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Phase 1 > Life Before Birth > Flashcards

Life Before Birth Flashcards

1
Q

what are the 3 broad stages of life before birth, and what are their timings?

A
  • week 1: preimplantation stage
  • week 2-8: embryonic stage (organogenesis and placental development)
  • week 9-38: fetal stage (growth and development)
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2
Q

what happens to the zygote in the few days after fertilisation?

A

cleavage - mitotic divisions of the fertilised oocyte

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3
Q

what are the 2 functions of the zona pellucida during week 1?

A
  • prevent the embryo from getting larger -> successive divisions increase the number of cells but not the size overall (prevents the zygote from getting stuck in the isthmus of the uterine tube)
  • prevent implantation in the uterine tube
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4
Q

what happens to the zygote at around day 4? (3)

A
  • cells maximise contact with each other (around 16 cells)
  • form a morula
  • enter the uterus
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5
Q

how is the blastocyst formed? (3)

A

1 - fist cellular differentiation
2 - inner cell mass will form embryo, surrounded trophoblasts that will contribute to placenta
3 - cavitation: fluid fills the space pressing the ICM to one side (blastocyst cavity)

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6
Q

describe hatching of the blastocyst (3)

A

1 - blastocyst begins to run out of nutrients, therefore it must implant
2 - zona pellucida begins to shed upon reaching the uterus
3 - blastocyst emerges from the weakened part of the zona pellucida

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7
Q

what happens after the blastocyst makes contact with the endometrium? (7)

A

1 - stromal cells of the uterus perform decidualisation
2 - process changes the endometrium in preparation for pregnancy
3 - endometrium produces chemicals with cause the trophoblasts to become invasive
5 - implanted trophoblast cells being differentiation
6 - cells closest to embryo become cytotrophoblasts
7 - outer layer (extensive and invasive) become syncytiotrophoblasts

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8
Q

what happens to syncytiotrophoblasts towards the end of week 2?

A
  • communicate with maternal placenta to allow the exchange of nutrients, waste etc.
  • begin to produce human chronic gonadotrophin hormone (detected in pregnancy tests)
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9
Q

what is an ecoptic pregnancy? (3)

A
  • implantation in abnormal sites
  • caused by slow transit in uterine tube or premature hatching
  • should cause a spontaneous miscarriage, otherwise can cause haemorrhage
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10
Q

what is the chorion? (3)

A
  • derived from trophoblasts
  • forms foetal component of placenta
  • lines chondral cavity (disappears later in pregnancy due to expansion of amniotic cavity)
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11
Q

what is the amnion? (3)

A
  • derived from ICM
  • continuous with epiblast of bilaminar disc
  • lines amniotic cavity - filled with fluid to protect embryo
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12
Q

what is the yolk sac? (4)

A
  • derived from ICM
  • continuous with hypoblast of bilaminar disc
  • important in nutrient transfer in weeks 2-3 (disappears in week 20)
  • important in blood cell and gut formation
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13
Q

what is the allantois? (4)

A
  • derived from ICM
  • outgrowth of yolk sac
  • contributes to umbilical arteries
  • connects to foetal bladder
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14
Q

what is gastrulation?

A

a process of cell division and migration resulting in the formation of 3 germ layers (trilaminar embryo from bilaminar epiblast)

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15
Q

what does the inner cell mass differentiate into?

A
  • epiblast - will form embryo

* hypoblast - will become yolk sac

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16
Q

what is the primitive streak?

A

midline condensation of cells from epiblast

17
Q

describe gastrulation (5)

A

1 - epiblast cells migrate towards the primitive streak
2 - descend downwards pushing the hypoblast outwards away from midline
3 - top layer of cells remain where the epiblast first formed: ectoderm
4 - some cells leave the streak between the 2 layers: mesoderm
5 - lower layer takes up space where hypoblast was: endoderm

18
Q

what structures does the ectoderm form? (3)

A

outside things
• skin epidermis
• epithelial linings of mouth + anus
• nervous system

19
Q

what structures does the mesoderm form? (5)

A 
middle things
• musculoskeletal system
• excretory system
• circulatory system
• reproductive system (not germ cells)
• dermis of skin
20
Q

what structures does the endoderm form? (4)

A 
inside things
• epithelial lining of digestive + respiratory tracts
• liver
• pancreas
• thymus

Phase 1 (14 decks)

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