Lec 33

Question 1

The human gestation period is approximately — days — weeks or — days — weeks

Answer 1

266 , 38
280 , 40

Question 2

What are the two systems of dating of pregnancy?

Answer 2

1- used by embryologists ( fertilisation age )
من اليوم اللي صار فيه الfertilisation
2- used by clinicians ( menstrual age )
بعد الfertilisation بأسبوعين

Question 3

What is the fertilisation age of a six week old embryo —

Answer 3

6 weeks from the day of fertilisation

Question 4

the menstrual age is ——— the fertilisation age , because ?

Answer 4

two weeks greater than
usually two weeks elapse between start of the last menstrual period and fertilisation

Question 5

An embryo with a fertilisation age of 6 weeks is assigned a menstrual age of — weeks ?

Answer 5

8

Question 6

the typical duration of pregnancy is — weeks [ fertilisation age ]
and — weeks [ menstrual age ]

Answer 6

38
40

Question 7

The duration of pregnancy is ——— ( 9 months )

Answer 7

Gestation period

Question 8

Clinicians divide 9 month period of pregnancy to —— intervals called——

Answer 8

3 month
Trimesters

Question 9

Embryologist divide pregnancy into —— periods , corresponding to the ———— that occur in each period

Answer 9

unequal
major developmental events

Question 10

What are the periods, which embryologists use?

Answer 10

1- pre-embryonic period -> 0-2 wks ( cleavage & implantation )
2- embryonic period -> 3-8 wks ( organogenesis )
3- fetal period -> 9-38 wks ( maturation of organs )

Question 11

What happens during the first week of development?

Answer 11

Fertilisation of oocyte
Zygote ( 2 - 4 - 8 cell )
Morula ( embryo hatch from zona pellucida )
Blastocyst

Question 12

What happens to the zygote ?

Answer 12

Divides many times within the zona pellucida , while moving down in the uterine tube towards uterus cleavage

Question 13

What happens during the morula ( Mulberry ) period ?

Answer 13

The solid mass of about 16 blastomeres is formed approximately 3 days after fertilisation

Question 14

The blasphemer consist of — parts , what are they?

Answer 14

2
1- Inner cell mass ( embryoblast ) -> will give rise to the embryo
2- outer cell mass ( trophoblast ) -> will form the fetal part of the placenta

Question 15

That the blastomere floats for about —— days , Zona pellucida gradually —— and —— to allow implantation to occur

Answer 15

2 - 3
degenerates , disappears

Question 16

During the second week of development , at day 8
✰the trophoblast cells at the embryonic pole differentiate into 2 layers :
✰Currently, cells of inner cell mass ( embryoblast ) also differentiate into 2 layers :
✰A ——— appears within the —— called ——

Answer 16

✰1- cytotrophoblast ( proliferative layer ) , 2- syncytiotrophoblast ( invasive layer )
✰1- epiblast , 2- hypoblast
✰Small cavity, epiblast , amniotic cavity

Question 17

At the second week of development at day 9
★ the amniotic cavity is ——
★ The embryo is now a bilaminar disc ( epiblast & hypoblast )
★ the epiblast forms a membrane known as ——— , which lines the exocoelmic cavity ———
★ syncytiotrophoblast continues to invade the ——— and start eroding the ——— and blood vessels

Answer 17

expanding
Exocoelomic membrane ( Heuser’s )
Primary yolk sac
endometrium
endometrial glands

Question 18

At the second week of development at day 9
★ Extra embryonic mesoderm has been developed and soon —— are formed in it , which then —— to form extraembryonic coelom ( —— )
★ the extra embryonic coelom / ( —— ) surrounds the —— and the —— except at the ——— which will become the umbilical cord
★ the extraembryonic mesoderm splits into — parts , what are they?

Answer 18

★ large cavities , fuse , Chorionic cavity
★ Chorionic cavity , primary yolk sac , amniotic cavity , connecting stock
★ 2 , 1- somatic layer “ SO “ 2- splanchnic layer “ Sp “

Question 19

What is the connecting stalk ?

Answer 19

[ where the embryonic desk is connected to the trophoblast ]

Question 20

 The somatic layer with cytotrophoblast & syncytiotrophoblast form a membrane called
 The exocelomic cavity ( primary yolk sac ) becomes smaller and is known as

Answer 20

Chorion
Secondary YS

Question 21

The rule of two’s for second week
the second week of development is called the week of two’s why ?

Answer 21

1- trophoblast differentiates into 2 layers
2- the embryoblast forms 2 layers
3- the extraembryonic mesoderm splits into 2 layers
4- 2 yolk sacs : primary then secondary
5- 2 new cavities are formed : amniotic and chorionic

Question 22

What happens during the third week of development?

Answer 22

Formation of 3 germ layers & establishing body axes

Question 23

What is the first major developmental event in the third week?

Answer 23

Gastrulation

Question 24

What does gastrulation mean?

Answer 24

Formation of gut

Question 25

What is the significance of gastrulation?

Answer 25

1- formation of 3 germ layers ( ecto,meso,endo derms ) 2- start organogenesis 3- establish body axis ( cranial - caudal axis ( head - tail ) , dorsal - ventral axis ( back - belly ) , medial lateral axis , left right axis

Question 26

The most important time in your life is not birth, marriage or death , but —— Lewis Wolpert 1986

Answer 26

gastrulation

Question 27

At the third week of development The amniotic cavity is —— to examine the ——side of the epiblast

Answer 27

Opened , dorsal

Question 28

What is the sequence of gastrulation?

Answer 28

1- formation of primitive streak ( ps ) 2- the primitive groove represents the area where cells are leaving the ps & moving into the interior of the embryonic disc 3- formation of endoderm 4- formation of mesoderm 5- formation of ectoderm 6- formation of Notochord

Question 29

What is the primitive streak ( ps ) ?

Answer 29

Longitudinal midline structure in the epiblast near the caudal end of the Bilaminar embryonic disc

Question 30

What is ingression ?

Answer 30

The inward movement of epiblast cells

Question 31

The formation of the endoderm happens in the days ——— the epiblast cells replace hypoblast to form ——— the formation of the mesoderm happens in day — A new layer formed in between is called —— when the epiblast cells that remain on the surface and do not migrate will form ——

Answer 31

14-15 Endoderm 16 mesoderm Ectoderm

Question 32

The —— through the process of gastrulation becomes the source of all 3 germ layers cells forming the primitive streak are —— [ they are able to form any type of cells in the body ]

Answer 32

epiblast pluripotent

Question 33

areas with no mesoderm are:

Answer 33

1- oropharyngeal membrane ( the site of the future mouth ) 2- cloacal membrane ( the future side of anus )

Question 34

Normally the primitive streak should —— degenerate and disappear by the end of the —— week .

Answer 34

completely , fourth

Question 35

abnormal gastrulation 1 occurs when there is ————— , which leads to ———

Answer 35

remnant of the primitive streak , totipotent / pluripotent

Question 36

What is Sacrococygeal teratoma

Answer 36

the most common tumour in newborn 1 : 37,000 ( totipotent cells / pluripotent cells )

Question 37

What leads to abnormal gastrulation 1 ?

Answer 37

the primitive streak contains tissues derived from all three germ layers . why ? because of pluripotent cells

Question 38

abnormal gastrulation 2 is ?

Answer 38

Caudal dysgenesis

Question 39

What is Caudal dysgenesis

Answer 39

a group of syndromes that result from insufficient mesoderm formation in the caudal region of the embryo

Question 40

Caudal dysgenesis is characterised by varying degrees of ?

Answer 40

1-hyperalgia & fusion of the lower limbs 2- anomalies of lumber & sacral Vertebrae 3- agenesis of the kidney and urinary tract 4- agenesis of internal genital organs 5- imperforate anus ( may result from the improper migration of caudal mesoderm in relation to the anal membrane )

Question 41

In extreme cases the deficiency and caudal development leads to ———— during early development , resulting in a condition called

Answer 41

fusion of the lower limb buds , sirenomelia

Question 42

a rare condition occurring 1 in 70,000 births.

Answer 42

Sirenomelia