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Med 105 > Third week of embryonic development > Flashcards

Third week of embryonic development Flashcards

1
Q

what is the beginning of morphogenesis

A

Gastrulation

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2
Q

what is gastrulation

A

process by which the bilaminar embryonic disc is converted into a trilaminar embryonic disc

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3
Q

what gives rise to specific tissues and organs

A

ectoderm, endoderm, and mesoderm

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4
Q

what does gastrulation start with

A

formation of the primitive streak on the surface of the epiblast

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5
Q

how does the streak look like on a 16 day embryo

A

clearly visible as a narrow groove with slightly bulging regions on either side

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6
Q

what is the cephalic end of the streak and what does it consist of

A

primitive node, consisting of a slightly elevated area surrounding the small primitive pit

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7
Q

what do the epiblast cells migrate towards

A

primitive streak

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8
Q

Cell migration and specification are controlled by

A

fibroblast growth factor 8 (FGF8)

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9
Q

how does the GF control cell movement

A

downregulating Ecadherin, a protein that normally binds epiblast cells together

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10
Q

FGF8 then controls cell specification into the _____________ by regulating ___________

A

mesoderm

Brachyury (T) expression

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11
Q

what happens once Cells of the epiblast have invaginated

A

some displace the hypoblast, creating the embryonic endoderm, and others come to lie between the epiblast and newly created endoderm to form mesoderm

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12
Q

what happens to the cells remaining in the epiblast

A

form the ectoderm

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13
Q

how is the notochordal process formed

A

Some mesenchymal cells (prenotochordal cells) migrate cranially from the primitive node and pit, forming a median cellular cord, the notochordal process

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14
Q

what does the notochordal process acquire

A

a lumen, the notochordal canal

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15
Q

The notochordal process grows cranially between the ectoderm and endoderm until it reaches _______

A

prechordal plate

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16
Q

what is the function of the prechordal plate

A

organizer of the head region.

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17
Q

what forms the definitive notochord

A

hypoblast replaced by endoderm cells notochordal plate proliferate and detach from the endoderm. They then form a solid cord of cells, the definitive notochord

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18
Q

what is the function of the definitive notochord

A

it underlies the neural tube and serves as the basis for the axial skeleton

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19
Q

where do the notochord and prenotochordal cells extend to

A

cranially to the prechordal plate (an area just caudal to the oropharyngeal membrane) and caudally to the primitive pit

20
Q

what is the neurenteric canal and what is its function

A

where the pit forms an indentation in the epiblast and it temporarily connects the amniotic and yolk sac cavities

21
Q

where is the cloacal membrane formed

A

at the caudal end of the embryonic disc

22
Q

what is the structure of the cloacal membrane

A

consists of tightly adherent ectoderm and endoderm cells with no intervening mesoderm

23
Q

what happens to the posterior wall of the yolk sac when the cloacal membrane appears

A

forms a small diverticulum that extends into the connecting stalk

24
Q

what is the diverticulum

A

allantoenteric diverticulum, or allantois

25
Q

what is the function of the allantois in

a) in lower vertebrates
b) in humans

A

a) reservoir for excretion products of the renal system

b) remains rudimentary but may be involved in abnormalities of bladder development

26
Q

what do these epiblast cells become (fate map)
a)cells that ingress through the cranial region of the node
b) migrating at the lateral edges of the node from the
cranial end of the streak
c) migrating through the midstreak region
d) migrating through the more caudal part of the streak
e) migrating through the caudal most part of the streak

A

a) prechordal plate and notochord
b) paraxial mesoderm
c) intermediate mesoderm
d) lateral plate mesoderm ( mesenteries: periton, pleura pericardium)
e) contribute to extraembryonic mesoderm

27
Q

what happens to the embryonic disc

A

becomes elongated, with a broad cephalic and a narrow caudal end (mainly in cephalic reagion)

28
Q

what happens to the primitive streak at the end of the fourth week

A

shrinks and disappears

29
Q

what begins to differentiate first, cephalic or caudal region

A

cephalic- mid 3rd week
caudal- end of 4th week
i.e embryo to develop cephalocaudally

30
Q

Appearance of the notochord and prechordal mesoderm induces the overlying ectoderm to thicken and form the _____________

A

neural plate

31
Q

cells of the neural plate make up the ___________, and their induction represents the initial event in the process of ______________

A

neuroectoderm

neurulation (process whereby the neural plate forms the neural tube)

32
Q

what happens to the neural plate by the end of the third week

A

the lateral edges of the neural plate become elevated to form neural folds, and the depressed midregion forms the neural groove

33
Q

where does fusion of the neural fold begin

A

in the cervical region (fifth somite) and proceeds cranially and caudally

34
Q

how doe the cephalic and caudal ends of the neural tube communicate with the amniotic cavity until fusion is complete

A

by way of the anterior (cranial) and posterior (caudal) neuropores respectively

35
Q

intraembryonic mesoderm on each side proliferates to form _________________

A

a thick, longitudinal column of paraxial mesoderm

36
Q

what happens to the paraxial mesoderm by the end of the third week

A

differentiates and begins to divide into paired cuboidal bodies, or somites, on each side of the developing neural tube

37
Q

what are used to determine the embryos age

A

somites because they are so prominent during the fourth and fifth weeks

38
Q

where do the first somites appear

A

near the cranial end of the notochord

39
Q

what do somites give rise to

A

most of the axial skeleton and the associated musculature, as well as to the adjacent dermis of the skin

40
Q

what sequence do somites form

A

craniocaudal sequence

41
Q

where does vasculogenesis begin

A

in the extraembryonic mesoderm of the umbilical vesicle, connecting stalk, and chorion

42
Q

what is the trophoblast characterized by the end of the third week

A

by primary villi that consist of a cytotrophoblastic core covered by a syncytial layer

43
Q

how is the secondary villus formed

A

mesodermal cells penetrate the core of primary villi and grow toward the decidua

44
Q

what is another name for tertiary villus and how is it formed

A

definitive placental villus formed when mesodermal cells in the core of the villus begin to differentiate into blood cells and small blood vessels, forming the villous capillary system

45
Q

Remnants of the primitive streak may persist and give rise to a large tumor known as __________________

A

sacrococcygeal teratoma (most common tumors in newborn infants)

46
Q

why does sacrococcygeal teratoma contain tissues derived from all three germ layers in incomplete stages of differentiation

A

Because it is derived from pluripotent primitive streak cells

Med 105 (16 decks)

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