Gas transport - oxygen Flashcards
Describe the structure of haem.
A porphyrin ring with an iron (Fe2+) ion at its centre
Which elements are present in the porphyrin ring of haem?
Carbon
Hydrogen
Nitrogen
What colour is haem when it is saturated with oxygen?
Red
What colour is haem when it is not saturated with oxygen?
Purple
Describe the structure of haemoglobin.
A tetramer – consisting of 2 alpha and 2 beta globin polypeptide chains
Each subunit of haemoglobin contains what?
A haem group
What are the 2 main conformations that haemoglobin exists in?
Relaxed and tense
How does the binding of oxygen change haemoglobins conformation state and how does this affect oxygen affinity?
Binding of oxygen causes haemoglobin to shift from the tense state to the relaxed state, increasing oxygen affinity and allowing for efficient loading of oxygen in the lungs
What relationship does the oxygen dissociation curve describe?
The relationship between the partial pressure of oxygen in the blood and the amount of oxygen bound to haemoglobin
When haemoglobin becomes saturated, what is the amount of oxygen bound then dependent on?
How much haemoglobin is available
When considering oxygen saturation, it’s important to remember that it is independent of what?
Haemoglobin concentration
Describe the meaning behind the S-shape of the oxygen dissociation curve.
Due to cooperative binding – as one molecule of O2 binds to haemoglobin, haemoglobin’s affinity for oxygen increases, making it easier for subsequent oxygen molecules to bind. This cooperative effect leads to a steep rise in the curve after the initial binding of O2 and then a plateau as haemoglobin becomes fully saturated
Describe why there needs to be the right balance of partial pressure of oxygen in the tissues (extracellular).
It needs to be low enough to promote oxygen offloading by haemoglobin but high enough to maintain an oxygen gradient between the tissues (extracellular) and cells so that diffusion into cells is not compromised
Which kind of tissues can tolerate greater falls in tissue oxygen partial pressure and why?
Tissues with high capillary density because diffusion is occurring across a shorter distance and higher surface area
Describe the affinity of haemoglobin for oxygen as the oxygen dissociation curve shifts left and right.
Right shift – decreased affinity
Left shift – increased affinity
List 4 things which shifts the oxygen dissociation curve to the right.
Increased temperature
Increased partial pressure of carbon dioxide
Decreased pH (increased acidity)
Increased 2,3-DPG
List 4 things which shifts the oxygen dissociation curve to the left.
Decreased temperature
Decreased partial pressure of carbon dioxide
Increased pH
Decreased 2,3-DPG
Which kind of tissues will have acidic / low pH conditions?
Metabolising tissues
Describe when 2,3 diphosphoglycerate is produced, how it affects haemoglobins affinity for oxygen and how it does this.
2,3-DPG is produced by red blood cells in response to hypoxia. It decreases haemoglobins affinity for oxygen, therefore facilitating offloading, and it does this by stabilising its tense state
What is the Bohr effect?
Haemoglobins affinity for oxygen decreases in response to lower pH and higher concentrations of carbon dioxide
In regards to the Bohr effect, how does low pH and higher concentrations of carbon dioxide decrease haemoglobins affinity for oxygen?
The binding of hydrogen ions and carbon dioxide stabilises haemoglobin in the tense state
How does increasing tissue metabolism affect tissue pH?
Tissue pH decreases progressively with increasing metabolism due to increased production of lactic acid and carbon dioxide
