Carriage of Oxygen and Carbon Dioxide

Question 1

What is the pO2 in the alveolar space?

Answer 1

100 mmHg

Question 2

what is the pCO2 in the alveolar space?

Answer 2

40 mmHg

Question 3

the blood coming away from the longs has a pO2 of what?

Answer 3

of 100mmHg b/c it equilibrates with the alveoli -

Question 4

what is the O2 content of arterial blood?

Answer 4

20ml%

Question 5

what is the percent content of CO2 in the arterial blood?

Answer 5

48 ml%

Question 6

why is the percent of oxygen in the veins so high? Isn’t it supposed to be deoxygenated?

Answer 6

it is a ‘reserve’ of oxygen - which is why we check venous gas during exercise b/c it should be less

Question 7

Describe this photo - compare venous vs. arterial side and memorize the numbers

Question 8

what are the two ways that O2 is carried through the blood?

Answer 8

O2 that is physically dissolved and O2 that is carried by haemoglobin in the form of oxyhaemoglobin (which consists of 4 haem groups attached to 4 protein chains)

Question 9

is the ‘dissolved’ oxygen in the plasma significant?

Answer 9

no - it’s rather small in comparison to the oxygen combined with haemoglobin

(each haem contains an atom of iron in the ferrous form)

Question 10

be able to draw the oxy-haemoglobin dissociation curve

Answer 10

describes the relationship between the percent saturation and the partial pressure of oxygen

Question 11

how does a pulse oxymeter measure percent saturation?

Answer 11

measures the oxygen content divided by the oxygen capacity (the volume of oxygen carried with a high PO2)

Question 13

how are arterial blood gases taken?

Answer 13

use arterial blood sample and a blood gas analyzer - one of the problems is that it’s not continuous - you have to take a sample every time you do it - it’s intermitent

Question 14

describe the significance of the shape of the oxygen saturation/pressure O2 curve

Answer 14

the sigmoid shape means that the plateau where the percent saturation is almost 100%, the PO2 can fall without uch of a fall in percent saturation

This is a protection against altitude and respiratory disease

You can drop the pressure of Oxygen in your environment quite significantly and your blood will still retain a significant amount of oxygen - so even at 60mmHg you’re at 90% saturation - however the plateau reduces the usefulness of hyperventilation and O2 therapy

Question 15

what occurs when the pressure O2 in the environment is below 60 mmHg?

Answer 15

they drop into a level where their haemoglobin readily gives off oxygen - and they lose it very quickly

Question 16

what is the ‘P50 value”?

Answer 16

it is the pressure value at which the haemoglobin is at 50% saturation

Question 17

what moves the % saturation vs. PO2 curve to the right?

Answer 17

• increase in PCO2,
• increase in H+
• increase in Temp
• increase in 2,3 DPG
• this means that the p50 increases

Question 18

are O2 therapies useful?

Answer 18

• we are already at a resting state - at a maximum PO2 - so if you add extra oxygen to the environment, you WONT add extra oxygen to your blood -

Oxygen therapy is essential if you are oxygen defficient, however in most occasions it’s not effective

Question 19

a rise in the CO2 shifts the curve to the right - What is the name of this effect?

Answer 19

the Bohr effect- note that a similar effect is also caused by an increase in temp and 2,3 disphosphoglycerate -

2,3 DPG is formed in the RBC and binds to the beta chains of hameoglobin causing O2 release

Question 20

in what conditions is 2,3 DPG increased?

Answer 20

increased in exercise, altitude, anaemia, and respiratory disease - b/c it causes blood to releaes more oxygen

Question 21

2,3 DPG is a product of what?

Answer 21

it is a product of metabolism - so in areas of tissue where there is a lot of actiivty and a lot of ATP required- it causes blood to release oxygen

Question 22

does ‘stored’ blood have a high or low level of 2,3, DPG?

Answer 22

stored blood has a low level of 2,3 DPG - this can cause problems in blood transfusions

Question 23

does haemoglobin F bind O2 better or worse than Haemoglobin A ?

Answer 23

Hameoglobin F binds O2 better than hameoglobin A b/c 2,3, DPG binds poorly to the gamma chains of haemoglobin F - this improves O2 transfer across the placenta -

myoglobin is found in skeletal and cardiac muscle - it has a higher O2 affinity than Hb and acts as a tissue store of O2

Question 24

what is the purpose of myoglobin?

Answer 24

it stores O2 - requires significant reduction in the pressure O2 before it releases oxygen

Question 25

in anaemia what happens to the PO2 and the O2 content in the blood?

Answer 25

PO2 remains normal

O2 content is reduced

Question 26

what occurs to the iron haem in haemoglobin when exposed to chemicals and drugs like nitrates, nitrites, sulfonamides, and local anaesthetics?

Answer 26

it can change form to methaemoglobin - which does not bind O2 - therefore the delivery of oxygen to your tissues will be compromised (note that methaemoglobin is blue so patients who are highly methaemoglobinaemic appear blue)

Question 27

why is carbon monoxide so dangerous?

Answer 27

it binds carbon monoxide 240 times more avidly than O2 forming carboxyhaemoglobin which does not bind O2

Question 28

What is cyanosis?

Answer 28

it is a blue colouration of the skin and mucous membranes, especially the tongue, mouth, lips and nail beds- it occurs when the arterial blood is 85% saturated or when the capillary blood is 70% saturated

Question 29

what is the cause of central cyanosis?

Answer 29

due to arterial blood desaturation (though many textbooks say that central cyanosis is when your lips and tongue are blue, and peripheral is when your fingers and toes are blue)

Question 30

what cuases peripheral cyanosis?

Answer 30

due to reduced tissue blood flow (vasoconstriction) - nothing is wrong with your respiratory system though -

Question 31

How is CO2 carried away?

Answer 31

physically dissolved

present in carbamino compounds (reaction between carbon dioxide and haemoglobin/other plasma proteins)

bicarbonate (majority)

Question 32

What reaction converts carbon dioxide to bicarbonate?

Answer 32

Question 33

haemoglobin can buffer what ion?

Answer 33

it can help mop up the extra ions produced from the carbon dioxide/bicarbonate conversion

Question 34

why is the blood in the veins at a lower pH than blood in the arteries?

Answer 34

because of the excess H+ present in the venous blood - it reacts with carbon dioxide

Question 35

What is the Haldane Effect?

Answer 35

the deoxygenated blood is better able to carry CO2 - it is cooperative binding - this is due to a conformational change of the haemoglobin