Embryology

Question 1

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

Answer 1

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

Question 2

What separates in m1 & m2 of meiosis

Answer 2

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

Question 3

Describe the phases of prophase 1

Answer 3

Leptotone: 
Zygotene: 
Pachytene:
Diplotene: 
Diakinesis:

Question 4

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

Answer 4

LH= Luteinising hormone

Question 5

Describe Leptotone

Answer 5

Leptotone: chromatin begins to condense

Question 6

Describe zygotene

Answer 6

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))

Question 7

Describe pachytene

Answer 7

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

Question 8

Describe diplotene

Answer 8

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

Question 9

Describe Diakinesis

Answer 9

Bivalents increase contraction nuclear envelope breaks down

Question 10

Describe prophase (mitosis)

Answer 10

Nuclear membrane breaks down
Chromosomes begin to condense
Spindle fibres appear

Question 11

Describe prometaphase

Answer 11

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

Question 12

Describe metaphase

Answer 12

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

Question 13

Describe anaphase (mitosis)

Answer 13

Chromosome pulled to opposite poles

Centromeres seperate

Question 14

Describe telophase

Answer 14

Daughter nuclear membranes reform
Chromosome decondense
Fibres disappear

Question 15

Describe cytokinesis

Answer 15

Cells divide

Question 16

What is recombination

Answer 16

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

Question 17

What are the stages of spermatogenesis

Answer 17

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)

Question 18

What are the stages of oogenesis

Answer 18

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

Question 19

What’s the function of the amniotic fluid

Answer 19

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.

Question 20

What’s the composition of AF

Answer 20

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

Question 21

What is the chorionic villi

Answer 21

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

Question 22

Name the cells types of the chorionic villi

Answer 22

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)

Question 23

When do you test a CVS

Answer 23

10-12 weeks

15-20mg

Rate of miscarriage: 1-2%

Question 24

When do you take an amniotic fluid sample

Answer 24

14-16 weeks is ideal

20ml

Rate of miscarriage: 0.5-1%

Question 25

What do you treat CVS with do digest it

Answer 25

Collagenase and trypsin

Question 26

When is fetal blood sampling done

Answer 26

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

Question 27

In prenatal sampling how can there be MCC

Answer 27

CVS: maternal decidua (remove by dissection) AF: bloodstaining (at culturing the bold cells don't settle/ amniocytes growth enhanced)

Question 28

When should MCC be suspected

Answer 28

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.

Question 29

Describe type 1 CPM

Answer 29

50% Error occurs in the trophoblast cell and only trophoblast cells are affected. Associated with normal pregnancy outcomes.

Question 30

Describe type 2 CPM

Answer 30

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.

Question 31

Describe type 3 CPM

Answer 31

20% Abnormality in trophoblast and chorionic villus stroma but are absent in the foetus. Associated with normal outcome and delayed fetal growth.

Question 32

What's the clinical significance of CPM

Answer 32

Most pregnancies continue to term without complications. Some pregnancies show IUGR (poor functioning placenta) Preg loss more common than non-CPM pregnancies

Question 33

What do you consider when predicting the outcome of CPM

Answer 33

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)

Question 34

What are the common Trisomies seen in CPM

Answer 34

2,3,7,8,16.

Question 35

How do you minimise CPM

Answer 35

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.