2 Embryology

Question 1

Pre-embryonic period

Answer 1

Weeks 1-2. Development through implantation.

Question 2

Embryonic period

Answer 2

Weeks 3-8. Through embryonic development, neurulation, and organogenesis.

Question 3

Fetal period

Answer 3

Week 9-38. Development post embryonic organization of body.

Question 4

Zygote

Answer 4

Unified male and female gametes. Diploid.

Question 5

Morula

Answer 5

16 cell mass post fertilization and cleavage.

Question 6

Blastocyst

Answer 6

c. 100 cels. Divided into two structures, embryoblast and trophoblast.

Question 7

Trophoblast

Answer 7

Outer cellular layer forming fetal half of placenta. Divides into two layers during the process of implantation, cytotrophoblast and syncytiotrophoblast, which help form the chorion.

Question 8

Chorion

Answer 8

Cellular structure formed from the syncytiotrophoblast and cytotrophoblast which develops into the fetal half of placenta.

Question 9

Cytotrophoblast

Answer 9

Derivative of trophoblast. Helps form the chorion which eventually becomes the placenta. Eventually forms inner layer of chorion, totally surrounding embryoblast and eventually epiblast/hypoblast.

Question 10

Syncytiotrophoblast

Answer 10

Derivative of trophoblast which forms outer layer of chorion. Directly in contact with the uterine wall. Surrounds cytotrophoblast.

Question 11

Inner cell mass

Answer 11

Embryoblast

Question 12

What two layers does the embryoblast divide into?

Answer 12

Epiblast and hypoblast.

Question 13

What does the epiblast become?

Answer 13

Embryo and amnion

Question 14

What does hypoblast become?

Answer 14

Yolk sack

Question 15

What are epiblast and hypoblast together called?

Answer 15

Bilaminar disk

Question 16

On what side of the bilaminar disk and in what layer does the primitive streak form?

Answer 16

Dorsal side of epiblast. i.e. the side away from the hypoblast, towards antrum of uterus.

Question 17

What happens at the primitive streak?

Answer 17

Gatrulation

Question 18

What is Gastrulation?

Answer 18

Movement of cells from epiblast into space between epiblast and hypoblast, forming three primary germ layers.

Question 19

Three primary germ layers from dorsal to ventral:

Answer 19

Ectoderm, mesoderm, endoderm.

Question 20

What structures derive from the ectoderm?

Answer 20

Integumentary and nervous tissue

Question 21

What structures derive from the mesoderm?

Answer 21

Everything not derived from ectoderm and endoderm, e.g. Heart, mucle, kidneys, reproductive organs, connective tissue

Question 22

What structure induces neurulation and where does it form?

Answer 22

Notochord. In the mesoderm deep to and parallel with the primitive streak.

Question 23

Where does the nueural tube form? What process forms it?

Answer 23

The neural tube forms superficial to and parallel with the primitive streak in the ectoderm, first as neural plate, then neural groove, then closing into neural tube. Induction.

Question 24

What are the two types of folding that occur in embryonic development?

Answer 24

Transverse folding where sides parallel with the primitive streak curl ventrally enfolding the endoderm and creating a central canal. cephalocaudal folding where peak and tail of embryo curl toward each other.

Question 25

How long is the embryo at week 8 and beginning of fetal period? What organ systems haven developed?

Answer 25

1 inch long. Most organ systems have developed.

Question 26

What is the earliest babies can survive?

Answer 26

As early as 30 weeks without medical interventions. Early as 22 with medical tech.

Question 27

What percentage of babies is born with a serious birth defect? Of these, what percentage of defects have a known cause?

Answer 27

3/100 or 3% of children. Only fifty percent have a known etiology.

Question 28

What is a teratogen?

Answer 28

Anything that causes a birth defect.

Question 29

What is the most common

Teratogen? What syndrome does it cause and what are its symptoms?

Answer 29

Alcohol. It causes fetal alcohol syndrome which is characterized by growth retardation, heart defects, microcephally, and is the leading cause of mental retardation.

Question 30

What percentage of babies born to mothers taking accurate have birth defects?

Answer 30

25% physical defects. 50% are mentally disabled.

Question 31

What does the epiblast form?

Answer 31

Amnion and embryo.

Question 32

What does the hypoblast form?

Answer 32

Yolk sac