Cleavage

Question 1

Cleavage =
one sentence definition

Answer 1

Rapid series of mitotic cell divisions which are inititated by the zygote within 24 hours after fertilisation

Question 2

Impact of cleavage on the size of the embryo
& what is the name of the daughter cells

Answer 2

Size stays the same
Because divisions are not accompanied by cell growth
So the mitotic divisions simply divide the large zygote into many smaller daugther cells called BLASTOMERES
+ Bonus point = embryo remains enclosed in the zona pellucida

Question 3

State the changes in the number of cell size in the first fve days after fertilisation of the egg cell and name any key names of what the mebryo is called at these stages

Answer 3

Day 0 = pronuclear stage
Day 1 = 2 cell
Day 2 = 4 cell
Day 3 = 8 cell
Day 4 = MORULA - 16 to 32 cells
Day 5 = BLASTOCYST

Question 4

Fertilisation occurs in the ….. of the oviduct

Answer 4

Ampulla

Question 5

During the first …. days the zygote undergoes …… as it travels down the ….. and enters the …..
On day … the …. hatches from the …. and is then able to implant into the uterine ….

Answer 5

5
cleavage
oviduct
uterus
5, blastocyst, zona pellucida, endometrium

Question 6

….. causes some blastomeres to segregate to the centre of the morula and others to the outside.
Centrally places blastomeres are called ….
Blastomeres placed at the periphery = constitute the …..

Answer 6

COMPACTION
ICM = inner cell mass
Trophoblast

Question 7

The inner cell mass gives rise to the ….. …. and is therefore also called the ….

Answer 7

embryo proper
embryoblast

Question 8

Trophoblast = primary source of the fetal component of the …..

Answer 8

Placenta

Question 9

Tranformation of Morula to Blastocyst
. What is the side of the embryo containing the ICM called
. And what is the opposite side called

Answer 9

• Embryonic pole
  -Abembryonic pole

Question 10

Explain the process which leads to the formation of blastoceol within the morula?

Answer 10

. The pumping of sodium into the interior of the morula through Na+/K+ ATPase
. Results in water moving in through osmosis to become BLASTOCOELIC FLUID
. As the hydrostatic pressure increases, a large cavity called the BLASTOCYST CAVITY (blastocoel) forms within the morula

Question 11

As the trophblast differentiates, it assembles into an epithelium in which adjacent cells are tightly adherent to one another - this adhesion results from the deposition on lateral cell surfaces of ……. which is a ….. dependent cell-adhesion molecule and the formation of intracellular junctions such as 1,2,3 and 4

Answer 11

E-cadherin
Calcium
Tight junctions,
Gap junctions,
Adheren junctions
Desmosomes

Question 12

The embryoblast cells (inner cell mass) then form a compact mass at one side of this cavity, and the trophoblast organizes into a thin, single-layered epithelium. The embryo is now called a…..

Answer 12

blastocyst

Question 13

End of ……..: Initiating Implantation
Blastocyst Hatches From ……….Before Implanting

Answer 13

first week
zona pellucida

Question 14

Before implanting the blastocyst hatches from the zona pellucida by using …. (basically to bore a hole in & to squeeze out)

Answer 14

enzymes

Question 15

Implantation
. ….. is adherent, attaches to the uterine epithelium

Answer 15

Blastocyst

Question 16

If an embryo implants, cells of the trophoblast produce the hormone ….. which supports the …. and thus maintains supply of ……. (maternal recognition of pregnancy)

Answer 16

hCG = human chorionic gonadotropin
corpus luteum
progesterone

Question 17

The corpus luteum continues to secrete sex steroids for 11 to 12 weeks of embryonic development, after which the ….. itself begins to secrete large amounts of progesterone and the corpus luteum slowly involutes, becoming a corpus albicans.
(in the absence of an implanted embryo, the …… normally degnerates.

Answer 17

placenta
corpus luteum

Question 18

What is the decidua?

Answer 18

It is the endometrium of the uterus in a pregnant woman - it is the functional layer of th endometrium that separates from the remainder of the uterus after childbirth

Question 19

In response to the ……. …. levels in the maternal blood
Connective tissue cells of the decidua …… to form decidual cells
these cells enlarge as glycogen & lipid accuulate in their cytoplasm

Answer 19

increasing progesterone
enlarge

Question 20

The cellular and vascular changes occurring in the endometrium as the blastocyst implants constitute the

Answer 20

Decidual reaction
Decidual reaction occurs and cells in endometrial stroma
- become more vascularised
- oedomatous (fluid filled)
- endometrial glands enlarge

Question 21

Implantation at abnormal sites =

Answer 21

results in ectopic pregnancy

Question 22

Clinical relevance of ectopic pregnancy

Answer 22

. Occurs when implantation occurs at an abnormal site like peritoneal cavity, fallopian tube, ovary
. Still results in decidual reaction so risk of vascular rupture increases
(because the epithelium at these abnormal sites still responds to the implanting blastocyst with increased vascularity & other supportive changes)

Question 23

Symptoms & Treatment of Ectopic Pregnancies

Answer 23

• symptoms = abdominal pain, vaginal bleeding
• treatment - embryo will never reach term
  usually surgical intervention is required to interrupt the pregnancy and prevent maternal death

Question 24

Name the drug used for ectopic pregnancies

Answer 24

Methyltrexate - blocks rapid cell division

Question 25

….. plug as the embryo becomes fully implanted

Answer 25

coagulation

Question 26

Invasive trophoblastwithout distinct cell boundaries=…..
what does that produce and do? is this the outer or the inner layer?
Name of the other layer & is that outer or inner

Answer 26

syncytiotrophoblast, they producehCG(human chorionic gonadotropin) whichmaintains the corpus luteum
- Inner layer of mononuclear trophoblasts = cytotrophoblast

Question 27

Development of the……. ….. disc
….. differentiates into two layers - ….. and ….

Answer 27

bilaminar germ
ICM
epiblast
hypoblast