1.  Molecules move randomly & rapidly in relation to each other  Net diffusion is from [high] to [low]  Partial pr. of the gas is proportional to [gas]  nitrogen  79%  600 mmHg  Oxygen  21%  160 mmHg  According to Henry's law the partial pr. of a gas in sln. depend on: 1- concentration 2- solubility coefficient  P gas = ______[gas]______ solubility coefficient gasSol. Co. O2O2 0.024 CO 2 0.57 CO0.018

2.  Net diffusion is determined by gradient  Vapor pr. of H 2 O is the partial pressure that water excretes to escape through the surface  at normal body temperature  47 mmHg  the greater the temperature  the greater kinetic activity  higher P H 2 O TemeraturePH2O 0 ̊ C 5 mmHg 100 ̊ C 760 mmHg

5. Diffusion rate (D) proportional to P x AxS d x MW  S : diffusion coefficient of gas.  √MW  Solubility high, more gases dissolved but exert less pressure. Partial pr.= concentration gas solubility coeff. A-cross- sectional area S-solubility of the gas d-distance P- pressure gradient GasDiffusio n co. O2O2 1 CO 2 20.3 CO0.81 N0.53

6.  Solubility Coefficient  O2 0.024  CO2 0.57  CO 0.018  N2 0.012  He 0.008

7.  Most gasses are lipid soluble so the diffusion in tissue is similar to diff. in water because these gases can pass easily through the cell membrane.  Rate at which alveolar air is renewed by atmospheric air  FRC 2.3 L only 350 ml of new air each breath. One seventh of the total, so many breaths are required to exchange most of the alveolar air.  Half of gas will be removed in 17sec.  Why this graduate clearance: - to prevent sudden change in [gas] in the blood. - to make respiratory control mechanism much more stable. - when respiration stopped, prevent incr. & dec. of oxygenation, and pH

10.  O 2 is supplied by inspiration and removed by diffusion  P O 2 is controlled by: a- rate of diffusion into blood (250ml/min) b- rate of O 2 entry by ventilation normally Po= 104 mmHg in alveoli  if alv. Ventilation 4.2L/min

12.  CO 2 in alveoli depends on: a- rate of CO 2 excretion b- ventilation rate If vent. Rate= 4.2 l/min, and rate of excretion = 200ml/min  P CO 2 40 mmHg  Expired air= alveolar air+ air in dead space

14.  300 million alveoli, each alveolus with the diameter of 0.2 mm.  Respiratory membrane: 1-fluid layer with surfactant 2-epithelium of alveoli 3-basement membrane of epithelium 4-interstitial space 5-capillary basement membrane 6-endothelial cells of the capillary

15.  Respiratory membrane specifications: 1- 0.2 – 0.6 μ m 2- 70m2 surface area 3- total volume of blood 60-140ml 4- capillary diameter is 5 μ m so RBCs squeeze through

16.  Diffusion rate depends on: 1- thickness (edema, diseases forming fibrosis) 2- surface area (emphysema, surgury) 3- P gas gradient 4- diff. coefficient

17.  the volume of a gas that will diffuse through the res. membrane each minute for a partial pressure difference of 1mmHg

19.  O 2  21 ml/min/mmHg.  11 mmHg Mean O 2 part. pr. In all lungs  230 ml/min “at rest”.  65 ml/min/mmHg “exercise”  CO 2  400 - 450 ml/min/mmHg “at rest”.  1200-1500 ml/min/mmHg “exercise”  average of P CO2 gradient is 1mmHg