Embryology 1

Question 1

Describe the timeline for fetal development.

Answer 1

When a woman goes to her doctor thinking she’s pregnant and the tests reveal she is pregnant, the doctor should ask when her last menstrual period was. Fertilization is presumed to be 2 weeks after the date of her LMP. The expected gestation time is then 38 weeks from the time of fertilization.

Question 2

What is happening in weeks 1 - 3 of fetal development?

Answer 2

• Fertilization
• Cleavage
• Blastocyst formation
• Implantation
• Gastrulation
• Neurulation

Question 3

What is happening in weeks 3 - 8 of fetal development?

Answer 3

Organogenesis

Question 4

What is happening in weeks 8 - 40 of fetal development?

Answer 4

Growth and maturation of organs

Question 5

What is the fetus’s response to teratogens during weeks 1 - 3?

Answer 5

All or none phenomenon - exposure to teratogen either has no effect or results in embryonic death

Question 6

What is the fetus’s response to teratogens during weeks 3 - 8?

Answer 6

Most vulnerable to teratogens during this time, more likely to result in death

Question 7

What is a teratogen

Answer 7

Any substance, agent or process that interferes with normal prenatal development causing the formation of one or more developmental abnormalities in the fetus

Question 8

What is the difference before embryonic age and gestational age?

Answer 8

Embryonic age refers to day 1 of fertilization (embryologists say pregnancy is only 38 weeks long as a consequence)

Gestational age refers to day 1 of LMP (OB/GYNs usually use this, thus they say pregnancy is 40 weeks long)

Question 9

Answer 9

Question 10

Answer 10

Question 11

Answer 11

Question 13

Gametogenesis is the _____ function of the gonads

Answer 13

Exocrine

Question 14

Where do the male and female gametes fuse to form the zygote?

Answer 14

The ampulla of the fallopian tube

Question 15

What does fertilization accomplish? (3)

Answer 15

• Restores diploid number of chromosomes
• Determines chromosomal sex
• Initiates cleavage of the zygote

Question 16

What is cleavage?

Answer 16

A series of mitotic divisions that occurs as the zygote is propelled toward the uterine cavity

Question 17

What is the morulla?

Answer 17

The 16-cell stage

Question 18

When is the blastocyst formed?

Answer 18

Day 5

Question 19

Describe the structure of the blastocyst.

Answer 19

There is a central hollow cavity and 2 layers of cells: trophoblasts on the exterior of the blastocyst and an inner cell mass called the embryoblast.

Question 20

All fetal structures derive from the _______ layer of the blastocyst.

Answer 20

Embryoblast

Question 21

The placenta and fetal membranes are derived from the ______ cell layer of the blastocyst.

Answer 21

Trophoblast

Question 22

When does implantation occur?

Answer 22

Day 6

Question 23

_____ cells drive implantation

Answer 23

Trophoblast

They invade the maternal endometrial epithelium

Question 24

When is the bilaminar disc formed?

Answer 24

Day 9

Question 25

What does the bilaminar disc consist of?

Answer 25

The epiblast and hypoblast

Question 26

What structures does the epiblast form?

Answer 26

The embryonic germ layers

Question 27

What structures does the hypoblast form?

Answer 27

The roof of the yolk sac

Question 28

What is the first morphologic sign of gastrulation?

Answer 28

Formation of the primitive streak

Question 29

Describe where the primitive streak occurs?

Answer 29

Caudally in the median plane of the dorsal aspect

Question 30

Which structures arise from the primitive streak?

Answer 30

Primitive groove Primitive node Primitive pit

Question 31

When does gastrulation occur?

Answer 31

week 3

Question 32

Explain how the embryonic endoderm and the embryonic mesoderm form.

Answer 32

Mesenchyme cells from the deep surface of the primitive sreak migrate to form these germ layers

Question 33

Answer 33

Question 34

Answer 34

Question 35

What is gastrulation?

Answer 35

The formation of 3 embryonic germ cell layers