Respiratory Physiology 4.2- Gas transport in the Blood

Question 1

What are the two forms that oxygen travels in- in the blood?

Answer 1

in solution in plasma and bound to haemoglobin protein in RBC

Question 2

How much oxygen travels in plasma and why?

Answer 2

only 3 ml oxygen dissolves per L of plasma
oxygen is not very soluble in water and plasma is 95% water

Question 3

How much oxygen in whole blood and how much in plasma?

Answer 3

200ml oxygen per litre whole blood (RBC and plasma)
197ml bound to haemoglobin in RBC

Question 4

How much and in what form is carbon dioxide transported?

Answer 4

77% of carbon dioxide is transported in solution in plasma - much more soluble in water
23% stored within haemoglobin

Question 4

What is important in determining how much oxygen can get into the haemoglobin in the red blood cells?

Answer 4

the small fraction of oxygen that is in solution in plasma

Question 5

What is the partial pressure of oxygen in our plasma?

Answer 5

100mmHg - oxygen mols will move until partial pressure on either side of membrane is same

Question 6

What is partial pressure of oxygen in our alveoli in a normal lung?

Answer 6

100mmHg

Question 7

What is the oxygen demand of resting tissue?

Answer 7

250 ml per minute

Question 8

How much arterial oxygen is extracted by peripheral tissues at rest?

Answer 8

only 25% as 1000ml/min is possible and the oxygen demand of resting tissues is 250ml/min

Question 9

Describe haemoglobin molecule?

Answer 9

contains 4 haeme groups- each of which contains one Fe2+ which binds one oxygen molecule

Question 10

Describe cooperative binding in haemoglobin?

Answer 10

when oxygen starts to bind to haemoglobin causes polypeptide chains to shuffle around and make it easier for oxygen to bind.
When oxygen wants to leave haemoglobin another polypeptide change and then makes it less attractive for other oxygen mols to bind to that haemoglobin and then they are more readily given up.

Question 11

What is the major determinant of the degree to which haemoglobin binds (is saturated with) oxygen?

Answer 11

partial pressure of oxygen in blood

Question 12

What does partial pressure of oxygen in blood refer to?

Answer 12

amount of oxygen that is in the solution in the plasma

Question 13

What determines the amount of oxygen that is in the solution of plasma?

Answer 13

partial oxygen pressure of alveoli

Question 14

What is the partial oxygen pressure of alveoli determined by?

Answer 14

alveolar ventilation

Question 15

What is outcome of adding red blood cells to circulation?

Answer 15

suck oxygen out of the plasma and by doing so it helps to maintain a lower partial pressure of oxygen in that plasma- which helps to maintain the partial pressure gradient between the blood and the alveoli.

Question 16

What is haemoglobin oxygen saturation at normal partial pressure of oxygen?

Answer 16

97-98% of the haemoglobin that is in our blood is jam packed full of oxygen.

Question 17

Describe the sigmoidal curve?

Answer 17

very little change in the saturation of haemoglobin until the partial pressure of oxygen falls below 60mmHg- meaning possible to have quite a big fall in partial pressure of oxygen in our plasma with very little impact on total oxygen content of our blood.

Question 18

What happens once the partial pressure of oxygen drops below 60mmHg?

Answer 18

Haem groups start to have a much lower affinity for oxygen.
Once one haem group gives off its oxygen, there is a reconfiguration of the polypeptide chains and means it is less likely for other oxygen molecules to stay bound to haemoglobin.
Small changes in the partial pressure of oxygen now have a much bigger impact on the total oxygen content within the blood

Question 19

What is the normal pressure of oxygen in our resting tissues?

Answer 19

40mmHg- haemoglobin 75% saturated (tissues have given off 25% of their oxygen)

Question 20

What does systemic venous blood reflect?

Answer 20

reflects partial pressure of oxygen in our peripheral tissues

Question 21

Describe anemia?

Answer 21

anaemia is defined as any condition where the oxygen carrying capacity of the blood is compromised (e.g. iron deficiency, haemorrhage, vit B12 deficiency)

Question 22

What would happen to the partial pressure of oxygen in systemic arterial blood in someone who’s anaemic?

Answer 22

Nothing.
Possible to have normal plasma partial pressure of oxygen while total blood oxygen content is low.
Because partial pressure of oxygen refers to the amount of oxygen that is in solution- that is determined by partial pressure of oxygen that’s in alveoli.

Question 23

Why is it not possible to have a low plasma partial pressure of oxygen and a normal total blood oxygen content?

Answer 23

because partial pressure of oxygen determines how much oxygen binds to haemoglobin
if partial pressure of oxygen was to fall - total oxygen content has to also fall

Question 24

Is it possible for red blood cells to be fully saturated with oxygen in anaemia?

Answer 24

Yes.
The primary thing that determines saturation of the haemoglobin molecules with oxygen is the partial pressure of oxygen.
And the partial pressure of oxygen in anaemia is normal.

Problem is you don’t have very much haemoglobin or the normal number of red blood cells.
But the red blood cells that you do have, the haemoglobin that you do have will be fully saturated as long as your partial pressure is normal.

Question 25

What is the only caveat to red blood cells being fully saturated with oxygen in anaemia?

Answer 25

only caveat is iron deficiency where number of oxygen binding sites will be reduced, but those present will still be saturated.
As long as normal partial pressure of oxygen

Question 26

What are the factors that change the affinity of haemoglobin for oxygen?

Answer 26

a change in pH

a change in partial pressure of carbon dioxide in arterial plasma

change in body temperature

change in disphosphoglycerate 2,3

Question 27

What would make standard partial pressure- haemoglobin saturation curve shift to the right? (affinity of oxygen has decreased)

Answer 27

a decrease in pH
increase in partial pressure of carbon dioxide
increase in body temperature

Question 28

What is the Bohr Effect?

Answer 28

aids oxygen unloading at the peripheral tissues- for any given partial pressure of oxygen, the haemoglobin becomes less saturated with oxygen

Question 29

What is 2,3 Diphosphoglycerate?

Answer 29

by-product of red cell metabolism

Question 30

What does 2.3 diphosphoglycerate do?

Answer 30

reduces the affinity of the red blood cells/haemoglobin for oxygen

Question 31

In what situations do red blood cells start to produce more 23DPG?

Answer 31

hypoxia- where less oxygen availible

Question 32

why is carbon monoxide highly toxic?

Answer 32

binds to haemoglobin to form carboxyhaemoglobin.
And carboxyhaemoglobin has a 250 x greater affinity for oxygen.

Question 33

What partial pressure of carbon monoxide is enough to start progressive carboxyhaemoglobin formation?

Answer 33

0.4mmHg

Question 34

What is the presence of carbon monoxide characterised by?

Answer 34

low oxygen content hypoxia, anaemia, nausea, headache, cherry red skin and mucous membranes

Question 35

How does respiration rate change in individuals with carbon monoxide?

Answer 35

respiration rate unaffected as normal arterial PCO2

Question 36

What is the treatment for those with carbon monoxide?

Answer 36

providing 100% oxygen to increase partial pressure of oxygen

Question 37

Describe the carbon dioxide transportation?

Answer 37

carbon dioxide much more soluble than oxygen so it travels more readily in solution

tissues produce carbon dioxide (by-product from aerobic cellular respiration)

carbon dioxide diffuses into the plasma down its partial pressure gradient

46mmHg in tissues and 40 in arterial plasma

7% remains in sol in plasma and other 93% moves into RBC

in RBC: about 23% of carbon dioxide combines with deoxyhaemoglobin to form carbamino compound
the other 70% reacts with an enzyme called carbonic anhydrase to form carbonic acid - which then immediately dissociates to bicarbonate ions and hydrogen ions.

The hydrogen ions get buffered quite effectively by the haemoglobin protein.
Bicarbonate ions are then exchanged back into the plasma across the red blood cell membrane in exchange for chloride ions (chloride shift)

Question 38

What are the percentages of various forms that carbon dioxide can travel?

Answer 38

70% of carbon dioxide travels in the blood in the form of bicarbonate ions in systemic venous blood.

7% travelling in solution just as dissolved carbon dioxide

23% travelling in the form of carbamino compounds bound to deoxy haemoglobin

Question 39

What is better at forming carbamino compounds, deoxyhaemoglobin or oxygenated haemoglobin?

Answer 39

deoxyhaemoglobin

Question 40

What happens when blood gets back to the level of the lungs and partial pressure of oxygen increases?

Answer 40

haemoglobin would much rather associate with oxygen than with carbon dioxide

so it then wants rid of that carbon dioxide because it wants to take oxygen back up again

haemoglobin release those hydrogen ions, that causes the bicarbonate to shift back into the RBC to neutralise those hydrogen ions and we ned up with carbonic anhydrase working in reverse to release carbon dioxide and water from carbonic acid that has formed.

Carbon dioxide diffuses into plasma and then into alveoli ( down its partial pressure gradient)

At the same time, haemoglobin dissociates from carbon dioxide and stops forming the carbamino compounds because it would much rather associate with oxygen. And carbon dioxide is released into solution and then RBC.