20 Blood gas transport

Question 1

What factors determine diffusion on gas exchange?

Answer 1

• Diffusion distance
• Surface area
• Moistness
• solubility of gases
• Coordination of bloodflow and airflow
• Concentration gradient (partial pressure)

Question 2

What is atmospheric pressure at sea level?

Answer 2

760 mmHg

Question 3

Percentage of gases at sea level:

Answer 3

N2 78.6
O2 20.9
CO2 0.04
H2O 0.46

Question 4

Percentage of gases in alveoli:

Answer 4

N2 75.4
O2 13.2
CO2 5.2
H2O 6.2

Question 5

What is alveolar partial pressure

Answer 5

Around 758mmHg

Question 6

What is daltons law?

Answer 6

The total pressure exerted by a mixture of gases is the sum of the pressures exerted by each gas in the mixture

Question 7

What is partial pressure?

Answer 7

The pressure exerted by each gas in a mixture. It is directly proportional to the percentage of each gas in the mixture.

Question 8

How do you work out partial pressure?

Answer 8

%gas x pressure

Question 9

What is the partial pressure of O2 and CO2 in the alveoli vs the arteriole end of capillaries?

Answer 9

AC: O2 - 40, CO2 - 45
Alveoli: O2 - 100 CO2 - 40
Once blood reaches the venous end of the capillaries the ppO2 and ppCO2 are the same as in the lungs

Question 10

What is Henrys law?

Answer 10

the amount of gas dissolved that dissolves in water is proportional to the gases partial pressure in air and its solubility

• at equilibrium the amount of gas dissolved in that substance is proportional to its pp
• higher pp means more dissolved gas

Question 11

How soluble are O2 and CO2

Answer 11

O2 - not very

CO2 -quite

Question 12

At ppO2 ____, __ of plasma will dissolve __ O2

Answer 12

100
IL
3ml

Question 13

How much blood flow to the tissues per minute do we have?

Answer 13

5L

Question 14

how much O2 do our tissues need?

Answer 14

AT LEAST 200ml/min

Question 15

How much O2 does 1L of blood contain?

Answer 15

195ml

Question 16

How is our blood able to take more oxygen than it should around the body?

Answer 16

using haemoglobin

we don’t dissolve nearly enough in our plasma

Question 17

What happens to haemoglobin as it takes on oxygen molecules?

Answer 17

It changes shape and has a higher affinity for oxygen (take on more oxygen molecules more easily)

Question 18

How many molecules of oxygen can each molecule of haemoglobin carry?

Answer 18

4

Question 19

How much oxygen is transported by haemoglobin vs plasma?

Answer 19

97% H

3% P

Question 20

What is haemoglobin saturation?

Answer 20

The percentage of haem units in Hb molecule that contain bound O2

Question 21

What effects O2 binding to Hb?

Answer 21

• Temp (excercise/illness)
• ppO2
• pH
• state of O2 binding in the Hb molecule

Question 22

Which way does the bohr shift move?

Answer 22

Right means easier unloading

Question 23

What makes the bohr curve shift to the right?

Answer 23

CADET 
Co2
Acid
Dpg
Exercise
Temperature

Question 24

What is 2,3 DPG?

Answer 24

Released in RBCs during glycolysis (their only form of resp due to lack of nutrients). More DPG = more O2 unloading. Is responsible for the limited shelf life of blood in transfusions as more and more DPG is released and effects unloading.

Question 25

What are the other types of haemoglobin?

Answer 25

Carboxyhaemoglobin | Methaemoglobin

Question 26

What happens in CO poisoning?

Answer 26

CO binds tighter than O2 - competitively binds permanently reduces O2 carrying capacity of blood

Question 27

How does methamoglobin come about?

Answer 27

Fe2+ is oxidised to Fe3+ by las drogas Unable to carry O2 can slowly be converted back

Question 28

Fetal haemoglobin

Answer 28

Has a higher affinity for O2 (shift to the left)

Question 29

What are the different ways in which CO2 is transported?

Answer 29

- dissolved in plasma - As carbonic acid - Bound to hameoglobin

Question 30

What % of CO2 is transported in plasma?

Answer 30

7%

Question 31

What % of CO2 is transported as carbonic acid?

Answer 31

70% - transported in the blood as HCO3-

Question 32

What % of CO2 is transported bound to haemoglobin?

Answer 32

23%

Question 33

What happens once CO2 enters the blood?

Answer 33

93% moves into RBC. 7% dissolves in plasma. 23% then combines with hameoglobin (to a different binding site than oxygen) forming carbaminohaemoglobin. 70% combines with water to form H2CO3 --> HCO3- and H+ HCO3- ions move out into the plasma and Cl- ions move in to keep the cell electrically neutral

Question 34

What transporter do HCO3- ions move out of RBCs via?

Answer 34

Band 3

Question 35

What is the chloride shift?

Answer 35

Cl- ions moving into RBCs to maintain electric neutrality

Question 36

How do RBCs buffer?

Answer 36

Haemoglobin and H+ ions released from H2CO3 molecules

Question 37

What are the best buffers in RBCs?

Answer 37

Imizadole groups of histidine residues in haemoglobin

Question 38

Which type of hamoglobin has the best affinity for H+?

Answer 38

Deoxygenated

Question 39

Describe the process of unloading of CO2 in the lungs:

Answer 39

- Oxygenation of Hb - Conformational changes of Hb - Lower affinity for H+ - Decreased buffering power - Release of H+ - Aids unloading of CO2

Question 40

Describe the process of CO2 uptake in the tissues:

Answer 40

- Deoxygenation of Hb - Conformational changes - Higher affinity for H+ - Increased buffering power - Increased H+ uptake - CO2 taken away from tissues