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Egg Composition and Formation - Anatomy & Physiology (view source)
Revision as of 12:19, 22 July 2008
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= Size =
* Varies greatly between species.
* Altricial species lay much smaller eggs than Precocial species.
** '''Precocial''': Chicks have natal down,hatch with their eyes open and can survive outside the nest within 1-2 days.
** '''Altricial''': Chicks are born blind and nakes,require long periods of feeding.
----
= Shell =
The shell provides physical protection. It protects the embryo from microorganisms and regulates evaporation so that the embryo does not become dessicated. The shell is also a source of calcium carbonate, which is important for bone formation in the embryo.
== Shell membranes ==
* Organised into an '''inner and outer''' layer which lie in close apposition.
* Part at one end to form the '''air cell''', where the hatching chick draws its first breath.
* Meshwork of protein fibres (protein and glycoprotein) with minor constituents collagen, hydroxyproline and hydroxylysine.
* '''Prevent dessication''' and infection.
== Testa ==
* Main thickness of the shell
* Matrix fibres and calcium carbonate
* Calcium carbonate layes contains pores to allow '''gas exchange'''.
* Pigmented by porphyrin and biliverdin
== Cuticle ==
* Water repellent
* Barrier to infection
----
== Yolk ==
* '''Protein and lipids''' are synthesized in the liver and travel to the oocyte in the ovary, where they are made into yolk ('''vitellogenesis''').
* Principle stored '''nutrients''', provides main nutrient for the embryo.
* Produces '''water and energy''', allowing survival in arid environments.
* Thick and viscous
* Contains '''maternal antibodies''', primarily IgG.
----
== Albumin ==
* Less viscous than yolk
* Composed mainly of '''water''' and '''protein'''.
* Buffers the embryo from sudden changes in temperature.
* Serves as a '''shock-absorber''' to protect the embryo.
* Thin layer encloses the yolk membranes and suspends the yolk in the centre of the egg by twisted strands called '''Chalazae'''.
----
= Germinal Disc =
* Small, circular, white spot on the surface of the yolk.
* Contains cytoplasm and the oocyte.
----
= Embryonic Membranes=
Within the egg, three extraembryonic membranes support the life & growth of the embryo:
== Amnion ==
* Surrounds only the embryo
* Inner layer of cells secretes amniotic fluid in which the embryo floats.
* Fluid keeps the embryo from drying out and provides protection.
== Chorion ==
* Surrounds all embryonic structures and serves as a protective membrane ('''chorioallantoic membrane''').
* Also important for:
** Transpiration
** Metabolism
** Waste collection
** Calcium transfer from the shell to the embryo.
== Allantois (or allantoic sac) ==
* Grows larger as embryo grows
* Fuses with the chorion and is called the '''chorio-allantoic membrane'''.
* Works together with chorion to permit respiration (exchange of oxygen and carbon dioxide) and excretion.
* Important in storage of nitrogenous wastes (uric acid).
<big><center>[[Reproductive_System#Exotics|'''BACK TO EXOTICS''']]</center></big>
<big><center>[[Exotics_-_Avian_Reproductive_Anatomy_and_Physiology_-_Anatomy_%26_Physiology|'''BACK TO AVIAN REPRODUCTIVE ANATOMY & PHYSIOLOGY''']]</center></big>
<big><center>[[Exotics_-_Reproduction_in_the_Female_Avian_-_Anatomy_%26_Physiology|'''BACK TO FEMALE AVIAN REPRODUCTIVE ANATOMY & PHYSIOLOGY''']]</center></big>
= Size =
* Varies greatly between species.
* Altricial species lay much smaller eggs than Precocial species.
** '''Precocial''': Chicks have natal down,hatch with their eyes open and can survive outside the nest within 1-2 days.
** '''Altricial''': Chicks are born blind and nakes,require long periods of feeding.
----
= Shell =
The shell provides physical protection. It protects the embryo from microorganisms and regulates evaporation so that the embryo does not become dessicated. The shell is also a source of calcium carbonate, which is important for bone formation in the embryo.
== Shell membranes ==
* Organised into an '''inner and outer''' layer which lie in close apposition.
* Part at one end to form the '''air cell''', where the hatching chick draws its first breath.
* Meshwork of protein fibres (protein and glycoprotein) with minor constituents collagen, hydroxyproline and hydroxylysine.
* '''Prevent dessication''' and infection.
== Testa ==
* Main thickness of the shell
* Matrix fibres and calcium carbonate
* Calcium carbonate layes contains pores to allow '''gas exchange'''.
* Pigmented by porphyrin and biliverdin
== Cuticle ==
* Water repellent
* Barrier to infection
----
== Yolk ==
* '''Protein and lipids''' are synthesized in the liver and travel to the oocyte in the ovary, where they are made into yolk ('''vitellogenesis''').
* Principle stored '''nutrients''', provides main nutrient for the embryo.
* Produces '''water and energy''', allowing survival in arid environments.
* Thick and viscous
* Contains '''maternal antibodies''', primarily IgG.
----
== Albumin ==
* Less viscous than yolk
* Composed mainly of '''water''' and '''protein'''.
* Buffers the embryo from sudden changes in temperature.
* Serves as a '''shock-absorber''' to protect the embryo.
* Thin layer encloses the yolk membranes and suspends the yolk in the centre of the egg by twisted strands called '''Chalazae'''.
----
= Germinal Disc =
* Small, circular, white spot on the surface of the yolk.
* Contains cytoplasm and the oocyte.
----
= Embryonic Membranes=
Within the egg, three extraembryonic membranes support the life & growth of the embryo:
== Amnion ==
* Surrounds only the embryo
* Inner layer of cells secretes amniotic fluid in which the embryo floats.
* Fluid keeps the embryo from drying out and provides protection.
== Chorion ==
* Surrounds all embryonic structures and serves as a protective membrane ('''chorioallantoic membrane''').
* Also important for:
** Transpiration
** Metabolism
** Waste collection
** Calcium transfer from the shell to the embryo.
== Allantois (or allantoic sac) ==
* Grows larger as embryo grows
* Fuses with the chorion and is called the '''chorio-allantoic membrane'''.
* Works together with chorion to permit respiration (exchange of oxygen and carbon dioxide) and excretion.
* Important in storage of nitrogenous wastes (uric acid).