Download practical lesson №5 Gastrulation Next stage of embryogenesis after

PRACTICAL LESSON №5
Gastrulation
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Next stage of embryogenesis after the cleavage.
Process of bilaminar and trilaminar germ disc formation.
It occurs in the embryo in the course of implantation.
Gastrulation lasts from 7th till 17th days.
Two stages of implantation:
A. Early (7-14 days) – two germ layers appear – ectoderm and endoderm.
B. Late (14-17 days) –the third layer – mesoderm is developed.
6. The type of gastrulation directly depends on the type of oocyte and cleavage.
Main processes in embryogenesis
Proliferation – increase of cells amount
Differentiation – appearances of differences
Induction – influence
Commiting – limiting
Expression – increase of genes activity
Repression – decrease of genes activity
Early gastrulation
Type of
gastrulation
Representatives
Ovum
Cleavage
Blastula
Invagination
Primitives
Olygolecital I
isolecital
Full equal
synchronic
Celoblastula
Epyboly
Amphibian
Moderate
polylecital
Full unequal
asynchronic
Amphyblastula
Insects
Polylecital
Peripheral
Periblastula
Birds, higher
Vertebrata
Olygolecital
II isolecital
Full subequal
asynchronic
Blastocyst
Migration
Delamination
Biologic significance – appearances of ecto- and endoderm
Late gastrulation
Type of late
gastrulation
Follows
Enterocolic
Invagination
Teloblastic
Epyboly
Migration with
primitive streak
formation
Migration and
delamination
Sources of
mesoderm origin
Mechanism
Endoderm
Invagination
The lateral lips of
blastopor
(teloblasts)
Migration
Ectoderm
Migration
Biologic significance – appearance of mesoderm
Mesoderm compounds: somits, nephrogonotom, splanchnotom
EXTRAEMBRYONIC ORGANS
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1. Аmnion
2. Yolk sac
3. Аllantois
4. Chorion
5. Placenta
6. Umbilical cord
7. Serous tunic
HUMAN EMBRYO GASTRULATION
Early gastrulation
1. 7th -14th days.
2. Embryoblast delaminates into epiblast and hypoblast.
3. Amnion originate from epiblast (primary ectoderm).
4. Yolk sac – from hypoblast (primary endoderm).
5. Trophoblast differentiates into cytotrophoblast and syncytiotrophoblast.
6. Embryonic disc – the attachment of amniotic vesicle bottom and the roof of
yolk sac.
7. Embryo’s body has one layer – the amniotic vesicle bottom.
Late gastrulation
1. 14th-17th days.
2. Migration with primitive streak formation.
3. Extraembryonic mesoderm migrate from embryonic disc
4. In embryo all three layers are formed at the same time from embryonic
ectoderm.
Peculiarities of the human embryo gastrulation:
1. Full subequal asynchronic cleavage – blastocyst.
2. Forestall development of extraembryonic organs.
3. Embryo implantation into endometrium and placenta formation.
4. All three germ layers are forming from primary ectoderm.
CHORION
Periods of chorion happening:
1) previllious –till 7-8th day
2) period of villi formation –9-50th day.
Types of villi.
A. Primary villi consist of trophoblast
B. Secondary (12-13th day) with mesodermal cells in the core
C. Tertiary villi (end of the 3rd week) with blood vessels inside
Types of chorion
A. Chorion frondosum (bushy chorion) – with villi on the surface (in
placenta).
B. Chorion laeve (chorion nodosum) – with smooth surface (by the third
month)
PLACENTA
Types of placentas due to their structure
A. Epitheliochorial
B. DESMOCHORIAL
C. Endotheliochorial
D. Hemochorial placenta
Types of placentas due to the type of embryo nutrition
A. First type (diffuse and numerous placentas).
B. Second type placentas are producing the proteins, which are typical to
embryo (tape and discoid).
Human placenta is of nutrition secondary type, discoid and hemochorial.
Human placenta (fetomaternal organ) portions
A. Fetal – develops from chorionic sac (bushy chorion with anchoring and
trophic villi)
B. Maternal – is derived from endometrium (decidua basalis with septa and
lacuna)
GENERAL STRUCTURE OF PLACENTA
DECIDUA – the layer of gravid endometrium, which is separated from the
remainder of the uterus at parturition)
REGIONS OF THE DECIDUA
A. Decidua basalis – maternal placenta
B. Decidua capsularis – overlies the embryo
C. Decidua parietalis – remaining endometrium
PLACENTA – discoid shape, 3 cm thick, 15 - 25 cm in diameter, 500-600 gm.
COTYLEDON – morphofunctional unit (15-20)
HEMOCHORIAL BARRIER
(placental membrane)
1.
Capillary endothelium.
2.
Basement membrane.
3.
Connective tissue of the villus (with Hofbauer cells).
4.
Cytotrophoblast basement membrane.
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6.
7.
Cytotrophoblast
Syncytiotrophoblast.
From the fourth month Langhance fibrinoid replace 4
TYPES OF CHORIONIC VILLI
PRIMARY
SECONDARY
TERTIARY
EXTRAEMBRYONIC ORGANS AT THE END OF 2-ND MONTH
References:
1. Medical Embryology. Langman J. Baltimore. Wilkins Co. 1969. P. 37-78.
2. L. Carlos Junqueira, Jose Carneiro, Robert O. Kelley. Basic Histology. - 7th ed.
Appleton and Lange. Norwalk, Connecticut, 1992.
3. Inderbir Singh. Textbook of Human Histology with colour atlas. – 4th ed. Jaypee
Brothers Medical Publishers (P) LTD, 2002.
4. Wheater P.R., Burkitt H.G., Daniels V.G. Functional Histology: a text and colour
atlas. - 2nd ed. Longman Group UK Limited, 1987.
1. Victor P. Eroschenko. Atlas of Histology with functional correlations. - 9th ed.
Lippincott Williams and Wilkins, 2000.