Transport of O2 and CO2 in blood Flashcards
Gas movement through the conducting airways occurs by convection. but gas exchange across the blood-gas barrier in the alveolus occurs by what?
Diffusion
Fick’s law
What is Fick’s law?
The rate of diffusion oxygen is equal to “Krogh’s Oxygen Permeation Coefficient” (3.3x10-8cm-2.min-1.mmHg-1)-the rate at which oxygen naturally diffuses through humidified gas in the alveolus
Why is maintaining a thin blood gas barrier more desired?
Optimal gas diffusion
Oxygen is transported in two forms of blood. What are they?
Physical and Chemical
What does the physical form of blood mean?
Plasma soluble O2 (2%)
What does the chemical form of blood mean?
O2 bound to haemoglobin (98%) -Most common
Rapid and reversible reaction between oxygen and heam
How much oxygen us carried by haemoglobin?
1g Hb binds 1.34 O2
15Hb/100ml total blood
O2 carrying capacity of hb=1.34x15=20mls O2/100ml
What is the total arterial blood oxygen content (CaO2)?
O2 carrying capacity of Hb (20mlsO2/100ml0+plasma soluble O2 (0.3mlsO2/100mls)
=20.3mlsO2/100ml total blood
What is the total venous blood oxygen content (CvO2)?
O2 carrying capacity of Hb (15mlsO2/100mls) + Plasma soluble O2 (0.28mlsO2/100mls)
=15.28mlsO2/100ml total blood
What is the difference between onxygen content and saturation?
Content- Determined by amount of Hb and O2 in blood
Saturation (usually SaO2)- proportion (%)
What is the calculation for SaO2?
Oxyhemoglobin/O2 carrying capacity of Hb
What can remain the same even if O2 content of blood differs?
Saturation
What is sued to view the oxygen uptake from the alveolus?
Oxyhemoglobin Dissociation Curve
P50 value gives what?
PO2 required fro half maximal Hb saturation
Venous blood enters the alveolus at what? This equilibrates to alveolar PO2 of what?
40mmHg, 75% saturation
100mmHg, 97% saturation
Arterial plateau phase ensures what?
Maximal HbO2 saturation even if alveolar PO2 is below the normal (normoxic) oxygen tension
What does the steep phase of the curve favour?
Off-load of arterial oxygen to tissues. Greater HbO2 diassociation for small xhanges in tissue PO2
Normal P50 = 27mmHg at pH 7.4 and PCO2 of 40mmHg. What happens to these numbers if there is a left or right shift?
Left= Increased Hb-O2 affinity and reduced O2 offloading to tissues (eg fetal Hb)
Right=Decreased Hb-O2 affinity and raised O2 offloading to tissues (eg high altitude)
What are factors that cause a right shift in the axyhemoglobin dissociation curve?
-Acidosis (pH down)
-Increase in PCO2
These are both Bohr effect
- Fever
- Hypoxic glycolysis
What is the Bohr effect?
pH alters the ability of oxygen to bind to haemoglobin
In the Bohr effect, increased blood pCO2 releases O2 from Hb in two ways. What are these two ways?
1) Production of carbonic acid in red cell
2) Carbamate reaction at N-terminal Amino Groups on Hb a-subunit
These both lead to acid stabilisation of a-b Hb subunit interaction and low Hb affinity for O2
What is the physical and chemical ways that CO2 is transported in the blood. Three ways
Physical- Plasma soluble CO2
1) Soluble CO2 gas
2) Bicarbonate ion
Chemical 3)Carbamate reaction at N-terminal amino group of Hb a subunit
In the red blood cell, what enables CO2 carriage as bicarbonate anion?
Carbonic Anhydrase
What are the 3 forms that CO2 is carried within the blood?
Hypoxia
Venous
Alveolar
What is the haldane effect?
Low tissue O2 favours CO2 carriage by blood
What reaction reeuces HbO2 affinity?
Carbamate
Oxygen equilibrates from alveolus to blood
CO2 equilibrates from blood to alveolus?
true or false
True
What is the equation for measuring the alveolar PO2 (pAO2)?
pAO2=proportion of oxygen in inhales gas - the partial pressure of CO2 (measured as arterial pCO2) x rate of O2 consumption by metabolism
In high altitude environments, how can you adapt to conserve pAO2?
- Increase breathing frequency
- High carb diet
- Climb when barometric pressure is high
Poor ventilation and large blood flow requires what and why?
Perfusion needs to be reduced due to hypoxia constricting pulmonary arterioles
Good ventilation and poor blood flow requires what and why?
A reduction in ventilation because low CO2 contrcits bronchioles
What does hypoxia mean?
Constricts pulmonary arteries to increase pulmonary transit time of blood
In the event of a collapsed lung what happens to the flow of blood?
Re-directed to well ventilated area of the lung
In the event of a blood clot and there is an obstruction which causes low CO2 what happens to the bronchioles and what happens to the air flow?
- Constricts bronchioles to area of vascular obstruction
- Re-directs air flow in lungs away from obstruction
