Chapter 3

Question 1

Between which two layers is the extraem- bryonic mesoderm located?
(A) Epiblast and hypoblast
(B) Syncytiotrophoblast and cytotrophoblast
(C) Syncytiotrophoblast and endometrium
(D) Exocoelomic membrane and syncytiotrophoblast
(E) Exocoelomic membrane and cytotrophoblast

Answer 1

E. The extraembryonic mesoderm is derived from the epiblast and is located between the exo- coelomic membrane and the cytotrophoblast. The overall effect is to completely separate the embryoblast from the trophoblast with the extraembryonic mesoderm serving as a conduit (con- nection) between them.

Question 2

During week 2 of development, the embry- oblast receives its nutrients via
(A) diffusion
(B) osmosis
(C) reverse osmosis
(D) fetal capillaries
(E) yolk sac nourishment

Answer 2

A. During week 2 of development, the embryoblast receives its nutrients from endometrial blood vessels, endometrial glands, and decidual cells via diffusion. Diffusion of nutrients does not pose a problem given the small size of the blastocyst during week 2. Although the beginnings of a uteroplacental circulation are established during week 2, no blood vessels have yet formed in the extraembryonic mesoderm to carry nutrients directly to the embryoblast (this occurs in week 3).

Question 3

Which of the following are components of the definitive chorion?
(A) Extraembryonic somatic mesoderm and epiblast
(B) Extraembryonic somatic mesoderm and cytotrophoblast
(C) Extraembryonic somatic mesoderm and syncytiotrophoblast
(D) Extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblast
(E) Extraembryonic visceral mesoderm, cytotrophoblast, and syncytiotrophoblast

Answer 3

D. The definitive chorion consists of three components: extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblast. The chorion defines the chorionic cavity in which the embryoblast is suspended and is vital in the formation of the placenta.

Question 4

Carcinoembryonic antigen (CEA) is an oncofetal antigen that is generally associated with which one of the following tumors?
(A) Hepatoma
(B) Germ cell tumor
(C) Squamous cell carcinoma
(D) Colorectal carcinoma
(E) Teratocarcinoma

Answer 4

D. Oncofetal antigens are normally expressed during embryonic development, remain unex- pressed in normal adult cells, but reexpress on transformation to malignant neoplastic tissue. CEA is associated with colorectal carcinoma.

Question 5

Future site of the mouth

Answer 5

E. The prochordal plate indicates the site of the future mouth. At this early stage of develop- ment, the orientation of the embryo in the cranial versus caudal direction is established. The pro- chordal plate is a thickening of hypoblast cells that are firmly attached to the epiblast cells.

Question 6

Forms definitive structures found in the

adult

Answer 6

C. The bilaminar embryonic disk develops definitive adult structures after gastrulation occurs, in contrast to the trophoblast, which is involved in placental formation.

Question 7

Chorion

Answer 7

D. The chorion consists of three layers; namely, extraembryonic somatic mesoderm, cytotro- phoblast, and syncytiotrophoblast. The chorion is vital in the formation of the placenta.

Question 8

Chorionic cavity

Answer 8

G. The chorion forms the walls of the chorionic cavity in which the conceptus is suspended by the connecting stalk. Note that the inner lining of the chorionic cavity is extraembryonic mesoderm.