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Birth and Human Development (Gasturla- 3 germ layers form. epiblast/…
Birth and Human Development
How does fertilization Occur
What Happens btw fertilization and implantation
How does the Embryo implant into the uterus wall and trigger development of the placenta?
Cleavage- first phase of development. produce small cells with high surface to volume ratio.
36 hrs after fertilization- first cleavage. --> 2blastomeres
2 blastomeres --> 4 cells. --> 8. etc.
72 hrs ( 4 days), 16 or more. =
morula
. embryo continued to transport to uterus.
Blastocyst Formation
4/5 days
. 100 cells. starting to accumulate fluid @ internal cavity. float free in uterus.
zona pellucida break down. inner structure =
blastocyst
Hatch.
blastocyst= fluid filled hollow sphere. with trophoblast cells & inner cell mass on the inside.
trophoblast cells= placenta formation. nourishment generator.
secrete immunosuppressive effects for protection.
inner cell mass= embryonic disc. form embryo proper and 3/4 extraembryonic membranes.
Blastocyst floate in uterin cavity for 3/4 days. nourished by glycoprotein rich uterine secretion.
6/7 days after ovulation, implantation
.
receptivity of endometrium to implantation opened by the
surging level of estrogen and progesterone
.
integrin
and
selectin
proteins bind to extracellular matrix collagen of endometrial cells and to selectin binding carbohydrates on inner uterine wall
blastocyst implant high in the uterus.
trophoblast overlying inner cell mass adhere endometrium and secrete
digestive enzyme/ growth factors
to endometrium surface.
endometrium quickly thickens at the point of contact -->characteristic of
acute inflammatory response
.
uterine blood vessles more permeable/ leaky. inflammatory cells ( lymphocyte, NK, Macrophages invade area.)
trophoblast then form 2 distinct layer.
8 days
Inner layer=
cytotrophoblast
/ cellular trophoblast. retain cell boundaries.
outer layer= lose plasma membtrane and form multinulear cyoplasmic mass
syncytiotrophoblast
cells of embryonic disc separated from amnion by fluid-filled space.
Implantation occur when embryo burrow into uterine wall and trigger placenta formation.
Successful implantation-
5 days
day 26 of menstrual cycle before endometrium normally get slough off.
viability of corpus luteum maintained by hCG.
hCG secreted by trophoblast.
hcG make corpus luteum continue secreting progesterone and estrogen. chorion continues this after on.
hCG promote placental development.
hCG levels rise untill end of 2 month when corpus luteum degernerate. placenta continue the orle of keeping up estrogen and progesterone.
when implantation is complete, inner cell mass give rise to a layer of extraembryonic mesoderm under cytotrophoblast
day 12
line inner surface of trophoblast= chorion.
day 16
chorionic vili elaborate.
embryo three germ layer; yolk sac, allantois ( umbilical cord)
4 1/2 Week
chorionic villi invaded w/ new b. vessel, compressed and eventually degenerate
blood filled lucanae ( intervillous space)
beneath embyro=
decidua basalis
( further from baby. after the chronic villi/ placenta.)
decidua capsularis
= surround uterine cavity face of implanted embryo ( closer to baby)
yolk sac, amnion well formed.
Placenta fully functional by 3rd month
before this, things are diffusing through choronic villi and endometrium of embryonic capillaries.
Meiosis II completed with fertilization.
fluction of calcium level, it burst zinc ions from egg which trigger completion of meiosis II.
sperm must penetrate Corona Radiata/ deeper zona pellucida.
sperm digest interceullular cement betw granulosa cells so they would fall away from oocyte.
Sperm receptor @ zona pellucida. opens calcium channels.
acrosomal reaction; release of acrosomal enzmes to digest holes through zona pellucida.. exocytosis.
sperm's collar bind to oocyte plasma membrane receptors. --> cause 1)oocyte to form microbilli surrounding sperm head. sperm/oocyte membranes fuse. 2)cytoplasmmic content of sperm enter oocyte. leave sperm's plasma membrane. like snake skinning.
gametes fuse together.
Polyspermy
Monospermy. one sperm per oocyte. embryo dies if have too many genetic material.
oocyte membtrane block and zona reaction.
oocyte membrane block- when a sperm bind to oocyte's sperm receptor, oocyte shed the rest of sperm receptors.
zona reaction alter physical characteristic of zona pellucida. ca released by oocyte's ER activate oocyte for mitotic division. cause cortical reaction. gradunles located inside plasma membrane spill enzymes to extraellular space beneath zona pellucida destroy zona pellucida sperm binding receptors. and also bind water. this detach all other sperm bound to zona pellucida.
How does pregnancy affect the mother?
How is a baby born
How does the infant adjust to extrauterine life?
Starte with estrogen from the placenta.
induce oxytocin/ oxytocin from fetus & mother's p.pituitary
stimulate uterus contraction
stimulate placenta to release prostaglandins which stimulate more vigorous contractions and this positive feedback to get more oxytocin
Lactation
Metabolic changes
hPL stimulate breast for lactation, promote fetus growth
glucose sparing effect in mother.
metabolize more fatty acid, less glucose for fetus
gestational diabetes might occur
parathyroid hormone activated Vitamin D increase.
GI
hCG, estrogen, progesterone cause nausea and vomiting
Herat burn
costipation
Urinary
more urine
because increased metabolic rate, more blood volume, more metabolic waste.
Respiratory system
nasal mucosa congested, edematous,
nose bleed due to nasal stuffiness
increaed tidal volume; dyspnea
cardiob
increase of blood volume
blood pressure decrease, but rise during timester
increased cardiac output
impare of venous return
How can infertile couples be helped?
Gasturla- 3 germ layers form.
epiblast/ hypoblast.
Primitive Germ layer
ectoderm, mesoderm, endoderm
Gastrulation= cellular rearrangements/ migration.
primitive streak
hypoblast cells of yolk sac form endoderm, followed by mesoderm.
mesodermal cells aggregate, form notochord
axial support of embryo
ectoderm= nervous system, skin
endoderm= digestive, respiratory, urogenital, glands
mesoderm= everything else.
Organogenesis
endoderm--> primitive gut
ectoderm --> neurulation
First major event
brain and spine chord.
mesoderm--> notochord= first event of meso.
Extra embryonic Membranes-
first two weeks
Amnion- develop when epiblast--> trasparent membranous sac. sac fill w/ amniotic fluid.goes all the way around the embryo
buoyant environment. protection. freedom of movement
fetal urine and maternal blood.
Yolk Sac- cells of primitive put. form part of gut ( digestive tube)
Source of earliest blood cells/ blood vessel.
Allantois- small outpocketing of embyronic tissue.
disposal site for solid metabolic waste.
umbilical cord. embryo + pacenta.
become urinary bladder.
teratogen
