transport of CO2

Question 1

what are the 6 layers of the respiratory membrane ( ie membrane found in bronchioles, alveolar ducts and alveoli)?

Answer 1

1. thin layer of fluid lining alveoli
2. alveoli epithelium
3. basement membrane of alveoli epithelium
4. thin interstitial space
5. basement membrane of capillary endothelium
6. capillary endothelium (simple squamous)

Question 2

What are the** 4 factors** affecting the** rate of gas diffusion**?

Answer 2

1.** thickness** of the membrane
2. diffusion co efficient of gas through membrane
3. surface area of membrane
4. delta P ( c**oncentration of gases) between the 2 sides **of the membrane

Question 3

If there is an increase in membrane thickness (eg during disease), what occurs to the rate of diffusion? & give an example of a disease that is affected by this?

Answer 3

• if the membrane thickness increases, the rate of diffusion decreases
  example disease- pulmonary odema

Question 4

what is the diffusion co-efficient?

Answer 4

the measure of how easily a gas diffuses through liquid or tissue

Question 5

what is the diffusion co efficient dependent on?

Answer 5

• the solubility of gas
• the size of the gas molecule / molecular weight

Question 6

what are examples of** lung diseases** that reduce the surface area of the membrane?

Answer 6

• lung cancer
• emphysema

Question 7

In terms of partial pressure, what** direction **does diffusion / gas exchange occur?

Answer 7

• when 1 side is greater than the other, the **diffusion occurs from higher to lower **
• normally O2 [ alveoli greater Pp of O2 than capillaries]
• normally CO2 [capillaries greater Pp than alveoli]

Question 8

what effect does** increasing ventilation **have on the partial pressure of oxygen & CO2?

Answer 8

• increasing ventilation **increases the partial pressure differences **between the alveoli and capillaries
• it** increases the PO2 in the alveoli** and decreases the PCO2 in the alveoli
• therefore** promotes gas exchange **

Question 9

what effect does** inadequate ventilation **have on partial pressure differences of O2 and CO2?

Answer 9

• it **reduces the partial pressure differences **
• decreases PO2 in alveoli and increases PCO2 in alveoli
• therefore,** reduces gas exchange **

Question 10

what is the partial pressure of CO2 in the cells (eg RBC), intersitial fluid, arterial blood, venous blood and alveolar air?

Answer 10

1. intracellular PCO2= 46mmHg
2. interstitial fluid PCO2= 45mmHg
3. arterial blood PCO2= 40mmHg
4. venous blood PCO2- 45mmHg
5. alveolar air PCO2= 40mmHg

Question 11

in what 3 forms is CO2 transported in the blood?

Answer 11

• dissolved CO2
• in combination with proteins eg HB - carbamino compounds
• as a bicarbonate - HCO3-

Question 12

Describe the transport of CO2 from tissues (eg skeletal muscle) to RBC’s

PART 1 -

Answer 12

• skeletal muscle produces CO2
• CO2 diffuses into plasma
• most of the CO2 goes into the RBC’s and some remains in plasma

Question 13

what happens to CO2 in the RBC’s?

Answer 13

• most of it combines with water and forms carbonic acid - which is catalysed by the enzyme carbonic anhydrase
• carbonic acid then dissociates into HCO3- and H+
• some of the H+ ions combines with Hb
• the HCO3- ions move out of the RBC in exchange for Cl- (chloride shift) - carried out by AE1 exchanger
• some of the CO2 binds to Hb and some remains dissolved

Question 14

why does the** first reaction** (CO2 +H20 - H2CO3) occur more slowly in the plasma?

Answer 14

• no carbonic anhydrase enzyme

Question 15

Give the equation for the reaction of dissolved CO2 reacting with water

Answer 15

CO2 + H20 - H2CO3
remember CA above this

Question 16

why can’t H+ ions diffuse readily out of the RBC membrane?

Answer 16

the membrane is relatively impermeable to cations

Question 17

Describe the steps of the** haldane effect**

Answer 17

• Haldane effect is the decrease of the carbon dioxide binding capacity of haemoglobin with the** rise in the concentration of oxygen**
• as oxygen enters the RBC it binds to oxyhaemoglobin
• this enourages the release of H+ from carbaminohaemoglobin,
• H+ then combines with HC03- to form H2CO3 which dissociates to form CO2 & H20
• CO2 diffuses from the RBC to the alveoli

Question 18

what does the haldane effect** aid in**?

Answer 18

it aids in the release of CO2 from carboxyhaemoglobin in the lungs

Question 19

What is the **difference **between the Bohr vs Haldane effect?

Answer 19

• the main difference is that the Bohr effect is the decrease of the oxygen binding capacity of haemoglobin with the increase in the concentration of CO2 or decrease in PH
• the** Haldane effect** is the **decrease in the CO2 binding capacity **of haemoglobin with the rise of the concentration of oxygen

Question 20

what are** carbamino compounds**?

Answer 20

• blood proteins that bind CO2 are called carbamino compounds
• eg the globin portion of Hb

Question 21

Describe the release of CO2 from carbaminohaemoglobin into the plasma

Answer 21

• when O2 enters the RBC, it converts deo-oxy Hb to** Oxy Hb**
• Oxy Hb has** low affinity for CO2 **and **releases CO2 from carbaminohaemoglobin **into plasma
• HALDANE EFFECT