A morphologic and mophometric study was conducted to elucidate the mechanism of O2 transport across the inner shell membrane and chorioallantoic blood-gas barrier in chick ambryos. The chorioallantois and shell membranes in 16-day-old incubating chicken eggs were fixed in situ, systemically sampled, and prepared for electron microscopic examination. Scanning and transmission electron micrographs are presented to described the pathway for respiratory gas exchange. Using stereologic methods that dimensions of important gas exchange parameters were measured and from those data the O2 diffusing capacity of the chorioallantois (DCA) was calculated. Our average DCA value of 6.8 μl O2 · min-1 · Torr-1 is quite similar to previous physiologic estimates. We found that the rate-limiting factor in chorioallantoic O2 uptake is O2-hemoglobin binding in erythrocytes, which is ten times slower than diffusion across the thin (harmonic mean thickness = 0.47 μm) blood-gas barrier. Our analysis provides strong support for te chorioallantoic gas exchange m,odel of Piiper et al. (1980), and implies that the inner shell membrane provides a negligible resistance to O2 movement at this development age.
Bibliographical noteFunding Information:
We wish to acknowledget he technical assitance Mosf. H. Classen, Ms. Fabienne Doffey and Mr. KarBl abl. This work was supported by Swiss National Science Foundation GranNtr . 3. 332.78, andw as done while D. Wagensteenw as supported by Senior International Fellowship F06-TW00387 t hf reo Fmo g a r t y International Center, NIH.
- Avian egg
- Diffusin capacity
- Electron microscope
- Gas exchange
- Inner shell membrane
- O-Hb binding