TLE 10: EGG STRUCTURE AND COMPOSITION

• SHELL - the egg's outer covering, accounts for about 9 percent to 12 percent of it's total weight depending on egg size. The shell is the egg's first line of defense against bacterial contamination. The shell is produced by the shell gland (uterus) of the oviduct, and has an outer coating, the bloom or cuticle. The cuticle somewhat seals the pores and is useful in reducing moisture losses and in preventing bacterial penetration of the eggshell.
• AIR CELL - this is the empty space between the white and shell at the large end of the egg which is barely existent in newly laid egg. When an egg first laid, it is warm. As it cools, the contents contract and the inner membrane separate from the outer shell membrane to form the air cell.
• ALBUMEN or EGG WHITE - accounts for most of an egg's liquid white, about 67 percent. This is produce by the oviduct and consists of four alternating layers of thick and thin consistencies. From the yolk outward, they are designated as the inner thick white or the chalaziferous white, the inner thin white, the outer thick white and the outer thin white.
• OUTER THIN WHITE - is a narrow fluid layer next to the shell membrane
• OUTER THICK WHITE - is a gel that forms the center of the albumen
• INNER THIN WHITE - is a fluid layer located next to the yolk
• INNER THICK WHITE - also known as the chalaziferous layer, is a dense, matted, fibrous capsule terminates on each end in the chalazae, which are twisted in opposite directions and serve to keep the yolk centered
• CHALAZA - this is the ropey strands of egg white at both sides of the egg, which anchor the yolk in place at the center of the thick white
• GERMINAL DISC - the entrance to the latebra, the channel leading to the egg yolk. Is barely noticeable as a slight depression on the surface of the yolk
• SHELL MEMBRANE - there are two types of membranes, one just under the shell and the other, covering the yolk. These are the shell membrane and vitelline membrane.
• OUTER MEMBRANE - sticks to the shell
• INNER MEMBRANE - sticks to the albumen or egg white
• VITELLINE MEMBRANE - is the covering that protects the yolk from breaking. It is the weakest at the germinal disc and tends to become more fragile as the egg ages
• YOLK - makes up about 33% of the liquid weight of the egg. The egg yolk is formed in the ovary
• GERMINAL DISC - the small white spot about 2 mm in diameter