Mod 5 - Embryology & Development - Part 3

Two ways amniotic cavity folds around germ layers

Longitudinally (lateral folds) and medial fold

What does the lateral fold form into

Gut tube, Coelom within mesoderm

What does the median fold form into

makes a head (cephalic) and tail (caudal) fold, allantois

Coelom

body cavity lined with mesoderm

What happens on day 20

Lateral and median plane folds begin to fold around germ layers

What happens on day 25

Folds of amniotic cavity come closer together

Cloacal and oropharyngeal membrane come in contact with amniotic cavity

Allantois

will become bladder

What happens on day 30

Lateral folds fuse amniotic cavity and ectoderm around the embryo, and gut tube which extends from oropharyngeal to cloacal membrane

Evaginations from gut tube form

Evaginations from gut tube

Anterior pituitary, thyroid gland, lungs, liver, pancreas

Timeline of limb bud development

24-28 days

Order of limb bud development

1. Blood supply built

2. bone structure

3. muscle and nerve supply

apical ectodermal ridge

thickening of the ectoderm - stimulates outward growth of limbs

Which direction is limb tissue laid down

proximal to distal sequence

How long does it take to grow all digits

7 days

What is Apoptosis and when does it occur

Webbing in between digits gets removed / week 8

What is thalidomide

A drug that inhibits the formation of blood cells

Why does thalidomide cause birth defects?

Mothers take the drug for morning sickness and it would stop blood supply from following the tissue in the limb bud. Then when mothers went off it, the limb would grow but it skipped the middle portions of the limb

Skeleton

develops from mesodermal or neural crest cells

myoblasts

stem cells that fuse to form each muscle fiber / migrate wherever muscle needs to be built

Nervous system

derived from neural tube and neural crest cells