Chapter 4

Question 1

At the 8th day of development, the blastocyst is partially embedded in the endometrial stroma. In the area over the embryoblast, the trophoblast has differentiated into two layers:
(1) an inner layer of mononucleated cells, the ____, and (2) an outer multinucleated zone without distinct cell boundaries, the ___

Answer 1

cytotrophoblast - syncytiotrophoblast

Question 2

Cells of the inner cell mass or embryoblast
also differentiate into two layers: (1) a layer
of small cuboidal cells adjacent to the blastocyst cavity, known as the ___, and (2) a layer of high columnar cells adjacent to the amniotic cavity, the ____

Answer 2

hypoblast layer - epiblast layer

Question 3

Together, the layers form a flat disc. At the
same time, a small cavity appears within the epiblast. This cavity enlarges to become the ___. Epiblast cells adjacent to the cytotrophoblast are called ____; together with the rest of the epiblast, they line the amniotic cavity

Answer 3

amniotic cavity - amnioblasts

Question 4

When these vacuoles fuse, they form large lacunae, and this phase of trophoblast development is thus known as the ____

Answer 4

lacunar stage

Question 5

At the abembryonic pole, meanwhile, flattened cells probably originating from the hypoblast form a thin membrane, the exocoelomic (Heuser) membrane that lines the inner surface of the cytotrophoblast. This membrane, together with the hypoblast, forms the lining of the ____, or ____

Answer 5

exocoelomic cavity - primitive yolk sac

Question 6

Concurrently, cells of the syncytiotrophoblast penetrate deeper into the stroma and erode the endothelial lining of the maternal capillaries. These capillaries, which are congested and dilated, are known as ____

Answer 6

sinusoids

Question 7

As the trophoblast continues to erode more and more sinusoids, maternal blood begins to flow through the trophoblastic system, establishing the ____

Answer 7

uteroplacental circulation

Question 7

In the meantime, a new population of cells appears between the inner surface of the cytotrophoblast and the outer surface of the exocoelomic cavity. These cells, derived from yolk sac cells, form a fine, loose connective tissue, the ____, which eventually fills all of the space between the trophoblast externally and the amnion and exocoelomic membrane internally

Answer 7

extraembryonic mesoderm

Question 7

Soon, large cavities develop in the extraembryonic mesoderm, and when these become confluent, they form a new space known as the ___ or ____

Answer 7

extraembryonic cavity, or chorionic cavity

Question 7

The extraembryonic mesoderm lining the cytotrophoblast and amnion is called the ____; the lining covering the yolk sac is known as the extraembryonic splanchnic mesoderm

Answer 7

extraembryonic somatic mesoderm

Question 7

Cells of the endometrium, meanwhile, become polyhedral and loaded with glycogen and lipids; intercellular spaces are filled with extravasate, and the tissue is edematous. These changes, known as the _______, at first, are confined to the area immediately surrounding the implantation site but soon occur throughout the endometrium

Answer 7

decidua reaction

Question 8

The extraembryonic mesoderm lining the cytotrophoblast and amnion is called the extraembryonic somatic mesoderm; the lining covering the yolk sac is known as the _____

Answer 8

extraembryonic splanchnic mesoderm

Question 8

These cells proliferate and gradually form a new cavity within the exocoelomic cavity. This new cavity is known as the ______ or ___

Answer 8

secondary yolk sac or definitive yolk sac

Question 8

During its formation, large portions of the exocoelomic cavity are pinched off. These portions are represented by ____, which are often found in the extraembryonic coelom or ____

Answer 8

exocoelomic cysts - chorionic cavity

Question 9

Cells of the cytotrophoblast proliferate locally and penetrate into the syncytiotrophoblast, forming cellular columns surrounded by syncytium. Cellular columns with the syncytial covering are known as ___

Answer 9

primary villi

Question 10

Meanwhile, the extraembryonic coelom expands and forms a large cavity, the ____

Answer 10

chorionic cavity

Question 11

The syncytiotrophoblast is responsible for
hormone production, including _____

Answer 11

human chorionic gonadotropin [hCG]

Question 12

The extraembryonic mesoderm lining the inside of the cytotrophoblast is then known as the _____

Answer 12

chorionic plate

Question 12

The only place where extraembryonic mesoderm traverses the chorionic cavity is in the _____. With the development of blood vessels, the stalk becomes the _____

Answer 12

connecting stalk - umbilical cord

Question 13

Because 50% of the implanting embryos
genome is derived from the father, it is a ____ that potentially should be rejected by the maternal system, similar to rejection of a transplanted organ

Answer 13

foreign body

Question 14

0ccasionally, the blastocyst implants close to the internal os [opening] of the cervix so
that later in development, the placenta bridges the opening [______] and causes severe, even life-threatening bleeding in the second part of pregnancy and during delivery

Answer 14

placenta previa

Question 15

In some cases, however, the trophoblast
develops and forms placental membranes, although little or no embryonic tissue is present. Such a condition is known as a _____

Answer 15

hydatidiform mole

Question 16

In the abdominal cavity, the blastocyst most frequently attaches itself to the peritoneal lining of the ____ or ____

Answer 16

rectouterine cavity, or pouch of Douglas

Question 16

Occasionally, implantation takes place outside the uterus, resulting in an ___ or ____

Answer 16

extrauterine pregnancy, or ectopic pregnancy

Question 17

The blastocyst may also attach itself to the peritoneal covering of the intestinal tract or to the omentum. Sometimes, the blastocyst develops in the ovary proper, causing a _____.

Answer 17

primary ovarian pregnancy

Question 18

Moles secrete high levels of hCG and may produce benign or malignant [___] tumors

Answer 18

invasive mole, choriocarcinoma

Question 19

For example, a microdeletion on chromosome 15 inherited from a father causes Prader—Willi syndrome [a condition characterized by hypotonia, intellectual disability, hypogonadism, and
obesity], whereas inheriting the same deletion from the mother causes Angelman syndrome [a condition characterized by seizures, little to no
speech, paroxysms of laughter, and severe intellectual disability]. This phenomenon, in which there is differential modification and/or expression of homologous alleles or chromosome regions depending on the parent from whom the genetic material is derived, is known as ______

Answer 19

genomic imprinting

Question 20

The second week of development is known as the week of 2’s:
1. The trophoblast differentiates into two layers: ____
2. The embryoblast forms two layers: ____
3. The extraembryonic mesoderm splits into two layers: ____
4. Two cavities form: ____

Answer 20

1. the cytotrophoblast and syncytiotrophoblast
2. the epiblast and the hypoblast
3. the somatic and splanchnic layers
4. the amniotic and yolk sac cavities