3rd -4th Week Flashcards

1
Q

What are the key events in the third week of pregnancy?

A

Gastrulation, notochord formation, formation of cloacal and buccopharyngeal membranes, neurulation, and allantois formation with three types of chorionic villi.

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2
Q

What is the definition of gastrulation?

A

The process by which the epiblast forms the three intra-embryonic germ layers (endoderm, mesoderm, ectoderm).

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3
Q

When does gastrulation occur?

A

During the third week of development.

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4
Q

What is the primitive streak?

A

A narrow groove on the epiblast’s surface in the midline near the caudal end of the embryo.

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5
Q

What is the primitive node?

A

A rounded elevation at the cephalic end of the primitive streak with a small pit called the primitive pit.

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6
Q

What happens during the migration phase of gastrulation?

A

Epiblast cells migrate toward the primitive streak, become flask-shaped, detach, and contribute to forming germ layers.

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7
Q

What do the first invaginated cells during gastrulation form?

A

The intra-embryonic endoderm.

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8
Q

What do the next invaginated cells form after the endoderm?

A

The intra-embryonic mesoderm.

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9
Q

What does the remaining epiblast form?

A

The ectoderm.

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10
Q

How does the shape of the embryonic disc change?

A

From rounded to oval to pear-shaped with a broad cranial end and narrow caudal end.

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11
Q

What are the two layers of the bilaminar embryonic disc?

A

Epiblast (dorsal layer of columnar cells) and hypoblast (ventral layer of cuboidal cells).

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12
Q

What are the three layers of the trilaminar embryonic disc?

A

Ectoderm, mesoderm, and endoderm (except at the buccopharyngeal and cloacal membranes, which lack mesoderm).

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13
Q

What is the notochord?

A

A solid cord in the axis of the embryonic disc between the ectoderm and endoderm, around which the vertebral column forms.

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14
Q

What is the notochordal process?

A

A tube-like structure formed by cells invaginated through the primitive pit moving cephalically to the future buccopharyngeal membrane.

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15
Q

What is the notochordal canal?

A

A canal formed by the extension of the primitive pit through the notochordal process.

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16
Q

What is the notochordal plate?

A

The roof of the notochordal canal that fuses with the endoderm, then folds to form the definitive notochord.

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17
Q

What is the function of the neuro-enteric canal?

A

A temporary communication between the amniotic cavity and yolk sac that closes as the endoderm regenerates.

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18
Q

What induces the formation of the neural plate?

A

The notochord.

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19
Q

What is the neural plate?

A

A thickened region of ectoderm overlying the notochord.

20
Q

What forms the neural crest?

A

Ectodermal cells on the sides of the neural plate.

21
Q

What are neural folds and the neural groove?

A

Elevated lateral edges of the neural plate form neural folds, while the depressed mid-region forms the neural groove.

22
Q

When do the neural folds fuse to form the neural tube?

A

By the end of the third week.

23
Q

What is the fate of the neural tube?

A

Its cephalic part forms the brain, and the caudal part forms the spinal cord.

24
Q

What does the remaining ectoderm form?

A

The epidermis of the skin.

25
Q

What major structures form during the fourth week?

A

Somites, primitive heart tube, and folding of the embryonic disc.

26
Q

What happens to the yolk sac and amniotic cavity in the fourth week?

A

The yolk sac reduces, and the amniotic cavity increases.

27
Q

What are the three parts of the mesoderm?

A

Paraxial mesoderm, intermediate mesoderm, and lateral plate mesoderm.

28
Q

What does the paraxial mesoderm form?

A

Somites, which later differentiate into the sclerotome, dermatome, and myotome.

29
Q

What is the sclerotome’s function?

A

It surrounds the notochord and spinal cord to form the vertebral column.

30
Q

What does the dermatome form?

A

The dermis of the skin.

31
Q

What does the myotome form?

A

Voluntary muscles.

32
Q

What does the intermediate mesoderm form?

A

Kidneys, gonads, and their ducts.

33
Q

What does the lateral plate mesoderm split into?

A

Somatopleuric mesoderm and splanchnopleuric mesoderm.

34
Q

What causes embryonic folding?

A

Rapid growth of the neural tube, somites, and expansion of the amniotic cavity.

35
Q

What axes are involved in embryonic folding?

A

The anterior-posterior (cephalo-caudal) axis and the transverse axis.

36
Q

What is the primitive gut?

A

The dorsal part of the yolk sac enclosed in the body of the embryo, forming the foregut, midgut, and hindgut.

37
Q

What is the fate of the foregut?

A

It forms structures in the head and thorax regions.

38
Q

What does the midgut form?

A

Structures of the small intestine and part of the large intestine.

39
Q

What does the hindgut form?

A

Structures in the distal colon and rectum.

40
Q

What is the vitello-intestinal duct?

A

A structure connecting the midgut to the yolk sac.

41
Q

What is the result of lateral folding?

A

The formation of dorsal and ventral mesenteries and the umbilical orifice.

42
Q

What is contained within the umbilical orifice?

A

The vitello-intestinal duct and the connecting stalk.

43
Q

What is the intra-embryonic coelom?

A

An inverted U-shaped cavity formed from spaces in the lateral plate mesoderm.

44
Q

What are the three serous cavities formed by the intra-embryonic coelom?

A

Pericardial cavity, pleural cavities, and peritoneal cavity.

45
Q

What is the fate of the cardiogenic area?

A

It contributes to forming the heart during early embryonic development.