Basic Embryology Homework \

Question 1

Embryonic period

Answer 1

• week 1 through week 8

- the basics of all the major organs are formed

Question 2

Fetal period

Answer 2

• week 9 through week 38 or at birth

- where the organs increase in size and are more complex

Question 3

prenatal period

Answer 3

the time between conception and birth

Question 4

Briefly describe the tube- within-a-tube body plan

Answer 4

The outer body wall makes up the outer tube, while the inner tube extends from the abdomen and makes up the digestive tube. The two tubes are separated by a serous cavity.

Question 5

Vertebral column

Answer 5

outer tube

Question 6

muscle of digestive tube

Answer 6

inner tube

Question 7

ribs

Answer 7

outer tube

Question 8

respiratory structures

Answer 8

inner tube

Question 9

trunk muscles

Answer 9

outer tube

Question 10

lining of the digestive tube

Answer 10

inner tube

Question 11

Zygote

Answer 11

a fertilized oocyte

Question 12

blastocyst

Answer 12

fluid-filled multi-cellular structure formed around day 4

Question 13

inner cell mass

Answer 13

cluster of cells on one side of the blastocyst cavity that will develop into the embryo

Question 14

morula

Answer 14

solid cluster of cells formed by 72hours after fertilization

Question 15

trophoblast

Answer 15

layer of cells surrounding blastocyst cavity that will help form the placenta

Question 16

Briefly describe the changes in the embryo and its supporting structures during week 2

Answer 16

The inner cell mass divides into two sheets of cells, the epiblast and the hypoblast. Extensions of these cell sheets form two fluid- filled sacs. Together the two layers make up the bilaminar embryonic disc.

Question 17

Epiblast

Answer 17

An extension of this structure forms the amnion, which encloses the amniotic sac.

Question 18

Hypoblast

Answer 18

An extension of this structure forms the yolk sac.

Question 19

Briefly describe the changes in the embryo and its supporting structures during week 3.

Answer 19

The embryo grows from a two-layred disc to a three layered disc. This is called gastrulation, and it forms the three primary germ layers. Ectoderm, mesoderm, and endoderm.

Question 20

Order of Gastrulation in week 3

Answer 20

1. Primitive streak appears on dorsal surface of epiblast around days 14-15.
2. Epiblast cells migrate inward at primitive streak to displace cells of hypoblast to form the endoderm.
3. Epiblast cells form a new layer called the mesoderm between the epiblast and endoderm.
4. Ectoderm arises from epiblast cells that remain on the embryo’s dorsal surface.

Question 21

Order of neurulation in week 3

Answer 21

1. Ectoderm in the dorsal midline thickens to form a neural plate.
2. Neural plate folds inward to form a neural groove.
3. Neural groove deepens until a hollow neural tube is pinched off into the body which will develop into the brain and spinal cord.
4. Closure of neural tube begins late in week three and will complete by the end of week 4.

Question 22

Epithelial tissue

Answer 22

• Makes up ectoderm and endoderm.

- Sheets of tightly joined cells.

Question 23

mesenchyme tissue

Answer 23

• makes up mesoderm
• embryonic tissue with star-shaped cells that do not attach to one another.
• contains cells that are free to migrate widely within the embryo.