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Y1 - Respiratory > Physiology 3: Gas Transport (L-4&5) > Flashcards

Physiology 3: Gas Transport (L-4&5) Flashcards

1
Q

Describe how PO2 change as oxygen travels from the lungs to the systemic capillaries

A

It decreases

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2
Q

What is the effect of partial pressure on gas solubility?

Henry’s Law

A

The amount of gas dissolved in a given type and volume of a liquid is proportional to the partial pressure of the gas in equilibrium with the liquid

(At a constant temp.)

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3
Q

What are the 2 mechanisms by which oxygen is transported in the blood?

A
  • Dissolved oxygen (1.5%)

- Oxygen bound to haemoglobin (98.5%)

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4
Q

Describe the structure of haemoglobin (Hb)

A
  • 4 haem groups (1 per subunit)
  • 2 Beta chains
  • 2 Alpha helices
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5
Q

Describe the binding of oxygen to Hb

A
  • Each Hb group reversibly binds to one oxygen molecule
  • PO2 is the primary factor determining %O2 saturation of Hb
  • Binding of oxygen to one subunit increases the other subunits oxygen affinity (Co-operativity)
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6
Q

Describe the oxygen delivery index (DO2I)

A

Oxygen delivery to tissue depends on the oxygen content of arterial blood and the cardiac output

DO2I = (Arterial O2 conc.) X (Cardiac Index)

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7
Q

Describe the factors that determine the oxygen content of arterial blood

A
  • Hb concentration

- Saturation of Hb with oxygen

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8
Q

What factors affect the partial pressure of inspired oxygen?

A
  • Total pressure

- Proportion of oxygen in the air

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9
Q

Give examples of ways that oxygen delivery to tissue can be impaired

A
  • Decreased partial pressure of inspired oxygen
  • Respiratory disease (Less oxygen can bind to Hb)
  • Anaemia (Less Hb so less oxygen)
  • Heart failure
  • Infarction/vessel occlusion
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10
Q

Describe co-operativity in Hb with regards to oxygen binding

A

When oxygen binds to one Hb subunit, the affinity of the other subunits for Hb increases

(This is positive cooperativity)

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11
Q

What is the reason for the sigmoid shape of the oxygen binding curve?

A

The positive cooperativity of Hb due to oxygen binding

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12
Q

Describe the effect of a change in PO2 on %Hb saturation at high PO2 values (e.g. in pulmonary capillaries), and lower PO2 values (systemic capillaries)

A

At a high PO2:

  • A change in PO2 will have a small impact on the %Hb saturation. (Graph is flat)

At lower PO2:

  • A change in PO2 will have a larger impact on the %Hb saturation. (Graph is steeper)
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13
Q

Explain the significance of the fact that, at a lower PO2, a change in PO2 will have a larger impact on the %Hb saturation

A
  • PO2 lower at peripheral tissues

- Smaller change in PO2 required to release the same amount of oxygen from the Hb into the tissues

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14
Q

Describe myoglobin

A
  • Present in skeletal and cardiac muscle
  • One haem group per molecule (1:1 ratio)
  • No cooperative effect
  • Provides short term storage of oxygen for anaerobic conditions
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15
Q

Does myoglobin exhibit a cooperative effect?

A

No

Only has one subunit

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16
Q

Compare the oxygen association/dissociation curves of haemoglobin and myoglobin

A

Haemoglobin:

  • Sigmoid (due to cooperativity)

Myoglobin:

  • Hyperbolic (due to no cooperativity)
17
Q

Describe the structure of foetal haemoglobin (HbF)

A
  • 2 alpha subunits

- 2 Gamma subunits

18
Q

Compare the interactions of HbF and Hb with 2,3-Bisphosphoglycerate (2,3-BPG)

What does this cause?

A

HbF interacts less with 2,3-Bisphosphoglycerate in red blood cells

Thus HbF has a higher oxygen affinity than Hb

19
Q

Compare the sigmoid curves of Hb and HbF

A

HbF has a sigmoid curve that is shifted to the LEFT

This means it has a higher oxygen saturation at a lower PO2

20
Q

Give an example of the significance of the differing oxygen affinities of Hb and HbF

A

Allows maternal Hb to lose oxygen to foetal HbF

21
Q

List changes in environment that would increase the release of oxygen at the tissues (i.e. decrease Hb% saturation)

A
  • PCO2 increase
  • pH decrease ([hydrogen ion] increase)
  • Temp increase
  • 2,3-Bisphosphoglycerate increase
22
Q

List changes in environment that would decrease the release of oxygen at the tissues (i.e. increase Hb% saturation)

A
  • PCO2 decrease
  • pH increase ([hydrogen ion] decrease)
  • Temp decrease
  • 2,3-Bisphosphoglycerate decrease
23
Q

What term describes the shift in Hb oxygen affinity under different environmental conditions?

A

Bohr Shift

due to the Bohr Effect

24
Q

List the 3 ways carbon dioxide is transported in the blood

And give their relative proportions

A
  • Dissolved (10%)
  • Bicarbonate (60%)
  • Carbamino compounds (30%)
25
Q

What determines the amount of carbon dioxide that is dissolved in the blood?

A

The partial pressure of the carbon dioxide gas (PCO2) in equilibrium with the solution

(Henry’s Law)

26
Q

Which is more soluble carbon dioxide or oxygen?

A

Carbon dioxide is roughly 20 times more soluble

27
Q

By which method is the majority of carbon dioxide transported in the blood?

A

As bicarbonate (HCO3)

28
Q

Describe the how bicarbonate is formed in the blood

A
  • In red blood cells
  • Water and carbon dioxide react to form carbonic acid
  • This is catalysed by Carbonic Anhydrase
  • Carbonic acid dissociates into bicarbonate and a proton
29
Q

Which enzyme catalyses the production of carbonic acid as part of the formation of bicarbonate?

A

Carbonic anhydrase

30
Q

Describe the Chloride shift

A
  • In order for more CO2 to diffuse into the cell the equilibrium of bicarbonate formation must shifted
  • By facilitated diffusion bicarbonate ions move out of the RBC into the plasma in exchange for chloride ions
  • Occurs at tissue, the reverse happens at the alveoli
31
Q

Describe how carbamino compounds are formed

A
  • Carbon dioxide reacts with the terminal amine group in blood proteins
  • Especially globin of haemoglobin (forming carbamino-haemoglobin)
  • Very rapid even without enzyme action
32
Q

Describe how is carbamino-haemoglobin HbCO2 formed

A
  • Carbon dioxide reacts with the terminal amine group in the globins (subunits) in haemoglobin
33
Q

How many carbon dioxide molecules can each haemoglobin molecules bind to?

A

4

One for each subunit

34
Q

Describe the Haldane Effect

A

HbO2 –> Hb

Increases the ability of Hb to bind to carbon dioxide and hydrogen ions

(O2 availability governs the binding of CO2 and H+ to Hb)

35
Q

Which 2 effects work together to ensure:

O2 liberation and uptake of CO2 & H+ at tissues

A
  • Bohr Effect

- Haldane Effect

36
Q

Why at the lungs does:

HbCO2 –> Hb + CO2

HbH –> Hb + Hydrogen ion

A

The Hb binds to oxygen with a higher affinity

Haldane Effect

37
Q

Provide an overview of the exchange of oxygen and carbon dioxide at tissue

A
  • Some CO2 is dissolves in plasma, some in the RBC
  • Oxyhaemoglobin releases oxygen, freeing up Hb
  • CO2 binds to form carbaminos (e.g. Carbamino-haemoglobin)
  • Bicarbonate ion formed
  • Bicarbonate ion is moved to the blood plasma during Chloride Shift
  • Free Hb binds to hydrogen ions making HbH
38
Q

Provide an overview of the exchange of oxygen and carbon dioxide at the alveoli

A
  • Carbaminos release their Hb and intracellular dissolved CO2
  • HbH releases its Hb and hydrogen ions
  • Free Hb binds to oxygen, forming oxyhaemoglobin
  • The chloride shift is reversed
  • Bicarbonate ions and freed hydrogen ions form carbonic acid
  • Carbonic acid released CO2
  • Intracellular and extracellular dissolved CO2 –> Alveoli

Y1 - Respiratory (7 decks)

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