Chapter 4

Question 1

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 GI tract

Answer 1

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

Question 2

Intermediate mesoderm gives rise to the
(A) neural tube
(B) heart
(C) kidneys and gonads
(D) somites
(E) notochord

Answer 2

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

Question 3

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

Answer 3

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 appearance at the end of week 8.

Question 4

The lateral mesoderm is divided into two distinct layers by the formation of the
(A) extraembryonic coelom 
(B) intraembryonic coelom 
(C) cardiogenic region
(D) notochord
(E) yolk sac

Answer 4

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.

Question 5

A woman has her pregnancy suddenly ter- minated because of intrauterine fetal death. At autopsy, the fetus shows severe pallor, general- ized edema, and hepatosplenomegaly. Which of the following would you suspect?
(A) VATER
(B) 13-Thalassemia minor
(C) 13-Thalassemia major
(D) Hydrops fetalis
(E) V ACTERL

Answer 5

D. Hydrops fetalis is the most severe form of a-thalassemia, which is a direct result of the lack of or decreased synthesis of the a-globin chain of hemoglobin.