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108: Normal Child - Embryology First 18 Days
Terms in this set (51)
3 ways of growth of cells
Proliferation: increase in cell number
Hypertrophy: cells increase in cell size e.g. muscle fibres
Accretion: increase in cell tissue - secretes extracellular matrix around itself, eg bone, cartilage.
Growth mostly happens after differentiation & organisation
Cells of the amniotic membrane. From the epiblast.
Programmed cell death - opposite of growth. used to create morphogenesis eg. in hand - region that forms hand is plate like to start with, inbetween digits the cells die very cleanly/neatly
The fluid-filled, central cavity of a blastocyst (or blastula).
Clinical time of pregnacy is 40 weeks (instead of 38 weeks in reality) - easiest to ask time since last menstrual period (2 weeks before fertilisation)
8 weeks - after this has reached stage where can see structures of embryo
Tissue grows by cells getting larger
The early embryo as a sphere of cells with a fluid-filled central cavity. (Sometimes called the blastula).
8 weeks - 38 weeks (or 10 weeks to 40 weeks). after 24 weeks considered viable by law - delivery before this is miscarriage, after is stillbirth. abortion laws on this limit. medically may be viable at 20-22 weeks depending on fetal size.
Diploid cell after fertilization - within zona pellucida. Before cleavage.
The thick, solid, transparent outer membrane of a developed mammalian ovum - where zygote is after fertilization (barrier sperm has to fight way through)
mitotic divisions take place in zygote - two cell stage, few divisions - number of cells increase but size of cells decrease - structure itself cannot get larger cos of zona pellucida
After 3 cells divisons of cleavage = 8 cells, increases cell contact with each other - get closer together
16 cells (stage after compaction). day 3. (looks like mulberry). have inner cell mass (embryo) and outer cell mass (placenta). all cells called blastomeres.
Any cell resulting from cleavage of a fertilized egg early in embryo development.
Inner cell mass of morulla - to be be embryo. Will go to one end of blastocyst - organisation (morphogenesis). Implants in uterus this side
Outer cell mass of morulla - to be placenta.
Embryoblasts produce fluid inside - called blastocyle - cavity
Whole thing after morulla stage (day 5) - travels down unterus, to implantation
When blastocyst implants into uterus, zona pellucida is lost. Embryoblasts pole contacts uterine lining, implants this side, trophoblasts meet it first (day 6)
what has to happen to uterine lining (endometrium) to allows trophoblast cells to penetrate/adhere. begins in late progestational phase of mestrual cycle
When trophoblast spilts in two - outside layer (cell walls have started to break down and join, still multi nucleus)
When trophoblast splits in two - inside layer (cell walls remain)
Embryoblast splits into two layers - epi - above layer. two layers form bi-laminar embryonic disc
Embryoblast splits into two layers - hypo - below layer. two layers form bi-laminar embryonic disc
Bi- laminar embryonic disc
2 layers - epiblast and hypoblast that will form embryo
forms in 2nd week. some cells at embryoblast end differntiate to become amnioblast - secrete amniotic fluid, makes cavity
cells from hypoblast form membrane that lines blastocyle cavity - becomes exocoelomic membrane,will become yolk sac.
area of syncitiotrophoblasts (implantation area) starts to get vacuoles - merge and get bigger = lacunae
Vacuoles in syncytium, will merge with maternal sinusoids (blood vessels in uterus), mothers blood floods into vacuoles, start to establish utero/placental circulation.(day 12)
blood vessles in uterus - form utero/placental circulation
end of week 2
whole blastocyst is totally implanted in uterus and epithelium closes back over. woman can expereince small bleed when this happens (2 weeks after fertilisation) so can be mistaken for period.
HCG (human chorionic gonadotropin)
made by placenta (syncytiotrophoblast) cells - 2 weeks after fertilisation - can detect via pregnancy test. also cancer marker
another cavity forms around the 2 cavities already present (amniotic and yolk). leave a gap for embryo still joined to placenta - connecting stalk - umbilical cord. end of week 2 (week of 2s)
will become umbilical cord - joins embryo to placenta (gap in chorionic cavity)
2 layers to 3 layers (bi-laminar disc to 3 layers). Epiblast forms 3 germ layers, ectoderm, endoderm and mesoderm, whcih give rise to every cell in body
formed by epiblast - flat shet of cells that organise, then morphogenisis. Forms epidermis, CNS, PNS, Retina (outside stuff)
formed by epiblast. epithelia of resp tract and GI tract, also glandular (inside stuff)
formed by epiblast. Forms connective tissue, bones, muscle, heart, reproductive/excretory organs (middle stuff)
formed by hypoblast i.e. outside embryo
forms down middle of epiblast - cells migrating to middle and diving down. as they migrate they differentiate
circular end of streak, at head end.
at head end - ectoderm and endoderm cells (no mesoderm) - forms mouth
at tail end - ectoderm and endoderm cells (no mesoderm) - forms anus
cells that go to primiteve streak, stay in middle, push all other cells out of way, form solid tube. are an important signalling centre, controls development of region
Cells or tissues become specialised. Nerve/muscle/epithlial cells etc are examples. From neural crest cells/stem cell - cell becomes 'determined'. Usually irreversible/terminal/stable - more than 200 in mammals
Neural crest cells
.stem cells - able to differentiate into different specialised cells dependent on environment
Pattern formation - cells know where to go. e.g. limb bud of arm,
Body plan - dorsal/ventral, caudal/cephalic axis. Cell has positional knowledge.
Signal from one group of cells influences the development of an adjacent group of cells - lots of types of signals and can travel short or long distance, has to affect specific receptor so doesnt affect all cells, and can affect -ve r +ve.
Eg. Cells on back surface produce a factor that diffuses across limb - signals to cells so each cell knows its place depending on concentration - see chick limb buds (can graft to opposite sides and get 2 high concentration areas and 2 arms)
lump of cells morphs into shape. generation of form - eg gastrulation, neurulation. migration of cells and adhesion of cells.
cell migration and changes in cell adhesion.
Cells may travel relatively long distances.
Migration is induced by environmental cues, and by adhesive differences
Expected date of delivery = date of LMP + 9 calendar months + 7days
(ten lunar months (40 wks, 280 days) about 7 days longer than 9 calendar months)
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