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ability of a cell to generate other cell types
What are the two different kinds of potency in cells and provide examples?
- totipotent: can give rise to all cell types ie. embryonic stem cells
- pluripotent: can give rise to a number of cell types, often in a within a specific developmental lineage/tissue type ie. mesenchymal stem cells
cell specialization which is determined by differential gene expression
What is a stem cell?
- A cell that is able to self-renew (divide/proliferate) and differentiate.
- Can be totipotent or pluripotent
What is an iPS?
'induced pluripotent stem cells' (iPS) are generated from adult cells by reprogramming them with transcription factors that normally initiate stemness (eg. the Oct and Sox transcription factors)
Describe the relationship between potency and differentiation.
- During normal development, potency decreases as differentiation occurs.
- The microenvironment (eg. the neigbouring cells, the soluble factors) that stem cells find themselves in (eg. the stem cell niche) determines whether they will self renew or differentiate.
- The potency of cells can be manipulated; 'induced pluripotent stem cells' (iPS) are generated from adult cells by reprogramming them with transcription factors that normally initiate stemness (eg. the Oct and Sox transcription factors).
What are the three periods of prenatal development?
pre-embryonic, embryonic, fetal
Where does fertilization occur?
uterine tube (oviduct)
How does the zygote develop as it moves down the uterine tube into the uterus?
The zygote proliferates (mitotic divisions) without differentiating, generates a solid mass of cells (morula; cells stick together via 'cell adhesion molecules').
How is the blastocyst formed?
Morula pumps fluid into its center to form central cavity.
What differentiation occurs at the blastocyst stage?
significant differentiation occurs consisting of inner 'embryoblast' cells (will form embryo proper) and outer 'trophoblast' cells (will help form placenta)
When does implantation begin?
About 6 days after fertilization
How does implantation occur?
outer trophoblasts attach to and fuse with the lining epithelium of the uterus (endometrium)
Describe the differentiation of the trophoblasts.
Trophoblasts split into two layers; the inner, fully cellularized 'cytotropholasts' and outer fused/multinucleate 'syncytiotrophoblasts' that send finger-like projections deep into the uterine wall and release proteolytic enzymes facilitate the implantation of the embryo
Which hormone is released by the syncytiotrophoblasts and what role does it play?
human chorionic gonadotrophin (hCG) which maintains corpus luteum in the ovary (will be studied in Lect 32); the latter keeps producing estrogen and progesterone which maintain the uterine wall (ie. prevents menstruation that would lead to the loss of the implanted early embryo)
What is a trophoblastic lucanae?
spaces that begin to form within the core of syncytiotrophoblast fingers, fill with maternal blood
Describe the differentiation of the embryoblast.
Embryoblast splits into two layers of cells: epiblast (consists of totipotent embryonic stem cells and gives rise to amnion) and hypoblast (gives rise to yolk sac lining).
Describe the differentiation of the epiblast.
Epiblast splits as the 'amniotic cavity' forms within it; the layer of epiblast cells adjacent to the cytotrophoblasts become 'amnioblasts' that ultimately form the 'extraembryonic' amniotic membrane that lines the amniotic cavity.
Which cell type gives rise to the extraembryonic mesoderm that contributes to all of the major extraembryonic membranes that surround the embryo proper and the placenta?
Which extraembryonic membrane gives rise to blood vessels and germ cells?
What is the function of the hypoblast?
generates the cells of the Heuser's membrane which delineate the margin of the yolk sac
Describe the maternal component of the placenta.
Maternal/Uterine component (='decidua basalis') which contains mostly maternal (ie. the Mom's) arteries and veins which supply and drain the 'trophoblastic lacuna' (see above for description); later, these lacuna expand and fuse to form the large 'intervillous spaces' of the fetal placenta that are filled with maternal blood
Describe the fetal component of the placenta.
Embryonic/Fetal component (='chorionic villi' = fingers that interdigitate with the trophoblastic lacunae/intervillous spaces); a single chorionic villus is a finger of extraembryonic (ie. the developing Baby's) tissues made up of syncytiotrophoblasts and cytotrophoblasts that surround a core of extraembryonic mesoderm that gives rise the extaembyronic blood vessels that exchange gases, nutrients and waste with the maternal blood in the trophoblastic lacuna
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