Embryology Flashcards
What does the mesoderm form?
skeletal, connective and muscle tissues
What does the endoderm form?
lining of gastrointestinal and respiratory systems
What do the somite differentiate into?
Dermatome, myotome and sclerotome
What are somites?
Paired blocks of tissue on each side of the notochord (formed from paraxial mesoderm)
How many pairs of somites are formed?
42-44 pairs (end up being 38)
What are the three layers of mesoderm called?
- paraxial mesoderm
- intermediate mesoderm
- lateral plate mesoderm
What condition arises if the cranial (anterior) neurpore doesn’t close?
Anencephaly
What condition arises if the caudal (posterior) neuropore doesn’t close?
Spina Bifida
What are the functions of neural crest cells?
they contribute to formation of the PNS
What is neurulation?
the process of the formation of the brain and spinal cord
Describe the formation of the notochord.
- cells derived from the primitive node migrate cranially towards buccopharyngeal membrane resulting in notochord plate
- notochord plate folds and forms notochord
Name 2 places where the original two germ layers remain intact in the formation of the trilaminar disc.
- prochordal plate (at cephalic end) - becomes buccopharyngeal membrane
- cloacal plate (at caudal end) - becomes cloacal membrane
Describe the formation of the intra-embryonic mesoderm.
Cells of the ectodermal layer migrate towards the primitive streak and detach from it, spreading laterally beneath it
What is the primitive streak?
Groove-like midline depression in the caudal end of the bilaminar embryonic disk
What does the ectoderm form?
epidermis and the nervous system, neural tube, neural crest
Describe the formation of the trilaminar disc
The epiblast becomes the ectoderm and the hypoblast becomes the endoderm. The intra-embryonic mesoderm is formed through the invagination of epiblast cells.
Define gastrulation.
The formation of the trilaminar embryonic disc from the bilaminar embryonic disc
What is the role of HCG and what creates HCG during the pre-embryonic stage
HCG maintains the corpus lute (so progesterone can be made), and it is produced by the syncytiotrophoblasts
What is the role of lacunae in implantation?
Communicate wit the maternal endometrial sinusoids, thereby deriving nutritional support for developing embryo
What is the role of the primary yolk sac?
Source of nutrition, theorised to also form some of early vascularisation
What are the roles of amnioblasts?
Secrete amniotic fluid
Describe the implantation process.
- Initiates the decimal reaction in the uterine storm (cells contribute to maternal components of placenta)
- trophoblast differentiates: inner part becomes single-layered cytotrophoblast, invasive layer called synctium
- synctium called synctiotrophoblast when it invades endometrium but not endometrial blood
- ICM becomes epiblast and hypoblast - the bilaminar embryonic disk
Where does fertilisation take place?
Ampulla of the uterine tube
What is the blastocyst composed of?
- trophoblast
- blastocoele
- Inner Cell Mass (ICM)
