Gas Transport in Blood

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13 Terms

1
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Is O2 & CO2 soluble in blood?

O2 is not soluble at all

CO2 is somewhat soluble, still mostly insoluble

2
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O2 transport

1.5-2% is carried within blood plasma

98% is carried within red blood cells, binding to the carrier molecule haemoglobin.

Equation: Hb + O2 ↔ HbO2

  1. Travels down the pressure gradient, from alveolus to capillaries

  2. Dissolves in plasma

  3. Diffuses into red blood cell (RBC)

  4. Reversibly binds Hb

  5. Moves through blood as HbO2

  6. Once at tissues, dissociates from Hb

  7. Diffuses out of RBC and into tissues

3
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Haemoglobin

  • Made up of 4 subunits

  • Each subunit contains a group of Iron (Haem group)

  • O2 binds to the iron within the Haem group

    • give blood its red colour (like how rust is red)

  • Each red blood cell can carry up to 4 O2 molecules

<ul><li><p>Made up of 4 subunits</p></li><li><p>Each subunit contains a group of Iron (Haem group)</p></li><li><p>O<sub>2</sub> binds to the iron within the Haem group</p><ul><li><p>give blood its <mark data-color="red" style="background-color: red; color: inherit">red colour</mark> (like how rust is red)</p></li></ul></li><li><p>Each red blood cell can carry up to 4 O<sub>2 </sub>molecules</p></li></ul><p></p>
4
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Is arterial and venous blood red and blue respectively?

No dummy

<p>No dummy</p>
5
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Is the Hb and O2 relationship directly propoertional?

No, as when one O2 molecule binds to Hb, it increases the affinity of other O2 molecules binding to the remaining Haem groups.

6
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O2/Hb dissociation curve

Curving Plateauing end

For oxygen absorbtion in lungs

Curve plateauing up top: pO2 (partial O2 pressure) present in lungs. essentially 100% saturation of haemoglobin.

But 40 pO2 in tissues.

Despite the partial pressure decreasing from 100 to 40, Hb saturation still remains high (from 100% to ~75%).

This is to ensure the red blood cells retain O2 even as the partial pressure drops from the lungs to around the body.

Lots of redundancy

<p>For <mark data-color="blue" style="background-color: blue; color: inherit">oxygen absorbtion in lungs</mark></p><p>Curve plateauing up top: pO<sub>2</sub> (partial O<sub>2</sub> pressure) present in lungs. essentially 100% saturation of haemoglobin.</p><p>But 40 pO<sub>2</sub> in tissues.</p><p>Despite the partial pressure decreasing from 100 to 40, Hb saturation still remains high (from 100% to ~75%).</p><p>This is to ensure the red blood cells retain O<sub>2</sub> even as the partial pressure drops from the lungs to around the body.</p><p>Lots of redundancy</p>
7
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O2/Hb dissociation curve:

Curving Plateau Steep start

  • For Oxygen delivery to tissues

  • Even small drops in pO2 (e.g. if a tissue is a bit more metabolically active) mean more much O2 will be released by Hb

  • Good for delivering O2 to tissues as needed

<ul><li><p>For <mark data-color="blue" style="background-color: blue; color: inherit">Oxygen delivery to tissues</mark></p></li><li><p>Even small drops in pO<sub>2</sub> (e.g. if a tissue is a bit more metabolically active) mean more much O<sub>2</sub> will be released by Hb</p></li><li><p>Good for delivering O<sub>2</sub> to tissues as needed</p></li></ul><p></p>
8
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O2/Hb dissociation curve:

Key point

Usually only deliver ~25% of the O2 carried by red blood cells (RBCs) to the tissues – lots of spare capacity if needed

  • ‘Deoxygenated’ blood in veins still has a lot of O2 in it!

<p>Usually only deliver ~25% of the O<sub>2 </sub>carried by red blood cells (RBCs) to the tissues – lots of spare capacity if needed</p><ul><li><p>‘Deoxygenated’ blood in veins still has a lot of O<sub>2</sub> in it!</p></li></ul><p></p>
9
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Factors that:

Decrease Haemoglobin/O2 affinity

  • Increase in temperature

  • increase in pCO2

  • decrease in pH (more acidic environment)

    • Haemoglobin is more likely to deliver O2 to a metabolically active tissue

10
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Factors that:

Increase Haemoglobin/O2 affinity

  • Decrease in temperature

  • Decrease in pCO2

  • Increase in pH (more basic environment)

11
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3 Ways of CO2 transport

  1. Bound to Hb (~20%)

  2. In the form of bicarbonate ions (~70%)

  3. Dissolved in plasma (~10%) as CO2 is more soluble than O2

<ol><li><p>Bound to Hb (~20%)</p></li><li><p>In the form of bicarbonate ions (~70%)</p></li><li><p>Dissolved in plasma (~10%) as CO<sub>2</sub> is more soluble than O<sub>2</sub></p></li></ol><p></p>
12
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CO2 binding to Haemoglobin

CO2 binds to a different part of Hb (i.e. the amino acid portion rather than the haem) but otherwise the same as O2/Hb transport

  • No competitive binding

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CO2 transported as Bicarbonate ions:

Carbonic anhydrase reaction

  1. Red blood cells secrete an enzyme (carbonic anhydrase). This enzyme facilitates the reaction.

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

(reaction occurs within the red blood cell)

Carbonate ion is able to travel within the plasma

Process is reversed when CO2 is entering the lungs