Transport of respiratory gases Flashcards
1
Q
How is O2 transported around the body?
A
- Through red blood cells that contain the oxygen-binding protein haemoglobin
2
Q
Explain the structure and adaptations of haemoglobin.
A
- Composed of 4 polypeptide chains and 4 heme groups
- Quaternary structure
- Contains prosthetic group (iron) to hold the structure together
- It can carry 4 O2 molecules and 1 CO2
- O2 binds to the heme group
- Depending on the surrounding O2 concentration, it can pick up or drop off O2
3
Q
Explain the affinity for oxygen.
A
- As O2 molecules bind to the haemoglobin, the more the shape of the haemoglobin is changed
- This makes the binding easier, more likely to gain O2 (high affinity)
- The haemoglobin will have a higher affinity for O2 in a O2-rich environment, promotes oxygen loading
- In a low O2 environment (body tissues) haemoglobin has a lower affinity for oxygen
4
Q
Why does the affinity decrease when there are less O2 molecules binded to the haemoglobin?
A
- When the haemoglobin drops off the O2 at a cell, it no longer wants to bind to the O2, since it is now needed by the cell
- The more oxygen is present, the more it wants to bind (e.g. in the lungs)
- The haemoglobin must be full
5
Q
What does an oxygen dissociation curve show?
A
- The relationship between oxygen levels (as partial pressure) and O2 % saturation of haemoglobin
- The O2 % saturation of haemoglobin says how many haemoglobins are full of O2
- The partial pressure: the more O2 the higher the pressure
- Look curve from right to left
- When the haemoglobin moves through the body, the concentration (partial pressure) decreases because the O2 is needed by the tissues
- The % saturation decreases too, most O2 used up
6
Q
What is foetal haemoglobin and its trend in the curve?
A
- Inside a fetus
- O2 binds with a higher affinity (high O2 environment) because foetal haemoglobin will load O2 when adult haemoglobin is unloading it in the placenta
- At lower partial pressures, it loses O2 easier than adult haemoglobin
- Has more affinity for O2 than adult
- Rapid dissociation of O2, since its concentration decreases
- Curve is to the left of adult haemoglobin
7
Q
What is adult haemoglobin and its trend in the curve?
A
- Rapid saturation (uptake) of oxygen in lungs
- Rapid dissociation of O2 as its concentration decreases
- Loses O2 easier, low affinity (low O2 environment)
8
Q
What is Myoglobin and its trend in the curve?
A
- Positioned to the left of the foetal haemo.
- Higher affinity for O2 than adult haemo.
- Only releases O2 when O2 is at very low concentrations in tissues (found in muscles)
- Hangs onto O2 longer than normal
- Tertiary structure, 1 polypeptide (1 heme group)
9
Q
What determines the difference in shape of the adult haemoglobin and myoglobin dissociation curve?
A
- The cooperative effect of four heme groups in haemoglobin
- Haemoglobin has 4 heme groups and myoglobin has 1
- The oxygenation of each haemoglobin chain causes structural changes that increase the afffinity to gain O2
- Myoglobin has a higher affinity to allow it to gain O2 at low partial pressure in the muscles and only release when necessary
10
Q
How do you analyse the oxygen dissociation curve for haemoglobin and myoglobin?
A
- Myoglobin has a higher affinity for oxygen (more likely to take up O2) than adult haemoglobin. Myoglobin takes up O2 at lower levels (normal takes up at high O2 levels)
- It holds on to its supply until levels in the muscles are very low
- The delayed released helps slow the inset of anaerobic respiration and lactic acid formation during exercise
11
Q
How is CO2 transported around the body?
A
- Its a waste product and diffuses out of the cell.
- Small amounts are dissolved in the plasma
- Some binds with haemoglobin in the erythrocyte (RBC) to form HbCO2
- 70% of CO2 is transformed in RBC into hydrogen carbonate ions
12
Q
How is CO2 converted into carbonic acid?
A
- CO2 enters the RBC and reacts with water. This reaction is catalysed by carbonic anhydrase to form carbonic acid H2CO3-
- Carbonic acid dissociates into H+ ions and hydrogen carbonate ions (HCO3-) a.k.a bicarbonate ions
See reactions in boook
13
Q
How do hydrogen carbonate ions affect the pH? What does the chloride shift do?
A
- The HCO3- decreases the pH (more acidic). This increases breathing rate to remove the CO2
- The H+ ions in the RBC (erythrocyte) make the environment more acidic, causes haemoglobin to release its O2
- The bicarbonate leaves the RBC to enter the plasma. To balance the electric charge, Cl- ions enter the RBC by diffusion (chloride shift)
- Plasma proteins maintain the pH range, they act as buffers
14
Q
What is the optimal pH range?
A
- 7.35-7.45
15
Q
What effect do plasma proteins have?
A
- They act as buffers to resist change to pH by removing excess H+ ions (H+ ions make it more acidic)
- Maintains the pH of the blood in a optimal range
- The amino acids have the amine group that may take the H+ ions while the carboxyl group may release H+ ions
