Embryology Flashcards
What are the stages of embryogenesis. From fertilisation to 16 cell stage?
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
What separates in m1 & m2 of meiosis
M1= random separation of chromosome pairs (92n to 46n) M2= separation of sister chromatids (46n to 23n)
Describe the phases of prophase 1
Leptotone: Zygotene: Pachytene: Diplotene: Diakinesis:
What’s the name of the hormone that stimulates M1 restart in eggs
LH= Luteinising hormone
Describe Leptotone
Leptotone: chromatin begins to condense
Describe zygotene
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))
Describe pachytene
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
Describe diplotene
Diplotene: homologues start to separate (desynapsis)/held together by chiasmta (maintained by cohesion).
Sex vesicle held together end-end
Describe Diakinesis
Bivalents increase contraction nuclear envelope breaks down
Describe prophase (mitosis)
Nuclear membrane breaks down
Chromosomes begin to condense
Spindle fibres appear
Describe prometaphase
Spindle fibres attach to kinetochores
Chromosome begin to migrate to plate
Continue to condense
Describe metaphase
Chromosome fully condensed and aligned along plate. Only in is stage momentarily
Describe anaphase (mitosis)
Chromosome pulled to opposite poles
Centromeres seperate
Describe telophase
Daughter nuclear membranes reform
Chromosome decondense
Fibres disappear
Describe cytokinesis
Cells divide
What is recombination
The alignment of 2 homologises, precise breakage of each strand, equal crossing over and sealing of the resultant recombined DNA
What are the stages of spermatogenesis
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)
What are the stages of oogenesis
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
What’s the function of the amniotic fluid
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.
What’s the composition of AF
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
What is the chorionic villi
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
Name the cells types of the chorionic villi
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)
When do you test a CVS
10-12 weeks
15-20mg
Rate of miscarriage: 1-2%
When do you take an amniotic fluid sample
14-16 weeks is ideal
20ml
Rate of miscarriage: 0.5-1%
What do you treat CVS with do digest it
Collagenase and trypsin
When is fetal blood sampling done
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
In prenatal sampling how can there be MCC
CVS: maternal decidua (remove by dissection)
AF: bloodstaining (at culturing the bold cells don’t settle/ amniocytes growth enhanced)
When should MCC be suspected
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.
Describe type 1 CPM
50%
Error occurs in the trophoblast cell and only trophoblast cells are affected.
Associated with normal pregnancy outcomes.
Describe type 2 CPM
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.
Describe type 3 CPM
20%
Abnormality in trophoblast and chorionic villus stroma but are absent in the foetus.
Associated with normal outcome and delayed fetal growth.
What’s the clinical significance of CPM
Most pregnancies continue to term without complications.
Some pregnancies show IUGR (poor functioning placenta)
Preg loss more common than non-CPM pregnancies
What do you consider when predicting the outcome of CPM
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)
What are the common Trisomies seen in CPM
2,3,7,8,16.
How do you minimise CPM
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.
