Repro - Embryology (Embryogenesis)

Question 1

Name 4 important genes of embryogenesis.

Answer 1

(1) Sonic hedgehog gene (2) Wnt-7 gene (3) FGF gene (4) Homebox (Hox) genes

Question 2

Where is sonic hedgehog gene produced?

Answer 2

Produced at base of limbs in zone of polarizing activity

Question 3

In what 2 processes is sonic hedgehog gene involved?

Answer 3

(1) Involved in patterning along anterior-posterior axis. (2) Involved in CNS development; mutation can cause holoprosencephaly

Question 4

What condition can a mutation in sonic hedgehog gene caused, and why?

Answer 4

Involved in CNS development; mutation can cause holoprosencephaly

Question 5

Where is Wnt-7 gene produced?

Answer 5

Produced at apical ectodermal ridge (thickened ectoderm at distal end of each developing limb).

Question 6

For what is Wnt-7 necessary?

Answer 6

Necessary for proper organization along dorsal-ventral axis.

Question 7

Where is FGF gene produced?

Answer 7

Produced at apical ectodermal ridge.

Question 8

What function does FGF gene serve?

Answer 8

Stimulates mitosis of underlying mesoderm, providing for lengthening of limbs.

Question 9

In what process is homeobox (hox) genes involved?

Answer 9

Involved in segmental organization of embryo in a craniocaudal direction.

Question 10

What effect do hox mutations have?

Answer 10

Hox mutations –> appendages in wrong location.

Question 11

What events occur at day 0 of early fetal development?

Answer 11

Fertilization by sperm, forming zygote, initiating embryogenesis

Question 12

What event occurs within week 1 of early fetal development?

Answer 12

hCG secretion begins around the time of implantation of blastocyst

Question 13

What events occur within week 2 of early fetal development?

Answer 13

Bilaminar disc (epiblast, hypoblast); Think: “2 weeks = 2 layers”

Question 14

What are the names of the layers in the bilaminar disc?

Answer 14

Epiblast, hypoblast

Question 15

What events occur within week 3 of early fetal development?

Answer 15

Trilaminar disc (Think: “3 weeks = 3 layers”); Gastrulation. Primitive streak, notochord, mesoderm, and its organization, and neural plate begin to form.

Question 16

What events occur weeks 3-8 of early fetal development? What is this time frame called?

Answer 16

Neural tube formed by neuroectoderm and closes by week 4. Organogenesis. Extremely susceptible to teratogens; Embryonic period

Question 17

What events occur at week 4 of early fetal development?

Answer 17

Heart begins to beat. Upper lower limb buds begin to form; Think: “4 weeks = 4 limbs”

Question 18

What events occur at week 6 of early fetal development?

Answer 18

Fetal cardiac activity visible by transvaginal ultrasound.

Question 19

What events occur at week 10 of early fetal development?

Answer 19

Genitalia have male/female characteristics.

Question 20

What time frame is extremely susceptible to teratogens during early fetal development?

Answer 20

Weeks 3-8 (Embryonic period)

Question 21

What forms neural tube? By what week in fetal development is the neural tube closed?

Answer 21

Neural tube formed by neuroectoderm and closes by week 4.

Question 22

What is gastrulation? What does it establish?

Answer 22

Process that forms the trilaminar embryonic disc. Establishes the ectoderm, mesoderm, and endoderm germ layers.

Question 23

How does gastrulation start?

Answer 23

Starts with the epiblast invaginating to form the primitive streak.