 | never make it to the cervix |
| destroyed by the acidic environment of the vaginal tract |
| blocked by the mucous of the cervix |
| destroyed by lymphocytes |
C). What prevents polyspermy?
Step 1. Contact with sperm opens Na+ channels. Membrane depolarizes
Step 2. Ca2+ is release
i. Readies for cell division
ii. cortical reaction. Destroys sperm receptors
iii. Bind with water swelling the membrane
II. Implantation
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 |
 |
|
blastocyst tries to implant high in the uterus
regulatory hormones prepare the uterus
trophoblast cells adhere to the endometrium
digests the uterine cells
blastocyst covered with uterine lining
corpus luteum maintains the uterine wall for 2 weeks after ovulation
The trophoblast cells of the blastocyst release human chrorionic gonadotropin (hCG) which acts like luteinizing hormone.
The embryo now takes over control of the uterus.
At the second month the placenta takes over the hormone role.
III. Formation of germ layers
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ectoderm
endoderm
mesoderm
Embryonic Folding
Embryo starts as a flat disc
of 3 germ layers
È
Folds laterally into a tube
È
both ends fold into the center
È
edges come together and fuse
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IV). How do structures originate? (organogenesis)
1). Ectoderm
Neurulation:
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 |
Notochord
È
neural plate
È
neural groove
È
neural folds
È
neural tube
È
pinches off:
anterior-forms brain
posterior-spinal cord
È
associated cells give rise to peripheral ganglia
2). Endoderm Specialization
forms epithelial linings
ends fuse the endoderm forms the gastrointestinal tract
È
Pharynx, esophagus, stomach, intestine form
È
oral and anal openings perforate
3). Mesoderm
divides into
Somite:
sclerotome
dermatome
myotome
Intermediate mesoderm:
Lateral mesoderm:
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V). embryonic development
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VI. Fetal Development