Chapter 21
General Embryology
---a science which study the processes and
regulations of development of human
fetus.(from 1 cell(zygote) to (5-7)X1012 cells )
---total 38 weeks:
preembryonic period: before 2 weeks
embryonic period: 3-8 weeks
fetal period: after 9 weeks
*perinatal stage: 26 weeks to birth
*Teratology: abnormal development of fetus
1.Fertilization
---definition: the process by
which the male and
female gametes(sperm
and ovum) unite to give
rise to zygote
---place: in the ampullary
region of the fallopian
tube
---conditions:
1)
maturation of oocyte
2)
maturation of spermatozoon:
/ductus epididymus: 2-3 weeks, forward
motility protein
3) capacitation of spermatozoa:
decapacitation
factor:
exist
in
epididymus, to inhibit the release of
acrosome enzymes
capacitation factor: secreted by epi.
cells of oviduct, capacity of releasing
acrosome enzymes
4) quality and quantity of spermatozoa:
2-6 ml, 100,000,000/ml,
<1.5 ml; or <10,000,000; abnormal
sperm >30%; or capacity for mobile<
70%
5) meeting of sperm and ovum
sperm: 20-24h
ovum: 15-18h(1-3ds)
---processes of fertilization:
1) acrosome reaction:
/hyaluronic acidase: dissolve corona radiate
* interact with ZP3(receptor glycoprotein, exist
in zona pellucide) molecules, release
/acrosin: dissolve zona pellucide
/enter perivitelline space
2)
spermatozoa fuse with the membrane of
ovum: nucleus enter cytoplasm of ovum
3)
monospermy:
cortical reaction: cortical granules(located in
cytoplasm of ovum) are released into
perivitelline space, and cause
zona reaction: change of ZP3 molecules in
zona pellucide
4)
formation of zygote(fertilized ovum)
secondary meiosis complete: form second
polar body
male pronucleus fuse with female
pronucleus, to restore the 2n chromasome
---significance of fertilization:
1) a new life begin(initiation of cleavage)
2)restoration of the diploid number of
chromosomes: cross-over
3) determination of the sex of the new individual:
ova(22+X) + X-bearing spermatozoon = girl
ova(22+X) + Y-bearing spermatozoon = boy
*klinefelter’s syndrome: 47XXY, 48XXXY
2. Blastocyst formation and implantation
1)
cleavage and blastocyst formation
①cleavage
---blastomere: cells formed by cleavage
/30h: 2
/40h: 4
/72h: 12-16- morula
②formation of blastocyst: by 5th day,
blastomere reach to 107, small space appear
between them
---blastocoele: filled with liquid
---trophoblast
---inner cell mass
---polar trophoblast
2) Implantation
---definition: the process by which the
blastocyst is embedded in endometrium
---time: 5th –6th day begin; 11th –12th day
complete
---processes: zona pellucide disappear → polar
trophoblast touch the endometrium→secrete
proteolytase →dissolve the endometrium →
embedded into endometrium→coagulation plug
seal the space
* trophoblast become into two layers when
blastocyst is embedding into endometrium
syncytiotrophoblast
cytotrophoblast
---place:
/posterior wall of fundus and body of uterus
placenta praevia
ectopic pregnancy
---decidual response of endometrium
/stroma
cell→predecidual
cell→decidual
cell(cell become larger and rich in glycogen
and lipid droplet)
/endometrium →decidua:
-decidua basalis
-decidua capsularis
-decidua parietalis
---conditions:
/endometrium is in secretory phase
/morula reach the cavity of uterus on time
/zona pellucide disappears in time
3. Formation and differentiation
of trilaminar germ disc
1) formation of endoderm and ectoderm: early
of 2 weeks, inner cell mass differentiate into
two layers of cells
---bilaminar germ disc: epiblast(columnar)
+hypoblast(cuboidal)
---epiblast: primary ectoderm
/amniotic membrane: amnioblast
/amniotic cavity
/amniotic fluid
/amnion
---hypoblast: primary endoderm
/extraembryonic endoderm→exocoelomic
membrane→primary yolk sac →
exocoelomic vesicle
/extraembryonic mesoderm: → extraembryonic
cavity: chorionic cavity
-visceral layer
-parietal layer
/secondary yolk sac: yolk sac
---body stalk: formed by extraembryonic
mesoderm
2) formation of mesoderm: early of 3 weeks
---primitive streak: cells of epiblast proliferate to
form a longitudinal arranged cell cord
---primitive groove
---primitive node
---primitive pit
---mesoderm: intraembryonic mesoderm
---endoderm: hypoblast cells are replaced by
epiblast cells
---ectoderm: epiblast changed the name into
ectoderm
* trilaminar germ disc: endoderm + mesoderm +
ectoderm
* determination of head and tail of germ disc
---head process→notochordal tube → notochord
---buccopharyngeal membrane
---cloacal membrane
3)differentiation of trilaminar germ disc: 4th –8th
weeks
---differentiation: same cells which are
primordial and inmuture differentiate into
different cells which have specific structure
and function
---induction:
some
tissues
effect
the
differentiation,
and
determine
the
differentiating orientation of another tissue
① differentiation of ectoderm: from 18th –19th days
---neural plate: neuro-epithelium(neural ectoderm):
pseudostratified columnar epi.
---neural fold
---neural groove
---neural tube: →CNS
/anterior neuropore: closed by 25th days
/posterior neuropore: closed by 27th days
---neural crest(mesoectoderm): two lines of cell
cords→ganglion
②differentiation of mesoderm: 17th days
---paraxial mesoderm
somite: 20th days, 3 pairs/per day, 42-44 pairs
by the end of 5th weeks
-sclerotome: →bone, cartilage
-myotome: →skeletal muscle
-dermatome: dermis and hypodermis
---intermediate mesoderm: →kidney and
reproductive gland
nephrotome: segmentation
nephrogenic cord:
---lateral mesoderm:
intraembryonic coelom: →body cavity
somatic or parietal mesoderm: →muscle, CT,
parietal layer of pleura, peritoneum and
pericardium
splanchnic or visceral mesoderm: →muscle, CT of
digestive tract, visceral layer of pleura, peritoneum
and pericardium
---mesenchyme: →cardiovascular and lymph system
③differentiation of endoderm:
---primitive gut: →digestive, respiratory
and urinary system
4. The
development
of fetal
membrane
and placenta
1) chorion:
---formed
by
trophoblast and
extraembryonic
mesoderm
---primary stem villus: projections of cytotrophoblast
and syncytiotrophoblast
---secondary stem villus: extraembryonic mesoderm
enter the primary stem villus
* chorionic plate: trophoblast + extraembryonic
mesoderm
* chorion: secondary stem villus + chorionic plate
---tertiary stem villus: extraembryonic mesoderm
differentiate into CT and BV
free villus: branches
anchoring villus
---cytotrophoblastic
cell
column:
→cytotrophoblastic shell
---chorion leave: 6 weeks later
---chorion frondosum
---hydatidiform mole
---chorion carcinoma
2) yolk sac:
---blood island: primitive blood cell- derived from
extraembryonic mesoderm on the wall of yolk
sac
---primordial germ cell: derived from endoderm
of yolk sac
3) amnion:
---amniotic membrane: amniotic
extraembryonic mesoderm
epi.
+
---amniotic fluid:
/secrete by amniotic epi.
/slight basic fluid: 500-1000ml
-polyhydramnios:
>2000
ml,
abnormal
digestive system or CNS
-oligohydramnios: <500 ml, abnormal urinary
system
/function:
-intraenvironment
-protecting
-preventing from adherence
-wash germ tract
4) allantois
---allantoic A: paired, →umbilical A
---allantoic V: paired
right: degenerate
left: umbilical V
5) umbilical cord
---cylindrical structure
---surface: amniotic membrane
---cord: mucous CT, umbilical A,V, yolk
sac and allantois
---40-60 cm long, 1.5-2.0 cm in D
---> 80 cm, or < 35 cm
6) placenta:
---the structure by which exchange of material
between fetus and mother takes place
---size: round, disc-shaped, 15-20 cm in D, 2.5
cm thickness, 500g in weight
fetal surface: smooth,
covered by amniotic
membrane
mother surface: rough,
15-30 cotyledons
---structure:
/chorionic plate
/chorion and chorion space
-chorion: 60 chorion stalks→branches
-chorion space: space between chorion,
filled with mother blood
/basal plate: cytotrophoblastic shell +
deciduas
-placental septa: separate the chorion into
cotyledon
---blood circulation of placenta
fetus: umbilical A →cap. of chorion
→umbilical V
mother: spiral A → chorion space →
uterus V
* placental barrier:
/the structure between fetal and
maternal blood
/components:
-endothelium of chorion capillary and its
basal lamina
-CT in the core of the villus
-trophoblast epithelium and its basal
lamina
---function:
a. the exchange of material between the
maternal and fetal blood streams
b. defense barrier
c. the production of hormones:
/human chorionic gonadotropin, HCG:
-begin: end of 2nd week
-highest lever: 9th –11th week
-lowest lever: 20th week, until birth
/human placental lactogen, HPL
-similar to HGH
-highest lever: 36th –37th week
/human placental progesterone, HPP and
human placental estrogen, HPE
-begin: 4th month
/other hormones: human chorionic
thyrotropin, HCT; human chorionic
adrenocorticotrophic hormne, HCATH;
prostaglandin