Embryology Flashcards
gametogenesis types:
oogenesis (female)
- 2 mil primary oocytes at birth
- 40 000 oocytes by adolescence
spermatogenesis (males)
- after puberty
brief procedure of fertilisation:
- 200-600 mil sperms in cervical os (uterus) after sex
- sperms pass through female reproductive system
- fusion of male and female gamete
- occurs in uterine tube 12-24hrs (after ovulation)
- secondary oocyte viable 24hrs
- sperm 48hrs
oocyte linings:
corona radiata and zona pelucida
zygote
fertilised ovum
dizygotic twins vs monozygotic twins:
dizygotic:
2 secondary oocytes fertilised by 2 sperm
monozygotic:
1 egg, 2 sperm in same placenta but different amniotic sacs
how does conjoined twins occur:
cell separation not within 8 days after fertilisation, may be conjoined
list first week development:
- fertilisation
- cleavage
- morula
- formation of blastocyst
- implantation
when does each occur: first-week development (5)
- fertilisation (12-24 hrs) a.o
- cleavage (30 hrs) a.f
- morula (3-4 days) a.f
- blastocyst (4.5-5 days) a.f
- implantation (6 days) a.f
o-ovulation
f-fertilisation
fertilisation features/ location:
near/ in uterine tube
- muscular uterine contractions help aid sperm
- cervix open during ovulation
- cilia push egg to uterus
define zygote:
fertilised ovum
cleavage features: define morula and name its membrane
- mitotic cell division of zygote, divide every 6 ish hrs
- solid cell mass (morula)
- surrounded by zona pellucida
- doesn’t grow in size
- only increase SA
define/ formation of blastocyst features/ location:
day 4-5:
- morula enter uterine cavity
- uterine milk penetrate morula/ blastomeres and form fluid cavity (blastocyst cavity)
- removes zona pellucida for embedding
hollow sac in cell mass
two layers of blastocyst and brief info:
trophoblast:
- squamous epithelial cells
- nourishes embryo
embryoblast: (inner cell mass)
- shifted to one side, forms the embryo
implantation: features/ location
blastocyst attaches to endometrium of uterus, implants onto posterior wall of uterus
endometrial lining (uterus mucous membrane) after implantation of blastocyst (Decidua)
list second week development:
- trophoblast development
- bilaminar embryonic disc (embryoblast)
trophoblast differentiation:
2 layers:
- syncytiotrophoblast
- cytotrophoblast
syncytiotrophoblast features:
- outer layer, no cell boundary
- secretes enzymes, can deepen in endometrium,
- produce HCG (pregnancy hormone)
placenta: function
- organ of pregnancy (after 28wks)
- exchange of nutrients and waste products btw mother/foetus
- produces hormones to sustain pregnancy
- develops from foetal and maternal sources
placenta: features
fetal surface:
- smooth with amnion membrane
maternal surface:
- bumpy surface where umbilical cord originates from
Bilaminar embryonic disc development: features
embryoblast cells differentiate:
- epiblast (amnion develops)
- hypoblast (yolk sac develops from migration of hypoblast cells)
list third week development:
- gastrulation
- neuralation
- somites
gastrulation: features/ location
3rd wk: differentiates
bilaminar –> trilaminar embryonic disc of 3 germ layers: ectoderm (epiblast), mesoderm (new cells), endoderm (hypoblast)
- thick structure forms near caudal end (primitive streak)
- near cranial end: primitive node, primitive groove
- epiblast cells migrate towards groove -> invaginate and push hypoblast = new endoderm layer
neuralation: features
notochord: rod-like mesoderm cells
- notochord induces ectoderm-> form neural plate
- invagination (end of 3rd wk) = neural grooves and folds
- fusion of neural folds = neural tube (-> brain and spinal cord)
neuralation: neural crest cells
- ‘disobedient’ cells which detach and migrate to help develop
- head and neck structures
- brain lining
- medullar
somites: features
mesoderm: adjacent to notochord/neural tube forms cube shaped structures
each somite has:
- myotome
- dermatome
- sclerotome
myotome somite develops into:
skeletal muscles of neck, trunk, limbs
dermatome somite develops into:
connective tissue, including dermis of skin
sclerotome somite develops into:
vertebrae and ribs
development of cardiovascular system:
early development of this is necessary
- heart tube (splanchnic (viscera) mesoderm = cell differentiation and angiogenesis (new blood vessels))
- heart beat detected by end of 3rd wk
- circulate nutrients/ oxygen around embryo
list fourth week of development:
- organogenesis
- embryonic folding
- pharyngeal arches
organgenesis: features
- embryo 3x size
- major external/internal structures established, main body systems developing
- minimal function though, except CVS
embryonic folding: features
head fold:
- brings adult position of heart and mouth
tail fold:
- adult position of anus
lateral folds:
- bend/incorporate yolk sac into embryo as primitive gut, primordia (earliest organ stage) of GIT
pharyngeal arches: features
- 5 pairs of pharyngeal arches develop
- gives rise to specialised structures in head and neck -> skeletal component, muscle, nerve and blood vessels
define zygote:
fertilised ovum
define morula:
mass of 16-32 blastomeres
define blastocyst:
appearance of cavity between blastomeres
define embryo:
human during developmental period (6th day after fertilisation -> end of 8th week)
define foetus:
human during developmental period (9th week -> end of 40th week)
define neonatal period:
first 28 days after birth
define teratology:
study of abnormal development
causes of congenital malformations: and eg.
defects caused by:
- genetic factors (chromosome abnormalities- Down Syndrome)
- environmental factors (pollution, radiation, drugs, viruses)
foetal alcohol syndrome:
microcephaly (small head), low nasal bridge, short nose, flat mid-face, thin upper lip, micrognathia (undersized jaw)
stem cells: features
unspecialised cells, able to divide infinitely, gives rise to specialised cells
eg. blastocyst in embryo
ectopic pregnancy: features
embryo attaches outside uterine cavity (eg. in fallopian tube) causing scarring, vaginal bleeding may lead to complications (death) if not treated
NTDs: and eg
neural tube defects:
- incomplete closing of neural tube, result in many defects
- Spina bifida: spinal cord sticks out of back
- anencephaly: absence of large portion of brain/ skull
placental previa: features
placenta attaches inside the uterus but over/ near cervical opening, vaginal bleeding (no pain), foetal growth restriction
- usually Caesarean section
