Early Embryonic Development III Flashcards
What are the two types of twinning?
Dizygotic
Monozygotic
What are dizygotic twins?
Twins arising form two ova, produced from two separate ovarian follicles and each is fertilzed by a single sperm
What are monozygotic twins?
Twins arising from single ovum fertilized by single sperm
3 ways that monozygotic twins can occur
- Two cell stage pre-implantation of embryo splits with each blastomere going on to produce an embryo with its own fetal membranes - can occur in cattle
- Duplication of the ICM. Twins develop with shared yolk sac and chorion but separate amnions - can occur in sheep
- Trhough formation of two primitive streaks giving rise to two offspring. Share common amnion, yolk sac and chorio. If streaks dont separate can get conjoined twins
5 consequences of twin pregnancies?
High rate of abortion
Poor neonatal viabiliyt
Growth retarded fetuses
Reduced fertility after twin abortions
Dystocia
How can twin pregnancie be dealt with in horses?
Before 40 days of gastration : manual trauma
After 40 days
- Manual trauma
- Ultrasound guided puncture of conceptus
- Surgical removal of fetus (high risk to remaining fetus and mare)
Ultrasound guided injection of the fetus
What is gastrulation?
Stage in the epiblast of cell proliferation, migration and differentiation that results in the formation of 3 germ layers
- ectoderm
- mesoderm
- endoderm
What are the 3 germ layers formed during gastrulation?
Ectoderm
Mesoderm
Endoderm
Explain the ectoderm>
Epidermis of the skin, epithelium of oral and nasal cavities, nervous system and sense organs
What does the mesoderm become?
Muscle, connective tissue including bone, components of circulatory, urinary and genital systems
What does the endoderm become?
Mucosal epithelium and glands of respiratory and digestive systems
What is the morphologicial beginning of gastrulation?
Formation of the primitive streak along the midline
What is ingression?
movement of epiblast cells inward between epiblast and hypoblast
What are ingressing cells known as?
Mesoendodermal cells and are described as mesenchymal
What are cells that inegrate and then displace the hypoblast become?
Endoderm
What is located under the endoderm and hypoblast?
Primitive yolk sac
What becomes intra-embryonic mesoderm?
Mesenchymal cells that move cranially and laterally but stay between endoderm and epiblast
What becomes the extra-embryonic mesoderm?
Cells migrating further laterally between hypoblast and trophectoderm
What does the extra-embryonic mesoderm split into?
Two sheets
- Somatic or parietal mesoderm
- Visceral of splanchnic mesoderm
What does the somatic or parietal mesdorm sheet associate with?
Trophectoderm
What does the visceral of splanchnic mesoderm sheet associate with?
Hypoblast
What is the cavity that forms between somatic and visceral mesoderm call?
Embryonic coelom
Where does primitive node move towards as grastrualtion progresses?
Towards tail
What is important for brain development?
Prechordal mesoderm
4 things to notice at the end of gastrulation?
- Pear shaped embryo
- Embryo with three germ layers
- Embryo with a column of mesoderm - the notochord established a cranial to caudal axis
- Relative to the notochord, the embryo has a right and left side
What are tissues do neural crest cells form?
Melanocytes - pigment cells of the skin
Neurons for central, sympathetic and enteric nervous system
Parts of craniofacial mesenchymal derivatives
- Otic capsul
- Palate
