Session 4 Flashcards
(36 cards)
What is normal cardiac output at rest?
Around 5 litres per minute.
What is normal maximum cardiac output?
Around 25 litres per minute.
How many oxygen molecules can Hb bind?
4.
How many oxygen molecules can Mb bind?
1.
What is the principal function of Mb in respiration?
Stores oxygen for use if blood [oxygen] is low.
Describe the dissociation curve of Mb.
Rectangular hyperbolic curve: very high affinity for oxygen even at low partial pressures so becomes saturated very quickly.
Why is Mb not useful as an oxygen carrier in the blood under normal resting conditions?
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.
Briefly describe the structure of Hb.
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.
Describe the T state of Hb.
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.
Describe the R state of Hb.
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.
Describe the dissociation curve of Hb.
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.
At what partial pressure does Hb become fully saturated? Why is this value significant?
Around 9-10kPa, it is much lower than alveolar pO2 (13.3kPa) so Hb is fully saturated when leaving the lungs.
Describe Bohr shift in Hb.
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.
What is the significance of Bohr shift in respiration?
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.
What is the effect of temperature on Hb dissociation?
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.
When might maximum unloading of oxygen occur in the body?
When pO2 in tissues can fall to a low level; where increased metabolic activity causes reduced pH and increased temperature.
What is the effect of 2-3-BPG on Hb?
Causes dissociation curve to move to the right so more oxygen can be offloaded at tissues.
When might 2-3-BPG levels increase?
Due to anaemia or altitude to allow tissues to be perfused effectively.
What happens if carbon monoxide is introduced to the blood?
Reacts with Hb to form COHb; increases Hb affinity for O2; O2 isn’t given up at tissues.
When is carbon monoxide poisoning fatal?
When HbCo levels are above 50%.
Why does cyanosis occur?
Poor perfusion; deoxygenated Hb is more blue than oxygenated Hb so often blueish periphery/face.
Describe pulse oximetry.
Detects Hb saturation using red and infrared light but doesn’t detect how much Hb is present.
Which type of blood does pulse oximetry analyze?
Only pulsatile arterial blood, not tissue blood or non-pulsatile venous blood.
What is measured in an ABG?
Blood pH, pCO2, pO2, HCO3, O2 sats, electrolytes (Na, K, Cl).
