Embryology: cleavage & hatching/implantation

Question 1

when does cleavage occur

Answer 1

days 1-3

Question 2

briefly describe cleavage

Answer 2

rapid mitotic division without increase in size

confined within the ZP

Question 3

how many cells are in a morula and a blastocyte

Answer 3

morula = 16+ cells
blastocyte = 200-300 cells

Question 4

what is the trophoblast

Answer 4

the outer layer( has gap junctions)

Question 5

what type of junctions does the ZP have and why

Answer 5

gap junctions to allow fluid to enter

Question 6

where does embryo implant in normal pregnancy

Answer 6

in endometrial lining on posterior or anterior of uterine wall

Question 7

what is an ectopic pregnancy

Answer 7

growth of the embryo where there isn’t enough space

when it implants somewhere that isn’t uterine wall(e.g. fallopian tube, rarely abdomen)

Question 8

when does gastrulation occur

Answer 8

week 3

Question 9

describe the process of gastrulation

Answer 9

epiblast cells move through the primitive streak, between epiblasts and definitive endoderm, to form 3 primary germ layers

Question 10

what parts of the body does the ectoderm form

Answer 10

skin epidermis and nervous system

Question 11

what parts of the body does the mesoderm layer form

Answer 11

axial skeleton, muscle, body wall lining, limb parts, urogenital

Question 12

what parts of the body does the endoderm layer form

Answer 12

gut, respiratory, bladder and urethral lining

Question 13

what are the 3 primary germ layers formed by gastrulation

Answer 13

ectoderm, mesoderm and endoderm