Early Embryonic 3

Question 0

Describe the differentiation of mesoderm into somites

Answer 0

The first lair of somites appears at day 20 in the occipital region. More sppear in cranio-caudal sequence at 3 pairs/day until 42 pairs, some dissapear leaving 31
-somites appear as regular block of mesoderm arranged around a small cavity, then organaised degeneration of the ventral walls forms sclerotome

Question 1

Describe differention of the mesoderm into the notochord

Answer 1

Mesoderm differentiates into the notochord during gastrulation. The notochord signals the ectoderm to convert to nueroectoderm which is thicker and the edges start to fold forming the nueral tube

Question 2

Describe differentiation of the mesoderm into the intermediate mesoderm and lateral plate (somatic and splanchic)

Answer 2

Appearance of somites organaises the mesoderm into segments. The lateral plate mesoderm splits into somatic and splanchic, with the intraembryonic coelem between
Mesoderm in between is the intermediate mesoderm

Question 3

Describe the formation of the coelom

Answer 3

As the mesoderm differentuates the intra embryonic coelom is formed between the somatic and splanchic mesoderm.
As the embryo folds laterally the lateral branches of mesoderm connect to form the coelom

Question 4

List derivatives of the paraxial mesoderm

Answer 4

Axial skeleton
Dermis
Muscles of axial body wall
Some limb muscles

Question 5

List derivatives of the somatic mesoderm

Answer 5

Connective tissue of limbs

Axial body wall

Question 6

Splanchic mesoderm

Answer 6

Smooth musculature

Connective tissue and vasculature of gut

Question 7

I mediate mesoderm

Answer 7

Urogenital system e.g. Kidney, ureter, gonads

Question 8

Describe the cephalo-caudal folding of the embryo

Answer 8

To start heart lies at cranial end
moves inwards with folding, until it ends up in the future chest
The yolk sac extends out of the embryo to form connection between yolk and gut

Question 9

Describe lateral folding of the embryo

Answer 9

Draws together margins of disc:

• Creating ventral body wall
• Amniotic membrane around disc so embryo suspended within amniotic sac
• pull connective stalk vertically

Creates the primordium of the gut from the yolk sac, puts the heart snd primordium of the diaphgram in the right place creating a new cavity within

Question 10

Describe the differentiation of the somites into dermatone, myotome and sclerotome and the fate of these in ,ater development

Answer 10

Organaised degradation of somites forms sclerotome
Further organaisation of the dorsal portion forms the dermomyotome
Myotome proliferates and migrates and the dermatome disperses

Dermatome - skin(dermis)
Myotome - muscle
Sclerotome - hard tissue (bone)

Question 11

Explain use of dermatone and myotome when describing innervation of skin and muscles in the adult

Answer 11

Dermatome is strip of skin supplied by a single spinal nerve
Myotome is a muscle group supplied by a single spinal nerve

Neural tube produces nerve that innervates the dermomyotome