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Medicine Semester 1 > Embryology > Flashcards

Embryology Flashcards

0
Q

Outline the stages leading up to fertilisation:

A
  • Oocyte released from ovary
  • Travels down Fallopian tube
  • Fertilised in ampulla
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1
Q

How long is the gestation period?

A
  • 40 weeks give or take 2 depending on circumstance.
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2
Q

What is a fertilised oocyte known as?

A
  • Zygote
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3
Q

Where is the ideal implantation site?

A
  • Posterior uterine wall.
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4
Q

How long is an oocyte and a sperm viable for?

A
  • Oocyte: 24hrs

- Sperm: 3 days

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5
Q

What occurs at 30 hours after fertilisation and what does it result in?

A
  • Cleavage (1st cell division)

- Two blastomeres of equal size

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6
Q

What surrounds the two blastomeres?

A
  • Glycoprotein shell: zona pellucida
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7
Q

What happens after the two blastomeres are formed?

A
  • A MORULA forms (more cell division, identical cells)

- Totipotent

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8
Q

Name an assisted reproductive technique and a test for genetic diseases.

A
  • Oocytes fertilised in vitro - Morula is transferred to uterus
  • Pre-implantation genetic diagnosis (PGD) - Cell removed from morula and tested for serious genetic diseases before transferral into uterus.
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9
Q

What is compaction?

A
  • Formation of first cavity
  • Outer cell mass: Trophoblast
  • Inner cell mass: Embryoblast
  • Embryoblast masses at top of cell leaving a cavity: Blastocyst
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10
Q

What is hatching?

A
  • Blastocyst hatches from zona pellucida
  • No longer constrained, free to grow
  • Can interact with uterine wall to implant.
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11
Q

How does implantation occur?

A
  • Embryoblast side of cell joins to uterine epithelium.
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12
Q

During week 2 the inner and outer cell masses change, how so?

A
  • Trophoblast: 1) Syncytiotrophoblast (transporting membrane)
    2) Cytotrophoblast (stem cell layer: repair)
  • Embryoblast: Bilaminar disk: - epiblast (upper) & hypoblast (lower)
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13
Q

What are the two cavities surrounding the Bilaminar disk?

A
  • Amniotic cavity (above)

- Blastocyst cavity/yolk sac (below)

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14
Q

The Bilaminar disk is suspended and supported by what two things?

A
  • Suspended by connective stalk

- Supported by chorionic cavity

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15
Q

What is the point of implantation?

A
  • Establishes maternal blood flow within placenta

- Establishes basic structural unit of materno-foetal exchange

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16
Q

What is implantation exactly?

A
  • Uterine epithelium breached and conceptus implants within uterine stroma.
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17
Q

Name two implantation defects.

A
  • Ectopic pregnancy

- Placenta praevia

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18
Q

What is ectopic pregnancy?

A
  • Implantation of conceptus not in uterus (Fallopian tube)
  • Peritoneal/ovarian
  • Life threatening
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19
Q

What is placenta praevia?

A
  • Implantation in the lower uterine segment
  • Haemorrhage
  • Requires C-section delivery
20
Q

On day 9 of development, two poles form, what are these and what else occurs?

A
  • Embryonic pole: rapid development of syncytiotrophoblast
  • Abembryonic pole: primitive yolk sac formation
  • Yolk sac is in contact with cytotrophoblast layer
21
Q

On Day 11 if development the yolk sac is pushed away from the cytotrophoblast by what and what happens to this?

A
  • Acellular extraembryonic reticulum

- Converted into an extraembryonic mesoderm layer by cell migration.

22
Q

What happens on day 12 of development?

A
  • Sinusoids are invaded by syncytiotrophoblast.
  • Lacunae become continuous with sinusoids
  • Uteroplacental circulation begins.
  • Uterine stroma prepares for support of embryo.
23
Q

On day 13 of development a secondary yolk sac forms, how does this occur?

A
  • Pinches off from primitive yolk sac.
24
Q

What percentage of births are:

a) lost in weeks 2-3
b) diagnosed but miscarried
c) recurrent miscarriages

A

a) 50%
b) 15%
c) 1%

25
Q

Why may intrauterine growth restriction occur?

A
  • Poor maternal nutrition

- O2 supply to foetus

26
Q

What is pre-eclampsia?

A
  • High blood pressure
  • High protein content of pregnant women
  • Leads to life threatening seizures.
27
Q

What is the role of gastrulation?

A
  • Production of 3 germ layers
  • Trilaminar disk
  • Axes
28
Q

What are the 4 different axes of the body?

A
  • Posterior/anterior
  • Superior/Inferior
  • Dorsal/ventral
  • Left/right
29
Q

What is the primitive streak, node and pit?

A
  • Primitive node is located at the cranial end of the streak and the pit is the centre of the zygote.
30
Q

When does the primitive streak regress and what direction does development occur?

A
  • When the 3 germ layers have been established

- Cranium -> Caudal

31
Q

How is the Trilaminar disk formed from the Bilaminar disk?

A
  • Migration and invagination of cells
  • Cells spread cephalad (towards the head) and laterally.
  • Displacement of hypoblast layer to form mesoderm
32
Q

How does the mouth and anus form during gastrulation?

A
  • Cells don’t invaginate at the head and end of the streak.
33
Q

What is the notochord’s role in development?

A
  • Drives NS development.
  • Basis for axial skeleton
  • Defines phylum cordata
34
Q

How is the notochord formed and what’s its role?

A
  • Epiblast migrating through the cranial part of the primitive pit
  • Forms a solid rod with signalling purposes.
35
Q

What is situs inverta, and why does it occur?

A
  • Mirror image of normal for internal organs
  • Results from immotile cilia
  • Only problems if mix of reverse and normal.
36
Q

How can twinning occur?

A
  • Embryo splits after cleavage.
  • Two embryos with their own placenta
    Or
  • Embryo cell mass duplicates
  • Share a placenta
37
Q

What is teratogenesis?

A
  • When normal embryonic development is disrupted

- Each organ has its own ‘sensitive window’

38
Q

Name 3 teratogenic agents.

A
  • Thalidomide
  • Rubella
  • Alcohol
39
Q

What is neuralation?

A
  • Notochord driven induction of ectoderm to form NS

- Neural plate -> neural tube which forms brain and spinal chord

40
Q

How does the neural plate change to form the neural tube?

A
  • Notochord signals to cause overlying ectoderm to thicken
  • ‘Slipper’ shaped neural plate
  • Edges elevate out of the plane of the disk and curls towards each other creating the neural tube.
41
Q

After neurulation what does the mesoderm split into and what is the space between these two layers called?

A
  • Splits into somatic and splanchnic mesoderm

- Intraembryonic coelom

42
Q

What are somites?

A
  • Organisation of paraxial mesoderm into segments
43
Q

How are somites formed?

A
  • Craniocaudal sequence, 3 pairs a day from day 20 -> 42/44 pairs
  • Some disappear to leave 31 pairs
44
Q

What is the next step after 31 pairs form?

A
  • Organised degeneration: ventral walls break down to form a sclerotome ( hard tissue section)
  • Further organisation of dorsal portion forms combined dermomyotome
45
Q

What happens to the dermomyotome?

A
  • Myotome (muscle section) proliferates and migrates

- Dermatome (skin section) disperses

46
Q

What does segmentation give rise to?

A
  • Vertebrae
  • Ribs
  • Intercostals
  • Spinal cord segments
47
Q

What is embryonic folding?

A
  • Head fold then a tail fold: cephalocaudal folding
  • Lateral folding (other edges to leave a small gap for the umbilical cord)
  • This is driven by expansion of neural tube
48
Q

What does embryonic folding achieve?

A
  • Creates a ventral wall around disks
  • Pulls amniotic membrane around disk (embryo becomes suspended within amniotic sac)
  • Pulls connecting stalk ventrally.
  • Creates primordium of gut from yolk sac
  • Puts heart and primordium of diaphragm into right place
  • This creates a new cavity within the embryo

Medicine Semester 1 (6 decks)

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