Calcium Homeostasis and Eggshell Biomineralization in Female Chicken

Abstract The chicken egg is a giant reproductive cell protected by an eggshell, which forms daily in the distal segment of oviduct, in an acellular uterine fluid that contains inorganic and organic precursors of the shell. Its distinctive features, as compared to bone or teeth, are the nature of the mineral and the absence of cell-directed assembly during its fabrication on eggshell membranes. Eggshell formation challenges calcium homeostasis because of the rapidity and intensity of the mineralization. Hens develop numerous physiological adaptations for supplying the shell calcium and carbonate by developing the estrogen-dependent medullary bone, by increasing sixfold intestinal calcium absorption, by stimulating the active metabolite of vitamin D in the kidney, and by developing the uterine capacity to transfer great quantities of Ca2+ and HCO3− ions and to synthesize eggshell matrix proteins. This review described the role of vitamin D and other regulating factors in control of eggshell formation and Ca metabolism in hens.