What happens after fertilization
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The zona pellucida has dissolved by the 5th day, when the embryo enters the uterus

The embryo floats free for several days, nourished by fluids from glands in the uterine wall

At this point, it is called a blastocyst

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Implantation

The embryo implants in the wall of the uterus on about the 7th day of development

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12-day Human Embryo

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Where does this all take place?

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The placenta is the site of nutrient, gas, and waste exchange

Secretes hormones that maintain pregnancy

Trophoblast cells release human chorionic gonadotropin (hCG) which signals the corpus luteum to enlarge and produce progesterone

The placenta develops from the embryonic chorion and maternal uterine tissue

Chorionic villi are formed from the chorion, and project into the endometrium of the uterus

The umbilical cord, containing two umbilical arteries and one umbilical vein connects the embryo and the placenta

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Development of the Placenta

Slide 27

Human Fetus at Ten Weeks

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