Lecture 4 - Embryology II

Question 1

Steps to somitogenesis

Answer 1

1. Epithelialization
2. Fissure formation (separation)
3. Periodically
4. Specification
5. Differentiation.

Question 2

Somite specification

Answer 2

Regionalisation along anterior to posterior axis (determined by the hox gene)

Question 3

Somite differentiation

Answer 3

Somites reorganises into

• epithelial dermamyotome (dermis, muscle)
• mesenchyme sclerotome

Question 4

Formation of vertebrae

Answer 4

Sclerotome splits into cranial and caudal sections as a result of spinal nerves growing to innervate the myotome. Caudal sections fuse with the cranial section of sclerotome of the one below it to form vertebral rudiment

Question 5

Formation of limb

Answer 5

Limbs form at discrete position (limb field). Mesenchyme cells from lateral plate mesoderm and somites migrate in to form the muscles, dermis and bones of the limb.

Question 6

Somitogenesis

Answer 6

Formation of somites

• swellings form along the paraxial mesoderm
• once 20 somitomeres had formed, the 8th pair starts to separate as separate somites
• additional somites begin to replace the somitomeres caudally until 44 somite pairs are formed