Lecture 26 - Formation of the Basic Body Plan

Question 1

At two weeks of development, the embryo is a disc-shaped structure consisting of two layers. What are their names?

Answer 1

Upper layer - epiblast

Lower layer - hypoblast

Question 2

Which are derivatives of the fertiilized egg?

A. embryonic regions of embryo

B. extra-embryonic regions of embryo

C. Both of the above are correct

D. Neither of the above are correct

Answer 2

C. Both embryonic and extra-embryonic regions are derived from the fertilized egg.

Question 3

What forms at approximately 15 days of development?

Answer 3

the primitive streak, which is the earliest trace of the embryo in the fertilized ovum of a higher vertebrae

Question 4

During gastrulation, cells from the epiblast move through the primitive streak and give rise to:

Answer 4

the endodermal and mesodermal germ layers

Question 5

During gastrulation, many cells from the epiblast move through “Hensen’s node” to give rise to germ layers. What happens to the remaining epiblast cells?

Answer 5

they become the ectoderm

Question 6

What happens to the original hypoblast after gastrulation?

Answer 6

it is displaced

Question 7

Where is the notochord found at the beginning of the third week in development?

Answer 7

midline mesoderm layer

Question 8

Development proceeds in a _____ to ______ direction.

Answer 8

cranial to caudal direction

Question 9

The cloacal membrane is the future site of the ________ and ____ openings.

Answer 9

urethral and anal openings

Question 10

The oropharyngeal membrane is the site of the future oral cavity. What is the ultimate fate of this membrane?

Answer 10

It breaks down (as does the cloacal membrane)

Question 11

Within the connecting stalk there is an extraembryonic sac called:

Answer 11

the allantois

Question 12

When is gastrulation largely over? (Select the BEST answer)

A. 8 day embryo

B. 16 day embryo

C. 18 day embryo

D. end of 3rd week - before primitive streak regresses caudally

E. end of 3rd week - after primitive streak regresses caudally

Answer 12

E. (This would probably never be a real question - too variable in real life.)

Question 13

At the end of the 3rd week, the ectoderm in the midline thickens to form:

Answer 13

a neural plate

Question 14

What germ layer region is found between the somites and the lateral mesoderm?

Answer 14

the intermediate mesoderm, which is the precursor to urogenital organs

Question 15

The intermediate mesoderm is a precursore to:

Answer 15

urogenital organs

Question 16

The lateral mesoderm is split by a fluid-filled space called the:

Answer 16

coelomic cavity, which is the precursor to adult body cavaties

Question 17

The ________ layer of lateral mesoderm underlies ectoderm.

Answer 17

parietal layer

Question 18

The ________ layer of lateral mesoderm overlies endoderm.

Answer 18

visceral layer

Question 19

Beneath the cranial end of the coelomic cavity is a region of visceral mesoderm termed the:

Answer 19

precardiac mesoderm

Question 20

The septum transversum is a thickened region of cranial mesoderm that will ultimately contribute to the:

Answer 20

diaphragm and liver

Question 21

The arrow in the photo is pointing to the:

A. Lateral mesoderm

B. Dorsal view of the epiblast

C. Transverse view of the epiblast

D. Neural crest

E. Neural plate

Answer 21

E.

Question 22

The embryo proper grows at a rapid rate as the yolk sac grows very little. As a result:

i) the embryo bulges up off the yolk sac
ii) the sides of the embryonic disc fold medially and downward
iii) the embryonic endoderm is tucked into the interior of the embryo

What process is being described?

Answer 22

lateral folding

Question 23

Cranial folding brings together what three structures beneath the cranial end of the neural tube?

Answer 23

1. Cranial end of coelomic cavity
2. Cardiogenic mesoderm
3. Septum transversum

Question 24

Caudal folding begins to bend the caudal end of the embryo and brings the ______ beneath the embryo.

Answer 24

allantois

Question 25

Neural tube closure occurs during the _______ week of embryonic development.

Answer 25

4th week

Question 26

Neural crest cells emerge from \_\_\_\_\_\_\_.

Answer 26

the dorsal part of the neural tube

Question 27

Neural crest cells from all levels give rise to what two types of cells?

Answer 27

1. peripheral nerve ganglia 2. pigment cells

Question 28

ONLY cranial neural crest cells (i.e. not trunk neural crest cells) give rise to what two types of cells?

Answer 28

1. Cartilage/bone cells 2. Heart outflow tract

Question 29

ONLY trunk neural crest cells (i.e. not cranial neural crest cells) give rise to what type of cells?

Answer 29

Chromaffin cells of the adrenal gland

Question 30

At 4 weeks, the coelomic cavity consists of a bent cranial end, two peritoneal regions, and two pericardiperitoneal canals. These canals close by the development of folds - **the pleuroperitoneal folds**. Along with the septum transversum, esophagus, and muscle cells, the pleuroperitoneal folds make up what structure?

Answer 30

The **diaphragm**

Question 31

It is important to realize that only the \_\_\_\_\_\_\_(a)\_\_\_\_\_\_\_ is derived from the primitive gut tube **endoderm.** The smooth muscle and connective tissue come from the \_\_\_(b)\_\_\_.

Answer 31

a) endoderm b) visceral mesoderm

Question 32

Cells from the medial part of each somite (the sclerotome) migrate around the notochord and neural tube to form:

Answer 32

the vertebrae

Question 33

Cells from the dorsal part of the somite (the dermatome) give rise to:

Answer 33

the dermis of the back

Question 34

Cells from the ________ and ________ of the somite form the myotome, which unergoes extensive migrations and gives rise to skeletal muscles.

Answer 34

lateral and middle

Question 35

The mesoderm in the head ultimately gives rise to what 2 structures?

Answer 35

1. branchial arch muscles 2. extraocular muscles

Question 36

\_\_\_\_\_\_ is a failure of closureof the neural tube at brain levels that may reflect failure of cranial neuropore closure. A. Myeloschisis B. Myelomeningocele C. Encephalocele D. Anencephaly E. Meningocele

Answer 36

D. Anencephaly (cranioschisis) is accompanied by degeneration of forebrain tissue and the absence of a skull roof.

Question 37

\_\_\_\_\_\_\_\_ is a failure of neural tube closure at spinal levels. A. Myeloschisis B. Myelomeningocele C. Encephalocele D. Anencephaly E. Meningocele

Answer 37

A. This is often reffered to as spinal bifida aperta.

Question 38

\_\_\_\_\_\_\_\_\_\_\_ is a defect at brain levels where brain tissue and surrounding membranes (meninges) protrude through the skull. A. Myeloschisis B. Myelomeningocele C. Encephalocele D. Anencephaly E. Meningocele

Answer 38

C.

Question 39

\_\_\_\_\_\_\_ is a type of spina bifida cystica in which there is a protrusion of meninges and spinal cord through a defect in the vertebral column. A. Myeloschisis B. Myelomeningocele C. Encephalocele D. Anencephaly E. Meningocele

Answer 39

B. Myelomeningocele is usually accompanied by disruption of function caudal to the lesion site.

Question 40

\_\_\_\_\_\_\_ is a type of spinal bifida cystica in which there is a protrusion of only meninges through a defect in the vertebral column. A. Myeloschisis B. Myelomeningocele C. Encephalocele D. Anencephaly E. Meningocele

Answer 40

E.

Question 41

When there is failure of formation of the pleuroperitoneal membrane, such that one of the pericardioperitoneal canals remains open, what results?

Answer 41

Diaphragmatic hernia

Question 42

What can occur as a result of a diaphragmatic hernia?

Answer 42

The viscera can herniate into the thoracic cavity and impair the development of the lungs and heart (via one of the pericardioperitoneal canals that remains open).