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Prenatal > Embryology > Flashcards

Embryology Flashcards

1
Q

What are the stages of embryogenesis. From fertilisation to 16 cell stage?

A

Cleavage stage: zygote divides (cells are called blastomers)
Cells undergo compaction: 8 cell stage: morula
Morula has has fluid filled cavity: blastocoele
16 cell stage: blastocyst: 2 cell types: trophoblasts: inner cell mass & embryoblasts: outer cells

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2
Q

What separates in m1 & m2 of meiosis

A 
M1= random separation of chromosome pairs (92n to 46n) 
M2= separation of sister chromatids (46n to 23n)
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3
Q

Describe the phases of prophase 1

A 
Leptotone: 
Zygotene: 
Pachytene:
Diplotene: 
Diakinesis:
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4
Q

What’s the name of the hormone that stimulates M1 restart in eggs

A

LH= Luteinising hormone

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5
Q

Describe Leptotone

A

Leptotone: chromatin begins to condense

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6
Q

Describe zygotene

A

homologues pairing to form a -bivalent synaptonemal complex
connecting points= chiasmata
sex vesicle: Obligate recombination between the PAR1 of X-Y in male meiosis (PAR2 rare))

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7
Q

Describe pachytene

A

early: synapsis (pairing of chromosome homologues)= complete pairing: bivalent= tetrad
Late: chroms thicken/ cross over- recombination (min: 1/arm) sperm~ 60 c/o; ova~0 c/o

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8
Q

Describe diplotene

A

Diplotene: homologues start to separate (desynapsis)/held together by chiasmta (maintained by cohesion).
Sex vesicle held together end-end

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9
Q

Describe Diakinesis

A

Bivalents increase contraction nuclear envelope breaks down

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10
Q

Describe prophase (mitosis)

A

Nuclear membrane breaks down
Chromosomes begin to condense
Spindle fibres appear

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11
Q

Describe prometaphase

A

Spindle fibres attach to kinetochores
Chromosome begin to migrate to plate
Continue to condense

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12
Q

Describe metaphase

A

Chromosome fully condensed and aligned along plate. Only in is stage momentarily

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13
Q

Describe anaphase (mitosis)

A

Chromosome pulled to opposite poles

Centromeres seperate

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14
Q

Describe telophase

A

Daughter nuclear membranes reform
Chromosome decondense
Fibres disappear

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15
Q

Describe cytokinesis

A

Cells divide

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16
Q

What is recombination

A

The alignment of 2 homologises, precise breakage of each strand, equal crossing over and sealing of the resultant recombined DNA

17
Q

What are the stages of spermatogenesis

A

Spermatogonia differentiates into primary spermocyte which undergoes meiosis
After M1 there are 2 secondary spermocytes
After M2 there are 4 spermatids
The spermatids mature into sperm (5wks)

18
Q

What are the stages of oogenesis

A

Between the 15th wk and 7mnth gestation:
Primordial germ cell migrates into forming gonads where they become oogonia
Oogonia proliferate and differentiate into primary oocytes
Primary ooctyes begin meiosis in the follicles and at 8 month gestation are held into prophase 1 (dictyate) until ovulation
Once ovualted they continue meiosis and wait at metaphase 2 until fertilisation

19
Q

What’s the function of the amniotic fluid

A 
Cushions foetus from impacts sustained by mother.
Enables symmetrical growth.
Allows free fetal movement.
Maintains a constant temp.
Prevents foetus adhering to the amnion.

Helps musculoskeletal development.
Essential for proper development of respiratory system.

20
Q

What’s the composition of AF

A

99% water.

Carbohydrates. Fats. Proteins. Enzymes. Hormones. Pigment.

CELLS (from epiblastic origin- fetal skin, epithelial surfaces: respiratory tract, gastrointestinal,genitourinary,extraembryonal membranes, amniocytes from the amnion).

10wks: 30ml.
20wks: 350ml

21
Q

What is the chorionic villi

A

Part of the extraembryonic tissue. part of the placenta.

Same genetic origin as foetus. Starts to differentiate from foetus at day 5-6. Grows rapidly so large amount early

22
Q

Name the cells types of the chorionic villi

A

Trophoblasts layers (outside of villi). (Direct prep)

Syncitrophoblast: Outer single cell layer.

cytotrophoblast: Rapidly dividing cells.

Inner core of chorionic villi is the mesenchymal core. (Long term culture)

Maternal decidua (needs removing)

23
Q

When do you test a CVS

A

10-12 weeks

15-20mg

Rate of miscarriage: 1-2%

24
Q

When do you take an amniotic fluid sample

A

14-16 weeks is ideal

20ml

Rate of miscarriage: 0.5-1%

25
Q

What do you treat CVS with do digest it

A

Collagenase and trypsin

26
Q

When is fetal blood sampling done

A

2nd trimester test (18-20wks) taken from umbilical cord or fetal blood vessel

Miscarriage rate: 2-2.5% within 2 was of procedure. Can be a s high as 10% if foetus has severe IUGR/abn scan or twins.

More commonly used for blood disorders

27
Q

In prenatal sampling how can there be MCC

A

CVS: maternal decidua (remove by dissection)

AF: bloodstaining (at culturing the bold cells don’t settle/ amniocytes growth enhanced)

28
Q

When should MCC be suspected

A

XX/XY cells.
XX/XX(abn) cell lines seen together.
XX K that discordant to previous PND or fetal sex.
Uncertainty around ID of tissue used.
Slow growth, especially if from a single piece of tissue/ small number of colonies.

29
Q

Describe type 1 CPM

A

50%

Error occurs in the trophoblast cell and only trophoblast cells are affected.

Associated with normal pregnancy outcomes.

30
Q

Describe type 2 CPM

A

30%

Error occurs in non-fetal cell of the inner cell mass so abnormality is confined to the chorionic villus stroma.

Normal pregnancy, sometimes with delayed fetal growth.

31
Q

Describe type 3 CPM

A

20%

Abnormality in trophoblast and chorionic villus stroma but are absent in the foetus.

Associated with normal outcome and delayed fetal growth.

32
Q

What’s the clinical significance of CPM

A

Most pregnancies continue to term without complications.

Some pregnancies show IUGR (poor functioning placenta)

Preg loss more common than non-CPM pregnancies

33
Q

What do you consider when predicting the outcome of CPM

A

Origin of error (somatic error is ass with less every outcome).
Level of mosaicism ( correlation with increase of aneuploid cells and poor outcome).
Specific chromosome (influence on fetal growth).
Type of chromosome abnormality ( markers more often seen in foetus than trisomy)

34
Q

What are the common Trisomies seen in CPM

A

2,3,7,8,16.

35
Q

How do you minimise CPM

A

Analyse mesenchymal core.
Use more than 1 frond.
Ideally fronds from different areas of biopsy.
Include material from entire biopsy (chopping).

If mosaic request ultrasound and AF.

Under NO circumstances should a pregnancy be terminated based entirely on a mosaic CVS result.

Prenatal (5 decks)

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