BI 233 A&P Lab-Ex. 44

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Three basic activites which ensure the formation of a viable offspring
- Increase in cell number and subsequent cell growth
- Cellular specialization
- Morphogenesis--the formation of functioning organ systems
Zygote
- Fertilized Egg
- Appears as a single cell immediately surrounded by a fertilization membrane and a jelly like membrane
- Contains a single nucleus composed of the fused nuclei of the egg and sperm
Fertilization

The penetration of an egg by a sperm and the subsequent fusion of nuclei
Fertilization Membrane
- Forms w/in 2-5 minutes after the sperm penetrates the egg
- Forms beneath the jelly coat
- Prevents the entry of additional sperm
Blastomere
- The successively smaller and smaller cells which are created during the cleavage stage as a zygote begins to divide
Cleavage
- The stage in which a zygote undergoes a series of mitotic divisions without intervening growth periods
- Produces a multicellular embryonic body composed of blastomeres
Morula

the 32-cell stage of zygote cleavage
Blastula/Blastocyst/Chorionic Vesicle
- Occurs when the morula hollows out to become a ball of cells surrounding a central cavity
- This is the final product of cleavage
Early Gastrula
- Form in which one portion of the blastula begins to collapse in on itself until a horse-shoe or bowl shape is created, thus producing a two-layered embryo
Gastrulation
- The process in which a blastocyst folds in upon itself thus causing the inner cell mass to create a bilayer (and ultimately tri-layered) embryo
- Occurs as blastocyst implants itself into uterine wall
Primary Germ Layer
- One of three layers produced from gastrulation
- Origination of all body tissues
- Endoderm/Mesoderm/Ectoderm
Epiblast

Layer of cells which later develops into the ectoderm
Hypoblast

Layer of cells which later develops into the endoderm
Endoderm
- Innermost primary germ layer which develops closest to the yolk sac
- Along with mesoderm this forms the internal organs
- Forms mucosa of digestive and respiratory tracts and associated glands
Mesoderm
- Middle primary germ layer which emerges in the center of the endoderm and ectoderm
- Along with endoderm this forms the internal organs
- Forms the skeleton
- Forms the walls of the digestive organs
- Froms the urinary tract
- Froms skeletal muscles
- Forms the circulatory system
- Forms virtually everything lying between the epidermis/nervous system and the mucosa of the digestive/respiratory tracts
Ectoderm
- Outermost of the primary germ layers which forms closest to the amniotic cavity
- Gives rise to the surface tissues of the body
- Forms the epidermis of the skin
- Forms the nervous system
Morphogenesis

The formation of functioning organ systems
Zona Pellucida
- Jellylike layer immediately external to the fertilized egg
- Area from which the early blastocyst "hatches" around day 4
Corona Radiata
- A crown of granulosa cells just external to the zona pellucida
Inner Cell Mass (ICM)
- Eccentric (non-centered) cell mass within a blastocyst
- During gastrulation this folds in upon itself eventually forming the embryo
Trophoblast
- Portion of the blastocyst excluding the ICM
- Sphere of cells enclosing the central cavity of the blastocyst and overlying the ICM
- Develops into chorion
Action of Trophoblast Cells

As blastocyst implants these cells secrete enzymes at the point of attachment which erode the uterine mucosa allowing access to the vascular supply of the submucosa
Chorion
- Extraembryonic membrane which arises from the trophoblast to form the fetal portion of the placenta
Blastocyst Cavity

Portion of blastocyst within the trophoblast which does not include the ICM
Implantation
- Occurs around day 7 through 14 after ovulation
- Free-floating blastocyst adheres to the uterine wall at the site of the ICM
- Uterine mucosa grows over the embryo
Decidua Basalis
- Portion of the uterine wall beneath the ICM which will later take part in placenta formation
Decidua Capsularis
- Portion of uterine wall which encapsulates the non-ICM portion of the blastocyst
Fetus
- Begins at week nine after ovulation
- Signals beginning of growth and tissue/organ specialization
- Occurs after primary germ layers have completed laying the groundwork for all body tissues
Placenta
- Composite of chorionic villi and uterine tissue
- Structure which is the site of all exchanges to and from the embryo
Chorionic Villi
- Large, elaborate vessels which float in the blood-filled sinusoid of the uterine tissue
- Waste/Nutrient exchange occurs through these membranes
What are the 3 embryonic membranes present after implantation
- Amnion
- Yolk Sac
- Allantois
Amnion
- Fluid-filled chamber which encases the embryo and protects it from:
- mechanical trauma
- temperature extremes
- adhesions during rapid embryonic growth
Yolk Sac
- Site of development of the embryo's first blood cells
- Site from which primordial germ cells migrate to seed the gonadal tissue
- Originally functioned to pass nutrients to the embryo after digesting the yolk mass (the placenta now has this function)
Allantois
- Protrudes from the posterior end of the yolk sac
- Largely redundant d/t placenta
- Repository (in birds/reptiles) for embryonic wastes
- Structural basis (in humans) on which the mesoderm migrates to form the body stalk/umbilical cord
Umbilical Cord
- "body stalk"
- Attaches embryo to the placenta
- Forms d/t migration of the mesoderm along the allantois

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TheRealHeatherMarie

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BI 233 A&P Lab-Ex. 44

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Survey of Embryonic Development amniotic sac/umbilical veins/umbilical artery/umbilical cord/intervillous space/maternal blood vessels/fetal blood vessels/chorionic villi/placenta--fetal portion/maternal portion/umbilical cord/allantois/yolk sac/amnion/placenta chorion/placenta chorionic villi/embryo

Updated

2012-12-07T02:48:06Z