Embryology Flashcards
What is the difference between gestational age and fertilisation age?
Gestational - Time since last period
Fertilisation - Time since fertilisation
What are the 2 periods?
Embryonic period = 0-8 weeks (fertilisation age)
Foetal period = 9 weeks-Birth
What are the 3 trimesters?
0-13 weeks
14-26 weeks
27-40 weeks
What is the morula?
A stage where to embryo is 12-16 cells in total
Inner cell mass collects at one pole and forms the embryoblast
Outer cell mass flattens to form the trophoblast
What is the Blastocyst?
Embryo is 6 days old sat beginning
Trophoblast splits into 2 layers - Cytotrophoblast and syncytiotrophoblast
What happens at day 9?
The embryo is now embedded
Inner cell mass forms the bilaminar disc - Hypoblast and Epiblast
Umbilical vesicle is evident
Amniotic cavity begins to form from epiblast
What happens at day 13?
Extraembryonic ceolom pinches off the primary umbilical vesicle forming the secondary umbilical vesicle (this is incoorpotated into embryo)
What happens to the Bilaminar disc at the end of week 2?
Forms the trilaminar disc - Ectoderm, Mesoderm, Endoderm
Primitive streak begins to form and the cells migrate towards the streak and move beneath (invagination)
Some cells replace the hypoblast and form the endoderm
Some remain between the hypoblast and the epiblast and form the mesoderm
Some remain in the epiblast and form the ectoderm
What does the ectoderm form?
Neuroectoderm - CNS, nerves, Retina, Posteria of pituitary gland, Pharyngeal arch and cartiage
Surface ectoderm - Skin, hair, nails,mammary glands, cutaneous glands, anterior of pituitary gland, teeth, ear, lens of eye
What does the mesoderm form?
Muscles, Connective tissues, linings of cavities, Urogenital, Cranium
What does the endoderm form?
Internal organs
Lymphatic system
What is neurulation?
3-4 weeks
Notochord induces thickening to produce the neural plate
The neural plate lengthens and the lateral edges elevateto for meural folds
Neural folds migrate ventrally and meet in the midline and fuse craniocaudally (think zip)
Trunk region forms - Melanocytes, sympathetic neurones, ganglions and schwann cells
Cranial region forms - Glial cells, connective tissues of face and skull, neurones of cranial ganglia
What changes occur in the mesoderm?
Mesoderm forms 2 sections - paraxial mesoderm (thickened area in medial area).
lateral plate mesoderm - 2 subtypes (Somatic and Visceral)
What is somatogenesis?
3-5 weeks
Somites form either side of neural tube in pairs
3 different forms - Sclerotome (vertebrae and ribs). Myotome (Skeletal muscle of back and limbs). Dermatome (dermis for skin of back and body wall)
What is lateral folding?
Week 4
Formation of paraxial mesoderm causes the ventral movement which leads to the pinching off of the yolk sac leading to the vitelline duct
It then pinches it off completely and the gut forms internaly and the external yolk sac slowly deteriorates
