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crv week 3 > Gas Exchange and Transport > Flashcards

Gas Exchange and Transport Flashcards

1
Q

what is the basic transport and exchange system of o2 and CO2 around the body?

A

CO2 from tissues to lungs
02 from lungs to tissues

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2
Q

why are lungs such a good gas exchange surface?

A
  • Large surface area for gas exchange.
    • Large partial pressure gradients.
    • Gases with advantageous diffusion properties.
    • Specialised mechanisms for transporting O2 and CO2 between lungs and tissues
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3
Q

What are the partial pressures seen in the different circuits of O2 and CO2?

A
  • Similar volumes of CO2 and O2 move each minute
  • The pressure gradient for O2 however is much higher than CO2
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4
Q

describe the alveolar capillary network and its properties?

A
  • Gas exchange occurs through dense mesh-like network of capillaries and alveoli.
  • Distance between alveoli and red blood cell 1-2μm
  • Ideal environment for gas exchange
  • Red blood cells pass through the capillaries in less than 1 second. This is sufficient time in order for complete gas exchange
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5
Q

how is dissolved oxygen transported in the body?

A
  • Only a small percentage of O2 in blood is in the dissolved form.
  • Amount of dissolved O2 in blood is proportional to its partial pressure.
    • For each mmHg of PO2 there is 0.003 ml O2/100 ml blood.
  • Arterial blood (PaO2) = 100 mmHg: contains 0.3 ml O2/100ml blood (3ml O2/litre of blood).
  • Transport of O2 in dissolved form NOT adequate for body’s requirements, even at rest.
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6
Q

how is oxygen transported around the body when it is bound to haemoglobin?

A
  • Haemoglobin (Hb) is major transport molecule for O2 found in red blood cells.
  • 280 million Hb molecules/red blood cell.
  • Binding and dissociation of O2 with Hb occurs in milliseconds to facilitate transport – necessary because red blood cells in capillaries for 1 second only.
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7
Q

what is the oxyhemoglobin dissociation curve?

A
  • Curve illustrates relationship between PO2 in blood and number of O2 molecules bound to Hb.
  • O2 binding to Hb is reversible.
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8
Q

what is the clinical significance of the flat portion in the oxyhaemoglobin dissociation curve?

A

drop in PO2 from 100 to 60 mmHg has minimal effect on Hb saturation.

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9
Q

what is the clinical significance of the steep portion of the oxyhaemoglobin dissociation curve?

A

large amount of O2 is released from Hb with only a small change in PO2, facilitating release into tissues.

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10
Q

what is oxygen saturation?

A
  • O2 saturation (SaO2) refers to the amount of O2 bound to Hb relative to maximal amount that can bind.
  • 100% saturation – all heme groups of Hb molecules fully saturated with O2.
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11
Q

how do we measure oxygen saturation?

A
  • Pulse oximeters used in clinic to measure O2 saturation.
  • Measures ratio of absorption of red and infrared light by oxyHb and deoxyHb.
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12
Q

how much CO2 is produced at rate?

A
  • Normal healthy conditions:
    • 200 ml CO2 / min produced
    • 80 molecules CO2 expired by lung for every 100 molecules of O2
      entering.
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13
Q

what is respiratory exchange ratio?

A

IN normal conditions, respiratory exchange ratio = 0.8 (80 CO2 to 100 O2)

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14
Q

how is CO2 transported in the blood stream?

A

CO2 carried in blood in three forms:
- 7% dissolved.
- 23% bound to haemoglobin (Hb).
- 70% converted to bicarbonate (this then moves out of RBCs in exchange for a chloride ion)

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15
Q

Outline the reaction to form bicarbonate and and the difference in this between the systemic and pulmonary capillaries

A
  • Direction and speed of the reaction is determined by the concentration gradients
  • Rightwards in systemic capillaries – CO2 produced by tissues expelled into blood.
  • Leftwards in pulmonary capillaries – CO2 to be expelled into alveoli.
  • The CO2 to HCO3- pathway plays a critical role in regulation of H+ ions and in maintaining acid- base balance in body.
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16
Q

explain the formation of the pH balance in the body wrt CO2 and the Henderson Hasselbach Equation

A
  • The concentrations of CO2, bicarbonate and hydrogen ions are linked.
  • This means changes in bicarbonate concentrations can be used to stabilise the pH.
  • This is a buffer reaction.
  • The high bicarbonate concentration makes buffering reaction strong.
17
Q

what is the Henderson Hasselbach equation?

A

acidity can be regulated by using ventilation to adjust the PCO2
or
By using the kidneys to regulate the bicarbonate conc

18
Q

what is the V/Q ratio and why is it important?

A
  • The V/Q ratio is the ratio of ventilation to blood flow and how matched these components are.
  • Ratio can be defined for single alveolus, a group of alveoli or entire lung.
  • Single alveolus: ratio defined as alveolar ventilation divided by capillary flow.
  • Lung: ratio defined as total alveolar ventilation divided by cardiac output.
  • This is important in disease processes, where we may see adequate perfusion of alveolar sacs but less blood flow or vice versa.
19
Q

what is the V/Q ratio in healthy individuals?

A
  • Alveolar ventilation ~ 4-6 L/min
  • Pulmonary blood flow ~ 5 L/min
  • V/Q FOR LUNG = 0.8-1.2
  • V/Q for individual units varies greatly.
  • When ventilation exceeds perfusion: V/Q > 1.
  • When perfusion exceeds ventilation: V/Q < 1.
  • Mismatching of pulmonary blood flow and ventilation results in impaired O2 and CO2 transfer.
20
Q

how many cell types are in the alveolar capillary networks and what are they?

A

type 1 epithelial cells
type 2 epithelial cells
alveolar macrophages

21
Q

what is the distance between red blood cells and alveoli?

A
  • Distance between alveoli and red blood cell 1-2μm due to Type 1 alveolar epithelial cell, capillary endothelial cell and basement membrane.
22
Q

why is the pressure gradient for O2 much higher Than CO2?

A
  • This is because CO2 is a more diffusible molecule
23
Q

why is dissolved O2 not adequate for tissue demand?

A

at rest cardiac output (CO)= 5 L/min. 3ml O2/litre of blood x 5 (CO) = 15 ml/min. BUT tissue requirements at rest 250 ml O2/min.
- E.g., during strenuous exercise CO = 30 L/min. 3ml O2/litre of blood x 30 (CO) = 90 ml/min. BUT tissue requirements may need 3000 ml O2/min.

24
Q

what is the structure of Haemoglobin?

A
  • Hb: four heme (iron porphyrin compounds) groups joined to globin protein (two α chains and two β chains polypeptide chains).
  • Each heme group contains iron in the reduced ferrous form (Fe+++), which is the site of O2 binding.
25
Q

how many O2 atoms can one molecule of Hb bind?

A

up to 4

26
Q

how do we measure dissolved O2 only?

A

you will need to take an arterial blood gas

27
Q

what is the respiratory exchange ratio?

A

ratio of expired CO2 to O2 uptake

crv week 3 (8 decks)

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