Prof. Alejandro Rodriguez Navarro - Mechanisms of eggshell biomineralization

Réalisation : 23 mars 2021 Mise en ligne : 23 mars 2021
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Theavian eggshell is a thin mineral layer (350 µm thick in chicken) that protectsthe egg content against mechanical impacts, dehydration and microorganismcontamination. Eggshell formation is a highly controlled and rapidmineralization process occurring while the egg is residing in the uterus duringthe night.The composition of the uterine fluid changes at each stage of eggshellformation (initiation, linear growth, termination) with the expression ofspecific proteins that actively regulate calcium carbonate precipitation,selecting the mineral phase to form (calcite), inducing the nucleation ofcrystals and controlling their growth, morphology and size. Eggshell formationis terminated with the deposition of the cuticle about 2 hours beforeoviposition. Egglaying is highly demanding and female birds have developed specific physiologicaladaptations for it. Theyneed a large and continuous supply of calcium. A stimulated production ofvitamin D leads to an increase in calcium absorption by intestinal and uterinetissues. Also, hens develop a new type of bone within the marrow cavities oftheir long bones (medullary bone) that serves as a calcium reservoir foreggshell calcification during the night when hens are not eating and theintestinal calcium supply is exhausted. The formation and resorption ofmedullary bone is synchronized with the egg daily cycle. Laying hens also provideenough respiratory CO2 to form carbonate ions needed for eggshellcalcium


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