Respiratory System Lecture 7- Diffusion: how gas gets across the blood-gas interface

scattered in walls of respiratory bronchioles
continuous in walls of alveolar ducts which lead to termial alveolar sacs
smallest units in which gas exchange occurs
thin walled spheriodal air filled spaces

very flattened cells
cover majority of alveolar wall
sit on basement membrane
terminally differentiate ( cannot divide)
allow gas diffusion across cytoplasm

cuboidal
cytoplasmic granules contain surfactant
divide to replace type I and type II cells

seperate alveoli

allow passage of air between alveoli

between the air and the blood plasam, oxygen must diffuse across:
alveolar fluid
alveolar epithlial cell
basement membrane of alveolar epithelium
basement membrane of capilliary endothelium
capiliary endothilial cells

.2-2 mico meters

eryhtrocytes then binds to hemaglobin

intravascular- assocaited with endothielium (pigs, ruminants)
interstital
alveolar- function to clear alveolar surface; remove via trachea or via intersitium--> lymphatic system

heamopoetic stem cells (monocyte-macrophage lineage)
can proliferate localy
also recruited from blood during infection

collagen and elastic fibers
blood vessels

squamous/cuboidal epithileium overlying elastic and collagen fibers

the pressure exerted by a given gas in a mix of gases
found by mutiplying by the total pressure

water vapor added to air suring inspiration --- change in partial pressure of gases, although total pressure remains the same

determined by concentration of gas dissolved in the fluid
oxygen bound to hemaglobin does not contribute to PO2 in blood
CO2 dissolved in blood undergoes following reaction
CO2+H2O <--> H+ + HCO3-

DR- diffusion rate
PD-partial pressure gradient across tissue barrier
A- surface area available for diffusion
DC- diffusion coefficient
T-thickness of tissue barrier