anhui medical university general embryology...
TRANSCRIPT
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Anhui Medical University
Anhui Medical University
General embryology II
Chao Liu Ph.D.
Department of Histology and EmbryologySchool of Basic Medical SciencesSchool of International Education
Anhui Medical University
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The fetal membrane and placenta
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1. chorion:2. amnion:3. yolk sac:4. Allantois5. umbilical cord
I. Fetal membrane
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1. Chorion
Chorion -- made up of the syncytiotrophoblast, cytotrophobalst and extraembryonic mesoderm.
a. Chorionic plateb. Villi:primary, secondary, tertiary
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Primary villi: a central core of cytotrophoblastcovered by a layer of syncytiotrophoblast.Adoining villi are separated by an intervillousspace.
cytotrophoblastsyncytiotrophoblast
intervillous space
extra-embryonic mesoderm
capillary
blood vessel
decidua
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secondary villi :• An inner layer extra-embryonic mesoderm• An intermediate layer cytotrophoblast• An outer layer syncytiotrophoblast
syncytiotrophoblast
intervillous space
extra-embryonic mesoderm
capillary
blood vessel
decidua
cytotrophoblast
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tertiary villi: are like secondary villi except thatextra-embryonic mesoderm differentiate intocapillaries and CT.
cytotrophoblastsyncytiotrophoblast
intervillous space
extra-embryonic mesoderm
capillary
blood vessel
decidua
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• Chorion frondosum:adjacent to decidua basalis with numerous, large and branched villi, forming fetal component of placenta.
• chorion laeve:The chorion associated with the decidua capsularis, the villi of which become degenerated.
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Excessive proliferation of the trophoblast may lead the hydatidiform mole with large amounts of vesicles and dead embryo.
Abnormalities
The malignant proliferation of trophoblast cells is called the chorion carcinoma.
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2. AmnionThin, transparent membrane made up of an amniogenic cell layer and outer extraembryonic mesoderm layer.
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Amnion
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Amniotic fluid
• is a dialysate of blood, first secreted by the amniotic membrane. By 16 weeks of gestation, the fetal urine is also a major contributor to the amniotic fluid.
• about 1- 1.5 liter at full term.
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Functions of amniotic fluid
• 1) provide a protective cushion and absorb jolts; • 2) allow for fetal movement and prevent adherence of
the fetus;• 3) maintain body temperature of the embryo;• 4) help to dilate and clean the cervical canal making
childbirth easier.• 5) Prenatal diagnosis: biochemical assay ,chromosome
or gene analysis.
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Circulation of the amniotic fluid
•30ml/10wk → 350ml/20wk → 1L/38wk •Totally renewed every 3h
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3. Yolk sac• Inner endoderm + outer extraembryonic mesoderm
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Its significance in development is
• a. Some endoderm cells of it form primordial germ cells.
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• b. Mesoderm cells of its wall differentiate into primitive blood cells.
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4. Allantois• 1) Formation: caudal part of yolk sac →
diverticulum extending into body stalk • 2) Significance: blood vessels in its wall →
umbilical arteries and vein.
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allantois-outpocketing of embryo’s gut, incorporated into umbilical cord, forms blood vessels of umbilical cord
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5. Umbilical cord
• Formation: body stalk → connecting the embryo or fetus to the placenta, 50 cm longat birth.
umbilical vesselsContents: body stalk, yolk sac stalk, allantois,
2 arteries and 1 vein, mucoid C.T.
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very long (>80cm) → encircling neck or extremities very short (<35cm) → prematurely detaching of placenta and bleeding
Abnormalities
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II. Placenta
• the structure by which exchange of material between fetus and mother takes place.
• it consists of chorionic plate and basal plate.• size: round, disc-shaped, 15-20 cm in D, 2.5 cm
thickness, 500g in weight
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• Components: fetal portion ← chorion frondosum • Maternal portion ← decidua basalis
fetal portion
Maternal portion
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• fetal surface:smooth,covered byamnioticmembrane
• mothersurface: rough,15-30cotyledons
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Chorionic plate→stem villi→cytotrophoblastic shell Basal plate→placental septa→cotyledonsFree villi + intervillous spaces (maternal blood)
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Placental barrier: the structure between fetal and maternal blood.Components:
• a. Endothelium and its basal lamina of the villous capillary.
• b. Connective tissue in the core of the villus.
• c. Basal lamina of cytotrophoblast and cytotrophoblast.
• d. Syncytiotrophoblast layer.
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• Exchange of gases, nutrients, metabolites between the maternal and fetal blood.
• Protection• Hormone production: all from syncytiotrophoblast
Human chorionic gonadotropin (HCG) Human placental lactogen (HPL)Progesterone and estrogen
Functions of placenta
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Key points
1. The component and function of fetal
membrane.
2. The structure and function of placenta.
3. Placental barrier.
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Homeworks?
1. What are the compositions of fetal
membranes?
2. Describe the structural features and
functions of Placental barrier.