Gas transport - oxygen Flashcards
What kind of ring is haem?
Porphyrin ring
Which 3 elements are present in the porphyrin ring of haem?
Carbon
Hydrogen
Nitrogen
Describe the structure of haemoglobin.
A tetramer – consisting of 2 alpha and 2 beta globin polypeptide chains
What are the 2 main conformations that haemoglobin exists in?
Relaxed
Tense
How does the binding of oxygen to one haem subunit change haemoglobin’s conformation state and how does this affect oxygen affinity?
What is this process known as?
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
Cooperative binding
Describe the affinity of haemoglobin for oxygen as the oxygen dissociation curve shifts left and right.
Left shift – increased affinity
Right shift – decreased 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
When is 2,3 diphosphoglycerate produced?
In what way does it change haemoglobin’s affinity for oxygen?
How does it do this?
2,3-DPG is produced by red blood cells in response to hypoxia
It decreases haemoglobin’s affinity for oxygen, therefore facilitating offloading
Stabilises 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
What is the value of basal oxygen consumption?
250ml / min
How many oxygen molecules can one molecule of haemoglobin bind?
4 oxygen molecules (2 O2s)
Haem has what at its centre?
Iron (Fe2+) ion
Describe haemoglobin’s affinity for oxygen when it is in a relaxed state.
High affinity for oxygen
Describe haemoglobin’s affinity for oxygen when it is in a tense state.
Low affinity for oxygen
The oxygen dissociation curve is S-shaped due to what mechanism?
Cooperative binding
In haemoglobin, what attaches iron to globin?
Histidine
What does the X axis of the oxygen dissociation curve represent?
Partial pressure of oxygen (kPa)
What does the Y axis of the oxygen dissociation curve represent?
Amount of oxygen bound to haemoglobin
At how many kPa of oxygen is haemoglobin 50% saturated?
3.5 kPa
What is the value of alveolar PAO2?
13.3 kPa
What is the value of tissue pO2 at rest?
6 kPa
If the extracellular partial pressure of oxygen became too low, how would this affect diffusion into cells?
Reduce diffusion by means of there being no oxygen concentration gradient for movement from the extracellular space into the intracellular space
Tissues with a high density of what can better tolerate greater falls in tissue pO2?
Give 2 reasons why.
Capillaries
Shorter diffusion distance
Large surface area
Low pH and high temperature shift the oxygen dissociation curve in which direction?
How does this change haemoglobin’s affinity for oxygen?
What is the physiological benefit?
Shifts to the right
Decreases haemoglobin’s affinity for oxygen - it’s more easily offloaded
Metabolising tissues (which have low pH due to lactic acid and high temperature due to respiration) have more oxygen delivered to them
