Trilaminar

Question 1

Cells from which layer of the bilaminar embryonic disk migrate through the primitive streak and pit. What 3 layers do these cells form?

Answer 1

Epiblast; ectoderm, intraembryonic mesoderm, and endoderm.

Question 2

What layers form the buccopharyngeal and cloacal membranes and where are they located?

Answer 2

These are membranes where the ectoderm and endoderm come into direct contact.
Buccopharyngeal- upper boundary of digestive tract (future mouth)
Cloacal- lower boundary of digestive tract (future anus)

Question 3

What does the notochord induce?

Answer 3

Induces overlying ectoderm to differentiate into neuro ectoderm to form neural plate.
Induces formation of vertebral bodies.

Question 4

What are the adult remnants of the notochord?

Answer 4

Nucleus pulposes in adult intervertebral discs.

Question 5

What is a sacrococcygeal teratoma and how does it arise.

Answer 5

Remnants of he primitive streak in the sacrococcygeal area that lead to a tumor containing tissue derived from all 3 germ layers. Most common tumor in newborns

Question 6

Briefly describe the process of neurulation

Answer 6

Notochord induces overyling ectoderm to form neural plate.
Neural plate invaginates to form median neural groove flanked by neural folds.
Neural folds fuse to form neural tube which separates from surface ectoderm.
Fusion proceeds in a cranial to caudal direction and is completed by week 4.

Question 7

What are the 3 types of mesoderm and how are they related anatomically?

Answer 7

Paraxial mesoderm- located on each side of midline; most medial
Intermediate mesoderm- between paraxial and lateral
Lateral- continuous with extraembryonic mesoderm along lateral edges of embryo.

Question 8

What do somites form?

Answer 8

Scleretome- cartilage and bone of vertebral column
Myotome- skeletal muscle
Dermatome- dermis of skin

Question 9

How are somites related to notochord

Answer 9

Line the notochord on both sides

Question 10

What type of mesoderm forms the kidneys

Answer 10

Intermediate mesoderm

Question 11

From what type of mesoderm does the visceral pleura develop

Answer 11

Splanchnic mesoderm from the lateral layer

Question 12

What is septum transversum, where is it located, and what does it form in the adult?

Answer 12

Thickened bar of mesoderm that arises early in week 4 rostral to cardiogenic area. Forms diaphragm in adults.

Question 13

What does embryonic folding accomplish?

Answer 13

Changes the shape of the embryo from 2 dimensional to 3 dimensional cylinder that has an anterolateral body wall and inner gut tube.

Question 14

How does the head fold reposition the developing heart, diaphragm, and mouth?

Answer 14

Repositions cardiogenic region ventrally toward future chest.
Folds buccopharyngeal membrane ventrally toward region of future mouth.
Shifts the septum transversum ventrally until it wedges between the future hear and yolk sac.

Question 15

What germ layer forms the allantois and what does it form in the adult?

Answer 15

Endoderm; forms the liamentous urachus which becomes the median umbilical ligament in adult.

Question 16

With what does the midgut communicate

Answer 16

Yolk sac

Question 17

What 3 things does the process of gastrulation accomplish?

Answer 17

Transforms the bilaminar disk into a trilaminar disk
Establishes the 3 definitive germ layers
Establishes the body axes (anterior-posterior, dorsal-ventral, left-right)

Question 18

Development of the uteroplacental circulation begins when

Answer 18

Trophoblastic lacunae form within the synctiotrophoblast

Question 19

Maternal capillaries near the synctiotrophoblast expand to form __ which anastomose with the lacunae

Answer 19

Maternal sinusoids

Question 20

As anastomoses develop, the cytotrophoblast proliferates to form __ that grow into the synctiotrophoblast

Answer 20

Primary villi

Question 21

Primary villi grow out into the __ with a covering of __

Answer 21

Lacunae; synctiotrophoblast

Question 22

Gastrulation is first indicated by the appearance of the

Answer 22

primitive streak on the surface of the epiblast

Question 23

The primitive streak consists of the

Answer 23

primitive groove, primitive node, and primitive pit

Question 24

The primitive streak disappears when

Answer 24

Gastrulation is over

Question 25

Conjoined twins result from partial splitting of the

Answer 25

primitive node and primitive streak

Question 26

What is sirenomelia?

Answer 26

mermaid syndrome. insufficient mesoderm is formed in the caudal region of the embryo. Kidney and bladder are underdeveloped so many babies afflicted die within a few days of birth.

Question 27

What is a cordoma

Answer 27

Tumor that arises from remnants of notochord. Intracranially or sacrally; more common in adult men in their 50s

Question 28

What is neurulation?

Answer 28

formation of the neural tube

Question 29

Large spaces develop within the lateral mesoderm to form

Answer 29

the intra-embryonic coelom (which will form pleural, pericardial and peritoneal cavities in adult)

Question 30

What are the 2 layers that the intraembryonic coelom split the lateral mesoderm into

Answer 30

Somatic mesoderm and splanchnic mesoderm

Question 31

What does the somatic and splanchnic mesoderm form?

Answer 31

Somatic- forms the parietal serous linings of body cavities

Splanchnic- forms the visceral serous coverings of the organs and some forms the cardiogenic area

Question 32

What forms the initial partition between the thoracic and abdominal cavities

Answer 32

Septum transversum

Question 33

Folding of the embryo occurs in what 2 planes

Answer 33

cranio-caudal (head-tail)

Transverse (lateral)

Question 34

Ectoderm covers the entire embryo except

Answer 34

the future umbilical region where the yolk sac and connecting stalk emerge

Question 35

Fusion of the lateral edges of the yolk sac endoderm creates the

Answer 35

gut tube

Question 36

What causes a gastroschisis

Answer 36

Embryonic folding fails to occur

Question 37

What is gastroschisis

Answer 37

abdominal wall defect where there is an opining in the wall. intestines and other abdominal organs herniate through the opening and spill out into the amniotic fluid.

Question 38

The cranial portion and caudal portion of the ingot form what?

Answer 38

Cranial- foregut

caudal- hindgut