Fourth Through Eighth Week Of Development

Question 1

What happens during the fourth through eighth week of development?

Answer 1

all major external features and organ systems have begun their development. The embryo has changed its shape from that of a trilaminar disc to a distinctly human form.

developmental errors during this period lead to major birth defects.

Question 2

What is the major event of week 4 development?

Answer 2

Folding of the embryo (part of morphogenesis)

Question 3

Where does ventral folding occur?

Answer 3

1) Cranial end 2) Caudal end 2) Lateral edges

Question 4

1) Cranial Folding

Answer 4

-Ventral folding of the head incorporates part of the endoderm into the head. -This becomes the foregut.
-This folding also causes the oropharyngeal membrane and heart to move ventrally.
-The brain now becomes the most cranially oriented part of the embryo.

Question 5

2) Caudal Folding

Answer 5

-Ventral folding of the caudal end incorporates part of the endoderm into it forming the hindgut.
-The terminal part of the hindgut forms the cloaca. -Folding moves the cloacal membrane to a ventral position on the embryo.

Question 6

3) Lateral Folding

Answer 6

-Ventral folding of the lateral edges (folds) of the embryo incorporates part of the endoderm into it, forming the midgut.
-The lateral folds eventually fuse at the ventral midline.
-This folding forms the lateral and ventral body walls.
-The body cavity enclosed within is called the intraembryonic coelom.
-The umbilical vesicle remains attached to the midgut by the omphaloenteric duct.

Question 7

What does the midgut form into

Answer 7

Small and large intestines

Question 8

Weeks 5 through 8 are characterized by what?

Answer 8

the ongoing development of the major organ systems of the body.