Gas transport and Exchange Flashcards
What is Dalton’s law?
law of partial pressures
Pressure of a gas mixture is equal to the sum (Σ) of the partial pressures (P) of gases in that mixture
What is Fick’s law?
Law of diffusion
Rate of diffusion proptional to conc. Gradient, SA, diffusion capaicty
Inversely proportion to thickness
What is Henry’s law?
Law of solubility
At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid
What is Boyle’s law?
Law of pressure
At a constant temperature, the volume of a gas is inversely proportional to the pressure of that gas
What is Charles’ law?
Law of temperature
At a constant pressure, the volume of a gas is proportional to the temperature of that gas
What are the percentages of inspiratory gases?
N2: 78.2 O2: 20.9 Ar: 0.9 C02: 0.04 neon, xenon, helium and hydrogen: 0.04
How is partial pressure calculated?
Fraction x pressure
What happens to air as it passes thorugh the airways?
- Warmed
- Humidified (increased atrial pressure of water vaour) in conducting airways
- Slowed
- Mixed
- Significant decrease in oxygen concentration and increase in CO2 concentrations in respiratory airways
What happens on the onset of tidal inspiration?
- Fresh air enters lungs
- Mixed with functional residual capacity
- Causes O2 to decrease and CO2 to increase in air reaching alveoli
What is the VO2 of oxygen consumed?
min. 250
Can’t be met by dissolved oxygen
What is the structure of haemoglobin?
- ferrous iron ion (Fe2+; haem- ) at the centre of a tetrapyyrole porphyrin ring
- connected to a protein chain (-globin)
- covalently bonded at the proximal histamine residue
- Haemoglobin tetramer has two alpha and two either (beta, delta, gamma)
What are the types of Hb?
HbA is main Hg
Isoform is A2
HbF
How does Hb bind?
Haemoglobin bad at bonding to O2 without O2 – cooperative binding
Binding site in midlle generated through binfing
What does allosteric mean?
Changes depending on what ligands are bound or unbound
- Conformation of Hb changes from tensed to relaxed state the more O2 binds to it
- Binding site for 2,3 DBG (disphosphoglycerate) is exposed in centre
○ Cofactor in red cell energy production - Binds to 2 beta subunits and pushes them into tense state
- Promotes oxygen unloading
What proportion of blood is methaemoglobin?
0.5 to 1%
How is haemoglobin converted into haemoglobin?
Methaemoglobin reductase
How do oxygen dissociation curves look?
see notes
Relationship is actually sigmoidal
- Remains almost fully saturated across physiological range of lung
- At level of respiring tissue steep relationship between PO2 and Hb saturation
- Very efficient at loading in lungs and unloading in respiring tissue
How are oxygen dissociation curves monitored?
P50: atrial pressure at 50% saturation
○ Used as index for oxygen affitnity
What is the principal factor affecting hb-o2 relationship?
Partial pressure of dissolved oxygen
How does the ODC change if the body needs more oxygen?
Steeper
What causes the ODS curve to be displaced to the right?
Increase temperature
Acidosis
Hypercapnia - inc CO2
Increased 2,3 DPG
What causes the ODS curve to be displaced to the left?
Increased affinity
Decreased temperature
Hypocapnia
Decreased 2,3 DPG
What causes the ODS curve to be displaced to the up?
related to amount of haemoglobin in the blood
Polycythaemia: Increased oxygen-carrying capacity (may be due to tumour secreting EPO)
What causes the ODS curve to be displaced to the down?
in downwards shift o2 saturation may be 100% but actual hemoglobin until low
Anaemia: Impaired oxygen-carrying capacity
What causes a downwards and leftwards shift?
Decreased capacity
Increased affinity
May be due to increased HbCO
What is the stucture of HbF?
- 2 alpha
- 2 gamma
What is the structure of methaemoglobin?
- Fe3+
What is the structure of myoglobin?
- Haem bound to protein chain
- Monomeric
- Storage molecule
How does myoglobin and HbF affinity compare to HbA?
Both greater
How does oxygen loading occur ?
- Venous blood has 75% of O2 that arriving
- When reaches respiratory exchange surface rapidly equilibrates with alveolar gas
- Passes into the pulmonary epithelial cells –> interstitial space –> vascular endothelial –> plasma –> red blood cells
- Binds to molecules of Hb that are not fully saturated.
- After equilibration, post-alveolar PaO2is equal to PAO2
- Post-alveolar venules converge into pulmonary veins but before draining into the left atrium
- Some deoxygenated blood enters the circulation from the bronchial venous drainage
How does oxygen unloading occur?
- Arterial blood leaving the heart remains unchanged from above until it reaches systemic capillary beds
- tissue PO2is considerably lower than PaO2
- gradient promotes diffusion of oxygen from the plasma into the endothelial cells –>interstitium –> respiring cells –>mitochondria
- When PaO2starts to decrease, oxygen unloads from Hb
- Follows the dissolved oxygen down the concentration gradient and out of the circulation
What is resting VO2 and oxygen flux?
Resting VO2 ca 250ml per minute
Oxygen flux is also ca. 250ml per minute
What are the two ways in which carbon dioxide are transported?
- CO2 more soluble than O2
Bicarbonate transports most CO2
- C02 diffusion across membrane to react with water to form carbonic acid
- Carbonic acids dissociates into protons and bicarbonate
- Exist in equilibrium
When plasma pH falls:
- CO2 also moves into RBC
- Combines with water in the presence of carbonic anhydrase
- Increases chances of CO2 and water meeting 5000x so significantly increases rate
- Dissociates
- Bicarb moves out, Cl- enters to maintain membrane pd using AE1 transporter
- draws in water molecule
- CO2 also binds onto hemoglobin (amine end of globin chains) forming carbominohaemoglobin
How do the changes of dissolved CO2 compare to dissolved O2?
Change in dissolved CO2 less significant than O2
+200ml of C02 produced per minute for every 250 ml oxygen consumed
Which way of transporting blood is more prevalent in less oxygenated blood?
carboaminohaemoglibin more prevalent than dissolved
What is the Haldane effect?
- When haem molecules saturated it globin chains do not binds any CO2
- If have lots of oxygen chances are you don’t have aby CO2 to transport
How does CO2 unloading occur?
- CO2in solution will diffuse into the alveoli first, which will trigger the reversal of all of the other binding mechanisms
- Bicarbonate will reenter erythrocytes
- re-associate with H+ to form carbonic acid, which the carbonic anhydrase enzyme will convert back into CO2and H2O.
What is pulmonary transit time?
Amount of time blood is in contact with repiratory exchange surface (time for gas excnahge)
What are pulmonary transit times for O2 and CO2?
O2: 0.75
C02: 0.25
What affects pulmonary transit time?
If cardiac output increases recruit more of capillary beds so goes through faster
How does gravity affect intrapleural pressure?
Airways at top stretched and at bottom pulled down
- At top greater takes more pressure to inflate them more
- At bottom smaller it’s easier to increase cross sectional area
What is the effect of changes in intrapleural pressure on ventilation?
Apex:
- PPL is more negative (-8 cmH2O) - Greater transmural pressure gradient (0 vs. -8) - Alveoli larger and less compliant - Less ventilation
Base
- PPL is less negative (-2 cmH2O) - Smaller transmural pressure gradient (0 vs. -2) - Alveoli smaller and more compliant - More ventilation
What is the effect of changes in intrapleural pressure for perfusion?
Apex:
- Lower intravascular pressure (gravity effect) - Less recruitment - Greater resistance - Lower flow rate
Base:
- Higher intravascular pressure - More recruitment - Less resistance - Higher flow rate
How does the effect on ventilation compare to the effect on perfusion
Much greater impact on perfusion in zones than ventilation
What is wasted ventilation and wasted perfusion?
V/Q tends towards 0 at the bottom = wasted perfusion
At top tends towards infinity so a lot of ventilation with little perfusion : wasted ventilation
