Chapter 21 General Embryology

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Chapter 21 General Embryology
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• ---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

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• embryonic period 3-8 weeks
• fetal period after 9 weeks
• perinatal stage 26 weeks to birth
• Teratology abnormal development of fetus

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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

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• ---conditions
• 1)      maturation of oocyte
• 2)      maturation of spermatozoon
• /ductus epididymus 2-3 weeks, forward
  motility protein

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• 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

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• 4)  quality and quantity of spermatozoa
• 2-6 ml, 100,000,000/ml,
• lt1.5 ml or lt10,000,000 abnormal sperm gt30 or
  capacity for mobilelt 70
• 5)  meeting of sperm and ovum
• sperm 20-24h
• ovum 15-18h(1-3ds)

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• ---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

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• 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

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• ---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(22X) X-bearing spermatozoon girl
• ova(22X) Y-bearing spermatozoon boy
• klinefelters syndrome 47XXY, 48XXXY

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2. Blastocyst formation and implantation

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• 1)      cleavage and blastocyst formation
• ?cleavage
• ---blastomere cells formed by cleavage
• /30h 2
• /40h 4
• /72h 12-16- morula

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• ?formation of blastocyst by 5th day, blastomere
  reach to 107, small space appear between them
• ---blastocoele filled with liquid
• ---trophoblast
• ---inner cell mass
• ---polar trophoblast

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• 2)     Implantation
• ---definition the process by which the
  blastocyst is embedded in endometrium
• ---time 5th 6th day begin 11th 12th day
  complete

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• ---processes zona pellucide disappear ? polar
  trophoblast touch the endometrium?secrete
  proteolytase ?dissolve the endometrium ? embedded
  into endometrium?coagulation plug seal the space

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• trophoblast become into two layers when
  blastocyst is embedding into endometrium
• syncytiotrophoblast
• cytotrophoblast

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• ---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)

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• /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

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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)

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• ---epiblast primary ectoderm
• /amniotic membrane amnioblast
• /amniotic cavity
• /amniotic fluid
• /amnion

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• ---hypoblast primary endoderm
• /extraembryonic endoderm?exocoelomic
  membrane?primary yolk sac ? exocoelomic vesicle

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• /extraembryonic mesoderm ? extraembryonic
  cavity chorionic cavity
• -visceral layer
• -parietal layer
• /secondary yolk sac yolk sac
• ---body stalk formed by extraembryonic mesoderm

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• 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

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• ---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

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• ---head process?notochordal tube ? notochord
• ---buccopharyngeal membrane
• ---cloacal membrane

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• 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

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• ? 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

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• ?differentiation 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

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• ---intermediate mesoderm ?kidney and
  reproductive gland
• nephrotome segmentation
• nephrogenic cord

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• ---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

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• ?differentiation of endoderm
• ---primitive gut ?digestive, respiratory and
  urinary system

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4. The development of fetal membrane and placenta
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• 1) chorion
• ---formed by trophoblast and extraembryonic
  mesoderm

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• ---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

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• ---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

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• 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

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• 3) amnion
• ---amniotic membrane amniotic epi.
  extraembryonic mesoderm
• ---amniotic fluid
• /secrete by amniotic epi.
• /slight basic fluid 500-1000ml
• -polyhydramnios gt2000 ml, abnormal digestive
  system or CNS
• -oligohydramnios lt500 ml, abnormal urinary
  system

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• /function
• -intraenvironment
• -protecting
• -preventing from adherence
• -wash germ tract

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• 4) allantois
• ---allantoic A paired, ?umbilical A
• ---allantoic V paired
• right degenerate
• left umbilical V

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• 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
• ---gt 80 cm, or lt 35 cm

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• 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

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• fetal surface smooth, covered by amniotic
  membrane
• mother surface rough, 15-30 cotyledons

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• ---structure
• /chorionic plate
• /chorion and chorion space
• -chorion 60 chorion stalks?branches
• -chorion space space between chorion, filled
  with mother blood

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• /basal plate cytotrophoblastic shell deciduas
• -placental septa separate the chorion into
  cotyledon

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• ---blood circulation of placenta
• fetus umbilical A ?cap. of chorion ?umbilical V
• mother spiral A ? chorion space ? uterus V

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• 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

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• ---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

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• /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