Home > Uncategorized > Respiratory Physiology Lecture 5 Notes: Diffusion

Respiratory Physiology Lecture 5 Notes: Diffusion


49 minutes of joy today on diffusion.



Oxygen must get to the mitochondria.  Diffusion comes after ventilation.  Passive diffusion occurs from high partial pressure to low partial pressure. 

The swim bladder in fish implicated active transport of oxygen which was proven wrong.   The interior of the swim bladder can be much more concentrated in oxygen than the concentration in water. 

Fick’s Law

Volume Gas = Area/Thickness x Diffusivity x Pressure Difference

Diffusivity = k Solubility/sqrt MW

The area of the blood gas barrier is 50 square meters in man, the size of half tennis court.  Very large. 

The ECM is the intestitium.  Type 4 collagen gives the BGB its strength. 

0.5 mv2 = KE = kinetic energy

v = k/ sqrt mass

Carbon dioxide is much more soluble in blood than oxygen. 

Diffusion Limitation

depends upon solubility and molecular weight.  CO2 is 20x faster in tissue than O2.

There are 3 important gases:  CO N2o O2

Carbon monoxide is toxic and can be used to measure diffusion properties.  The blood spends 0.75 seconds in the capillary.  The cardiac output is 5L/second. 

CO is diffusion limited.  N2O is limited by blood flow or perfusion limited.  Any difference at all, diffusion limited.  If there is no different at the end of the capillary, then it is a perfusion limited.  O2 is diffusion limited.

Into the lung with a pO2 of 40, goes out with pO2 of 100.

How to Change the Rate of diffusion

1) Exercise reducing the time, .75 to .25

2) Thickness of BGF

3) Lower alveolar pO2 – high altitude

Measurement of Diffusion Capacity

V gas = Dl P1-P2

Diffusion Capacity

DL = Volume of Gas/ P1-P2

Perfusion limitations

Distension in the capillaries will increase the diffusion capacity.

Rate of reaction of O2 with Hb. 

O2 + Hb = HbO2

The transfer of CO2 is not limited by diffusion.

There are two things occuring: physical diffusion and the rate of reaction of blood/hemoglobin. 


Visible Light – 400 to 700 nm

Aromatic: planar, cyclic, Huckels Rule – 4n+2 electrons

Fibrous – sclera, cornea

Sensory – retina

Vascular – choroid, iris, pupil, ciliary body

Kingdoms – monera, protista, fungi, plant, animal

HSbF6 pKa = 25

Electrophiles are positive, nucleophiles are negative

EDTA is a tetraprotic acid.

Tissue: nervous muscular epithelial connective

Epithelial: simple stratified pseudostratifed/ cuboidal columnar squamous

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