BRS Embryology - Week 3-8: Embryonic Period Flashcards Preview

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Flashcards in BRS Embryology - Week 3-8: Embryonic Period Deck (15)
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1

Which germ layers are present at the end of week 3 of development (day 21)?

(A) Epiblast only
(B) Epiblast and hypoblast
(C) Ectoderm and endoderm
(D) Ectoderm, mesoderm, and endoderm
(E) Epiblast, mesoderm, and hypoblast

D.
During week 3 of development, the process of gastrulation, which establishes the three primary germ layers (ectoderm, intraembryonic mesoderm, and endoderm), occurs. The origin of all tissues and organs of the adult can be traced to one of these germ layers because these are whence they “germinate.”

2

Which process establishes the three definitive germ layers?

(A) Neurulation
(B) Gastrulation
(C) Craniocaudalfolding
(D) Lateral folding
(E) Angiogenesis

B.
Gastrulation establishes the three primary germ layers during week 3 of development. Neurulation is the process by which neuroectoderm forms the neural plate, which eventu- ally folds to form the neural tube.

3

The first indication of gastrulation in the embryo is

(A) formation of the primitive streak
(B) formation of the notochord
(C) formation of the neuraltube
(D) formation of extraembryonic mesoderm
(E) formation of tertiary chorionic villi

A.
The formation of the primitive streak on the dorsal surface of the bilaminar embryonic disk is the first indication of gastrulation.

4

Somites may differentiate into which of the following?

(A) Urogenital ridge
(B) Kidneys
(C) Notochord
(D) Epimeric and hypomeric muscles
(E) Epithelial lining of the gastrointestinal
tract

D.
Approximately 35 pairs of somites form. They are derived from a specific subdivision of intraembryonic mesoderm called paraxial mesoderm. Somites differentiate into the com- ponents called sclerotome (cartilage and bone of the vertebral column), myotome (epimeric and hypomeric muscle), and dermatome (dermis and subcutaneous area of skin).

5

Intermediate mesoderm will give rise to the

(A) neural tube
(B) heart
(C) kidneys and gonads
(D) somites
(E) notochord

C.
Intermediate mesoderm is a subdivision of intraembryonic mesoderm that forms a longitudinal dorsal ridge called the urogenital ridge from which the kidneys and gonads develop.

6

The developing embryo has a distinct human appearance by the end of

(A) week 4
(B) week 5
(C) week 6
(D) week 7
(E) week 8

E.
The embryo starts the embryonic period as a two-dimensional disk and ends as a three-dimensional cylinder. This dramatic change in geometry is caused by formation of all the major organ systems. As the organ systems gradually develop during the embryonic period, the embryo appears more and more human-like; it has a distinct human appear- ance at the end of week 8.

7

The lateral mesoderm is divided into two distinct layers by the formation of the

(A) extraembryonic coelom
(B) intraembryonic coelom
(C) cardiogenicregion
(D) notochord
(E) yolksac

B.
The lateral mesoderm is a subdivision of intraembryonic mesoderm and initially is a solid plate of mesoderm. The intraembryonic coelom forms in the middle of the lateral mesoderm, thereby dividing it into the intraembryonic somatic mesoderm and intraembryonic visceral mesoderm.

8

Very often the first indication a woman has that she is pregnant is a missed menstrual period. In which week of embry- onic development will a woman experience her first missed menstrual period?

(A) Start of week 3
(B) Start of week 4
(C) Start of week 5
(D) Start of week 8
(E) End of week 8

A.
Given a regular 28-day menstrual cycle, a woman who starts menses on, say, February 1 will ovulate on February 14, and the secondary oocyte will be fertilized, if she becomes pregnant, within 24 hours. So, the zygote undergoes week 1 of development from February 15 to 21. Week 2 of development is from February 22 to 28. On the next day, March 1, the woman would enter her next menstrual cycle if she were not pregnant, but because she is pregnant, she does not menstruate. Therefore, this first missed menstrual period corresponds with the start of week 3 of embryonic development. The embryonic period (week 3–week 8) is a time of high susceptibility to teratogens.

9

A female newborn was found to have a large midline tumor in the lower sacral area, which was diagnosed as a sacrococcygeal tumor. Which of the following courses of treatment is recommended for this child?

(A) Immediate chemotherapy and radiation treatment
(B) Surgical removal by age 6 months
(C) Surgical removal at age 4–5 years
(D) Surgical removal at age 13–15 years
(E) No treatment because this tumor
normally regresses with age

B.
The preponderance of sacrococcygeal tumors are found in female newborns. Because these tumors develop from pluripotent cells of primitive streak origin, malignancy is of great concern, and the tumor should be surgically removed by age 6 months. Occasionally, these tumors may recur after surgery, demonstrating malignant properties

10

A woman has her pregnancy suddenly terminated due to intrauterine fetal death. At autopsy, the fetus shows severe pallor, gener- alized edema, and hepatosplenomegaly. Which of the following would you suspect?

(A) VATER
(B) ß-Thalassemia minor
(C) ß-Thalassemia major
(D) Hydrops fetalis
(E) VACTERL

D. Hydrops fetalis is the most severe form of

11

The specialized group of mesenchymal cells that aggregate to form blood islands centrally and primitive blood vessels periph- erally are called

(A) fibroblasts
(B) cardiac progenitor cells
(C) angioblasts
(D) myoblasts
(E) osteoblasts

C.
The angioblasts are the mesenchymal cells that form blood vessels in embryonic devel- opment, as well as embryonic blood cells.

12

The epiblast is capable of forming which of the following germ layers?

(A) Ectoderm only
(B) Ectoderm and mesoderm only
(C) Ectoderm and endoderm only
(D) Ectoderm, mesoderm, endoderm
(E) Mesoderm and endoderm only

D.
The epiblast is capable of forming all three germ layers (ectoderm, mesoderm, and endoderm) during gastrulation. Epiblast cells migrate to the primitive streak and invaginate into a space between the epiblast and hypoblast. Some of these epiblast cells displace the hypoblast to form the definitive endoderm. Migrating epiblast cells also form the intraembryonic mesoderm. The remaining epiblast cells form the ectoderm.

13

A male newborn has a hemangioma on the left frontotemporal region of his face and scalp. The cells forming the hemangioma are derived from which of the following cell layers?

(A) Ectoderm only
(B) Mesoderm only
(C) Endoderm only
(D) Ectoderm and mesoderm
(E) Endoderm and mesoderm

B.
A hemangioma is a vascular tumor that can be present at birth in which the abnormal proliferation of blood vessels leads to a mass resembling a neoplasm. Hemangiomas are mesodermal in origin, in that they are formed by embryonic blood cells and the vascular endothelium formed by angioblasts.

14

Which structure is derived from the same embryonic primordium as the dorsal root ganglia?

(A) Gonads
(B) Kidney
(C) Pineal gland
(D) Liver
(E) Adrenalmedulla

E.
Both the chromaffin cells of the adrenal medulla and the dorsal root ganglia are derived from neural crest cells.

15

Which structure is derived from the same embryonic primordium as the kidney?

(A) Gonads
(B) Epidermis
(C) Pineal gland
(D) Liver
(E) Adrenal medulla

A.
Both the kidneys and the gonads are derived from intermediate mesoderm. This longi- tudinal dorsal ridge of mesoderm forms the gonadal ridge, which is involved with the for- mation of the future kidneys and gonads.