Lecture 6 - O2 in blood

Question 1

Respiratory pigements

Answer 1

Contain haem which allows O2 to bind

Question 2

Difference between haemoglobin and myoglobin

Answer 2

Haemoglobin:

• found in blood
• tetramer - binds 4 O2
• Sigmoid saturation curve

Myoglobin:

• found in muscles
• monomer - binds 1 O2
• normal saturation curve

Question 3

Saturation curve

Answer 3

Independent of pigment saturation
x axis - percentage saturation
y axis - pO2

Question 4

How to calculate the amount given up

Answer 4

Amount given up = difference in saturation x amount taken up when 100% saturated

(normally 8.8 mmol/L when 100% saturated)

Question 5

Haemoglobin

Answer 5

Tetramer - 2 alpha and 2 beta subunits

Each subunit contains 1 heam and 1 globin

Question 6

T state

Answer 6

Low O2 affinity
Tense state
Difficult to bind first O2 - as each O2 binds it becomes more relaxed and easier to bind
Prefer to unload at low partial pressures
In tissue

Question 7

R state

Answer 7

High O2 affinity 
Relaxed state 
Easy to bind oxygen 
Prefer to load than to unload 
In lungs

Question 8

Hyperventilation

Answer 8

Increasing the po2 in lungs above 13.3 kPa will not increase the O2 content in blood much as Hb 100% saturated (98% of O2 content in blood)

Question 9

Mixed venous blood

Answer 9

Mixture of blood returning from various tissues

IJV
SJV
Coronary veins

Question 10

Metabolically active tissues

Answer 10

Have a high capillary density e.g. heart
Therefore a short diffusion pathway
pO2 can fall lower as less drive to get into cells required

pO2 can’t fall below 3kPa

Question 11

Bohr shift

Answer 11

Metabolically active tissues - acidic condition 
Lower pH 
Decreases O2 affinity 
Promotes T state
More O2 unloaded 
Shifts curve to the right

Question 12

Temperature

Answer 12

Increased temperature shifts the curve to the right
Decreases affinity for O2
More O2 is unloaded

Question 13

Maximum unloading

Answer 13

50 - 70% of bound O2 can be given up

In tissues that are highly metabolically active, have a high capillary density, more acidic and high temperature

Question 14

Exercise

Answer 14

CO increases 5x

5L/min to 25 L/min

Question 15

2,3 - bisphosphoglycerate

Answer 15

Shifts curve to the right
Increased concentration in anaemic patients and at high altitude
Normally 5mM
Allows more O2 to unload
2,3 bisphosphoglycerate levels drop in stored blood due to refrigeration

Question 16

Carbon monoxide poisoning

Answer 16

CO reacts with Hb and tightly binds to form COHb
Increased infinity for O2 in unaffected subunits
Less O2 is unloaded
Fatal if 50+% COHb

Question 17

Hypoxaemia

Answer 17

Low O2 in arterial blood

Question 18

Hypoxia

Answer 18

Low O2 in body or tissues

Not all the Hb will be saturated

Question 19

Hypovolemic shock

Answer 19

Reduce blood flow
Peripheral vasoconstriction
Peripheral hypoxia

Question 20

Tissues using O2 faster than delivered

Answer 20

Peripheral arterial disease

Raynaud’s

Question 21

Cyanosis

Answer 21

Bluish discolouration due to unsaturated Hb
Peripheral or central
Due to cardiac defect or mixing of oxygenated and deoxygenated blood

Question 22

Pulse oximetry

Answer 22

Detects pulsatile arterial blood saturation

Oxygenated and deoxygenated haemoglobin absorb different wavelengths of light.

Oxgenated Hb appears redder as absorbs red less.

Doesn’t say how much Hb present

Question 23

Advantages of pulse oximetry

Answer 23

Quick
Easy
Non invasive

Question 24

ABG

Answer 24

How much Hb present in arterial blood

Invasive