anp lab2

• the inital period of embryological and fetal development
• by the end of this first three months all of the organs systems have rudimentarliy developed.
• four major events occur during the first trimester
• -cleaveage
• -implantation
• -placentation
• -embryogeneis

• when the secondary oocyte is fertilized it becomes a single cell that is acalled the zygote
• the zygote then undergosed a series of subdivisions
• these subdividons reduce the amount of cytoplasm in the cells, which are called blastomers

subdivide for about three days to form a solild ball of celles called the morula

reaches the uterus about day four and during the next two days it develops inot a hollow ball of cells called the blastocyst

• is composed of two cell layers
• the outher layer develops into the placenta
• the cells of the inner layer are clustered at on end of the blastocyst. and eventually develop inot the embryo

• occurs when the blastocyst becomes embedded in the endometrium of the mothers uterus.
• the outer cell layer becomes intimately associated with the maternal circulatory system for nutrient and gas exchange.
• meanwhile the inner cell layer of the blastocyst also differentiates
• the inner cell lay becomes detached form the outer cell layer
• the separtation yeilds a fliuid filled cavity called the amniotic cavity
• by the twelfth day a third cell layer develops and the blasotcyst become a struture called the gastrula
• during gaturaltion three germ layers form that five ries to the various organs systems
• -ectoderm
• -mesoderm
• -endoderm
• these three germ layers form a sheet of cells called the embryonic disk
• and these three germ layeres then develop into the four extaembyonic membranes
• and these membrans protect the embryo

• this sac is a pouch formed from the endodem and mesderm.
• it is an intital site of blood cell formation

• this membrane is formed from the ectoderm and mesoderm
• it lilnes the innersurface of the amniotic cavity
• the fluid contained within the cavity is called the amniotic fluid
• the amnion and the amniotic fluid surround and protect the growing embryo

• this membrane is forme from the endoderm and mesoderm
• it eventually gives rise to the urinary bladder

• this membrane is formed from the mesoderm and the outer cell layer of the blastocyst
• the chorion differentiates into the featl portion of the placenta as the embryo enlarges

is the development and differentiaiton of the featal and maternal portions of the placenta

• fingerlike projections that chorion devlopes
• which make contact with the endometruim

• as the placenta enlarges it creates a large bulge on the surface of the endometrium
• blood ruputured maternal blood vessels slowly leaks through small chambers in the materanl placenta called lacunae

• the differentation of the nbody of the embryo and the rudiimentary development of the organ system
• the body of the embryo begins to emereg from the embryonic disk, and devlops into a bulge that has head and tail folds

• the fetus gains weight and the organ systems continue to devleop
• by the end of the pregnacy th uteus with the fetus occupy a large portion of the materanl abdominal cavity. s