Trilaminar Learning Objectives

Question 1

Cells from which layer of the bilaminar embryonic disk migrate through the primitive streak & pit? What three layers do these cells form?

Answer 1

Epiblast cells migrate laterally to form the mesoderm (intraembryonic mesoderm), endoderm (displace hypoblast cells), ectoderm (epiblast cells that don’t migrate).
Rostral migration creates the prechordal plate/notochord.

Question 2

What layers form the buccopharyngeal & cloacal membranes? Where are these membranes located?

Answer 2

Ectoderm and endoderm. The buccopharyngeal is located at the rostral/cranial end of the embyro. The cloacal membrane is located at the caudal/ventral end of the embryo.

Question 3

How is the notochord formed?

Answer 3

Slow migration of epiblast cells rostrally until reaching the prochordal plate. The hollow lumen structure drops down until it fuses with endoderm layer (notochordal plate). Neurenteric canal formed. Cells ball back up to form a definitive, solid notochord.

Question 4

What does the notochord induce?

Answer 4

Notochord stimulates differentiation of nervesous system in overlying ectoderm.

Question 5

What are the adult remnants of the notochord?

Answer 5

Nucleus pulposus of the vertebral body

Question 6

What is a sacrococcygeal teratoma and how does it arise?

Answer 6

This is the most common tumor in new borns. It contains tissue of all three germ layers. It arises when the primitive streak does not fully disintegrate.

Question 7

Briefly describe the process of neurulation

Answer 7

Invagination results in a midline grove (neural folds) of the neural plate (thickening of the ectoderm above notochord). Fusion of these folds result in the neural tube.This is the creation of the CNS.

Question 8

What are the 3 types of intraembryonic mesoderm? How do they relate to each other anatomically?

Answer 8

From medial (closest to neural tube) to lateral:

1) paraxial mesoderm (somites)
2) intermediate mesoderm (kidneys and gonads)
3) lateral mesoderm (continuous with extraembryonic mesoderm, serous linings of body cavity)

Question 9

From what type of mesoderm does the visceral pleura develop?

Answer 9

Sphlanchnic part of lateral mesoderm

Question 10

What do somites form? How are they related to the notochord?

Answer 10

Formed from the paraxial layer of the mesoderm, they are blocks of tissue along lengths of the notochord that develop into the dermis of the skin, skeletal muscles of the body, bone & cartilage. Specifically related to the notochord because they become the vertebral column.

Question 11

What type of mesoderm forms the kidneys?

Answer 11

Intermediate mesoderm

Question 12

What is the septum transversum? Where is it located? What does it form in the adult?

Answer 12

Thickening of the lateral mesoderm rostral to the cardiogenic and buccopharyngeal area. This forms the central tendon of the diaphram in an adult

Question 13

What does embryonic folding develop?

Answer 13

A tube within a tube.

Question 14

What germ layer forms the allantois? What does it form in the adult?

Answer 14

Endoderm layer. This is part of the connecting stalk/umbilical cord where blood cells form (in walls) to circulate nutrients/blood into the embryo from the placenta. This forms the fibrous medial umbilical ligament in an adult

Question 15

With what does the midgut communicate?

Answer 15

The midgut is connected to the yolk sac via the vitelline duct/yolk stalk.

Question 16

Briefly describe the process of embryonic folding

Answer 16

yeah, not gonna type that out.

Question 17

What 3 things does the process of gastrulation accomplish?

Answer 17

1) Bilaminar disk to trilaminar disk (three germ layers)
2) Bilateral Symmetry (cranio-caudal axis)
3) Notochord establishment