Chicken Egg Anatomy and Dissection

• Yolk is released into the oviduct within the reproductive system, where sperm fertilizes it internally.
• Chicken egg formation begins as a yolk inside a hen.
• The hen's ovary produces the yolk through ovulation.
• Yolk is released into a spiraling tube in the hen's reproductive system and fertilized internally by rooster sperm.
• Only fertilized eggs develop into chicks; not all eggs are fertile.

Egg Observation and Dissection

• Methods involve material collection, observing the egg's exterior, and carefully cracking it open into a bowl.
• The inside of the egg can be observed including the air cell pocket, typically found at the rounded end of the shell.
• The shell membrane, a thin, flexible layer, is removed and placed on paper towel.
• Egg contents should be examined to find the yolk and the albumen (egg white)

Albumen Examination

• Division between the thin and thick albumen should be identified, the protein in which is used by the developing embryo for growth.
• The albumen fills the space between the yolk and shell membrane in an intact egg.
• The yolk is the yellow component, rich in carbohydrates, and the embryo uses it for energy.
• The germinal disk, a small white spot on the yolk's surface, is the location of fertilization and embryo development.
• If fertilized, the germinal disk appears red or brown, indicating embryo growth.
• Chalazae are whitish strands connecting the yolk to the membrane, keeping the germinal disk and embryo oriented at the top. Remove the chalazae with a toothpick.

Yolk Examination

• The yolk needs to be separated from the egg white.
• The yolk is surrounded by a membrane that helps it maintain its shape.
• The yolk should be placed in its designated area on the specimen sheet

Egg Yolk Production

• Yolk develops entirely within a female bird’s ovary inside a follicle.
• The follicle releases the yolk to initiate egg-laying.
• Liver synthesizes yolk material, transporting it via bloodstream to ovary, forming layers in follicle.

Egg Types

• Classified by yolk amount and distribution.
• Yolk amount categories:
  • Alecithal: Little to no yolk.
  • Microlecithal: Small amount of yolk.
  • Mesolecithal: Moderate amount of yolk.
  • Macrolecithal: Large amount of yolk.
• Yolk distribution categories:
  • Homolecithal: Yolk distributed throughout cytoplasm.
  • Telolecithal: Yolk concentrated towards the vegetal pole.
  • Centrolecithal: Yolk evenly distributed.

Embryo Nourishment and Shell Function

• The embryo uses the yolk for energy, that contains proteins, fats, and nutrients.
• The placenta provides nutrients in mammals.
• The embryo uses the yolk for growth, that provides essential nutrients like proteins and fats.
• The placenta supplies nutrients in mammals instead of a yolk
• The shell has pores for gas exchange, allowing oxygen in and carbon dioxide out that helps the embryo breathe.

Shell Formation and Membrane Function

• The hard calcium shell forms in the uterus of birds and reptiles post-fertilization, before laying.
• Shell formation does not affect fertilization.
• The shell membrane protects the embryo and regulates gas exchange.
• The yolk membrane encapsulates the yolk, providing accessible nutrients for development.