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23 Cards in this Set

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  • Back
When can an egg be fertilized?
Within 12-24 hours following ovulation.
What happens when more than 1 egg is fertilized?
Fraternal Twins
What is cleavage?
Series of rapid mitotic division during early embryonic development.

Increase in number of cells, no increase in overall size of tissue mass.

Increases surface area:volume ratio of each cell.
What is indeterminate cleavage?
Division that results in cells that maintain the ability to develop into complete organism.

Twins are a result of this cleavage.
What is determinate cleavage?
Division that results in cells whose future differentiation path is already determined.
What are identical twins a result of?
Indeterminate cleavage.
When do cleavages occur?
First complete cleavage: 32 hours
Second: 60 hours
Third: 72 hours

8 Celled Embryo now reaches uterus
What is a Morula?
Solid ball of embryonic cells
What is Blastulation?
Blastulation occurs when the morula develops a fluid-filled cavity called the blastocoel. Which by fourth day becomes a blastula.
What is a blastula?
Hollow sphere of embryonic cells.
What is gastrulation?
Once implanted in the uterus, cell migrations transform the single cell layer of the blastula into a three-layered structure call a gastrula.

Three layers are responsible for development of various tissues and organs.
What is a gastrula?
Three layered cell mass created by gastrulation.
What are the three primary germ layers?
What does the ectoderm develop into?
Integument (epidermis, hair, nails, epithelium of nose, mouth, anal canal), lens of the eye, the retina, nervous system.
What does the Endoderm develop into?
Epithelial linings of the digestive and respiratory tract (including lungs), parts of the liver, pancreas, thyroid, and bladder lining.
What does the mesoderm develop into?
Musculoskeletal system, circulatory system, extretory system, gonads, connective tissue throughout the body, and portions of digestive and respiratory organs.
How does external development work?
Early development occurs outside of the mother's body (eggs).

Fish and amphibians lay eggs that are fertilized externally in the water.

Reptiles, birds, and some mammals develop externally on land after an internal fertilization.
What membranes do External Development eggs contain?
Chorion - Lines the inside of the shell that is moist membrane and permits gas exchange

Allantois - Sac-like structure is involved in respiration and excretion and contains numerous blood vessels to transport O2, CO2, water, salt, nitrogeneous wastes.

Amnion - Membrane encloses the amniotic fluid. Amniotic fluid provides an aqueous environment which protects the developing embryo from shock.

Yolk Sac - Encloses the yolk that contains blood vessels that transfer food to the developing embryo.
What is Non-Placental Internal Development?
Early development occurs within the mother.

No placenta => very little gas and nutrient exchange between young and mother.

Young may be born very young.
What is Placental Internal Development?
Growing fetus receives oxygen, nutrients, and removal of CO2, and wastes directly from/to the mother via specialized circulatory system.

Two components: Placenta and Umbilical Cord, both develop in first few weeks following fertilization.
What are the four membranes in Placental Internal Development?
Amnion - Thin, tough membrane containing watery floud called amniotic fluid.

Chorion - Membrane that completely surrounds the amnion.

Allantois - Develop as an outpocketing of the gut and ultimatly becomes the umbilical cord.

Yolk Sac - Site of early development of blood vessels, becomes associated with the umbilical vessels.
When do fetal lungs begin working?
AFTER BIRTH, all gas exchange prior to birth occurs via the placenta.
Stages of Labor
First - Cervix thins out and dilates, amniotic sac ruptures, releasing its fluids. Contractions are mild.

Second - Characterized by rapid contractions, birth, cutting of cord.

Third - Uterus contracts, expelling the placenta and umbilical cord.