embryology Flashcards
what are the testis tubules called?
seminiferous tubules
what are the cells in the seminiferous tubules called?
spermato gonia
what do the follicles in the ovary contain?
oogonia, which divide to form an ovum
how many chromosomes do gametes (sperm and ovum) have combined?
46
44 autosomes (not sex)
1 pair of sex chromosomes
xy in male, xx in female
what is a morula?
a solid ball of cells
what 2 lots does morula divide into?
trophoblast - the outer lining of cells
blastocyst - inner cell mass
what structure helps the blastocyte travel to the uterine cavity?
ciliated epithelium
what is an ectopic pregnancy?
damaged ciliated epithelium prevents the zygote from moving down the uterine tube leading to implantation outside the uterine cavity
what does the trophoblast form?
2 layers, forming chorion
what are the chorion finger-like processes called?
chorionic villi
what are the 3 functions of chorionic villi?
- helps the implantation process
- forms part of the placenta
- secretes human chorionic gonadotropin (HCG)
–> used to detect pregnancy
what is the uterine wall (endometrium) called after implantation?
decidua basalis
what are the 3 functions of the placenta?
foetal nutrition
transport of waste and gas
immune system
during the second week, the blastocyst flattens itself into what 2 layers?
epiblast - top layer
hypoblast - bottom layer
what divides the blastocyst cavity?
2 layer flat disc/ bilaminar disc
what 2 cavities are formed from the blastocyst cavity?
amniotic cavity - top layer
yolk sac - bottom layer
what is the primitive streak that’s formed in the 3rd week? what is its function?
formed in midline of epiblast by dipping of cells
gives embryo axis - helps to identify if anterior, posterior etc.
Why do epiblast cells sink from epiblast?
to form a new layer between epiblast and hypoblast
what are the three germ layers (gastrulation) formed from cells replacing hypoblast? In descending order
ectoderm
mesoderm
endoderm
How is the notochord formed? What is the function of the notochord?
cells from primitive streak sink to form notochord which sits between the meso and endoderm
notochord induces ectodermal cells in the midline to form a neural tube
describe neurulation(neural tube formation)
Thickening of the neural plate in ectoderm sinks down
2 neural crests come together to form a neural tube, which gets disconnected from the ectoderm
forms the brain and spinal cord
what 3 parts is the mesoderm split into?
- paraxial mesoderm
- intermediate plate mesoderm
- lateral plate mesoderm
what 2 arms does a lateral plate mesodermal split into?
Somatic mesoderm
splanchnic mesoderm
What is the cavity between the somatic and splanchnic mesoderm called?
intraembryonic coelom/ cavity
what are somites formed from?
paraxial mesoderm
how many somites are there?
44 initially
35-37 Finally
What three structures does each somite divide into?
dermatome
myotome
sclerotome
where does dermatome migrate to and form?
migrates to underneath ectoderm
- dermis of skin
where does myotome migrate to and form?
different regions
- muscles
where does sclerotome migrate to and form?
neural tube
- bones
in weeks 4-8, what does the neural tube form?
forebrain, midbrain, hindbrain and spinal cord
define teratology and teratogens:
Teratology - the study of when things go wrong during development
Teratogens - environmental factors that cause abnormal development
list some teratogens:
alcohol & smoking
drugs
pathogens
radiation
what weeks embryo development has the least and greatest sensitivity to teratogens?
Weeks 1-2 of pre-embryonic phase:
high risk of death (abortion), so less risk of a fetus born with teratogens.
Weeks 3-8 of embryo development: the periods of greatest sensitivity to teratogens.
Weeks 9-38 of embryo development: have decreasing sensitivity to teratogens.
what 3 factors does risk posed by a teratogen depend on?
Exposure during critical periods of development
Dosage of drug/chemical/factor
Genetic constitution of embryo
state 3 prenatal diagnosis of malformations:
Maternal Blood - Alpha Feto Protein
Ultrasound scan – 12 week anomaly scan
- Invasive tests: chorionic villus sampling and amniocentesis
