transport of CO2 Flashcards
what are the 6 layers of the respiratory membrane ( ie membrane found in bronchioles, alveolar ducts and alveoli)?
- thin layer of fluid lining alveoli
- alveoli epithelium
- basement membrane of alveoli epithelium
- thin interstitial space
- basement membrane of capillary endothelium
- capillary endothelium (simple squamous)
What are the** 4 factors** affecting the** rate of gas diffusion**?
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
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?
- if the membrane thickness increases, the rate of diffusion decreases
example disease- pulmonary odema
what is the diffusion co-efficient?
the measure of how easily a gas diffuses through liquid or tissue
what is the diffusion co efficient dependent on?
- the solubility of gas
- the size of the gas molecule / molecular weight
what are examples of** lung diseases** that reduce the surface area of the membrane?
- lung cancer
- emphysema
In terms of partial pressure, what** direction **does diffusion / gas exchange occur?
- 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]
what effect does** increasing ventilation **have on the partial pressure of oxygen & CO2?
- 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 **
what effect does** inadequate ventilation **have on partial pressure differences of O2 and CO2?
- it **reduces the partial pressure differences **
- decreases PO2 in alveoli and increases PCO2 in alveoli
- therefore,** reduces gas exchange **
what is the partial pressure of CO2 in the cells (eg RBC), intersitial fluid, arterial blood, venous blood and alveolar air?
- intracellular PCO2= 46mmHg
- interstitial fluid PCO2= 45mmHg
- arterial blood PCO2= 40mmHg
- venous blood PCO2- 45mmHg
- alveolar air PCO2= 40mmHg
in what 3 forms is CO2 transported in the blood?
- dissolved CO2
- in combination with proteins eg HB - carbamino compounds
- as a bicarbonate - HCO3-
Describe the transport of CO2 from tissues (eg skeletal muscle) to RBC’s
PART 1 -
- skeletal muscle produces CO2
- CO2 diffuses into plasma
- most of the CO2 goes into the RBC’s and some remains in plasma
what happens to CO2 in the RBC’s?
- 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
why does the** first reaction** (CO2 +H20 - H2CO3) occur more slowly in the plasma?
- no carbonic anhydrase enzyme
Give the equation for the reaction of dissolved CO2 reacting with water
CO2 + H20 - H2CO3
remember CA above this
why can’t H+ ions diffuse readily out of the RBC membrane?
the membrane is relatively impermeable to cations
Describe the steps of the** haldane effect**
- 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
what does the haldane effect** aid in**?
it aids in the release of CO2 from carboxyhaemoglobin in the lungs
What is the **difference **between the Bohr vs Haldane effect?
- 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
what are** carbamino compounds**?
- blood proteins that bind CO2 are called carbamino compounds
- eg the globin portion of Hb
Describe the release of CO2 from carbaminohaemoglobin into the plasma
- 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
