Embryology - Fate of the Mesoderm

Question 1

What has happened by the end of week 3?

Answer 1

The embryo has gastrulated
Bilaminar disc is now the trilaminar disc
Axes have been set

Question 2

What is neurulation?

Answer 2

The notochord-driven induction of ectoderm to form the nervous system

Question 3

What happens to the ectoderm overlying the notochord?

Answer 3

Notochord directs it to convert into neurectoderm
It thickens
Edges elevate out of the plane of the disc and curl towards eachother, creating the neural tube

Question 4

When does the first pair of somites appear?

Answer 4

Day 20

Question 5

What is organised degeneration?

Answer 5

When the ventral wall of the somite breaks down, leading to formation of the sclerotome

Question 6

What is a sclerotome?

Answer 6

A derivative of a somite which will go onto form hard tissue such as bone

Question 7

What is an epimere and a hypomere innervated by?

Answer 7

Epimere - dorsal branch of spinal nerve for that segment

Hypomere - ventral branch

Question 8

How many somites are there?

Answer 8

31

Question 9

In embryology, what is a dermatome?

Answer 9

Part of the somite that gives rise to the dermis

Question 10

In embryology, what is a myotome?

Answer 10

Part of the somite that gives rise to muscles

Question 11

What will the paraxial mesoderm differentiate into?

Answer 11

Axial skelton 
-vertebral column and ribs
Dermis
Muscles of A/L wall
Some limb muscles

Question 12

What will the somatic mesoderm become?

Answer 12

Connective tissue of limbs

Contributes to A/L wall

Question 13

What will the splanchnic mesoderm become?

Answer 13

Smooth musculature
Connective tissue
Vasculature of the gut

Question 14

What will the intermediate mesoderm become?

Answer 14

Urogential system such as kidneys, ureters, gonads

Question 15

What does folding achieve?

Answer 15

Creates a ventral body wall
Pulls amniotic membrane around the disk so that the embryo is suspended within the amniotic sac
Pulls connective stalk ventrally

Question 16

What has happened by the end of the fourth week?

Answer 16

The nervous system has began to form
Segments have appeared, assigning specific tasks to specific cells
The embryo has folded