module 4: embryology and development part 2

bilaminar embryonic disk

1. epiblast cells (top layer): they become the embryo - 3 germ layers

2. hypoblast cells (bottom layer): does not become the embryo - instead it helps for extra embryonic tissues (alongside amniotic sac and syncytiotrophoblast cells)

amniotic cavity

• forms inside inner cell mass and surrounded by layers of cells called amnion or amniotic sac

• eventually surrounds the entire embryo providing a protective layer

amniotic sac

eventually surrounds the embryo

yolk sac

forms inside blastocle (blastocyst cavity) from hypoblast

FORMATION OF GERM LAYERS

gastrulation

• day 13 - 14

• going from epiblast layer and turning into 3 germ layers 

• epiblast layer gets longer

primative streak

thickened region of cells that half the length of the epiblast

cephalic end

• the head end of the developing embryo - furthest away from the primitive streak 

• has the notochord 

caudal end

tail end of the developing embryo - closest to the primitive streak

ectoderm layer

• forms skin and most of the nervous system

• outer layer

• brain

mesoderm layer

• forms blood supply, bones, and muscles 

• middle layer

• notocord

endoderm layer

• forms digestive tract and derivative (things that branch off digestive tract)

• inner layer

• lining of the GI tract

FORMATION OF NOTOCHORD

• day 16

• from mesodermal cells

• solid cylinder of cells under ectoderm

induction

sends a signal from the mesoderm to the ectoderm layer to form the neural plate

neural plate

• a thicken region of ectoderm layer that surrounds the notochord

• becomes the spinal cord and brain

oropharyngeal membrane

becomes the mouth

cloacal mebrane

becomes the anus

FORMATION OF THE NEURAL TUBE

mesoderm layer 

steps of forming the neural tube

1. neural plate

   • the lateral sides begin to rise (to form nural folds)

   • starts to form neural groove

2. neural folds become higher and groove becomes larger, crest of neural folds begin (theyre trying to form the tube)

3. crest of the neural fold become closer together and some break off forming something called neural crest cells

4. neural tube is formed - forming spinal cord and brain!! we get a layer of skin aswell and those neural crest cells break off and can form into parts of the nervous system

neural tube

forms the brain and spinal cord (central nervous system)

neural crest

• PNS (peripheral nervous system)

• they form sensory nerves

• autonomic nervous system (post ganglion)

• general connective tissues of the head (skull bones)

somites

• they are formed from mesoderm

• theyre adjacent to the neural tube and bilateral 

• eventually become vertebral column, ribs, some skeletal muscle