?

Answer 14

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

Question 15

R state of haemoglobin?

Answer 15

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

Question 16

Cooperative binding explains?

Answer 16

Explains the oxygen-haemoglobin dissociation curve

Question 17

Hb carrying capacity is dependent on?

Answer 17

Depends on surrounding PO2 of blood.

Question 18

Describe the flat curve at PO2 > 70 mm Hg

Answer 18

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

Question 19

Describe steep curve at PO2 < 50 mmHg

Answer 19

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.

Question 20

Factors that affect oxygen-haemoglobin curve: lower binding affinity

Answer 20

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

Question 21

What is BPG (2,3-Biphosphoglycerate)?

Answer 21

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

Question 22

Lower binding affinity allows for?

Answer 22

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

Question 23

Hb F has higher affinity which?

Answer 23

Shifts O2-Hb curve left.

Question 24

Polycythaemia is when?

Answer 24

Hb = 20

Question 25

Normal blood O2-Hb level

Answer 25

Hb = 15

Question 26

Anaemia blood O2-Hb level

Answer 26

Hb = 10

Question 27

Carbon monoxide poisoning happens by?

Answer 27

- CO binds at oxygen binding site of Hb | - CO-induced hypoxia does NOT cause breathlessness

Question 28

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

Answer 28

- 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

Question 29

CO-induced hypoxia does NOT cause breathlessness because?

Answer 29

- 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.

Question 30

Define hypoxia

Answer 30

Diminished supply of oxygen below metabolic requirements

Question 31

Hypoxic hypoxia

Answer 31

Failure of oxygen to reach blood in lungs

Question 32

Stagnant hypoxia

Answer 32

Failure to transport sufficient oxygen due to inadequate blood flow

Question 33

Anaemic hypoxia

Answer 33

Oxygen carrying capacity of blood inadequate

Question 34

Histotoxic hypoxia

Answer 34

Failure of tissues to utilize oxygen

Question 35

Carbon dioxide is transported in 3 forms:

Answer 35

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

Question 36

Carbaminohaemoglobin (HbCO2)

Answer 36

- Different binding site than oxygen | - CO2 has higher affinity for reduced Hb (i.e. after unloading of oxygen) - Haldane effect

Question 37

Bicarbonate ions (HCO3)

Answer 37

- 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)

Question 38

What does Bohr effect and Haldane effect work to?

Answer 38

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

Question 39

Bohr effect

Answer 39

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

Question 40

Haldane effect

Answer 40

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