15.1 Flashcards
What are the 2 main periods of prenatal development?
The embryonic period and the fetal period
When does the Embryonic period of development take place?
The first 8 weeks, or the first 2/3rds of the first trimester
What happens in the embryonic stage of development?
Cells divide and become redistributed. tissues and organs form, as do structures that support and nourish the developing embryo
When does the Fetal period of development take place?
From the start of the 9th week till birth
What happens in the fetal period of development?
The body grows rapidly and organs begin to function and coordinate to form organ systems
What is fertilization?
The joining of male and female gametes that join to form a single cell with 23 chromosomes from each parent
How many days after ovulation does it take the ova to reach the uterus?
4 days
How many hours after ovulation must an egg be fertilized?
12 to 24 hours
When and where must the sperm meet the egg?
During the early part of its movement through the oviduct
Where must sperm go once its it ejaculated?
It must makes its way through the cervix and then through the uterus and finally the oviduct and into the egg
Why don’t most sperm survive the journey?
Because of the naturally acidic environment of the vagina and other go the wrong way
What is the membrane of the egg surrounded?
A thin clear layer of protein and carbohydrates called zona pellucida
What is the Zona Pellucida surrounded by?
Several jelly like layers of follicle cells that loosley adhere to one another called the Corona Radiata
What were the Corona Radiata to an egg?
A source of nourishment when it was in an ovarian follicle
What happens when sperm meets the corona radiate?
The sperms enzyme containing acrosome releases its contents
What do the enzymes released by the Acrosome do?
The enzymes digest a path through the corona zona pellucida
What happens once a sperm enters the egg?
The eggs plasma membrane depolarizes, preventing other sperm from binding and entering
What is a Zygote?
The single cell that is created when an egg and sperm join
What happens within 30 seconds of a zygote forming?
The 0.1 mm zygote divides by mitosis until it forms eight cells and so one
What is cleavage?
The process of cell division by a zygote with out the enlargement of cells
What is the morula stage?
When a zygote is a sphere of 16 cells
How many days after fertilization does the morula reach the uterus?
Within 3 to 5 days after fertilization
What happens as the Morula begins to fill with fluid?
2 different groups of cells form
What is the Blastocyst stage?
The stage after the Morula fills with liquid and 2 cell groups form
What is one of the cell groups in the Blastocyst?
The trophoblast, which forms the outer layer
What does the Trophoblast develop in?
A membrane called the Chorion
What does the Chorion in turn develop into?
The placenta
What is the Placenta?
The structure that provides nutrients and oxygen and removes wastes from developing offspring
When does the other group of cells within the blastocyst form?
The Inner Cell Mass (embryoblast)
What does the Inner cell mass develop into?
The embryo itself
How many does after fertilization does the blastocyst attach itself to the endometrium?
Between the fifth and seventh day after fertilization
What does the Trophoblast do after the Blastocyst attaches itself to the endometrium?
The Trophoblast cells secrete enzymes that digest some of the tissues and blood vessels of the endometrium to allow the blastocyst to sink into the uterine wall
What is implantation?
The nestling of the blastocyst into the endometrium
On what day of fertilization does implantation take place?
By day 10-14
What does the Trophoblast secrete after implantation?
A hormone called human chorionic gonadotropin (hCG)
What does hCG do?
It has the same effects as as LH and maintains the corpus luteum past the time it would otherwise degenerate