BSCI-1105 Lecture Notes - Lecture 12: Human Chorionic Gonadotropin, Chorionic Villi, Adult Stem Cell
4 Feb 2020
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BSCI1105 10/4
STAGES OF DEVELOPMENT
Cleavage→Blastula (in mammals, Blastocyst)
• Trophoblasts interact with endometrium (because outermost layer) forming close connection
between blood of mother and the developing embryo (prior to implantation in uterine wall,
embryo self-reliant, BUT with the placental connection, nutrients/etc. are provided by
mother)→TROPHOBLASTS KEY IN DEVELOPING THE PLACENTA WHICH IS EXTREMELY
SIGNIFICANT WITH CONNECTING THE MOTHER AND THE EMBRYO
“Stem Cells”
• Stem cells are undifferentiated cells
• Can be removed from Inner Cell Mass (ICM) of the blastocysts and grown in the lab
• Can be induced to differentiate using certain signal molecules in vitro or by transplanting them
into different locations in vivo, where they take on the identity of that region
o IVF is almost the sole source of any embryonic stem cell research (extra/leftover pre-
embryos that are stored in nitrogen tanks→BUT there are regulations)
• **ICM cells therefore do not yet have a developmental identity (have not even been
determined yet)
o determination
▪ once stem cells have been determined, they are referred to as “adult stem
cells”
o differentiation/specialization
• Medical applications?
• Ethical questions/implications
Identical Twins
• If the cells in an embryo separate at an early stage, two embryos can result (TWO SEPARATE
PLACENTAS)
• Or an equivalent event can occur if there is a separation of the inner cell mass (ONE PLACENTA)
• Since the two embryos come from the same zygote, they are both monozygotic
twins/genetically identical twins. On the other hand, fraternal twins are the result of two
separate eggs fertilized by two separate sperm and are not genetically identical
Gastrulation Gives Rise to Differentiated Cells (starts with determination)
• 3 types of cells (earliest determination)
o Ectoderm
o Endoderm
o Mesoderm
• Extraembryonic membranes…
Extraembryonic Membranes Support Development
• Trophoblast specializes into what becomes the Chorion
o Chorion produces HCG (human chorionic gonadotropin)
o Chorionic villi interact with maternal side of the placenta
Amniocentesis and CVS
• cells from the embryo that are in the embryonic fluid can be sampled and tested for defects
(cannot be done before 15-20 weeks)→this test is called amniocentesis
• A newer technique is chorionic villus sampling (CVS) which makes earlier detection possible (10-
15 weeks)
• There is an even earlier and more accurate way to test→PGD (8 cell stage)
Embryo→Fetus (1st Trimester)
Document Summary
Significant with connecting the mother and the embryo. If the cells in an embryo separate at an early stage, two embryos can result (two separate. Placentas: or an equivalent event can occur if there is a separation of the inner cell mass (one placenta, since the two embryos come from the same zygote, they are both monozygotic twins/genetically identical twins. On the other hand, fraternal twins are the result of two separate eggs fertilized by two separate sperm and are not genetically identical. Gastrulation gives rise to differentiated cells (starts with determination: 3 types of cells (earliest determination, ectoderm, endoderm, mesoderm, extraembryonic membranes . Extraembryonic membranes support development: trophoblast specializes into what becomes the chorion, chorion produces hcg (human chorionic gonadotropin, chorionic villi interact with maternal side of the placenta. 15 weeks: there is an even earlier and more accurate way to test pgd (8 cell stage)
