second week embryology

Question 1

what is implantation?

Answer 1

It is the process by which the blastocyst embeds itself in the decidua. →day7

Question 2

at what time does implantation occur?

Answer 2

This process begins at the end of the 1st week & is completed by the end of 2nd week of the human development.

Question 3

at which site does implantation occur?

Answer 3

commonly attached to the junction of the fundus and posterior wall of the uterus or anywhere in the upper part of uterine cavity

Question 4

when does the zona pellucida disappear during fertilization?

Answer 4

5th day

Question 5

what is syncytiotrophoblast?

Answer 5

covering the embryonic pole of the blastocyst
has finger-like processes which invade & erode the glands &the blood
vessels of the decidua through the release of proteolytic enzymes.

Question 6

Decidua

Answer 6

The decidua is the specialized layer of endometrium that forms the base of the placental bed.

Question 7

what is the embryonic disc?

Answer 7

it is when the embryoblast changes into a
flattened, circular, bilaminar disc

Question 8

what are the 2 layers that the embryonic disc consist of?

Answer 8

The epiblast (ectoderm),the thicker
layer, consists of high, columnar cells.
The hypoblast (endoderm), the thinner
layer, consists of small, cuboidal cells.
( Bilaminar germ disc gives rise to embryo
proper)

Question 9

what are the formation of extra embryonic structures?

Answer 9

Amnion & amniotic cavity

Question 10

what are the peripheral cells of epiblast
(ectoderm) called?

Answer 10

amnioblasts

Question 11

why do aminioblasts migrate dorsally to form what?

Answer 11

to form a thin membrane known as amniotic
membrane

Question 12

the membrane encloses an amniotic cavity which is called ?

Answer 12

amniotic cavity

Question 13

what forms the floor of the
amniotic cavity ?

Answer 13

the epiblast

Question 14

what is the chorionic sac?

Answer 14

The extra-embryonic mesoderm
develops between trophoblast
externally and amnion and primary
yolk sac internally. It enlarges &
isolated extra-embryonic spaces
appear within it.

Question 15

The extra - embryonic coelom splits
the extra - embryonic mesoderm into
2 layers which are?

Answer 15

Extra – embryonic somatic
mesoderm which lines the
trophoblast & covers the amnion.

Extra -embryonic splanchnic
mesoderm which surrounds the
primary umbilical vesicle so it
become, secondary umbilical vesicle.

Question 16

chorionic membrane consists of?

Answer 16

synciotrophoblasts t + Cyto- trophoblast + Extra-embryonic somatic mesoderm lining the trophoblast.

Question 17

What is connecting stalk ?

Answer 17

it is one place at which the extra
-embryonic mesoderm doesn’t split,
the dorso -caudal end of the
embryonic disc where the disc is
attached to the trophoblast

Question 18

what are the isolated cavities?

Answer 18

Isolated cavities called lacunae
appear in the syncytio-trophoblast.

Question 19

By the 12th day, the lacunae fuse
together to form what?

Answer 19

to form lacunar networks
that are prominent around the
embryonic pole.
They are the primordia of the
intervillous spaces of the
placenta.

Question 20

by the end of the 2nd week what appears?

Answer 20

The primary chorionic villi appears

Question 21

The cells of the anterior part of endoderm of the embryonic disc, became
columnar, forming a thick circular area which is called?

Answer 21

the prochordal plate

Question 22

the prochordal plate indicates what?

Answer 22

This plate indicates the future site of the mouth