Three Germ Layers and Body Folding

Question 1

central to diversifying cells into new tissues and establishing the body plan in the embryo

Answer 1

epithelial-mesenchymal transformation (EMT)

Question 2

which epithelial cells are converted into migratory mesenchymal cells?

Answer 2

epiblast

Question 3

what determines the fate of epiblast cells?

Answer 3

their location

Question 4

gastrulation sets the stage for……

Answer 4

-development of body form: morphogenesis
-organ development: organogenesis

Question 5

what signifies the beginning of gastrulation?

Answer 5

the formation of the primitive streak

Question 6

how is the primitive streak formed?

Answer 6

epiblast cells migrate to the midline of the embryonic disc and form a thickening

Question 7

primitive groove

Answer 7

where cells move into the interior of the embryo

Question 8

primitive node

Answer 8

expanded anterior end of the streak

Question 9

primitive pit

Answer 9

continuation of the groove into the primitive node

Question 10

what takes place once the epiblast cells around the cranial end of the primitive streak move in first?

Answer 10

-they replace the hypoblast and form the definitive endoderm
-the prechordal plate between the tip of notochord oropharyngeal membrane

Question 11

where does cardiogenic mesoderm arise from?

Answer 11

the lateral side of the cranial end of the streak

Question 12

which end of the streak does the extraembryonic mesoderm arise from?

Answer 12

caudal

Question 13

which mesoderm contributes to the amnion, yolk sac, and allantois?

Answer 13

extraembryonic mesoderm

Question 14

cells of the primitive node and pit give rise to?

Answer 14

the notochordal process which will develop into the notochord

Question 15

cells from the primitive groove give rise to?

Answer 15

intraembryonic mesoderm

Question 16

what are the functions of the notochord?

Answer 16

-first supporting structure in the embryo
-involved in the induction of the neural tube and vertebral bodies
-forms the primary nucleus pulposus of the intervertebral disk
-might play roles in organizing and patterning of the caudal organs

Question 17

what structure extends along the entire length of the future vertebral column

Answer 17

notochord

Question 18

what are the different components of the intraembryonic mesoderm?

Answer 18

paraxial mesoderm in the head, paraxial mesoderm in the trunk, intermediate mesoderm, lateral plate mesoderm

Question 19

paraxial mesoderm in the head

Answer 19

-remains unsegmented
-supplemented with neural crest cells—> head mesenchyme

Question 20

paraxial mesoderm in the trunk

Answer 20

-becomes segmented into somites
-gives rise to most of the skeleton and skeletal muscles of the neck, limbs and trunk

Question 21

intermediate mesoderm

Answer 21

develops into the urinary and parts of the genital systems

Question 22

what are the 4 regions of the epiblast during the late stages of gastrulation and when the streak is fully elongated?

Answer 22

neural plate —>CNS
neural crest —->neural crest cells
placodal ectoderm —-> sensory systems of the head
surface ectoderm —-> epidermis of the skin

Question 23

after gastrulation (day 20), remnants of the remaining portion of the streak give rise to the ________________, which contributes to the formation of the caudal structures of the body.

Answer 23

caudal eminence (tail bud)

Question 24

when does the primitive streak disappear?

Answer 24

Day 25

Question 25

which membrane forms at the cranial end of the embryonic disk?

Answer 25

oropharyngeal

Question 26

which membrane forms at the caudal end of the embryonic disk?

Answer 26

cloacal

Question 27

future oral opening

Answer 27

oropharyngeal membrane

Question 28

future anal opening

Answer 28

cloacal membrane

Question 29

what are the 4 stages of neuralation?

Answer 29

week 3 1) neural induction- part of the ectoderm forms the thickened neural plate 2) shaping of the neural plate 3) lateral folding of the plate- forms the neural groove week 4 4) closure of the neural tube

Question 30

what does the neural tube give rise to?

Answer 30

-the brain -the cervical, thoracic, and lumbar spinal cord levels

Question 31

on day 18, the primitive node inhibits formation of surface ectoderm overlying the notochordal process by inhibiting __________, and ________________forms

Answer 31

Bmp neural plate forms

Question 32

the neural plate extends from the _________to the ________

Answer 32

oropharyngeal membrane to the primitive streak

Question 33

the neural plate is shaped into the cephalic end and caudal end. what do those form?

Answer 33

-cephalic: broad and will form the brain -caudal: narrow and will form the spinal cord

Question 34

when does closure of the neural tube begin?

Answer 34

day 20

Question 35

when do the anterior and posterior neuropores close?

Answer 35

day 25 day 27

Question 36

the tail bud contributes to the formation of which caudal structures?

Answer 36

-sacral and coccygeal portions of the neural tube (secondary neurulation) -rudiments of lower limbs, terminal portions of GI and urogenital systems, lower vertebrae

Question 37

caudal structures that form from the tail bud form without the development of germ layers and.....

Answer 37

-initiated after primary neurulation is complete -connects around the 6th week without the tri-laminar formation

Question 38

ectoderm

Answer 38

-organs and structures that remain in contact with the outside world (nervous system, neural crest cells, epidermis, tooth enamel, etc.)

Question 39

mesoderm

Answer 39

structures that support other tissues (cartilage, bone, connective tissue, muscle tissue)

Question 40

endoderm

Answer 40

-epithelial lining of the digestive and respiratory tract and urinary bladder -secretory portions of the glands associated with the digestive tract and glands of pharyngeal arch origin

Question 41

α-fetoprotein (AFP)

Answer 41

-produced in the liver of fetus (peaks at 14 weeks) -excreted by the fetal kidneys -absorbs into maternal circulation (concentrations decline after week 30)

Question 42

what does elevated AFP lead to?

Answer 42

neural tube defects (NTD) abdominal wall defects

Question 43

what does decreased AFP lead to?

Answer 43

trisomy 18, 21 sex chromosome abnormalities