Gas exchange and acid-base regulation in the blood and extraembryonic fluids of the developing chicken embryo.

Measurements of pH, PCO2, PO2 and total CO2 were recorded simultaneously in samples of chorioallantoic fluid, amnionic fluid and blood of the chorioallantoic artery from chicken embryos on days 8, 10, 12, 14, 16, 17 and 18 of incubation. During the incubation period studied, PCO2 levels similarly increased in the blood and extraembryonic fluids. The pH of the blood and amnionic fluid remained approximately constant while the chorioallantoic fluid became progressively acidic. Increases of amnionic fluid and blood HCO-3 indicated that respiartory compensation processes regulate pH. In addition, the disappearance of chorioallantoic fluid HCO-3 suggested that reabsorptive processes may conserve these ions and contribute them to the amnionic fluid by either a direct transfer through the amnioallantoic membrane or by way of the chorioallantoic vascular system.