Embryology

Question 1

what are the three trimesters called?

Answer 1

weeks 0-3: conceptus/embryo
weeks 3-8: embryonic period
weeks 9-40: petal period

Question 2

what is gametogenesis?

Answer 2

formation of gametes, consisting of mitosis and meiosis, leading to genetic variation

Question 3

what is oogenesis?

Answer 3

formation of female gametes

Question 4

what is spermatogenesis?

Answer 4

formation of male gametes

Question 5

what happens during fertilisation?

Answer 5

union of gametes, formation of zygote: diploid, single cell embryo, sex determination

Question 6

what happens during cleavage?

Answer 6

period of rapid mitotic cell division
many daughter cells called blastomeres
up to 8 cell stage blastomeres are thought to be totipotent
no increase in size, formation of morula (16 cells) then blastocyst (days 1-4)

Question 7

what happens during gastrulation?

Answer 7

formation of the germ layers (week 3): ectoderm, mesoderm, endoderm

Question 8

what happens during organogenesis?

Answer 8

formation of organs and systems, basis of these in place by the end of embryonic period, continues to develop through foetal period

Question 9

what happens during foetal period?

Answer 9

growth and weight gain (mainly grows in second trimester and adds weight in the third), tissue mature and become functional, overt sexual differentiation, bone laid down and connections made in CNS

Question 10

what does induction mean?

Answer 10

ability of one cell type to cause another to differentiate

Question 11

what are primary processes from zygote to human?

Answer 11

cell division, differentiation, cell attachment, apoptosis, induction, cell migration

Question 12

what are secondary processes from zygote to human?

Answer 12

axis formation/polarity (cells need to know where they are in relation to each other and the embryo), folding and rotation (gives embryo 3D from, allows formation of complex structures)

Question 13

two controls of development?

Answer 13

genetic - gene expression tightly regulated in time and space
epigenetic - preferential expression of either the maternal or paternal copy of the gene

Question 14

what does sperm bind with in a human specific interaction?

Answer 14

zona pellucida glycoprotein (ZP3)

Question 15

what is released from the sperm head?

Answer 15

acrosomal enzymes

Question 16

what are the two sperm entry tiggers?

Answer 16

completion of meiosis 2

release of cortical granules by oocyte

Question 17

what is mosaicisom?

Answer 17

individuals with two of more cell lines with different chromosome complements

Question 18

what is a morula?

Answer 18

16+ blastomeres, cells confined within zone pellucid

Question 19

what happens with compassion of the morula?

Answer 19

to maximise available space by coming into closer contact with each other and begin cell junctions

Question 20

when and where does implantation occur?

Answer 20

day 6, on the posterior or anterior uterine wall

Question 21

what does a trophoblast divide into?

Answer 21

cytotrophoblast = made of individual cells 
syncytiotrophoblast = single multinucleated cell

Question 22

what two layers does the embryo split into?

Answer 22

epiblast = dorsal surface of the embryo
hypoblast = ventral surface of the embryo
forming the amniotic cavity

Question 23

what happens after the embryo has been organised into two layers?

Answer 23

implantation is complete and closure by fibrin coagulum, vacuoles appear in the synctiotrophoblast and unite to form lacunae. formation of two cavities: amniotic cavity (epiblast) and primitive yolk (hypoblast)

Question 24

what happens on day 9?

Answer 24

blastocyst embedded in the endometrium

lacunae formation

Question 25

what happens on day 15?

Answer 25

gastrulation