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Respiratory System > Session 4 > Flashcards

Session 4 Flashcards

1
Q

What is normal cardiac output at rest?

A

Around 5 litres per minute.

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2
Q

What is normal maximum cardiac output?

A

Around 25 litres per minute.

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3
Q

How many oxygen molecules can Hb bind?

A

4.

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4
Q

How many oxygen molecules can Mb bind?

A

1.

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5
Q

What is the principal function of Mb in respiration?

A

Stores oxygen for use if blood [oxygen] is low.

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6
Q

Describe the dissociation curve of Mb.

A

Rectangular hyperbolic curve: very high affinity for oxygen even at low partial pressures so becomes saturated very quickly.

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7
Q

Why is Mb not useful as an oxygen carrier in the blood under normal resting conditions?

A

Affinity for oxygen is too high and will not give up oxygen until partial pressures are below 5kPa so wouldn’t supply oxygen effectively to tissues.

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8
Q

Briefly describe the structure of Hb.

A

Tetramer of 2 alpha and 2 beta subunits with a haem group attached, can be seen as 2 dimers, each comprising of an alpha and beta subunit.

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9
Q

Describe the T state of Hb.

A

Low affinity for oxygen due to tensile state: ionic and hydrogen bonds constrain the movement of peptide chains, found when no oxygen is bound to the Hb.

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10
Q

Describe the R state of Hb.

A

High affinity for oxygen due to relaxed state: binding of oxygen breaks some ionic and hydrogen bonds so peptide chains have more freedom of movement, more oxygen binding increases R state.

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11
Q

Describe the dissociation curve of Hb.

A

Sigmoidal curve: initially low affinity for oxygen as Hb is in T state; binding of first oxygen molecule brings it more into the R state so affinity begins to increase and saturation increases more quickly; curve flattens when molecules begin to get saturated.

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12
Q

At what partial pressure does Hb become fully saturated? Why is this value significant?

A

Around 9-10kPa, it is much lower than alveolar pO2 (13.3kPa) so Hb is fully saturated when leaving the lungs.

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13
Q

Describe Bohr shift in Hb.

A

Decreased pH causes the Hb dissociation curve to shift to the right so Hb has a lower affinity to oxygen because Hb moves more into the T state. The converse occurs at higher pH values.

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14
Q

What is the significance of Bohr shift in respiration?

A

More metabolically active tissues are at a lower pH so extra oxygen is given up due to the Bohr shift, allowing them to maintain a higher metabolic level.

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15
Q

What is the effect of temperature on Hb dissociation?

A

Increased temperature lowers the affinity of Hb to oxygen: Hb dissociation curve moves to the right. More metabolically active tissues are warmer so more oxygen is offloaded at them.

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16
Q

When might maximum unloading of oxygen occur in the body?

A

When pO2 in tissues can fall to a low level; where increased metabolic activity causes reduced pH and increased temperature.

17
Q

What is the effect of 2-3-BPG on Hb?

A

Causes dissociation curve to move to the right so more oxygen can be offloaded at tissues.

18
Q

When might 2-3-BPG levels increase?

A

Due to anaemia or altitude to allow tissues to be perfused effectively.

19
Q

What happens if carbon monoxide is introduced to the blood?

A

Reacts with Hb to form COHb; increases Hb affinity for O2; O2 isn’t given up at tissues.

20
Q

When is carbon monoxide poisoning fatal?

A

When HbCo levels are above 50%.

21
Q

Why does cyanosis occur?

A

Poor perfusion; deoxygenated Hb is more blue than oxygenated Hb so often blueish periphery/face.

22
Q

Describe pulse oximetry.

A

Detects Hb saturation using red and infrared light but doesn’t detect how much Hb is present.

23
Q

Which type of blood does pulse oximetry analyze?

A

Only pulsatile arterial blood, not tissue blood or non-pulsatile venous blood.

24
Q

What is measured in an ABG?

A

Blood pH, pCO2, pO2, HCO3, O2 sats, electrolytes (Na, K, Cl).

25
Q

Why are there large amounts of CO2 present in arterial blood?

A

Used in blood pH control.

26
Q

What happens when carbon dioxide dissolves in blood?

A

Dissolves in water to form carbonic acid which dissociates into hydrogen ions and carbonate ions. Reversible reaction.

27
Q

What affects the amount of carbon dioxide dissolved in blood?

A

Partial pressure of CO2; directly determined by pCO2 in alveoli which is determined by breathing rate.

28
Q

What is the pH of plasma, why?

A

Alkaline, due to high carbonate ion concentration preventing most of the CO2 from reacting.

29
Q

What is the Henderson-Hasselbach equation used for?

A

Calculating pH.

30
Q

What is the Henderson-Hasselbach equation?

A

pH=pK + log([A-]/[HA])

31
Q

How are high carbonate levels in the blood achieved?

A

RBCs produce hydrogen carbonate using carbonic anhydrase as an enzyme, bicarb produced leaves the RBC via a bicarb-Cl exchanger, hydrogen ions produced are bound to Hb.

32
Q

What factors affect blood pH?

A

Amount of CO2 present (controlled by breathing rate) and amount of bicarb present (controlled by kidney excretion).

33
Q

How is excess acid in the blood buffered?

A

Using hydrogen carbonate which reacts with the acids to produce carbon dioxide. Co2 produced is removed in breathing.

34
Q

Describe the effect of Hb state on hydrogen ion binding, what is the significance of this?

A

T state causes more hydrogen ions to bind. If more H is bound then more bicarb is produced so more CO2 is present in the plasma; when Hb reaches the lungs O2 binds and causes H to be offloaded due to R state so CO2 reforms and is breathed off; ensures adequate CO2 removal from blood.

35
Q

Describe the interactions between CO2 and proteins.

A

Co2 can bind to amine groups on proteins (mainly Hb) to form carbamino compounds; CO2 is then offloaded at the lungs.

36
Q

How is the majority of CO2 transported in the blood?

A

As hydrogen carbonate (60%).

Respiratory System (9 decks)

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