Lecture 26 - Formation of the Basic Body Plan Flashcards
At two weeks of development, the embryo is a disc-shaped structure consisting of two layers. What are their names?
Upper layer - epiblast
Lower layer - hypoblast
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
C. Both embryonic and extra-embryonic regions are derived from the fertilized egg.
What forms at approximately 15 days of development?
the primitive streak, which is the earliest trace of the embryo in the fertilized ovum of a higher vertebrae
During gastrulation, cells from the epiblast move through the primitive streak and give rise to:
the endodermal and mesodermal germ layers
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?
they become the ectoderm
What happens to the original hypoblast after gastrulation?
it is displaced
Where is the notochord found at the beginning of the third week in development?
midline mesoderm layer
Development proceeds in a _____ to ______ direction.
cranial to caudal direction
The cloacal membrane is the future site of the ________ and ____ openings.
urethral and anal openings
The oropharyngeal membrane is the site of the future oral cavity. What is the ultimate fate of this membrane?
It breaks down (as does the cloacal membrane)
Within the connecting stalk there is an extraembryonic sac called:
the allantois
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
E. (This would probably never be a real question - too variable in real life.)
At the end of the 3rd week, the ectoderm in the midline thickens to form:
a neural plate
What germ layer region is found between the somites and the lateral mesoderm?
the intermediate mesoderm, which is the precursor to urogenital organs
The intermediate mesoderm is a precursore to:
urogenital organs
The lateral mesoderm is split by a fluid-filled space called the:
coelomic cavity, which is the precursor to adult body cavaties
The ________ layer of lateral mesoderm underlies ectoderm.
parietal layer
The ________ layer of lateral mesoderm overlies endoderm.
visceral layer
Beneath the cranial end of the coelomic cavity is a region of visceral mesoderm termed the:
precardiac mesoderm
The septum transversum is a thickened region of cranial mesoderm that will ultimately contribute to the:
diaphragm and liver
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
E.
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?
lateral folding
Cranial folding brings together what three structures beneath the cranial end of the neural tube?
- Cranial end of coelomic cavity
- Cardiogenic mesoderm
- Septum transversum
Caudal folding begins to bend the caudal end of the embryo and brings the ______ beneath the embryo.
allantois
Neural tube closure occurs during the _______ week of embryonic development.
4th week
Neural crest cells emerge from _______.
the dorsal part of the neural tube
Neural crest cells from all levels give rise to what two types of cells?
- peripheral nerve ganglia
- pigment cells
ONLY cranial neural crest cells (i.e. not trunk neural crest cells) give rise to what two types of cells?
- Cartilage/bone cells
- Heart outflow tract
ONLY trunk neural crest cells (i.e. not cranial neural crest cells) give rise to what type of cells?
Chromaffin cells of the adrenal gland
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?
The diaphragm
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)___.
a) endoderm
b) visceral mesoderm
Cells from the medial part of each somite (the sclerotome) migrate around the notochord and neural tube to form:
the vertebrae
Cells from the dorsal part of the somite (the dermatome) give rise to:
the dermis of the back
Cells from the ________ and ________ of the somite form the myotome, which unergoes extensive migrations and gives rise to skeletal muscles.
lateral and middle
The mesoderm in the head ultimately gives rise to what 2 structures?
- branchial arch muscles
- extraocular muscles
______ 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
D. Anencephaly (cranioschisis) is accompanied by degeneration of forebrain tissue and the absence of a skull roof.
________ is a failure of neural tube closure at spinal levels.
A. Myeloschisis
B. Myelomeningocele
C. Encephalocele
D. Anencephaly
E. Meningocele
A. This is often reffered to as spinal bifida aperta.
___________ 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
C.
_______ 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
B. Myelomeningocele is usually accompanied by disruption of function caudal to the lesion site.
_______ 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
E.
When there is failure of formation of the pleuroperitoneal membrane, such that one of the pericardioperitoneal canals remains open, what results?
Diaphragmatic hernia
What can occur as a result of a diaphragmatic hernia?
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).
