transport of CO2 Flashcards

1
Q

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

A
  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)
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2
Q

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

A

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

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3
Q

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?

A
  • if the membrane thickness increases, the rate of diffusion decreases
    example disease- pulmonary odema
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4
Q

what is the diffusion co-efficient?

A

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

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5
Q

what is the diffusion co efficient dependent on?

A
  • the solubility of gas
  • the size of the gas molecule / molecular weight
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6
Q

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

A
  • lung cancer
  • emphysema
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7
Q

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

A
  • 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]
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8
Q

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

A
  • 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 **
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9
Q

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

A
  • it **reduces the partial pressure differences **
  • decreases PO2 in alveoli and increases PCO2 in alveoli
  • therefore,** reduces gas exchange **
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10
Q

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

A
  1. intracellular PCO2= 46mmHg
  2. interstitial fluid PCO2= 45mmHg
  3. arterial blood PCO2= 40mmHg
  4. venous blood PCO2- 45mmHg
  5. alveolar air PCO2= 40mmHg
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11
Q

in what 3 forms is CO2 transported in the blood?

A
  • dissolved CO2
  • in combination with proteins eg HB - carbamino compounds
  • as a bicarbonate - HCO3-
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12
Q

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

PART 1 -

A
  • skeletal muscle produces CO2
  • CO2 diffuses into plasma
  • most of the CO2 goes into the RBC’s and some remains in plasma
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13
Q

what happens to CO2 in the RBC’s?

A
  • 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
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14
Q

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

A
  • no carbonic anhydrase enzyme
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15
Q

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

A

CO2 + H20 - H2CO3
remember CA above this

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16
Q

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

A

the membrane is relatively impermeable to cations

17
Q

Describe the steps of the** haldane effect**

A
  • 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
18
Q

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

A

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

19
Q

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

A
  • 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
20
Q

what are** carbamino compounds**?

A
  • blood proteins that bind CO2 are called carbamino compounds
  • eg the globin portion of Hb
21
Q

Describe the release of CO2 from carbaminohaemoglobin into the plasma

A
  • 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