Oxygen In The Blood

Question 1

What is the solubility factor for oxygen?

Answer 1

0.01 mmol

Question 2

What is the cardiac output for the average 70kg man?

Answer 2

5L/min

Question 3

What are the oxygen binding pigments?

Answer 3

Haemoglobin - tetramer (bind 4 oxygen molecules)

Myoglobin - monomer (binds 1 oxygen molecule)

Question 4

What oxygen binding pigment has the highest affinity for oxygen?

Answer 4

Myoglobin

Question 5

What is myoglobin?

Answer 5

Pigment found in muscles that contains haem.

It is similar to haemoglobin but has only a single subunit.

Question 6

What is the shape of the myoglobin dissociation curve?

Answer 6

Curve is hyperbolic.

Question 7

How is dissociation presented?

Answer 7

As a percentage

Question 8

What are the two different states Hb can be in?

Answer 8

T - Tense - this is the low affinity for oxygen state (difficult for oxygen to bind). Occurs when pO2 is low

R - Relaxed - high affinity for oxygen (easier for oxygen to bind). Occurs when high pO2

Question 9

What is the shape of the haemoglobin dissociation curve?

Answer 9

Sigmoidal

Question 10

At what kPa is Hb saturated?

Answer 10

9-10kPa

Question 11

At what kPa is the Hb half saturated?

Answer 11

3.5-4kPa

Question 12

What is the oxygen content of arterial blood?

Answer 12

8.8mmol/L.

If anaemic, pO2 will be normal but oxygen content will be lower.

Question 13

What is tissue pO2?

Answer 13

5kPa. But, it depends on how metabolically active the tissue it.

Question 14

How low can tissue pO2 get?

Answer 14

Must be high enough to drive diffusion of O2 to cells.

It cannot fall below 3kPa in most tissues.

But, the higher the capillary density, the lower the pO2 can fall (as it doesn’t have to diffuse as far). Very metabolically active tissues will have higher capillary densities.

Question 15

What is the Bohr shift?

Answer 15

When curves shifts to the right.
Decreases pH, promotes T state, give up more O2.

If pH increases - alkaline - shifts to left - R state so take more oxygen.

This is why, in metabolically active tissues, the pH is lower.

Question 16

In what situation can the amount of oxygen from arterial blood that can be given up increase?

Answer 16

Exercise

Normally only about 27% is given up.

In extreme exercise, metabolism can increase by 10x but cardiac output only goes up by 5x

Question 17

Why would 2,3-BPG increase and what happens if it is?

Answer 17

It increases with anaemia or at altitude

It shifts Hb dissociation curve to the right so gives up more oxygen.

Question 18

How much 2,3-BPG is normally in RBCs?

Answer 18

5mM

Question 19

When do the levels of 2,3-BPG increase?

Answer 19

They increase with anaemia or altitude

Question 20

At what level is CO fatal?

Answer 20

Fatal is over 50%.

It also increases the affinity of the unaffected subunit of O2 so that oxygen won’t be given up at tissues.

Question 21

What is the difference between hypoxemia and hypoxia?

Answer 21

Hypoxemia = low levels of oxygen in arterial blood

Hypoxia - low levels of oxygen in the body or tissues.

Question 22

What is the difference between peripheral or central cyanosis?

Answer 22

Peripheral - hands or feet go blow due to poor local (peripheral circulation)

Central - (mouth, tongue, lips. mocous membrane) due to poorly saturated blood in systemic circulation

Question 23

What is cyanosis?

Answer 23

Blueish colouration due to unsaturated haemoglobin.

Question 24

What is pulse oximetry?

Answer 24

Detects level of Hb saturation of pulsatile, arterial blood.
(ignores tissues and venous blood).
It detects the difference in absorption of light between oxygenated and deoxygenated blood.

Question 25

Where is arterial blood gas commonly taken from?

Answer 25

Radial artery

Question 26

How can you calculate the amount of oxygen given up to tissues?

Answer 26

• Work out the fraction of oxygen given up (different in % saturation)
• Times this by 8.8mmol/L