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Gas exchange, blood gases and acid-base status in the chick before, during and after hatching
Insights
This study tracked blood gases in chicks during hatching, revealing significant changes in oxygen and carbon dioxide levels. Despite these shifts, vital blood oxygen transport remained stable throughout the critical transition to lung-based breathing.
Area of Science:
- Physiology
- Comparative Biology
- Avian Development
Background:
- Birds transition from chorioallantoic to pulmonary gas exchange during hatching.
- Understanding this physiological shift is crucial for avian development studies.
Purpose of the Study:
- To investigate blood gas and acid-base changes in domestic fowl chicks during the hatching transition.
- To assess the efficiency of gas exchange before, during, and after hatching.
Main Methods:
- Blood samples were analyzed for gases and acid-base variables from arterial and venous equivalents.
- Oxygen uptake and gas exchanger blood flow were determined using the Fick principle.
Main Results:
- Pre-hatching: Decreased PO2, increased PCO2, with pH changes buffered by bicarbonate.
- Post-hatching: Pronounced hypocapnia (low CO2) and partial respiratory alkalosis compensation.
- Blood oxygen transport was maintained despite hypoxia and blood loss during hatching.
Conclusions:
- Avian hatching involves complex, yet effectively managed, cardiorespiratory adjustments.
- The transition to pulmonary gas exchange is robust, ensuring adequate oxygenation.
- Chick blood gas homeostasis approaches adult levels shortly after hatching.
Abstract:
To study the transition from chorioallantoic to pulmonary gas exchange in birds, blood gases and acid--base variables were measured in chicks of domestic fowl before, during and after hatching. Measurements were made in samples of 'venous' blood (from allantoic arteries or the right ventricle, respectively) entering the gas exchanger (chorioallantois or lungs, respectively) and arterialized blood (from allantoic veins or the left ventricle, respectively) leaving the gas exchanger. Also, O2 uptake was measured and blood flow of the gas exchanger was determined according to the Fick principle. During the last days of incubation PO2 decreased PCO2 increased in both arterialized and 'venous' blood, but the changes of pH were small due to a concomitant increase in bicarbonate concentration, in accordance with the results of previous studies. After external pipping and hatching pronounced hypocapnia developed, but the respiratory alkalosis was partiallY compensated by a transitory non-respiratory reduction of bicarbonate. In spite of arterial hypoxia at the end of incubation and some loss of blood during hatching, blood O2 transport was not seriously impaired during pipping and hatching as revealed by 'venous' blood gases. The blood gases and pH of 17-day-old chicks were close to those of adult chickens.