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Embryo Development

Embryo Formation After fertilization, the embryo divides repeatedly by mitotic division
Development Growth and differentiation that produce a fully formed embryo
Cleavage repeated cell division of the zygote; produces a hollow ball with a single layer of cells called the blastula; cells do not grow so the blastula stays the same size as the zygote
Gastrulation one side of the blastula becomes indented, forming the gastrula; 3 layers form; ectoderm, endoderm, and mesoderm
Ectoderm The outer layer; nervous system; epidermis of skin
Endoderm The inner layer; lining of the digestive and respiratory tract; liver and pancreas
Mesoderm The middle layer; muscles and skeleton; circulatory, excretory, and reproductive system,
Growth Results from an increase in the number of cells as well as an increase in cell size
External Development Development that occurs outside the female's body
Internal Development the embryo develops inside a female organ called the uterus
Umbilical Cord Developing embryo obtains nutrients and oxygen and releases wastes through a structure, which is attached to the wall of the uterus
Placenta Region of attachment of the umbilical cord; rich in blood vessels of mother and embryo; no direct connection between the two circulatory systems
Exchange in the Placenta by diffusion and active transport
Exchange of gas in the Placenta only by diffusion
In water external development the eggs of most fish and amphibians are fertilized externally and develop externally in an aquatic environment
Yolk stored in the egg the source of food for the developing embryo; develops to an advanced stage of development before emerging into the environment
on land external development the eggs of birds, many reptiles, and some mammals develop externally in a land environment after internal fertilization; these eggs have special adaptations to insure survival under the conditions of a land environment
Shell hard provides protection for the embryo
Chorion lines the shell
Allantois functions in the exchange of respiratory gases and excretion of wastes
Amnion contains amniotic fluid provides watery environment, protects against shock
Yolk sac surrounds the yolk and is penetrated by blood vessels, which transports food to the developing embryo
Pouched Mammals some internal development but no attachment to the uterus; called non-placental mammals; born before fully developed; climbs to a pouch on mother's outside and obtains nutrients from the mammary glands in the pouch
Created by: eileenc4



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