Figure 39.26 Flashcards
Describe what happens during days 1-2 after fertilization.
The first cleavage furrow extends between the two polar bodies. Later cuts are angled, so cells become asymmetrically arranged. Until the eight-cell stage forms, they are loosely organized, with space between them.
Describe what happens during day 3 after fertilization.
After the third cleavage, cells abruptly huddle into a compacted ball, which tight junctions among the outer cells stabilize. Gap junctions formed along the interior cells enhance intercellular communication.
Describe what happens during day 4 after fertilization.
By 96 hours there is a ball of sixteen to thirty-two cells shaped like a mulberry. It is a morula (after morum, Latin for mulberry). Cells of the surface layer will function in implantation and will give rise to a membrane, the chorion.
Describe what happens during day 5 after fertilization.
A blastocoel (fluid-filled cavity) forms in the morula as a result of surface cell secretions. By the thirty-two-cell stage, differentiation is occurring in an inner cell mass that will give rise to the embryo proper. This embryonic stage is the blastocyst.
Describe what happens during days 6-7 after fertilization.
Some of the blastocyst’s surface cells attach themselves to the endometrium and start to burrow into it. Implantation has started.
Describe what happens during days 10-11 after fertilization.
The yolk sac, embryonic disk, and amniotic cavity have started to form actual from parts of the blastocyst.
Describe what happens during day 12 after fertilization.
Blood-filled spaces form in maternal tissue. The chorionic actual cavity starts to form.
Describe what happens during day 14 after fertilization.
A connecting stalk has formed between the embryonic disk and chorion. Chorionic villi,
which will be features of a size placenta, start to form.
