Lecture 23 - O2 And CO2 Transfer Between Alveolus, Blood And Tissue Flashcards
Where does gas exchange occur
Across the blood-gas barrier
Gas exchange across the alveolus occurs by
Diffusion
What is Ficks law of diffusion
Dt = (Kt)(S)(1/Tnt)
In what to forms is the oxygen transported in blood
Physically and chemically
How is oxygen physically transported
Plasma soluble oxygen (2%)
Why is there a partial pressure of oxygen in the alveolus
As plasma soluble oxygen is less soluble than carbon dioxide
How is oxygen transported chemically
By being bound to haemoglobin
What is the interaction between oxygen and Hb like
It is rapid and reversible
What does the reversibility of the oxygen-Hb bond allow
For oxygen to off-load onto tissues
How is oxygen content determined
By the amount of Hb and oygen in the blood
What is oxygen saturation
The proportion of oxygen-saturated Hb relative to the total Hb in the blood
What does the P50 value represent
The Poxygen required for half the maximal Hb saturation
What pressure does the venous blood enter the alveolus at
40mmHg
What doe sthe arterial plateau phase ensure
That maximal Hb-oxygen saturation even in alveolar Poxygen is below the normal oxygen level
What does normoxic mean
Normal levels of oxygen
What does the steep phase of the oxygen-haemoglobin dissociation curve favour
Off-loading of arterial oxygen to tissues
What happens to the Hb-oxygen dissociation for small changes in the tissue Poxygen
There is greater Hb-oxygen dissociation
What factors shift the oxyhaemoglobin dissociation curve to the left
Foetal Hb
What happens when the oxyhaemoglobin dissociation curve is shifted to the left
There is an increased Hb-oxygen affinity and a reduced carbon dioxide off-loading
What factors shift the oxyhaemoglobin dissociation curve to the right
Fever, hypoxic glycolysis and the Bohr effect
What causes the Bohr effect
Acidosis and an increase in Pcarbon dioxide
What happens when the oxyhaemoglobin dissociation curve is shifted to the right
There is a decreased Hb-oxygen affinity and an increased carbon dioxide off-loading
What is Hb
A heterotetramer
What is Hb composed of
2 alpha and 2 beta subunits
What does Hb contain
4 iron-binding HEME domains
Within Hb what is the oxygen bound to
The Fe3+ ions in the centre of the HEME ring
What alters the affinity of oxygen to Hb
Carbon dioxide, pH and 2,3 BPG
How do carbon dioxide, pH and 2,3 BPG cause a change in affinity of oxygen to Hb
By interacting with the charged amino groups between the alpha and beta subunits
What does the amino terminus of the Hb-alpha subunit bind to
The carboxy-terminal histidine in the beta subunit
The interaction between the Hb-alpha subunit and the carboxy-terminal histidine in the beta subunit is sensitive to what
pH and carbon dioxide
What happens to interactions during acidosis
The decreased pH favours the alpha-beta interaction and reduces the binding of oxygen to the HEME
WHat effect does carbon dioxide have
It lower blood pH and reduces Hb affinity for oxygen
In what two ways does increased Pco2 release o2 from Hb
The production of carbonic acid in the red blood cells and the carbamate reaction at the N-terminal amno group of the Hb alpha-subunit
What effect does carbon monoxide have on the oxyhaemoglobin curve and why
Its afiinity for Hb is 240 times greater than oxygen, it forms carboxyhaemoglobin and causes the curve to shift left which reduces oxygen off-loading
What effect does anemia have on the oxyhaemoglobin curve
It causes it to shift right as the oxygencapacity is lowered
How is carbon dioxide carried physically
By plasma soluble carbon dioxide
What are the two forms of plasma soluble carbon dioxide
Soluble carbon dioxide gas (5%) or the bicarbonate ion (90%)
How is carbon dioxide chemically transported
through carbamino haemoglobin (5%)
What is the carbon dioxide dissociation curve altered by
Tissue oxygenation
What improves the carriage of carbon dioxide
The deoxygenation of blood
What effect is tissue oxygenation
The Haldane effect
What do the Bohr and Haldane effects enable
Reciprocal oxygen and carbon dioxide gas exchange
What defines the ventilation:perfusion relationship in the lung
Oxygen and carbon dioxide
Where does the oxygen equilibriate from
The alveolus to the blood
Where does the carbon dioxide equilibriate from
The blood to the alveolus
What allows fine tuning of oxygen uptake and carbon dioxide clearing
Breathing and lung-perfusion
in what situation is the fine tuning of oxygen uptake and carbon dioxide clearing needed
High altitude mountaineering, tolerance of G-force and external pressure (diving)
Equation to calculate alveolar Poxygen
pAoxygen = F1oxygen(pATM-SVP)-pAcardon dioxide(F1oxygen + (1-F1oxygen)/RQ))
