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SA respiratory > S4) Carbon Dioxide in the Blood > Flashcards

S4) Carbon Dioxide in the Blood Flashcards

1
Q

Describe 3 chemical properties of carbon dioxide in the blood

A
  • CO2 is more soluble than oxygen
  • CO2 reacts chemically with water
  • CO2 also reacts with Hb (different site from O2)
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2
Q

Compare and contrast the content of O2 and CO2 in arterial blood

A
  • Total content CO2 in arterial blood ≈ 21 mmol.l-1
  • Total content O2 in arterial blood ≈ 8.9 mmol.l-1
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3
Q

What is the normal range of arterial blood pH?

A

pH 7.35 – pH 7.45

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4
Q

What is the most important substance in controlling blood pH?

A

CO2

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5
Q

What is the solubility factor for CO2 at 37oC?

A

0.23

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6
Q

How does one calculate the [CO2]dissolved in blood?

A

[CO2]dissolved = solubility factor x pCO2

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7
Q

What is the role of dissolved CO2 in plasma and in red blood cells?

A
  • Not a waste product
  • Reacts with water to act as a buffer
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8
Q

What is the result of dissolved carbon dioxide reacting with water?

A
  • Dissolved CO2 reacts with water to form carbonic acid
  • Carbonic acid very quickly dissociates to hydrogen ions and hydrogen carbonate ions
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9
Q

pH of blood plasma depends on how much CO2 reacts to form H+.

What determines this?

A
  • [CO2]dissolved (pushes reaction to right)
  • [HCO3- ] (pushes reaction to left)
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10
Q

Explain the relationship between the plasma pH and pCO2 of the alveoli

A

[CO2]dissolved depends directly on pCO2:

  • If pCO2 rises = plasma pH falls
  • If pCO2 falls = plasma pH rises
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11
Q

Using the Hendersson-Hasselbach equation, what is the formula to calculate pH from pCO2 and [HCO3-] ?

A
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12
Q

How does one calculate the pH of blood plasma using the Hendersson-Hasselbach equation?

A
  • pK is a constant (6.1 at 37oC)
  • 20x more HCO3- than dissolved CO2 (log20 = 1.3)

pH = 6.1 + 1.3 = 7.4

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13
Q

Which values determine the pH of arterial blood?

A
  • Ratio of [HCO3-] and pCO2 determine pH
  • pCO2 determined by alveolar pCO2
  • Alveolar pCO2 is determined by rate of ventilation
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14
Q

How is the plasma concentration of hydrogen carbonate established

A

Hydrogen carbonate production in red blood cells:

– C02 can recat with water inside RBC

  • H+ ions bind to Hb(-) inside RBCs
  • Chloride-bicarbonate exchanger transports HCO3- out of RBCs in exchange for Cland creates a plasma concentration of 25mmol.l-1 HCO3-
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15
Q

Which enzyme catalyses the production of hydrogen carbonate in red blood cells?

A

Carbonic anhydrase

this is a rapid reaction unlike in plasma as there is a high conc of it

C02 + H20 → H + Hco3

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16
Q

Describe the role of haemoglobin in the production of hydrogen carbonate ions by red blood cells

A
  • Haemoglobin has a large capacity for binding H+ ions
  • The amount of HCO3- that erythrocytes produce depends on the binding of H+ to haemoglobin
17
Q

Explain the role of the kidney in [HCO3-]

A
  • Kidney controls the amount of HCO3- by varying excretion
  • Hence, pH is dependent on how much CO2 and HCO3- is present
18
Q

Hydogen carbonate buffers extra acids.

Identify 3 of these

A
  • Lactic acid
  • Keto acids
  • Sulphuric acid
19
Q

Explain how hydrogen carbonate buffers extra acids

A
  • Acids react with HCO3- to produce CO2
  • [HCO3-] decreases
  • CO2 is produced & removed through ventilation
  • pH changes are buffered
20
Q

Why is pCO2 is higher in venous blood?

A

More CO2 from metabolically active tissues

21
Q

Explain how the buffering of H+ by Hb depends on level of oxygenation

A
  • If more O2 binds Hb → R-state and less H+ ions bind (lungs)
  • If less O2 binds Hb → T-state and more H+ ions bind (tissues)
22
Q

Explain the processes occurring in venous blood at the tissues

A
  • Hb has lost O2 and so binds more H+
  • More HCO3- forms & is exported to the plasma
23
Q

Explain the processes occurring in venous blood at the lungs

A
  • Hb picks up O2 and goes into R-state
  • Hb gives up the extra H+ (from tissues)
  • H+ reacts with HCO3- to form CO2
  • CO2 is breathed out
24
Q

How are carbamino compounds formed?

A
  • CO2 binds directly to amine groups on globin of Hb
  • This contributes to CO2 transport
25
Q

Why are more carbamino compounds are formed at the tissues?

A
  • pCO2 is higher
  • Unloading of O2 facilitates binding of CO2 to Hb
  • CO2 is then given up at the lungs
26
Q

Identify the 3 forms in which carbon dioxide is transported

A
  • Dissolved CO2 (10%)
  • Hydrogen carbonate (60%)
  • Carbamino compounds (30%)
27
Q

How much carbon dioxide is actually transported?

A

Transported CO2

= CO2 venous blood – CO2 arterial blood

= 23.3 – 21.5 mmol.l-1

= 1.8 mmol.l-1 (8% of the total is transported)

28
Q

What is the role of the CO2 in the blood that is not transported?

A

Remaining CO2 is part of the pH buffering system

29
Q

what is the range of Ph that shows acidotic blood and what range shows alkalotic

A
  1. 35-7.4 → acidotic
  2. 4-7.45 → alkalotic
30
Q

what is the pH of bodily fluids determined between the relationship of

A
  • amount of CO2 dissolved in the plasma
  • amount of HC03 formed from c02 in the red blood cell involving haemoglobin
  • as long as there is 20x as much HCO3 dissolved as Co2 in plasma then pH will be 7.4
31
Q

what organ controls the levels of HCO3

A

kidney

32
Q

what is pCo2 at venous blood give 3 reasons for this

A

6 pKa

more co2 in venous blood as:

  1. tissue produce c02, increasing pco2, more dissolves
  2. oxygen is removed from heat at tissue so more c02 can attach and recat in RBC
  3. 10% more co2 reacts in venous bloods
33
Q

what is the relationship between Pco2 and the content of `co2 in the blood

A
  • linear
  • so with hyperventilation both will reduce
34
Q

what is the difference between the speed of the lungs and kidneys

A

lungs can make changes in co2 much faster

kidney takes much longer to alter HCo3 levels

35
Q

what the body response to increase Co2

A

hypoventilate

SA respiratory (23 decks)

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