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Body Systems > Blood Gas Transport > Flashcards

Blood Gas Transport Flashcards

1
Q

What mechanism does gas exchange occur through?

A

Diffusion

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2
Q

What is diffusion in gas exchange dependent on?

A
  • Diffusion surface area (many moist alveoli)
  • Diffusion distance for gases (short alveolar and capillary walls)
  • Concentration between alveolar air and blood (large difference in partial pressure)
  • Solubility of gases
  • Coordinated blood flow and airflow to allow the passage of both of the gases efficiently
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3
Q

What is Dalton’s law of partial pressures?

A

the total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture

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4
Q

What is partial pressure?

A

the pressure exerted by each gas. Directly proportional to its percentage in the total gas mixture

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5
Q

If there is 20.9% of oxygen in the atmosphere and the atmospheric pressure at sea level is 760 mmHg what will be the partial pressure of oxygen?

A

20.9% (0.209) x 760mmHg = 159 mmHg

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6
Q

What are the partial pressure differences in the pulmonary circuit and what does this mean?

A

 In the alveolus there is a partial pressure of 100 of oxygen and 40 of CO2. In the pulmonary capillary the partial pressure of oxygen is 40 and carbon dioxide is 45
 This pressure difference allows oxygen to diffuse out of the alveolus and CO2 to diffuse in

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7
Q

What are the partial pressure differences in the systemic circuit and what does this mean?

A

 The partial pressure of O2 in the systemic capillary is 95 and CO2 is 40. The partial pressure of O2 in the interstitial fluid is 40 and CO2 is 45.
 Therefore, oxygen can diffuse into the cells and carbon dioxide can diffuse out due to the differences in partial pressure

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8
Q

What is Henry’s law and why?

A
  • at a given temperature the amount of a particular gas in solution is directly proportional to the partial pressure of that gas
  • this is because when a gas under pressure contacts a liquid the pressure tends to force gas molecules into solution
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9
Q

What does the amount of gas dissolved in solution depend on as well as partial pressure?

A

Solubility

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10
Q

Is oxygen soluble?

A

It isn’t very soluble. CO2 is more soluble

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11
Q

If oxygen isn’t very soluble how comes there is so much in the blood?

A

Because of haemoglobin

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12
Q

What is the haemoglobin structure?

A
  • Conjugate protein
  • 4 globular protein subunits (2 alpha + 2 beta)
  • Each subunit
     Protein (globin)
     Non-protein group (haem)
  • Haem: Fe2+ in a porphyrin ring
  • Fe2+ is the binding site for oxygen
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13
Q

What happens when Hb binds oxygen?

A
  • Hb + O2 HbO2
  • Deoxyhaemoglobin oxyhaemoglobin
  • Rapid and reversible
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14
Q

How many molecules of oxygen can each Hb molecule bind?

A

four

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15
Q

What happens as Hb starts to bind oxygen?

A
  • Deoxyhaemoglobin has lower affinity for oxygen but when one oxygen binds the structure changes and it’s affinity for oxygen increases allowing us to bind the oxygen more easily
  • After binding with O2 Hb changes shape to facilitate further uptake – positive feedback
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16
Q

How is oxygen transported?

A
  • Approx. 97% of O2 transported in blood in combination with Hb
  • Remainder in plasma
17
Q

What is O2-Hb saturation?

A

The percentage of haem units in a Hb molecule that contain bound oxygen (4 molecules of O2 bound to Hb – fully (100%) saturated)

18
Q

What is O2 binding to haemoglobin affected by?

A

 PO2 (partial pressure of oxygen) of blood
 Blood pH
 Temperature
 State of O2 binding of the Hb molecule (how many molecules are bound to the Hb at any onetime)

19
Q

What is the oxygen-Hb dissociation (saturation) curve?

A
  • Relates the saturation of Hb (y axis) to the PO2 (partial pressure of oxygen – x-axis)
  • About 75% Hb saturation in the systemic tissues when there is a partial pressure of 40 of oxygen
  • In the alveoli the partial pressure of oxygen is 100 and the percentage of Hb saturation is 100%
  • The higher the partial pressure of oxygen the more combines with haemoglobin
20
Q

What aids haemoglobin unloading of oxygen?

A
  • A lower pH with increased carbon dioxide leads to better unloading of oxygen: ‘Bohr shift’. This would happen for example when you are exercising
  • A high temperature leads to more unloading. This happens in active tissues
  • Increased 2,3 -DPG (product of anaerobic metabolism is red blood cells) leads to better unloading. Binds much more strongly to deoxyhaemoglobin than oxyhaemoglobin.
  • increased BPG production (anaerobic product) due to increased pH
21
Q

What happens as atmospheric pressure gets lower and lower as you increase in altitude?

A
  • Impact on the partial pressure of oxygen and amount that can be delivered to body.
  • Faster, deeper breathing at a high altitude
  • Hypoxia (blood oxygen concentration very low) at a very high altitude
  • ‘foggy’ brain, weak muscles at an extremely high altitude
22
Q

What happens with carboxyhaemoglobin?

A

 CO binds tighter than O2 (200x greater)

 Dramatically reduce ability of O2 to bind to Hb

23
Q

What happens with methaemoglobin?

A

 Fe2+ oxidised to Fe3+ by drugs etc.
 Unable to carry O2
 Slowly converted back

24
Q

What is foetal haemoglobin?

A

 2 alpha and 2 gamma subunits
 Higher affinity for O2
 Important in transferring O2 across the placenta
 Makes it easier for foetus to get oxygen from it’s mother

25
Q

How are CO2 molecules transported?

A

 70% converted to carbonic acid formation H2CO3- in haemoglobin and transported in plasma as bicarbonate ion HCO3-
 Bound to haemoglobin: carbaminohaemoglobin (23%
 Dissolved in plasma (7%)

26
Q

What does 93% of Carbon dioxide produced from the cells do?

A

diffuses into RBCs to either become carbonic acid or to bind to haemoglobin

27
Q

What is the chloride shift?

A
  • CO2 + H2O
  • with carbonic anhydrase ->
  • H2CO3
  • Which dissociates into
  • H+ and HCO3-
  • The bicarbonate ions (HCO3-) move into the plasma with the aid of a counter-transport mechanism that exchanges intracellular bicarbonate ions for extracellular chloride ions
  • H+ removed by buffers
28
Q

How is carbaminohaemoglobin formed?

A
  • Hb is attached to NH2

- NH2 combines with CO2 to become NHCOOH and this binds to Hb (different binding site to oxygen)

29
Q

How does buffering in RBCs take place?

A
  • Every CO2 -> HCO3- yields an H+
  • pH would become very acidic
  • haemoglobin minimises the size of pH changes by consuming or releasing H+
  • best buffers in red cells: imidazole groups of histidine residues in haemoglobin
30
Q

What is the Haldane effect in the lungs and in the tissues?

A
  • In the lungs:
  • Oxygenation of Hb -> lower affinity for H+ ions -> decreased buffering power -> release of H+
  • Aids unloading of CO2 in lungs
  • In the tissues
  • Deoxygenation of Hb -> higher affinity for H+ ions -> increased buffering power -> H+ uptake
  • Aids CO2 transport from tissues
31
Q

Why is diffusion easier due to the fact that CO2 and O2 are lipid soluble?

A

they can diffuse through the surfactant layer and the alveolar and endothelial plasma membranes

32
Q

When do gases diffuse in/ out until?

A

until the partial pressure either side of the membrane have reached equilibrium

33
Q

Why can you still survive at high altitudes?

A

because even when there is a lower PO2 because of the fact that haemoglobin changes shape as it binds more O2 it will still have a fairly high affinity for oxygen due to it’s curve: Hb binding is not linear

34
Q

Why does venous blood still have a relatively large oxygen reserve?

A

Because haemoglobin still retains 75% of it’s oxygen

35
Q

What is Bohr’s effect?

A

• When the pH decreases the shape of haemoglobin molecules changes and the molecules release their oxygen more readily

Body Systems (20 decks)

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