week 1 Flashcards
1
Q
cleavage
A
- proliferation: very fast mitosis
- 24h after F! zygote initiates rapid series of mitosis resulting in smaller daughter cells
- interphase virtually limited to S phase
- subdivides zygote without increasing its size
- remains enclosed in zona pellucida
- 2-cell, 4-cell,8-cell
2
Q
morula
A
- 16-cell stage: morula
- formed of blastomeres, hollow inside
- by 4 days
- zygote gene expression begins
- cells can be manipulated
3
Q
blastomeres
A
- pluripotent stem cells
- polarisation starts at the 4-cell stage
- can be seen by tagging certain cell-surface molecules with fluorescent dyes
- at 8: glycoproteins are predominantly found at the poles farthest from centre of aggregate
- influenced by interactions: separated blastomeres loses polarisation
4
Q
symmetrical and asymmetrical divisions
A
- development begins with drastically asymmetric divisions of oocyte
- become symmetric after several rounds
- later on asymmetric divisions are required again to send two generations of daughter cells into interior of embryo
5
Q
compaction
A
- occurs after 8-9 cell stage
- blastomeres (round, loosely adherent) begin to flatten maximising cell to cell contact
- outer surfaces of cells become convex, inner concave/flat
- involves changes in cytoskeleton: monitored by fluorescent protein expression
6
Q
specific surface proteins play a role in compaction
A
- E-cadherin synthesised at 2-cell stage uniform in csm
- as compaction occurs it becomes restricted to those sited where adjacent membranes are in contact
- formation of tight junctions underly blastocyst formation: between outside cells
- gap junctions between inside cells
7
Q
differentiation of morula into embryo-blast and trophoblast
A
- as a result of compaction
- morula cells also give rise to placenta and embryo annexes
- this differentiation leads to the separation of trophoblast (primaty source of fetal component of placenta) from inner cell mass (embryoblast to body proper)
8
Q
2 mechanistic models to explain first cell-fate decisions
A
- 8-cell late: apical and basolateral domains
1. asymmetric partitioning of polarised subcellular components
2. differential extent of cell to cell contact
8
Q
cavitation
A
- formation of a cavity within the blastocyst
- fluid is pumped within the blastocele
- trophoblast cells express basally polarized membrane Na/K ATPase
- pumps Na in and water follows to become blastocoelic fluid
- as HP increases a larger cavity called blastocyst cavity (blastocoele) forms
9
Q
embryo-blast
A
- inner cell mass gives rise to embryo
- located at a pole in blastocyst
- embryonic pole and abembryonic pole
9
Q
OCT-4 and Nanog
A
- trophoblasts express Cdx2 TS factor which is responsible for downregulation of Oct4 and Nanog TS factors uniformly present in blastomeres
10
Q
blastocyst hatches from zona pellucida as it eneters the uterus
A
- by day 5
- by enzymatically boring a hole in and squeezing out
- now naked and can directly interact with endometrium
- repeated contractions induce hatching
10
Q
implantation: maintains trophism of endometrium
A
- cells of trophoblast produce human chorionic gonadotrophin (hCG) which supports the corpus luteum to maintain progesterone: maternal recognition of pregnancy
- CL continues to secrete sex steroid for 11-12 weeks until placenta takes over
10
Q
changes of uterus before implantation
A
- enters a receptive stage controlled by estrogen and progesterone
- amount of glycocalyx decreases
- large protrusions form: pinopodes
- pinopode presented cells separated by single ciliated cells
11
Q
the decidual reaction
A
- cells of endometrial stroma respond to progesterone of CP by differentiating into metabolically active secretory cells: decidual cells
- endometrial glands also enlarge
- local uterine wall becomes more highly vascularised and edematous
- GFs and metabolites are released
