Session 4: Carbon Dioxide In The Blood

Question 1

How much CO2 is there in arterial blood compared to O2?

Answer 1

Almost 2.5x as much

Question 2

What is the total CO2 content of arterial blood?

Answer 2

21mmol/L

Question 3

What is the total O2 content of arterial blood?

Answer 3

8.9mmol/L

Question 4

What is the solubility factor for CO2 at normal body temperature?

Answer 4

0.23

Question 5

What does dissolved CO2 form when it reacts with water?

Answer 5

Carbonic acid

Question 6

What does carbonic acid dissociate into?

Answer 6

H+ and HCO3-

Question 7

What is normal plasma concentration of HCO3-?

Answer 7

25mmol/L

Question 8

What is the normal average concentration of dissolved CO2?

Answer 8

1.2mmol/L

Question 9

How does increase in dissolved CO2 affect the position of equilibrium?

Answer 9

Pushes it to the right (increases production of HCO3-)

Question 10

What two factors does the pH of plasma depend on?

Answer 10

Concentration of dissolved CO2

Conc. of HCO3-

Question 11

What happens to plasma pH if pCO2 rises?

Answer 11

Falls (more acidic)

Question 12

What happens to plasma pH if pCO2 falls?

Answer 12

Rises (more alkaline)

Question 13

How is pCO2 of alveoli controlled?

Answer 13

By controlling the rate of ventilation

Question 14

Which cation is mostly associated with HCO3-?

Answer 14

Na+

Question 15

Why is pH of plasma alkaline?

Answer 15

High HCO3- concentration preventing dissolved CO2 from reacting

Question 16

What is pK at normal body temp?

Answer 16

6.1

Question 17

How much HCO3- is dissolved compared to CO2?

Answer 17

20x

Question 18

Give the equation to calculate pH

Answer 18

pH = pK + log([HCO3-]/(pCO2 x 0.23))

Question 19

What does carbonic anhydrase do?

Answer 19

Speeds up the reaction between CO2 and H2O

Question 20

Why is production of HCO3- favoured in RBCs?

Answer 20

The RBCs will mop up the H+ ions and extrude the HCO3-

Question 21

What transporter is used to extrude HCO3- from RBCs?

Answer 21

Chloride-bicarbonate exchanger

Question 22

What does the ‘mopping up’ of H+ in the RBCs?

Answer 22

Negatively charged Hb

Question 23

What is plasma HCO3- mostly determined by?

Answer 23

Binding of H+ to Hb

Question 24

How are the kidneys involved in control of HCO3-?

Answer 24

They vary its excretion

Question 25

How does HCO3- act as a buffer?

Answer 25

Reacts with acids produced to produce CO2

Question 26

Why does the buffering action of HCO3- not affect pH greatly?

Answer 26

CO2 produced is removed by breathing

Question 27

Where is pCO2 higher, in venous or arterial blood?

Answer 27

Venous

Question 28

In which state of Hb do more H+ ions bind?

Answer 28

T state

Question 29

In high pO2 will more or less H+ ions bind?

Answer 29

R state

Question 30

Why is CO2 higher in the venous system?

Answer 30

It’s coming from metabolically active tissues

Question 31

Why does more HCO3- form in venous blood?

Answer 31

Hb has been deoxygenated so will bind more H+

Question 32

Why when dissolved CO2 increases in blood is there little change to pH?

Answer 32

More is converted to HCO3- as Hb binds more H+ (both HCO3- and pCO2 increase)

Question 33

Why are carboamino compounds formed more at the tissues?

Answer 33

PCO2 is higher and unloading of O2 facilitates CO2 binding to Hb

Question 34

Where on Hb does CO2 bind?

Answer 34

Directly to the amine groups of the globin of Hb

Question 35

What three forms can CO2 be transported in?

Answer 35

Dissolved CO2
HCO3-
Carboamino compounds

Question 36

What is the total CO2 content in whole venous blood?

Answer 36

23.3mmol/L

Question 37

What percentage of total CO2 is transported?

Answer 37

8%

Question 38

What is the majority of CO2 doing in the plasma?

Answer 38

Acting to buffer the pH

Question 39

How much CO2 is transported at rest?

Answer 39

1.8mmol/L

Question 40

What form does CO2 mostly travel in?

Answer 40

HCO3-

Question 41

Is CO2 more commonly transported as carboamino compounds of dissolved CO2?

Answer 41

Carboamino compounds