Gas transport and acid-base balance

Question 1

What is oxygen content, binding capacity and haemoglobin saturation?

Answer 1

• Total O2 content in the blood is 200mL
○ 197mL in haemoglobin (98.5%) and 3ml in blood (1.5%)
○ O2 is less soluble than CO2 therefore less O2 can l=dissolve into the blood (little O2 dissolved in blood).
• Binding capacity is the maximum amount of oxygen that can be bound to haemoglobin
○ Anaemia ( lack of haemoglobin) will decrease the binding capacity
○ Haemoglobin concertation varies with age and gender
• Haemoglobin saturation is the % of haemoglobin binding sites that are occupied with oxygen.
○ At 12kPa in alveoli most haemoglobin is occupied
○ Haemoglobin= (O2 bound to Haemoglobin/o2 binding capacity)x100
○
○ The graph is sigmoidal because- The shape of hemoglobin changes after the 1st binding of O2- binding sites are closer to the outside so O2 can associate more easily. Increased affinity/attraction for O2 as more hemoglobin is binds to O2. As you drop an O2 the affinity decreases (opposite of increased affinity process). So forms sigmoidal curve
○ Affinity of O2 increases as hemoglobin binding sites become occupied
○ The graph is sigmoidal because- The shape of haemoglobin changes after the 1st binding of O2- binding sites are closer to the outside so O2 can associate more easily
The graph is sigmoidal because- The shape of haemoglobin changes after the 1st binding of O2- binding sites are closer to the outside so O2 can associate more easily

Question 2

How is O2 transported in the blood? (talk about opposite of chloride shift)

Answer 2

• What happens inside the red blood cell when O2 enters
○ O2 from alveoli binds enters the red blood cell (RBC) and binds with hemoglobin
○ The oxygenation of hemoglobin promotes the release of H+ through the dissociation of hemoglobin
▪ This increases the H+ concertation/acidity in the RBC
○ HCO3- enters the RBC
▪ HCO3- is exchanged for Cl- to maintain the negative charge inside the RBC
○ H+ binds to HCO3- to form H2CO3 to neutralise the H+/acid
○ H2CO3 disassociates into H2O and CO2 ( the CO2 is breathed out)

Question 3

What factors affect the affinity of haemoglobin for O2 in the lungs and tissues?

Answer 3

• Right shift of curve (Bohr effect)
○ At tissues there is a higher concentration of CO2 so more H+ ( due to H2CO3). See Bohr effect
▪ Haemoglobin has a higher affinity for H+ than O2 so O2 is unloaded and H+ is loaded at respiring tissue. Tissue also respire anaerobically which increases this more. A higher concentration of CO2 causes the dissociation curse to shist to the left (decreased affinity for O2)
▪ Wants to give up O2 for respiratory tissue and making room for CO2
○ Affinity for O2 decreased due to increased: acidity, temperature, 2,3-DPG and increased metabolism
• Left shift due to decreased of acidity, temperature, 2,3-DPG and increased metabolism (O2 affinity increase)
○
• CO has a greater affinity to hemoglobin than O2 does therefore will displace O2
• At 0.1% Co % 50% of binding sites are occupied with CO
○ Increased affinity for remaining O2 so difficult to disassociated
○ Because Co is only 0.1% the O2 partial pressure is the same in blood so can’t detect it in the body
• CO binds irreversibly with haemoglobin so O2 can associate

Question 4

How is CO2 transported in the blood? (chloride shift)

Answer 4

• 30% bound to hemoglobin and other proteins (147ml)
○ CO2 reacts with amino groups in proteins especially Hb
○ Forms carbanion compounds and releases a H+ which increases the acidity
○
• 10% dissolves in blood (49ml)
○ CO2 is more soluble than O2 so more CO2 dissolved into blood
• 60% forms HCO3- (294ml)
• Total= 490ml which raises to 540ml in venous blood
○ CO2 + H2O -> H2CO3 (catalysed by carbonic anhydrase)
○ H2CO3 -> H+ + HCO3- (H2CO3 dissociation)
○

Question 5

Explain the chloride shift.

Answer 5

○ After H2O and CO2 reacts to form H+ and HCO3- the RBC acidity is increased
○ The HCO3- exits the RBC and is exchanged with Cl- ( to maintain charge)
○ HCO3- is now in the blood and reacts with Na+ to form NaHCO3
○ The free H+ binds to hemoglobin to dissociate the O2.
○ Acidity in RBC is neutralised and O2 has been unloaded to respiring tissue
○ Chloride bicarbonate exchange = chloride shift
○ Increased CO2 in blood which is breathed out
○

Question 6

What factors affect the CO2 content in the blood?

Answer 6

• Metabolic rate
• Temperature
• Ventilation rate ( more breathing gets rid of more CO2)

Question 7

Explain the Bohr and Haldane effect in the lugs and tissues and how they work together.

Answer 7

• Bohr effect: an increase of CO2 makes the affinity for O2 weaker. O2 is more readily unloaded from Haemoglobin . More O2 is released to make space for CO2
• Haldane effect = increase CO2 carrying capacity of Hb due to the Bohr effect. More CO2 in blood at venous vessels.

Question 8

How are H+ buffered to maintain a pH (emphasis the carbonic system).

Answer 8

• H+ reacts with heamoglobin
• Reacts with plasma proteins
• Reverse formation of H2CO3 to produce CO2 ( most important)
○ HCO3- enters the RBC (via exchange with Cl-) and reacts with H+ to form H2CO3
○ H2CO3 dissociates into H2O and CO2
CO2 concentration in blood increases and CO” is breathed out

Question 9

What is acidosis and how is blood pH maintained after this?

Answer 9

• Too much H+
• Kidneys can send in more HCO3- to neturalise the acid
○ H+ and HCO3- react to form H2O and CO2
• CO2 and H2O created
• Too many H+ increases CO2 levels and increases respiration to remove CO2 (trying to use up)
• if metabolic acidosis respiratory system will compensate by increasing ventilation rate to remove more CO2 this will drive the equilibrium position towards the CO2 side to produce more CO2 will be breathed out
• Is respiratory problem (hypoventilation) kidneys will compensate by secreting more H+ into the urine and reabsorbing more HCO3-
Respiratory problem compensated with action in Kidneys ( and reverse)

Compensation = changing not correcting the problem ( eg problem in lungs causes a change in the kidneys)

• Drug A will cause a bigger effect as the respiratory System removes removes CO2 faster than kidneys remove H+ into kidneys
• Lungs are more effective at compensating for acidosis (100x more efficient than kidneys)
• Lungs are quicker to respond

Question 10

What is alkalosis and how is blood pH maintained after this?

Answer 10

• Not enough H+
• if metabolic alkalosis respiratory system will compensate by decrease ventilation rate to remove less CO2 this will drive the equilibrium position towards the H+ side to produce more H+ and less CO2 is breathed out will be breathed out
• Is respiratory problem (hyperventilation) kidneys will compensate by retaining H+
• Kidneys can send in H+ to increase concentrations of acid
Reduced breathing/ respiratory frequency removes CO2 slower so more CO2 remains in blood.