Elongation fo the extra embryonic membrane
- Trophoblast filled up uterus completely
- If filling up uterus going to fill up shape of uterine wall
- End up with elongated sigar shaped trophoblast with embryonic disk somewhere in the middle of it
- Within trophoblast is hypoblast which also follow the trophoblast
- Everything is cocuring on ebryonic disk
Neural tube formation
- Neural tubes form from an axial thickening of the ectoderm and all the nervous stuff originates frome ctordoerm
- On top of the embryo overlying the notochord
- Localised thickening running above the neural chord
- Notochord guides development
- Increase in thickness locally above the notochord inneural plate
- And somites are slowly pushing the neural plate higher and higher to form neural folds ending up wth a v shape and eventually moves together and forms a neural groove and a secondary proliferation of neural crest cells which put autonimc, sympathetic and parasympathetic nervous system.
- Organised segmentally
- Neural tube seasl with neural crest on either side with epidermis over the top of the tube.
- Cranial and caudal ends bth open initially, closure progresses rom middle block of somites which push the neural block up first
- Cranial part becomes the hind brain (most primitive aprt of the brain)
- Failure to close is spina bifida
- Fo critical importance
Extra embryonic membranes
- At the same time as crest is forming, other things are happening, our layers of ectoderm and somatic mesoderm and endoderm and spanchnic mesoderm have 'run off' to the side
- Somatopleure keep growing really fast
- Eventually fold takes place
Chorion Development
- If amnion fuses gget separate layer called chorion which is the outer skin of the whole of the embryo and was trophoblasts and with the new mesoderm becomes the chorion and with the amnion is called the choroamniotic fold.
- Chorioamniotic raphe
- Horses are one of the few mammals that rely on yolk sac nutrition for about 17 days and a lot of failure in that time due to yolk sac problems, yolk sac is extremely important in horses.
Tubular embryo
- Sside of the animal starts to fold down as part of the same organisation of the devleopment of the amnion
- Lateral folds and head folds
- This folding creates the space and the feature of the ceolomates, animals with cavities.
- Holocylindrical embryo with gut tube down the middle in which all future gut development takes place.
- Neural plate attached to outermost ectoderm
- Formation of diapharmg arises from head fold
- Underfold carries through cardiogenic plate where cardiac system is born and is derived from
- Brings ventrally and caudlly underneath the embryo
- Plate thickens and becomes developing heart
- Cranial nerves are only named because they come out of somitomeres out of the head and the brnachioplexus
- Cranial nerves travel through body
Tail fold
- Ocurs as aprt of the same process as the head fold and forms the hind gut while the head fold forms the foregut
- Continues to grow and pushes in further and further into the layer that was the splahcnopleure (hypoblast and mesoder) and is pushing inwards and closes the space further and further off and the ventrum fuses in the midline.
- From coalescing splanchopleure
- Dorsal mesentary (along whole length)
- Ventral mesentary
- Only midgut has dorsal mesentary)
Learn More
Embryology Made Easy
Veterinary Developmental Anatomy
Embryology Animations
Simbryo