Transcript 1. dia - Semmelweis University

BLASTULATION, IMPLANTATION,
FORMATION OF THE ECTODERM
AND ENDODERM
Dr. Andrea D. Székely
CAVITATION OF THE MORULA
4 days after the ovulation
early blastocyst formation
0.1 - 0.2 mm
BLASTOCYST
- continuous mitotic divisions
- cavity formation (blastocoel)
- the cells start to compact and flatten
- BUT the zona pellucida does not enlarge
-2 cell types will differentiate:
- embryoblast (inner)
- trophoblast (outer)
EARLY BLASTOCYSTS
BLASTULATION
Within the BLASTOCYST an inner cell mass (ICM) is separated,
this contains the EMBRYOBLASTS
The surrounding cells will be the TROPHOBLASTS, responsible for
the formation of the chorion.
HATCHING OF THE BLASTOCYST
- enters the uterus 0.1 - 0.2 mm
- „hatches" from the zona pellucida
The implantation starts 5 - 6 days
after the ovulation, the blastula
descends in the uterine cavity, then
adheres to the endometrium (the
trophoblasts produce enzymes which
pierce the endometrium)
APPOSITION (the embryo turns
towards the endometrium with
the ICM being deep)
- The superficial proteoglycans bind
to the cells
- hCG, progesterone release grows
Pregnancy test!!
The glands enlarge
The endometrium thickens
A richer vascular network grows
IMPLANTATION
STEPS OF IMPLANTATION
APPOSITION – the ICM faces the endometrium
ADPLANTATION – the endometrial cells grow processes
(they swell and catch the blastocyst - reversible binding)
ADHESION – the microvilli of the trophoblasta interact with the cells of the
endometrium (proteoglycans) irreversible binding
DIFFERENTIATION - trophoblast derivatives - syncytiotrophoblast
- cytotrophoblast
IMPLANTATION – the syncytiotrophoblasts form a syncytiumot and penetrate
the membrana basalis as well as the endometrium
DECIDUAL REACTION – apoptosis within the endometrial cells, then the stroma
cells undergo an epitheloid transformation.
The extracellular vacuoles will be filled with blood and merge to form the
LACUNAE
the invasive growth will be stopped by the zona compacta
By week 2. the pregnency can be tested from urine too.
MOLECULAR FACTORS OF IMPLANTATION
BILAMINAR EMBRYO
EMBRYOGENESE
= Hypoblast
Cindy C Lu*, Jane Brennan† and Elizabeth J Robertson‡
Current Opinion in Genetics & Development 2001, 11:384–392
Extraembryonic
structures
SEPARATION OF EMBRYONIC AND
EXTRAEMBRYONIC STRUCTURES :
EPIBLAST/HYPOBLAST SEGREGATION
TRENNUNG DER EMBRYONALEN UND
EXTRAEMBRYONALEN STRUKTUREN
EMBRYONIC DISK, HYPOBLAST – EPIBLAST
2. week
the blastocyst partially is implanted, the primitive yolk sac is
formed from the blastocoel
EMBRYOBLASTS:
FORM THE EMBRYONIC DISK
hypoblast - cuboidal cells, line the primitive yolk sac
epiblast - tall cylindrical cells lining the amnion cavity
D 11-12. a minimal enlargement of the implanted embryo – bulges into the uterine cavity
extraembryonic mesoderm – formed between the trophoblasts and amnion, or yolk sac –
the cavities here merge to form the extraemberyonic coelom which surrounds the
embryonic disk (except for the site of the body stalk „allantois” – later umbilical cord
D 13. the endometrium is completely sealed
Hypoblasts form the secondary or definitive yolk sac
So the extraembryonic coelom will turn to the cavity of the chorion
CRANIAL changes a thickening forms - praechordal plate (BPM)
CAUDAL changes a similar fusion - cloaca membrane,
Similar to the praechordal plate, it is formed by the adjacent layers of
hypo- and epiblast cells
HSG
IN VITRO FERTILIZATION
ICSI – „intracytoplasmic sperm injection”
Ovarian stimulation (FSH)
Embryo biopsy
Ultrasound assisted
harvesting of the oocyte
„assisted hatching”
FURTHER MOVIES
http://www.visembryo.com/baby/index.html
http://embryo.soad.umich.edu/
www.advancedfertility.com
http://www.med.uc.edu/embryology/contents.htm