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Kofi: Pure Clinical Sem 3 > Resp: Oxygen Exchange > Flashcards

Resp: Oxygen Exchange Flashcards

1
Q

What are the features of oxygen binding?

A
  • Reaction has to be reversible
  • Oxygen must dissociate at the tissue to supply them
  • Oxygen combines reversibly
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2
Q

What are 2 examples of oxygen binding pigments?

A
  • Haemoglobin: Tetramer to bind 4 oxygen molecules

- Myoglobin: binds 1 oxygen molecule

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3
Q

What is myoglobin?

A
  • Pigment found in muscles

- Contains 1 subunit of haem

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4
Q

Why is myoglobin not a good carrier of oxygen?

A
  • It will not give up oxygen at the tissues due having a high affinity for oxygen even at low partial pressure.
  • It acts as a storage molecule that will give up oxygen if the oxygen in the tissue gets very low. Also acts as a pigment for the muscle giving it the red appearance
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5
Q

What is the structure of haemoglobin?

A
  • Tetramer consisting of 2 alpha and 2 beta subunits
  • Each subunit has a haem group and a globin group
  • 4 oxygen molecules bind to each molecule of haemoglobin
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6
Q

What are the forms of haemoglobin?

A
  • Low affinity T state

- High affinity R state

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7
Q

What happens to haemoglobin when the pO2 is low?

A

The haemoglobin shift to the low affinity T state so it is harder for the first O2 molecule to bind

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8
Q

What happens as each O2 molecules bind to the haemoglobin?

A

The molecule becomes more relaxed and the binding of the next O2 molecule is easier

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9
Q

What is the shape of the haemoglobin dissociation curve?

A

Sigmoidal curve

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10
Q

What are the features of the haemoglobin dissociation curve?

A
  • Saturation changes greatly over a narrow range

- Reaction is highly reversible and depends on pO2 levels

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11
Q

What happens to the oxygen content and pO2 if the patient is anaemic?

A
  • pO2 is normal

- Oxygen content is much lower

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12
Q

What is the oxygen content of blood when the haemoglobin is saturated (13.3 kPa)?

How would you work out the amount of oxygen given up?

A

-2.2 mmol/l if the Hb concentration is normal

Each haemoglobin bind 4 oxygen molecules
2.2X4 = 8.8 mmol/l

Amount of oxygen given up = ((100 - Saturation at Partial pressure in the site)/100) X 8.8

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13
Q

What happens to the dissociating at tissue with a lower pO2 and the result of this on venous blood?

A
  • Increased dissociation

- Lower saturation of venous blood

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14
Q

What is the saturation of haemoglobin in venous blood?

A

-Over half the oxygen is still bound

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15
Q

What is the adaptation of very metabolically active tissue to allow them to receive sfficnet oxygen?

A

Very high capillary density so that pO2 will fall lower due to decreased diffusion distance

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16
Q

What is the Bohr effect?

A
  • pH affects the affinity of haemoglobin
  • Acid condition shifts dissociation curve to the tight
  • Lower pH promotes gift to the T state and higher ph promotes a shift to the R state
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17
Q

Why is the Bohr effect beneficial to the metabolically active tissues?

A

-pH is lower in most metabolically active tissue so extra O2 is given up

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18
Q

What is maximum unloading of oxygen?

A
  • Occurs in tissues where pO2 can fall to a low level
  • In conditions where increased metabolic activity results in more acidic environment and higher temperature
  • Under these conditions about 70% bound oxygen can be given up
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19
Q

In extreme exercise , metabolism can increase 10x but the cardiac output only goes up by 5x. What supplies the tissues with oxygen?

A

Tissues have improved extraction of oxygen.

This is due to a number of factors

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20
Q

What is the function of 2,3 BPG?

A

Increased 2,3-BPG shift the Hb dissociation curve for O2 to the right
This allows more O2 to be given up to tissues because of a shift in the curve

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21
Q

What is the result of carbon monoxide poisoning?

A
  • Reacts with Hb to form COHb
  • Increased affinity for unaffected subunits for O2
  • Therefore O2 is not given up at tissues
  • This is fatal if the HbCO is greater than 50%
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22
Q

What is hypoxaemia?

A

Low pO2 in arterial blood

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23
Q

What is hypoxia?

A

Low oxygen levels in the body and tissues

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24
Q

What is cyanosis?

A
  • Bluish coloration due to unsaturated haemoglobin

- Can be peripheral due to poor local circulation or systemic due poorly saturated blood in systemic circulation

25
Q

Why is cyanosis difficult to detect sometimes?

A
  • Poor lighting

- Skin colouration

26
Q

What is pulse oximetry?

A
  • Detection of level of Hb saturation by detection of difference in absorption of light between oxygenated and deoxygenated Hb
  • It only detect the pulsatile arterial blood
  • Venous blood and blood in tissues is ignored
27
Q

What is the limitation of pulse oximetry?

A
  • It doesn’t say how much haemoglobin is present

- It will not detect anaemia but just how well saturated a person blood is

28
Q

Why does cyanosis appear blue?

A

-Deoxygentated haemoglobin is less red that oxygenated haemoglobin

29
Q

What are the features of carbon dioxide when compared with oxygen

A

It is more soluble
It reacts chemically with water
React with haemoglobin as well at a different site
2.5 times as much in arterial blood

30
Q

CO2 control is more important for pH than for transporting it from the tissues to the lungs. True/False

A

True

31
Q

What is the pH range that arterial blood must be kept in?

A

7.35-7.45

32
Q

How does CO2 interact with arterial blood?

A
  • Reacts with water in plasma to form carbonic action
  • Reacts with water in red blood cells.
  • It is not there as a waste product
33
Q

What happens to carbonic acid in the blood?

A

Dissociates quickly to hydrogen ions and hydrogen carbonate ions.

34
Q

The reaction that form carbonic acid from CO2 and water is irreversible. True/False

A

False. It reversible and rate of reaction depends on amount of reactants and products

35
Q

What does the pH of plasma depend on?

A

-Depends on how much CO2 reacts to form H+ (dissolved CO2 pushes the reaction to the right and HCO3- pushes the reaction to the left)
This depends on dissolved CO2 and concentration of hydrogen carbonate

36
Q

What determines how much CO2 dissolved in the plasma?

A

-Partial pressure of CO2

37
Q

What happens to plasma pH when pCO2 rises?

A

Becomes more acidic

38
Q

What happens to the plasma pH when the pCO2 falls?

A

It will become more alkaline

39
Q

What is the determining factors for dissolved CO2?

A

pCO2 of alveoli which is controlled by rate of breathing

40
Q

What does high HCO3- prevent from happening in the blood?

A

Prevent nearly all dissolved CO2 from reacting by shifting the equilibrium

41
Q

What determines the pH of arterial blood?

A

Ratio of HCO3- and pCO2.

42
Q

What is the Henderson-Hasselbalch equation?

A

pH=pK+log([HCO3-])/(pCO2 X 0.23))

43
Q

What enzyme speeds up the reaction that speeds up hydrogen carbonate production in red blood cells?

A

Carbonic anhydrase

44
Q

How do the red blood cells produce hydrogen carbonate?

A
  • H+ ions bind to the negatively charged Hb inside the red blood cells
  • Chloride-bicarbonate exchanger transports HCO3- out of red blood cells which is left front he reaction between CO2 and H2O.
45
Q

Eythrocytes control concentration of HCO3- in plasma. True/False

A

False. They merely produce HCO3-.

46
Q

What determine the amount of HCO3- that is produced by the erythrocytes?

A

Binding of H+ to haemoglobin

47
Q

What is the main determant of plasma hydrogen carbonate? pCO2 or erythrocytes ?

A

Most of the HCO3- comes from the red blood cells

48
Q

What is the role of the kidney in controlling HCO3-?

A

The kidney controls the amount of HCO3- by varying the excretion of bicarbonate. Concentration present in blood is controlled by the kidneys

49
Q

How does hydrogen carbonate buffer extra acid?

A

Acids react with HCO3- to produce CO2. Therefore the bicarbonate decreases.
CO2 produced is removed by breathing and pH changes are minimised

50
Q

What determine arterial pCO2?

A

Alveolar pCO2 which determine how much CO2 is dissolved. This therefore affects pH.

51
Q

pCO2 is higher in venous blood than arterial blood. True/false

A

True. It is returning from metabolically active tissue so more CO2 is dissolved

52
Q

What does the buffering of H+ by the haemoglobin depend on?

A

Level of oxygenation

53
Q

What happens to the amount of H+ ions that can bind to Hb as more O2 binds to Hb?

A

The haemoglobin switches into the R state

-Less H+ ions bind as a result

54
Q

What happens to the amount of H+ ions that can bind to Hb as less O2 binds to Hb?

A

The haemoglobin switches to the T state

-More H+ ions bind

55
Q

How does the amount of CO2 increase in plasma in the venous system?

How does this affect the pH?

A
  • Less O2 bound to Hb so haemoglobin switches to the T state
  • More H+ ions bind to Hb
  • More HCO3- can be produced and is exported to the plasma
  • Therefore more CO2 is present in plasma in venous system.

-More HCO3- is also present so therefore ratio is similar. Small change in plasma pH as both CO2 and HCO3- have increased

56
Q

What happens when venous blood arrives at the lungs?

A
  • Hb picks up O2 and goes into R-state
  • Causes Hb to give up the extra H+ it took on at the tissues
  • H+ reacts with HCO3- to form CO2
  • CO2 is breathed out
57
Q

How are carbamino compounds formed?

A
  • CO2 binds directly to amine groups on the globulin on Hb.
  • This contribute to the CO2 transport but it is not part of the acid base balance
  • This is CO2 given up at the lungs
58
Q

Why are more carbamino compounds formed at the tissues?

A

-The pCO2 is higher and unloading of oxygen facilitates binding of CO2 to haemoglobin

59
Q

What are the forms that CO2 is transported in?

A
  • Dissolved CO2
  • Hydrogen carbonate
  • Carbamino compounds

Kofi: Pure Clinical Sem 3 (44 decks)

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