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Semester 3 > Resp Session 4 > Flashcards

Resp Session 4 Flashcards

1
Q

What are the two respiratory pigments used to carry oxygen and what in their structure allows them to do this?

A

Myoglobin and haemoglobin which both contain haem groups that can combine reversibly with O2

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2
Q

What is myoglobin?

A

Monomer present in myocytes which gives them their red colour

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3
Q

What is haemoglobin?

A

Tetramer (2 alpha and 2 beta subunits) present in blood which gives it its red colour

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4
Q

How do the two different states of haemoglobin vary?

A

T state has low affinity for oxygen

R state has high affinity for oxygen

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5
Q

Does the dissociation curve for either myoglobin or haemoglobin tell you how much of oxygen is present?

A

No, they do not show how much of either pigment is present

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6
Q

Why is myoglobin good for oxygen storage in cells of active tissues?

A

It is fully saturated at 5 kPa and half saturated at 1 kPa so is fully saturated at arterial pO2 and doesn’t released oxygen until pO2 drops significantly

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7
Q

What causes the sigmoidal shape of the haemoglobin binding curve?

A

Co-operative binding

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8
Q

Describe Hb in the arterial blood leaving the lungs.

A

Alveolar pO3 ~13.3 kPa so Hb is well saturated and carries four O2, therefore at Hb=2.2 mmol per litre, oxygen content is 8.8 mmol per litre

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9
Q

How is pO2 and oxygen content affected by anaemia?

A

If anaemic pts have normally functioning lungs, pO2 is normal but oxygen content is low

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10
Q

What usually happens to Hb saturation in the tissues?

A

Decreases to 65% but this depends on the pO2 of the tissue determined by its metabolic activity

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11
Q

What saturation does mixed venous blood have and when is this altered?

A

> 50% but will decrease if tissue pO2 is lowered

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12
Q

What determines how low tissue pO2 can get?

A

Needs to be high enough to drive oxygen diffusion to cells so in most tissues cannot fall below 3 kPa
Increased capillary density allows tissue pO2 to fall lower

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13
Q

What is the capillary density of cardiac muscle?

A

Each myocyte has its own capillary

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14
Q

What effect does increasing pH have on haemoglobin?

A

Causes it to adopt R state

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15
Q

Why does decreasing pH cause Hb to adopt its T state?

A

H+ ions bind voraciously causing it to change shape and promote oxygen dissociation

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16
Q

Why is Bohr shift favourable?

A

pH is lowest in most metabolically active tissues due to carbonic, lactic and sulphuric acid production so ensures oxygen delivery to tissues with highest demand

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17
Q

What is the effect of increasing temperature on Hb?

A

Shifts dissociation curve to R as it promotes oxygen dissociation

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18
Q

What is the benefit of the action of increasing temperature on oxygen dissociation from Hb?

A

Metabolically active tissues have a slightly higher temperature so extra oxygen can be released to meet higher demands

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19
Q

What percentage increases in oxygen dissociation is seen with the Bohr shift?

A

50%

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20
Q

What is maximum unloading?

A

Where ~70% of oxygen can be given up in tissues with extremes metabolic rates that can tolerate low pO2 and have an environment which is more acidic and higher temperature

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21
Q

Why is there an oxygen reserve in mixed venous blood?

A

So cardiac output doesn’t have to change as much if the demand for oxygen dissociation from the mixed blood rises above the ~27% usually dissociated

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22
Q

When do levels of 2,3-BPG increase in the RBCs?

A

Anaemia

Altitude

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23
Q

What is the action of 2,3-BPG on Hb?

A

Changes how it behaves so dissociation curve becomes more of a rectangular hyperbola

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24
Q

How is 2,3-BPG synthesised?

A

Shunt in the glycolytic pathway

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25
Q

How does carbon moodier exposure lead to decreased oxygen transport?

A

CO+Hb–> carboxyhaemoglobin and this increases the affinity of unaffected subunits for oxygen therefore it is not released at the tissues

26
Q

When does carbon monoxide poisoning become fatal?

A

If HbCO >50%

27
Q

What is cyanosis?

A

Bluish colouration due to unsaturated Hb close to the skin

28
Q

What causes peripheral cyanosis?

A

Poor local circulation

29
Q

What causes central cyanosis?

A

Poorly saturated blood in systemic circulation

30
Q

How does pulse oximetry measure blood O2?

A

LED emits a range of wavelengths to detect differences in absorption of light between oxygenated and deoxygenated Hb

31
Q

What are the disadvantages of using pulse oximetry to measure blood O2?

A

Only detects pulsatile blood so ignores venous and tissue O2 levels
Doesn’t indicate how much Hb is present so in anaemic pts will paean normal

32
Q

What is the benefit of using ABG to measure blood O2?

A

Can be used to investigate possible causes including acid-base disturbance or electrolyte imbalance

33
Q

What are the disadvantages of using ABB to measure blood O2?

A

Invasive

Very painful

34
Q

When is ABG used to assess blood O2 content?

A

In acutely ill pts with suspected acid-base of electrolyte disturbance (not used for O2 sats alone)

35
Q

What two features does the reaction of oxygen binding need to have in order to allow for effective transport?

A

Reaction must be reversible

Must use molecular oxygen so it can dissociate at tissues and be used

36
Q

Why is there more CO2 present in the plasma than O2?

A

It is more soluble and reacts with water

37
Q

Does CO2 react with Hb?

A

Yes but at a different site to oxygen

38
Q

How does the arterial blood content of CO2 compare to that of O2?

A

2.5x as much CO2

39
Q

What is the main function of CO2 in the blood?

A

Control of blood pH

40
Q

What does the amount of dissolved CO2 on arterial blood depend directly on?

A

pCO2

41
Q

What is the determining factor of the amount of CO2 dissolved in blood?

A

Rate of breathing controlling alveolar pCO2

42
Q

What is the purpose of the high [HCO3-] in the plasma?

A

Stops nearly all dissolved CO2 from reacting so the pH of plasm is alkaline

43
Q

What are most HCO3- associated with in the blood and why?

A

Na+ to stop it becoming too acidic

44
Q

What is the Hendersson-Hasselbalch equation?

A

pH = pK + (log([HCO3-]/(pCO2xsolubility factor))

45
Q

What is the usual ratio of [HCO3-]/dissolved CO2 meaning blood pH is 7.4?

A

20

46
Q

What increases the reaction rate of hydrogen carbonate production in RBCs?

A

Carbonic anhydrase

47
Q

Why does the reversible for HcO3- production in RBCs proceed in the forward direction?

A

Mop of products

48
Q

What does the amount of HCO3- production in RBCs depend on?

A

H+ binding to Hb which depend on O2 binding

49
Q

How are the products of HCO3- production by RBCs removed?

A

HCO3- reacts with lactic, keto and sulphuric acid

CO2 E moved by breathing

50
Q

How does Hb in the RBCs favour HCO3- production?

A

Binds to H+ which removes a product

51
Q

How is HCO3- produced by RBCs?

A

In RBC: CO2+H20 H+ + HCO3-
HCO3- moved out by cotransporter which moves Cl-
HCO3- + H+ H2O and CO2

52
Q

What happens in HCO3- production at tissues?

A

Less O2 on Hb –> Hb in T state so more H+ binds –> more HCO3- can be produced –> more CO2 in plasma due to HCO3- exportation

53
Q

Why is there only a small change in pH between arterial and venous blood despite the relatively large changes in dissolved CO2 and HCO3- amounts?

A

Because both have increased so ratio remains almost constant

54
Q

What happens to Hb on arrival of venous blood at the lung?

A

In R state so gives up extra H+ from tissues which reacts with plasma HCO3- to form CO2 which can be breathed out

55
Q

What role do carbamino compounds have in CO2 transport?

A

CO2 can bind directly to proteins e.g. amine groups on globin of Hb for transport not acid-base balance

56
Q

Why are more carbamino compounds formed at the tissues?

A

pCO2 is higher and O2 unloading from Hb facilitates CO2 to Hb binding

57
Q

Can CO2 in carbamino compounds formed at tissues be breathed out?

A

Yes

58
Q

How do the amounts of CO2 in arterial and venous blood compare?

A

Arterial has less dissolved in plasma, lower [HCO3-] in plasma, less dissolved in RBCs, lower [HCO3-] in RBCs and less carbaminos present

59
Q

How is transported CO2 calculated?

A

Total in venous - total in arterial

60
Q

What proportion of total blood CO2 is transported and where is the rest?

A

Only ~8%, rest is part of pH buffering system

Semester 3 (50 decks)

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