of a Chicken Egg
eggshell is made almost entirely of calcium carbonate (CaCO3)
and is covered with as many as 17,000 tiny pores. It is a semipermeable
membrane, which allows air and moisture to pass through its pores.
The shell also has a thin outermost coating called the bloom or
cuticle that helps keep out bacteria and dust (see below 15).
3. Inner shell membrane
membranes -- outer and inner -- are just inside the shell surrounding
the albumen (white). The two membranes provide an efficient defense
against bacterial invasion and are made partly of keratin. The
outer membrane sticks to the egg shell while the inner membrane
sticks to the albumen. When an egg is first laid, it is warm.
As it cools, the contents contract and the inner shell membrane
separates from the outer shell membrane to form the air cell (see
-- are twisted in opposite directions and serve to keep the yolk
centered. The more prominent the chalazae, the fresher the egg.
albumen (outer thin albumen) -- The
outer thin albumen is a narrow fluid layer next to the shell membrane.
albumen (inner thick albumen) --The
inner thick white (chalaziferous layer) is a dense, matted, fibrous
capsule of albumen around the vitelline membrane of the yolk.
The matted fibrous capsule terminates on each end in the chalazae,
which are twisted in opposite directions and serve to keep the
yolk centered. This part of the egg is a excellent
source of riboflavin and protein. In high-quality eggs, the inner
thick albumen stands higher and spreads less than thin white.
In low-quality eggs, it appears thin white.
membrane -- The
clear casing that encloses the egg yolk. When
an egg is said to be "mottled", the yolk surface is covered with
many pale spots or blotches. The strength and integrity of the
vitelline membrane are very important in preventing egg yolk mottling.
of pander -- a plug of whitish yolk, with no particular significance
for development and whose function is purely a nutritive one,
like the rest of the yolk. (See: Int. Schmitt S., (2005) J. Dev.
Biol. 49: 1-8).
disk (blastoderm) -- a small, circular, white spot (2-3 mm
across) on the surface of the yolk; it is where the sperm enters
the egg. The nucleus of the egg is in the blastodisc. The embryo
develops from this disk, and gradually sends blood vessels into
the yolk to use it for nutrition as the embryo develops.
a major source of vitamins, minerals, almost half of the protein,
and all of the fat and cholesterol. The
yolk contains less water and more protein than the white, some
fat, and most of the vitamins and minerals of the egg. These include
iron, vitamin A, vitamin D, phosphorus, calcium, thiamine, and
riboflavin. The yolk is also a source of lecithin, an effective
emulsifier. Yolk color ranges from just a hint of yellow to a
magnificent deep orange, according to the feed and breed of the
yolk -- Also known as, the latebra is an area of white yolk
located in the center of the yolk. It is lower in fat and therefore
stands out as a bright white area in many Magnetic Resonance Images.
The specific function of the latebra is uncertain but it may act
as a central structure around which the additional layers of the
yolk are formed.
albumen (Chalaziferous albumen)-- The inner thick white (chalaziferous
layer) is a dense, matted, fibrous capsule of albumen around the
vitelline membrane of the yolk. The matted fibrous capsule terminates
on each end in the chalazae, which are twisted in opposite directions
and serve to keep the yolk centered.
chalazae, which are twisted in opposite directions and serve to
keep the yolk centered. The more prominent the chalazae, the fresher
the egg. chalazae, which are twisted in opposite directions and
serve to keep the yolk centered.
cell -- An air space forms when the contents of the egg cool
and contract after the egg is laid. The air cell usually rests
between the outer and inner membranes at the egg’s larger end.
egg ages, moisture and carbon dioxide leave through the pores
of the shell, air enters to replace them and the air cell becomes
or bloom -- 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
egg shell. Most of cuticle is removed from table eggs when they
are mechanically washed.