module 5: embryology and development part 3

when does embryonic folding and gut formation occur?

day 20

longitudinal fold (lateral)

• folding along the length of the embryo

• forming the gut tube from the endoderm

• they start to pinch off the endoderm from the yolk sac

• the coelom forms within the mesoderm - becomes body cavities

• ectoderm layer - forms the skin

medial fold

• to make head and tail fold

• foregut and hindgut

• allantonis - will form part of the bladder (day 20)

3 layers derived from the trilaminar embryonic disk are called?

1. ectoderm

2. mesoderm

3. endoderm

ectoderm

• the outer most layer

• forms our skin

mesoderm

• located between ectoderm and endoderm 

• forms muscle, bones and circulatory system

endoderm

• the inner most layer

• responsible for the formation of the gastrointestinal tract, digestive tract

• as folding continues moves toward the midline and fuzes causing the primitive gut tube

primitive gut tube

• foregut

• midgut

• hindgut

foregut

• at the cranial end

• temporarily closed by the oropharyngeal membrane which ruptures around week 4 to form the mouth

midgut

• between foregut and hind gut

• stays connected to the yolk sac until the 5 week of development

hindgut

• caudal end of embryo

• temporarily closed by the cloacal membrane which ruptures during the 7th week of development to form the anus

by day 30

• lateral folds fuse to form

  • amniotic cavity which surrounds entire embryo

  • gut tube which extends from the oropharyngeal to the clocal membrane

• evaginations from the gut tube

  • anterior pituitary, thyroid gland, lungs, liver, pancreas, auditory tubes

• brachial arches

  • pharynx, auditory tubes, thymus, parathyroid gland

• coelom

  • fuses first around the heart as the pericardium cavity

  • expands to become the pleural and peritoneal cavities

  • cavities eventually become separate 

LIMB BUD DEVELOPMENT

upper limbs develop when?

they develop around day 24

lower limbs develop when?

they develop around day 28

what does limb bud mean

essentially its know as the apical ectodermal ridge and its job is to thicken the ectoderm - which will stimulate outward growth

limb building starts from what?

starts from proximal to distal

arms it takes 7 weeks to form

what is apoptosis?

its pre-programed cell death

what does the sonic hedgehog protein do?

helps stimulate limb bud growth

THALIDOMIDE CASE STUDY

what was it?

what was thalidomide?

a drug prescribed to woman in the 1950 to help with morning sickness but actually ended up giving babies birth limb defects

why did the limb defects happen?

this happened because the thalidomide inhibits the formation of blood vessels causes babies to have very shorten limbs

SKELETON, MUSCLE AND NERVES 

skeleton

• develops from the mesoderm layer or neural crest cells

• our skeleton develops as a cartilage skeleton first which causes our embryo to become very flexible 

muscle

myoblasts - derived from somites are early embryonic cells that develop into skeletal muscle fibers 

nervous system

derived from the neural tube and neural crest cells