Part 1: Trilaminar Embryo

Question 1

When does the primitive streak form?

Answer 1

beginning of the third week

Question 2

Fluid of the primitive node contains:

Answer 2

vesicles containing sonic hedgehog protein

Question 3

Sonic hedgehog protein vesicles are pushed from the right to the left side of the embryo via the singlar cilia on each cell of the primitive node.

What is the role of sonic hedgehog in this setting?

Answer 3

• induce asymmetric gene expression.
• sets up the “sidedness” of embryo.

Question 4

What two parts of the embryo do the epiblast cells not invade during gastrulation?

Answer 4

• buccopharyngeal membrane
• cloacal membrane

Question 5

What layers of the embryo are derived from the epiblast?

Answer 5

• all three (endoderm, mesoderm, ectoderm)

Question 6

Initial formation of the notochord process:

Answer 6

• epiblast cells of the primitive node delaminate and establish the midline notochord between the ectoderm and endoderm cranial to the primitive streak

Question 7

Role of the notochord:

Answer 7

• induces the overlying ectoderm to form the nervous system.

Question 8

When does elongation of the embryo occur, and what drives it?

Answer 8

• immediately following the formation of the mesoderm.
• mesoderm proliferation drives elongation.

Question 9

As the embryo elongates, the mesoderm differentiates into what 3 regions?

Answer 9

1. paraxial mesoderm
2. intermediate mesoderm
3. lateral plate mesoderm

Question 10

Paraxial mesoderm gives rise to:

Answer 10

somites

Question 11

Intermediate mesoderm gives rise to:

Answer 11

urinary and reproductive systems

Question 12

Lateral plate mesoderm gives rise to:

Answer 12

limb bones and connective tissue

Question 13

The three types of folding that occur to the embryo during gastrulation:

Answer 13

1. lateral folding
2. cranial folding
3. caudal folding

Question 14

Lateral folding of the embryo:

Answer 14

• driven by mesoederm proliferation
• forms gut tube and body cavities
• brings embryo into the amniotic cavitiy

Question 15

Cranial folding of the embryo:

Answer 15

• driven by developing forebrain
• brings buccopharyngeal membran from dorsal to ventral surface
• brings developing heart into thorax

Question 16

The two structures moved by cranial folding:

Answer 16

• buccopharyngeal membrane
  
  • dorsal to ventral surface
• heart
  
  • moves into developing thorax

Question 17

Caudal folding of the embryo:

Answer 17

• brings cloacal membrane from the dorsal surface to the ventral surface

Question 18

As the embryo begins lateral folding the notochord induces:

Answer 18

• overlying ectoderm to become neural plate.
• neural plate forms neural folds and a neural groove.

Question 19

The neural plate forms:

Answer 19

• neural folds and a neural groove
• neural folds eventually fuse to form the neural tube

Question 20

Where do the lateral sides of the neural fold first meet and fuse?

Answer 20

• dorsal midline
• thoracic region

Question 21

What population of cells originate from the portions of the neural fold that fuse together to form the neural tube?

Answer 21

neural crest cells

Question 22

What tissue comes together on the dorsal surface to cover the neural tube?

Answer 22

ectoderm

Question 23

Fusion of the neural tube proceeds in what directions from the initial fusion site in the thoracic region?

Answer 23

cranially and caudally simultaneously

Question 24

Neuropores are formed by:

Answer 24

• Fusion of the neural tube from the thoracic region in the caudal and cranially directions simultaneously.
• Defects in neuropore closure are termed neural tube defects.

Question 25

When do the cranial and caudal neuropores close?

Answer 25

end of the fourth week

Question 26

When is lateral, cranial, and caudal folding complete?

Answer 26

end of the fourth week

Question 27

Neural tube defects are due to:

Answer 27

failures of fusion/closure at the neuropores

Question 28

What defect results if the cranial neuropore does not close?

Answer 28

anencephaly (no brain)

Question 29

What defect results if the caudal neuropore does not close?

Answer 29

* spina bifida * failure of vertebrae (mesoderm) to cover the spinal cord dorsally

Question 30

Spina bifida occulta:

Answer 30

* neural tube defect * caudal neuropore does not close * spinal cord in place * lumbar region * look for tuft of hair * NO NEUROLOGICAL DEFECTS

Question 31

Meningocele:

Answer 31

* neural tube defect * caudal neuropore does not close * spinal cord in place * arachnoid and subarachnoid space protruding * lumbar region

Question 32

Meningomyelocele:

Answer 32

* neural tube defect * caudal neuropore does not close * spinal cord NOT in place * arachnoid and subarachnoid in spinal canal * lumbar region

Question 33

Rachischisis:

Answer 33

* neural tube defect * caudal neuropore does not close * neural tissue does not fold properly * PARALYSIS

Question 34

What tissue do somites develop from?

Answer 34

mesoderm

Question 35

Where do the somites develop?

Answer 35

* in pairs, one on each side of the neural tube

Question 36

There are the same number of somites as:

Answer 36

* vertebrae * spinal nerves

Question 37

What happens to the developing neural tube as the somites form?

Answer 37

* nerve fibers/axons from the neural tube grow into the somites, induces the somites to change and migrate, and the somites take the axons with them as they migrate.