first week embryology

Question 1

what are the events that occur during the first week?

Answer 1

Fertilization, cleavage, implantation

Question 2

where does capacitation occur? ( maturation of the sperm )

Answer 2

occurs in the uterus and the uterine tube

Question 3

which layer is removed within the sperms during capacitation?

Answer 3

glycoproteins

Question 4

does the capacitation process increase the activity of the sperms?

Answer 4

yes

Question 5

where does the acrosome reaction of the sperms occur?

Answer 5

only in the ampulla of the uterine tube

Question 6

what develops in the acrosome reaction?

Answer 6

development of multiple perforations in the acrosome of the sperms to release enzymes

Question 7

what is the zona reaction?

Answer 7

Lysis of zona pellucida

Question 8

what causes zona reaction?

Answer 8

caused by acrosin and zonalysin

Question 9

what happens once a sperm penetrates the zona pellucida

Answer 9

a zona reaction occurs, resulting in change in its physical properties and making it impermeable to other sperms

Question 10

what does zona reaction prevent?

Answer 10

prevents polyspermy ( penetration of more than one sperm into the oocyte ) to avoid the occurrence of polyploidy

Question 11

what is fertilization?

Answer 11

is the fusion of a single sperm and secondary oocyte to form a zygote

Question 12

what does the secondary oocyte convert to during fertilization?

Answer 12

a mature ovum

Question 13

where does fertilization occur?

Answer 13

in the ampulla of the uterine tube

Question 14

how long does fertilization last for?

Answer 14

24HRS

Question 15

what happens if the oocyte is not fertilized?

Answer 15

slowly passes along the uterine tube into the cavity of the uterus where it degenerates

Question 16

what are the results of fertilization?

Answer 16

the 2ry oocyte completes its 2nd meiotic division producing a mature ovum & 2nd polar body.
( Restoration of the diploid number of the chromosomes (46). )

Question 17

what factor determines the sex of the embryo ?

Answer 17

*XX – Female
*XY- Male

Question 18

where does the cleavage of the zygote occur?

Answer 18

in the uterine tube

Question 19

what results into having a cleavage of the zygote?

Answer 19

mitotic cell divisions of the zygote ( within its zona pellucida ) resulting in a rapid increase in
the number of cells.

Question 20

during the cleavage of the zygote, cells are formed what are these cells called?

Answer 20

are called blastomeres,
become smaller in size with each cleavage
division.

Question 21

what is morula?

Answer 21

When there are 16 - 32 blastomeres by the
3rd day, the zygote is called a morula.

Question 22

is the early morula surrounded by zona pellucida?

Answer 22

yes

Question 23

when does the morula reach the uterine cavity?

Answer 23

by the 4th day after fertilization

Question 24

where does the uterine fluid pass?

Answer 24

Uterine fluid passes through zona pellucida
and outer cells of morula

Question 25

what does the accumulation of fluid convert the morula to?

Answer 25

Accumulation of fluid converts morula into
fluid filled cavity called the blastocystic cavity
or blastocoele.

Question 26

on which day does the zona pellucida disappear?

Answer 26

Zona pellucida disappears by 5th day of
fertilization

Question 27

Fluid increases in the blastocystic cavity, the
blastomeres are separated into 2 groups which are?

Answer 27

Trophoblast-outer cell mass
* Embryoblast –inner cell mass

Question 28

Trophoblast: Outer cell mass
what is it structured like ?
what is its function?

Answer 28

Thin outer cells that forms the wall of the blastocyst.
It is the nutritive part of the blastocyst

Question 29

The embryoblast (inner cell mass):

Answer 29

Centrally located blastomeres.
Form embryo.
Projects into the blastocystic cavity

Question 30

The late blastocyst has 2 poles which are?

Answer 30

Embryonic pole: overlies the embryoblast & is adjacent to the
uterine endometrium.
*Abembryonic pole: away from the embryoblast &uterine endometrium

Question 31

what is the endometrium of the uterus changed to?

Answer 31

Endometrium of the uterus is changed to decidua

Question 32

on which day does the blastocyst attach himself to the uterine endometrium?

Answer 32

6th day

Question 33

At the 7th day the trophoblast starts to proliferate rapidly & differentiate
into 2 layers which are?

Answer 33

• The cyto – trophoblast-:The inner original layer of cells (overlying embryoblast).
• The syncytio – trophoblast:The outer layer of a multi-nucleated fused
  cells

Question 34

what is implantation?

Answer 34

It is the process by which the blastocyst embeds itself in the
endometrium.

Question 35

when does implantation occur?

Answer 35

This process begins at the end of the 1st week(7th day of
fertilization)& is completed by the end of 2nd week of the human
development.

Question 36

what is the process of implantation?

Answer 36

They are finger like processes, that secrete proteolytic enzymes that erode the uterine endometrium enabling the blastocyst to burrow into the endometrium (implanted).

Question 37

by the end of which week is the blastocyst superficially implanted?

Answer 37

by the end of the 1st week

Question 38

what are the cuboidal layer of cells called that appear on the surface of the embryo blast facing the blastocystic cavity

Answer 38

Hypoblast cells