Embryology Weeks 1-3

Question 1

Where does fertilization take place?

Answer 1

Ampulla of the uterine tubes

Question 2

What is the acrosome reaction?

Answer 2

Acrosomal enzymes released by the sperm allow it to penetrate the oocyte

Question 3

What is the cortical reaction?

Answer 3

Renders the oocyte impenetrable to other sperm

Question 4

What is a morula?

Answer 4

Zygote consisting of 12-32 blastomeres

Forms approximately 3 days after fertilization

Question 5

Describe implantation

Answer 5

Implants within the functional layer of the endometrium during the secretory phase of the menstrual cycle

Usually in the posterior wall of the uterus

Begins at the end of the first week and is completed by the end of the second week

Question 6

What is an ectopic tubal pregnancy?

Answer 6

When the blastocyst implants within the uterine tube

Question 7

What is the role of the syncytiotrophoblast?

Answer 7

Grows into the endotemtrium, does not divide mitotically

Produces human chorionic gonadotropin hormone

Question 8

What is the function of hCG?

Answer 8

Stimulates the production of progesterone in the corpus luteum

Can be detected at 10 days for pregnancy tests

Question 9

What is the role of the cytotrophoblast?

Answer 9

Divides mitotically, adding to the growth of the syncytiotrophoblast

Question 10

What are Primary chorionic villi?

Answer 10

Protrusions of the cytotrophoblast into the syncytiotrophoblast and are the first stage in development of the chorionic villi of the placenta

Question 11

What is the role of the extra-embryonic somatic mesoderm?

Answer 11

Lines the inner side of the cytotrophoblast (together forming the chorion)

Question 12

What is the role of the extra-embryonic visceral mesoderm?

Answer 12

Covers the yolk sac

Question 13

What is a hydatidiform mole?

Answer 13

A blighted blastocyst leads to the death of the embryo, followed by hyperplastic proliferation of the trophoblast within the uterine wall

Question 14

What is a choriocarcinoma?

Answer 14

Malignant tumor arising from trophoblastic cells that may occur following a normal pregnancy, abortion, or hydatidiform mole

Question 15

What is week 3 of human development characterized by?

Answer 15

Appearance of primitive streak

Development of the notochord

Differentiation of the three germ layers

Question 16

What is gastrulation?

Answer 16

Conversion of the epiblast from a bilaminar disc into a trilaminar embryonic disc consisting of ectoderm, mesoderm, and endoderm.

Begins with the formation of the primitive streak

Question 17

What is the primitive streak?

Answer 17

Linear band of thickened epiblast that first appears at the caudal end of the embryo and grows cranially

Normally undergoes degeneration and disappears by the end of the fourth week

Question 18

How is the mesoderm formed?

Answer 18

Epiblastic cells migrate into the ECF between the epiblast and hypoblast (endoderm) as mesenchymal cells, eventually forming the mesoderm

Question 19

What is a sacrococcygeal teratoma?

Answer 19

Remnants of the primitive streak may persist and give rise to this germ cell tumor.

Can be benign or malignant

Most common tumor in neonates

Question 20

What is the notochord?

Answer 20

Cord of mesodermal cells

Signals ectoderm to make nervous system and some mesoderm to make vertebral bodies

Eventually becomes the nucleus pulposus of the vertebral discs

Question 21

What is the oropharyngeal membrane?

Answer 21

Site of the future mouth where ecotderm and endoderm connect directly with no mesoderm

Question 22

What is the prechordal plate?

Answer 22

Thickened mesoderm between the oropharyngeal membrane and the notochord

Contributes to forebrain and oral cavity structure

Question 23

What is the cloacal membrane?

Answer 23

Site of future anus where ectoderm and endoderm meet directly