Oxygen in the Blood

Question 1

Why cant myoglobin be used as a oxygen transporter

Answer 1

• Myoglobin has higher affinity than haemoglobin
• Fully saturated at 5kPa of pO2
• Cannot be used as transporter as wont give up oxygen under normal circumstances
• Can act as store in active tissue until oxygen levels low

Question 2

Describe the affinity for oxygen in the tense and relaxed state

Answer 2

• Tense state - low affinity for oxygen

- Relaxed state - high affinity for oxygen

Question 3

When oxygen is low, is haemoglobin in tense or relaxed state

Answer 3

• When pO2 is low, haemoglobin in tense state

- Hard for first oxygen molecule to bind but becomes easier later on

Question 4

State the values of alveolar and capillary pO2

Answer 4

• Alveolar pO2 = 13kPa

- Capillary pO2 = 5kPa

Question 5

State the axis of a oxygen-haemoglobin dissociation graph

Answer 5

• Saturation (%) over pO2 (kPa)

Question 6

Describe the effects on the haemoglobin oxygen dissociation curve for a fall in pH

Answer 6

• Acidic condition shifts oxygen dissociation curve to the right
• Decrease in pH promotes tense state as pO2 decreases
• Increase in pH promotes relaxed state
• pH is lower in more metabolically active tissue, so more oxygen is given up

Question 7

Describe the effects on the haemoglobin oxygen dissociation curve for a rise in temperature

Answer 7

• Increase in temperature shifts dissociation curve to the right
• Metabolically active tissue have slightly higher temperature so give up extra oxygen

Question 8

Describe the effects on the haemoglobin oxygen dissociation curve for a rise in 2,3 DBG

Answer 8

• 2,3-Bisphosphoglycerate increase shifts curve to right
• Levels increase with anaemia or high altitude
• Allows more oxygen to be given up by the curve

Question 9

Describe the effects on the haemoglobin oxygen dissociation curve during exercise

Answer 9

• Exercise shifts curve to the right
• Within the whole body, about 27% of oxygen is given up
• In extreme exercise, metabolism can increase x10 but cardiac output only can increase x5
• Improved extraction of oxygen by tissues needed

Question 10

Describe the effect of carbon monoxide on haemoglobin

Answer 10

• Carbon monoxide poisoning reacts with haemoglobin to form COHb
• Increases affinity of unaffected subunits for oxygen
• Therefore wont give up oxygen at the tissues
• Fatal if COHb > 50

Question 11

Define cyanosis and explain its types

Answer 11

• Cyanosis - bluish colouration due to unsaturated haemoglobin
• Deoxygenated haemoglobin is less red than oxygenated haemoglobin
• Can be peripheral (hands and feet) due to poor local circulation
• Can be central (mouth tongue, lips, mucous membranes) due to poorly saturated blood in systemic circulation
  - Due to congenital heart defects where right to left shunt causes deoxygenated blood to leave the aorta

Question 12

Distinguish between hypoxia and hypoxaemia

Answer 12

• Hypoxaemia - low pO2 in arterial blood
• Hypoxia - low oxygen levels in tissues
• Hypoxaemia can cause hypoxia

Question 13

Outline how haemoglobin saturation can be measured

Answer 13

• Pulse oximetry
  
  • Detects level of haemoglobin saturation - measures oxygen sats
    
    • Detects difference in absorption of light between oxygenated (red) and deoxygenated (blue) haemoglobin
  • Only detects pulsatile arterial blood
  • Doesn’t say how much haemoglobin present
• Arterial blood gas analysis
  - Requires arterial blood sample - radial artery

Question 14

Explain the difference between oxygen saturations (‘Sats’) partial pressure of oxygen PaO2 and oxygen content of blood

Answer 14

• Oxygen saturation - % of oxygen-saturated haemoglobin relative to total haemoglobin
• Partial pressure - pressure exerted by oxygen in blood
• Oxygen content - amount of oxygen in blood