Chapter 3 - Week 2 of Human Development (Days 8-14)

Question 1

Which of the following components plays the most active role in invading the endometrium during blastocyst implantation?
(A) Epiblast
(B) Syncytiotrophoblast
(C) Hypoblast
(D) Extraembryonic somatic mesoderm
(E) Extraembryonic visceral mesoderm

Answer 1

(B) Syncytiotrophoblast

The syncytiotrophoblast plays the most active role in invading the endometrium of the mother’s uterus. During the invasion, endometrial blood vessels and endometrial glands are eroded and a lacunar network is formed.

Question 2

Between which two layers is the extra embryonic 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 2

(E) Exocoelomic membrane and cytotrophoblast

The extraembryonic mesoderm is derived from the epiblast and is located between the exocoelomic membrane and the cytotrophoblast. The overall effect is to completely separate the embryoblast from the trophoblast, with the extra embryonic mesoderm serving as a conduit (connection) between them.

Question 3

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

Answer 3

(A) diffusion

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 4

The prochordal plate marks the site of the future
(A) umbilical cord
(B) heart
(C) mouth
(D) anus
(E) nose

Answer 4

The prochordal plate is a circular, midline thickening of hypoblast cells that are firmly attached to the overlying epiblast cells. The plate will eventually develop into a membrane called the oropharyngeal membrane at the site of the future mouth. It is interesting to note that at this early stage of development the cranial versus caudal region of the embryo is established by the prochordal plate, and since the prochordal plate is located in the midline, bilateral symmetry is also established.

Question 5

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 5

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 6

A 16-year-old girl presents on May 10 in obvious emotional distress. On questioning, she relates that on May 1 she experienced sexual intercourse for the first time, without using any means of birth control. Most of her anxiety stems from her fear of pregnancy. What should the physician do to alleviate her fear?
(A) Prescribe diazepam and wait to see if she misses her next menstrual period
(B) Use ultrasonography to document pregnancy
(C) Order a laboratory assay for serum hCG
(D) Order a laboratory assay for serum progesterone
(E) Prescribe diethylstilbestrol (“morningafter pill”)

Answer 6

(C) Order a laboratory assay for serum hCG

Human chorionic gonadotropin (hCG) can be assayed in maternal serum at day 8 of development and in urine at day 10. If this teenager is pregnant, the blastocyst would be in week 2 of development (day 10). Laboratory assay of hCG in either the serum or urine can be completed; however, serum hCG might be more reliable. It is important to note that if she is pregnant, she will not miss a menstrual period until May 15, at which time the embryo will be entering week 3 of development.

Question 7

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 7

(D) Colorectal carcinoma

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

Question 8

A 42-year-old woman presents with complaints of severe headaches, blurred vision, slurred speech, and loss of muscle coordination. Her last pregnancy 5 years ago resulted in a hydatidiform mole. Laboratory results show a high hCG level. Which of the following conditions is a probable diagnosis?
(A) Vasa previa
(B) Placenta previa
(C) Succenturiate placenta
(D) Choriocarcinoma
(E) Membranous placenta

Answer 8

(D) Choriocarcinoma

After a hydatidiform mole, it is very important to assure that all the invasive trophoblastic tissue is removed. High levels of hCG are a good indicator of retained trophoblastic tissue because such tissue produces this hormone. In this case, the trophoblastic tissue has developed into a malignant choriocarcinoma and metastasized to the brain, causing her symptoms of headache, blurred vision, and so on.

Question 9

At what location does the amniotic cavity develop?
(A) Between the cytotrophoblast and syncytiotrophoblast
(B) Within the extraembryonic mesoderm
(C) Between the endoderm and mesoderm
(D) Within the hypoblast
(E) Within the epiblast

Answer 9

(E) Within the epiblast

The amniotic cavity develops within the epiblast, and it is a cavity that contains the embryo and amniotic fluid.