Week 20: (B) O2 & CO2 Transfer Between Alveolus, Blood & Tissue. Flashcards
What does Fick’s law refer to?
Gas exchange across the Blood-Gas barrier in the Alveolus occurs by diffusion
What is the Fick’s Law equation?
Dt=KtS(1/T)
What does Dt refer to?
Rate of Oxygen Transfer to
Hemoglobin (mlO2.cm-2.min-1)
What does Kt refer to?
Rate at which oxygen travels through liquid
“Krogh’s Oxygen Permeation Coefficient”
(3.3x10-8 cm-2.min-1.mmHg-1)
What does S refer to?
Surface Area (cm2)
What does (1/T) refer to?
Mean Barrier
Thickness (10-4cm)
Why are the capillaries thin?
Needed for optimal O2 transfer to haemo
What are the 2 forms of oxygen transport?
physical- Plasma soluble O2 (2%)
chemical- O2 bound to Haemoglobin (98%)
What are features of Plasma soluble O2?
-Less Soluble than CO2
-Function of Partial Pressure of O2 in alveolus
-0.3ml O2/100ml blood at PO2 of 100mmHg
(= normoxic alveolar PO2 )
What are features of O2 bound to haemoglobin?
-Rapid and reversible interaction
-Reversibility enables O2 off-loading to tissues
Hb + O2 ↔ HbO2
What is deoxyhaemoglobin?
form of haemoglobin without O2
What is Oxyhaemoglobin?
The form of haemoglobin bound to O2
What is the O2 carrying capacity of Hb?
1.34 x 15 = 20mls O2/ 100ml
1g Hb binds 1.34ml O2
15gHb/100ml total blood
What is the total arterial blood O2 content? (CaO2)
20.3mlsO2/100ml total blood
What is the total venous blood oxygen content? (CvO2)
15.28mlsO2/100ml total blood
What is the tissue O2 uptake?
5mlsO2/100mls
total blood
What is the difference between oxygen content and saturation?
- Content (CaO2 or CvO2): -Determined by amount of Hb and O2 in blood
- Saturation (usually SaO2): Proportion (%)
What is the Oxygen saturation equation?
oxyhaemoglobin/ O2 Carrying Capacity of Hb
What happens to saturation if O2 content differs?
saturation can remain the same
Hb content can differ but saturation is a percentage so it is all proportional
What is polycythaemia and anaemia?
Polycythaemia is high Hb content, carrying capacity and oxyhaemoglobin
Anaemia is Low
What defines the total oxygen content of blood?
Hb O2 Carrying Capacity and HbO2
deoxyhaemoglobin + oxyhaemoglobin
On the oxyhaemoglobin dissociation curve what does the EC50 tell us?
gives PO2 (mmHg) required for half max Hb saturation
What pressure does the venous blood enter the alveolus?
40 mmHg (75% sat)