The transport of oxygen and carbon dioxide 3.2.7, 3.2.8 Flashcards
How is oxygen transported throughout the body?
By erythrocytes (red blood cells), within the protein haemoglobin.
State 4 features of erythrocytes and explain how these are adapted to their function.
- Flattened, biconcave disc shape; ensures a large surface area for efficient gas exchange
- Large amount of haemoglobin; for transporting oxygen
- No nucleus or organelles; maximises space for haemoglobin so more oxygen can be transported
- Diameter of 6-8 micrometers; very small to enable fast diffusion of oxygen
Describe the structure of haemoglobin
A complex protein with a quaternary structure - meaning it has 4 subunits which consist of a polypeptide chain and a ham group.
What is the function of the haem group in haemoglobin?
It attracts and holds 1 oxygen molecule - and consists of a single iron ion.
This means 8 oxygen atoms (4 molecules) can bind to each haemoglobin.
Where is oxygen loaded into haemoglobin?
In areas of high concentration (partial pressure), for example the alveoli
Where is oxygen unloaded from haemoglobin?
In areas of low concentration (partial pressure), for example muscle cells
What does affinity mean?
Attraction
What is the saturation of haemoglobin measured in?
Percentage (%) - 100% being fully saturated
What is the saturation of oxygen in haemoglobin at the lungs?
95-97% saturation
What is the saturation of oxygen in haemoglobin at respiring tissues?
Only 20-25% saturation
Why does haemoglobin not readily associate with oxygen molecules at low oxygen tension?
As haem groups are in the centre and difficult for the oxygen to get to with a low diffusion gradient.
Why does haemoglobin then readily associate as oxygen tension increases?
Due to a conformational change occurring in haemoglobin as one oxygen molecule enters and associates - which allows more oxygen to enter and associate relatively easily.
Why does the oxyhemoglobin dissociation curve level off in an S shape?
Due to the positive cooperativity of haemoglobin, allowing more molecules of oxygen to bind with haemoglobin until reaching the maximum concentration.
How does foetal haemoglobin differ from adult haemoglobin?
Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin does
How is foetal haemoglobin’s high affinity for oxygen beneficial?
As it helps to maximise oxygens uptake from the mothers blood stream, which has already lost some of its oxygen by the time it reaches the placenta.
How is carbon dioxide transported?
- Dissolved in plasma
- Carbaminohaemoglobin
- Carbonic acid / hydrogen carbonate ions
How are hydrogen carbonate ions formed?
- CO2 diffuses into RBC’s
- It combines with water to form carbonic acid, which is catalysed by carbonic anhydrase
- Carbonic acid dissociates to release hydrogen ions and hydrogen carbonate ions
- These diffuse out of the RBC’s into the plasma
- The charge inside the RBC is maintained by the movement of chloride ions from the plasma - the chloride shift.
What is haemoglobinic acid?
Hameoglobinic acid helps to reduce acidity inside the red blood cells, and it is formed when hydrogen ions associate with haemoglobin to produce haemoglobinic acid.
What is the effect of increasing carbon dioxide concentration?
When more CO2 is present, haemoglobin becomes less saturated with oxygen.
More carbonic acid = more hydrogen ions = increased acidity = change in protein shape = reduced affinity = more oxygen release
Describe the Bohr effect
It describes the affect of high carbon dioxide concentration on haemoglobin affinity for oxygen
