Hen’s egg shell structure and function

Abstract

The formation of the physical barrier to bacterial ingress into the egg takes more than 20 h. During this time the yolk and albumen move from the isthmus region of the oviduct, in which the paired shell membranes are elaborated, to the tubular shell gland and shell gland pouch where mineralization proceeds (Arias et al., 1993). The latter process is preceded by the addition of plumping fluid to the albumen. This increases the total volume of the latter and renders the flaccid shell membranes taut. Calcium salts from the oviducal fluid in which the egg is bathed, precipitate onto selected (nucleation) sites on the outer shell membrane. These sites are referred to as the mammillary knobs and the whole as the mammillary layer. The true shell consists of five morphologically distinct regions which, proceeding outwards from and including the mammillary knob layer, are designated the cone, palisade, vertical crystal layer and cuticle (Figure 1.1).