Embryology Introduction Flashcards
When is the pre-embryonic phase?
0-3 weeks
When is the embryonic phase?
4-8 weeks
When is the foetal phase?
9-40 weeks
How are the gametes sperm and ovum produced?
Spermatogonium and oogonium due to meiosis
Describe fertilisation
Several sperm surrounds ovum, only one penetrates - (pro) nucleus of the sperm enters and fuses with the (pro) nucleus of the ovum to give diploid cell - Zygote
What is a summary of week 1 of pre-embryonic phase?
Zygote is formed and divides to form a blastocyst
Moves through uterine tube and reached uterine cavity
What is the first cell of the body?
Zygote
How is morula formed?
A solid ball of cell formed by mitosis of cells from zygote
Describe a zygote
First cell in the body - 23 chromosomes of mum and 23 of dad
Mitochondria and cell organelle from mum
Who are mitochondrial diseases inherited from?
Inherited from the mother
What is the blastocystic cavity?
Cavity develops as morula increases with number of cells - nutrition to central core starts becoming difficult
Describe a blastocyst
Has blastocystic cavity
Cells accumulate at one end to form an inner cell mass
Outer layer of cells is called the throphoblast
Describe timing of zygote to blastocyst
Ovum released from ovary
Fertilisation in fallopian tube
Zygote
Then after 3 days morula
By day 5 morula reached inside of uterus cavity an becomes blastocyst
What is lining the uterine tube?
Cilia
How could an ectopic pregnancy occur?
If cilia function is abnormal
What is the summary of week 2 of pre-embryonic phase?
Implantation occurs in the uterine endometrial layer and placenta begins to develop
Cells that later form embryo form a bilaminar disc
Sacs, membranes and cord to nourish the human conceptus start to form
Describe trophoblast forming chorion?
Trophoblast divides to form 2 layers - chorion
Develops finger like processes called chorionic villi
What does a chorion do?
Implantation process - chorionic villi burry into endometrium
Forms part of placenta in due course
Secretes human chorionic gonadotropin (HCG) used to detect pregnancy
When does implantation begin?
At 7 days blastocyst begins to burrow into uterine wall and chorion plays important role in burrowing
What is the decidua basalis?
Part of the endometrium deep to the implanted conceptus
Describe endometrium after implantation has occurred?
Has myometrium, endometrium and decidua basalis (with maternal blood vessels)
NCG secreted by chorion to help maintain decidua
Maternal blood levels of HCG increases at 12 weeks gestation
What happens to the inner cell mass of blastocyst?
Cells of inner cell mass form a 2 layered flat disc called a bilaminar disc and 2 cavities begin to form
What are the cavities which from from bilaminar disc?
Amniotic cavity with epiblast
Yolk sac with hypoblast
What are the main functions of the placenta?
Foetal nutrition
Transport of waste and gases
Immune etc
Describe the foetal part and surface of the placenta
Smooth with foetal blood vessels and end of umbilical cord
Describe the maternal part of the placenta
decidua basalis of endometrium is rough and has maternal blood vessels
When does placenta mature?
18-20 weeks
What are the two types of twins/multiple births?
Fraternal/ dizygotic
Identical/ monozygotic
What is a summary of week 3 of pre-embryonic phase?
Formation of the germ layers - gastrulation
Formation of the neural tube - neurulation
Development of somites
Early development of cardiovascular system
What is the primitive streak?
Formed in the midline of the epiblast by dipping in of cells - invagination
Once forms then axis of the embryo is formed
Describe gastrulation
Formation of 3 germ layers
Epiblast cells migrate to lie in between epiblast and hypoblast layers
Cells then displace hypoblast and forms 3 germ layers
Trilaminar disc is formed
What are the 3 layers formed making the trilaminar disc?
Ectoderm
Mesoderm
Endoderm
What does each germ layer form?
Ectoderm - epidermis of skin and nerves
Mesoderm - heart muscle, bones and connective tissue
Endoderm - respiratory system and gut
Describe the process of neurulation
Neural tube formation
Notochord formation - cells sink down from primitive streak to form solid tube then notochord
Then a neural plate in the ectoderm which sinks down to form neural tube and notochord induces ectodermal cells in midline to from a neural tube
What is the effect of neural tube on the mesoderm?
Mesoderm thickens and separates into 3 parts and lateral plate mesoderm splits
What are the 3 parts the mesoderm splits into called?
Paraxial mesoderm
Intermediate plate mesoderm
Lateral plate mesoderm
Describe formation of somites?
Paraxial mesoderm forms somite formation - 43 pairs of somites
What are the names of the 3 divisions of the somite?
Dermatome
Myotome
Sclerotome
What does each division of somite develop into?
Dermatome - dermis of skin
Myotome - muscles
Sclerosis - bones including the vertebrae
When does the heart start to beat?
Days 24
What does the intermediate plate mesoderm form?
Urogenital system - kidneys and repro.
What does lateral plate mesoderm form?
Body cavity and coverings
What happens during the embryonic/ organogenetic period?
Folding into a tube - lateral folds
Neural tube forms forebrain, hindbrain, spinal cord
Gut formation
Limb buds from
Neck development
What is teratology?
Study of when things go wrong during development
What are teratogens?
Environmental factors that cause abnormal development
How can you diagnose malformations prenatally?
Blood - AFP
US scan at 12 weeks
Invasive tests - chorionic villus sampling and amniocentesis
How can you diagnose malformation postnatally?
Hip stability
Testes
Fingers and toes
Hearing
