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Anatomy > third week embryology > Flashcards

third week embryology Flashcards

1
Q

what is gastrulation?

A

the formation of the primitive streak at the 16th day .

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2
Q

where does the primitive streak form?

A

It is a thickened band that appears caudally in the median plane of of the epiblast.

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3
Q

why does gastrulation occur?

A

This occurs as a result of the proliferation & migration of cells of the epiblast from lateral to the median plane of the embryonic disc.

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4
Q

the appearance of the primitive streak determines what?

A

The appearance of a primitive streak determines the cranio-caudal axis of the embryo.
It will give rise to notochord & intra-embryonic mesoderm

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5
Q

there three primary germ discs in which all body tissues develop from them

A

ectoderm
mesoderm
endoderm

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6
Q

a narrow depression is known as ?

A

primitive groove

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7
Q

what is the cranial end of the groove called ?

A

primitive pit

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8
Q

the groove is surrounded by how many folds ?

A

2 primitive folds

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9
Q

The cranial end of the folds proliferates to form a?

A

primitive node

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10
Q

what is Sacro - coccygeal teratoma

A

Remnants of the primitive streak may persist & give rise to a large tumor known as a sacro - coccygeal teratoma

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11
Q

what is an intraembryonic mesoderm?

A

It separates ectoderm & endoderm except in the prochordal plate.

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12
Q

how is the intraembryonic mesoderm formed?

A

Intra embryonic mesoderm is formed by proliferation of the cells in the primitive streak

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13
Q

is there a mesoderm in the prechordal plate?

A

No

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14
Q

how is the prechordal plate formed?

A

Localized area of thickening of the Hypoblast(endoderm)

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15
Q

the prechordal plate determines which future site?

A

future site of oral cavity (mouth)

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16
Q

what is the notochordal process?

A

Extension of mesenchymal cells from primitive node to oropharyngeal membrane forming a median cellular cord

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17
Q

how does the notochord grow?

A

It grows cranially between the ectoderm & the endoderm until it reaches the oro -pharyngeal membrane, where it cannot grow further.

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18
Q

Does the process require a lumen which this lumen is called?

A

A notochordal canal

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19
Q

what is the notochordal plate?

A

the remaining roof & sides of the notochordal canal form the notochordal plate.

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20
Q

what does the definitive notochord mean?

A

when the plate enfolds to form the definitive notochord

21
Q

what are the 3 functions of the notochord?

A
  • Define the axis of the embryo.
  • Serves as the basis for the development of the axial skeleton.
  • Induces the formation of the neural tube from the overlying ectoderm.
22
Q

The notochord degenerates & disappears when the vertebral bodies form, but parts of it?

A

persist as the nucleus pulposus of each intervertebral disc.

23
Q

formation of the endoderm

A

Mesenchymal cells separate from the deep surface of the primitive streak.

24
Q

some of the mesenchymal cells migrate ventrally to form what?

A

to form the definitive endoderm

25
Q

the intraembryonic mesoderm is divided into three parts, what are they?

A

Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm

26
Q

intraembryonic mesoderm is absent in?

A

Region of the oropharyngeal membrane.
Region of the cloacal membrane.

27
Q

how is intraembryonic coelom developed?

A

The intra-embryonic coelom (body cavity) appears as small spaces in the cardiogenic mesoderm.
These spaces coalesce to form a single, horse shoe-shaped cavity (the intra-embryonic coelom).

28
Q

uring the 2nd month ,the intra- embryonic coelom is divided into 3 body cavities which are?

A

The pericardial cavity (Heart) ,the pleural cavities ( lungs ) &the peritoneal cavity ( abdomen) .

29
Q

The intra-embryonic coelom that divides the lateral mesoderm into 2 layers which are?

A

Somatic (the parietal layer that is in contact with the ectoderm
Splanchnic (the visceral layer that is in contact with endoderm)

30
Q

what is an allontois?

A

It is dorso - caudal invagination of the endoderm of the umbilical vesicle into the connecting stalk

31
Q

when does the extra embryonic vasculogenesis ( blood vessels ) formation occur?

A

At the beginning of 3rd week (16th day).embryonic nutrition is obtained from
the maternal blood by diffusion of nutrients through the chorion, extra-
embryonic coelom & umbilical vesicle

32
Q
  • Extra embryonic vasculogenesis begins in the?
A

chorionic membrane
connecting stalk
umbilical vesicle.

33
Q

when does Extra-embryonic Blood formation (HEMATOGENESIS) begin? and where?

A

begins during the 3rd – 5th week in the walls of the umbilical vesicle &the connecting stalk as mesodermal blood islands.

34
Q

in the Extra-embryonic Blood formation (HEMATOGENESIS) the peripheral cells form what and the central cells form what?

A

the peripheral cells of each island form the wall of blood vessels and the central cells form the blood cells

35
Q

formation of the intra-embryonic blood vessels does not begin within the embryo until the ?

A

5TH week

36
Q

Extra-embryonic Blood formation (HEMATOGENESIS)
this process occurs first in?

A

This process occurs first in the liver (6th week) , then in the spleen &later on, in the bone marrow.

37
Q

the primary chorionic villi appears at the end of? and is formed by what?

A

appears at the end of the 2nd week, and is formed by cytotrophoblast and syncytiotrophoblast

38
Q

the secondary chorionic villi appears when and is made up of what?

A

appears at the beginning of the 3rd week and is made up of cytotrophoblast+ syncytiotrophoblast + extraembryonic mesoderm

39
Q

the tertiary ( definitive ) chorionic villli is made up of ?

A

mesenchymal cells

40
Q

the mesenchymal cells at the core of the tertiary villi can differentiate to ?

A

into capillaries and blood cells

41
Q

the capillaries in the chorionic villi fuse together to form?

A

to form networks and become connected with the embryonic heart

42
Q

development of somites

A

At the end of the 3rd week (22nd day), the paraxial mesoderm begins to divide in a cranio- caudal direction into paired cuboidal masses called somites.

43
Q

The 1st pair of somites appear near ?

A

appear near the cranial end of the notochord & on each side of the developing neural tube.

44
Q

during the development of somites by the end of the 5th week how many pairs are formed ?

A

42 – 44 pairs are formed.

45
Q

by the end of the 5th week 42-44 pairs of somites are formed in which they are categorized into:

A

they are 4 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral & 8–10 coccygeal somites.

46
Q

each somite is divided into?

A

Ventro - medial part which is called the sclerotome
Dorso - lateral part which is called dermomyotome.

47
Q

the somites are divided into 2 parts one of them is Ventro - medial part which is called the sclerotome what will the sclerotome surround?

A

Sclerotome will surround the neural tube and notochord to form the vertebral column & (ribs, sternum, skull).

48
Q
A

Anatomy (5 decks)

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