3rd week of development- trilaminar germ disc

Question 1

most characteristic event happening in 3rd week and what happens in it

Answer 1

gastrulation

establishment of 3 germ layers

Question 2

gasturlation begins with

Answer 2

the formation of primitive streak within the epiblast

Question 3

primitive node is where

Answer 3

caudal end of primitive streak has a primitive pith with elevations on side

Question 4

cells migrate into the primitive streak, so upon the arrival they become what and what happens

Answer 4

they become flask shaped and detach from the epiblast

Question 5

cell migration and specification is controlled by

Answer 5

fibroblast growth factor 8

Question 6

what binds epiblast cells together

Answer 6

E-cadherin which is down regulated by FGF-8

Question 7

cell specification into mesoderm is regulated by

Answer 7

BRACHYURY (T) expression

Question 8

on the cephalic direction they come in contact with

Answer 8

prechordal plate

Question 9

prechordal plate is made where

Answer 9

between the tip of the notochord and the oropharyngeal membrane

Question 10

prechordal plate is important

Answer 10

induction of forebrain

Question 11

where oral cavity is made

Answer 11

oropharyngeal membrane at the cranial end of the disk has a small region of tightly adherent ectoderm and endoderm that represent future opening of the oral cavity

Question 12

formation of notochord

Answer 12

the pronotochordal cells invaginate into the primitive streak cranially until they reach prechordal plate and get intercalated with the hypoblast so for time being the embryo has 2 layers of cells that make up the notochord plate
the cells of notochord plate proliferate and detached from epiblast to form a definitive notochord (because the hypoblast cells are getting replaced by endodermal cells)

Question 13

neurenteric canal

Answer 13

primitive pith makes an indentation in the epiblast which temporarly connect the yolk sac and amnion

Question 14

cloacal membrane is made where and what does it do

Answer 14

its made at the caudal end of the embryonic plate
when the coacal membrane appears the posterior wall of yolk sac forms a diverticulum which is called as allantoenteric diverticulum or allontois which appears on 16th day

Question 15

allontois in humans

Answer 15

remains rudimentary and can be involved in the making abnormalities of bladder development

Question 16

explain the formation of secondary villi

Answer 16

mesodermal cells penetarte into the primary villi and grow towards the decidua and make secondary villi

Question 17

explain formation of tertiary villi

Answer 17

the mesodermal cells differentiate into blood cells and vessels forming the villous capillary system which is called the tertiry villi aur definitive placental villus

Question 18

how the embryo is given the oxygen and nutrients

Answer 18

the tertiary villi capillaries make contact with the capiliaries in the mesoderm of of chorionic plate and in connecting stalk
which make contact with intramebryonic circulatory system and connects the embryo with placenta so when in the 4th week of development the heart starts beating the embryo is givng nutrients etc

Question 19

outer trophoblast shell

Answer 19

the cytotrophoblast penetrate and poliferate into the surrounding syncytium until they reach the maternal endometrium and make connections with the neighbouring villous extension stems and make the outer trophoblast shell

Question 20

where the placenta is made

Answer 20

the part of villi that extends from the chorionic plate into the decidual plate in the endometrium and thats where placenta is made