Early embryology Flashcards
Zona pellucida:
thick basement membrane-like structure immediately surrounding ovum after its release
Results of fertilization
o 2nd meiotic division completed o Restores diploid number o Variation of species o Sex determination o Initiation of cleavage
Cleavage
1st stage of rapid cell division after fertilization
- Results in compaction since cells divide and do not grow, but become progressively smaller
Trophoblast
involved in implantation, it is the ring around the blastocyst; becomes the fetal part of the placenta
Embryoblast
-part of blastocyst that will become the amnion, embryo and yolk sack
Hypoblast-
endodermal layer of the embryoblast
Epiblast-
ectodermal layer of embryoblast
Cytotrophoblast-
outermost ring of that differentiates from the trophoblast of the embryoblast after initial implantation
Syncytiotrophoblast
- differentiates from the trophoblast and invades endometrium and uterus
Implantation-
occurs approximately 6-8 days after ovulation; superior, posterior wall of uterus is ideal location
Placenta/plakuos
- Multifunctional, temporary organ
- Nutrient, gas exchange
- Protection
- Hormones (endocrine)
- Umbilical cord attaches embryo/fetus to placenta
- Complete separation of fetal and maternal blood
- Highly vascular structure with maternal blood bathing the fetal villi
- Development progesses until approx. the 7th month
- Full term – consists of chorionic villi from embryo and decidua basalis from mother
Decidua
– the uterine lining during pregnancy formed due to progesterone
- decidual change in the endometrium
- forms highly characteristic cells
- Becomes the maternal part of the placenta
- This plus the trophoblast becomes the placenta
- Has 3 parts: basalis, capsularis, and parietalis
Decidua basalis
- majority of placenta
- At base of placenta/trophoblast
Decidua Capsularis
- capsule around embryo: will eventually disappear
Decidua Parietalis
-forms the rest of the uterus
Bilaminar disc-
14 day embryo before gastrulation; consists of endoderm and ectoderm and has the primitive streak that starts with the primitive node
Trilaminar disc
-after gastrulation, the embryo has 3 layers, the ecto, meso and endoderm
- 3 areas do not form trilaminar membrane:
o Oropharyngeal or buccopharyngeal membrane
o Cloacal membrane
o Notochordal process
Primitive streak, node
- node is first indication of primitive streak-invagination of the bilaminar disc; these are cells that congregate on the central dorsal aspect of the embryo ectoderm; ectodermal cells migrate into the primitive streak through the bilaminr disc to form the mesoderm
Neural plate-
- Formation (neurulation) induced by notochord that forms during gastrulation
- formed from neuroectoderm
o thickening of ectoderm over notochord=neural plate - folds over to form neural tube that becomes sealed neural tube
o begins closing during 3rd week
o complete closing of cranial neuropore on day 26 and caudal neuropore on day 28 - forms brain and spinal cord and PNS (formed from ECTODERM)
Neural crest-
- group of cells that separate from the neural plate
- form much of head and neck musculature and bones by migrating to the arches
- also forms peripheral neural ganglia, melanocytes in skin and part of the adrenal gland
- smooth muscle cells, osteoblasts/clasts, adipocytes, chondrocytes, schwann cells and neurons
Notochord
- Forms during gastrulation
- Adds rigidity to embryo
- Induces formation of the nueral tube
- Disappears except for remnants in the nucleus pulposus of intervertebral discs
Folding (lateral and cranio-caudal)
- Lateral
o Folding of nueral plate to form neural tube
o Amniotic cavity folds around embryo and yolk sack forming gut - Cranio-caudal
o Cranial and caudal portions of embryo fold inward forming a C shaped embryo
Anterior neuropore-
at the caudal region of the neural tube- closes on day 26
Posterior neuropore
- posterior of the neural tube- closes on day 28
Holoprosencephaly-
caused by halted formation of anterior neuropore
Stomodeum-
future oral cavity/primitive mouth- location of buccopharyngeal membrane
Buccopharyngeal membrane-
at the stomodeum- only 2 layers, no mesoderm-ruptures to form oral cavity
Cloacal membrane-
membrane at the caudal portion of gut- only 2 layers, no mesoderm- ruptures to form anus
Dichorionic/diamniotic
Cleavage of morula at days 1-2
Monochorionic/diamniotic
Cleavage of blastocyst at days 4-8
Monochorionic/monoamniotic
Cleavage of implanted blastocysts at days 8-12
-Creates mirror image twins
Conjoined twins
Cleaved after formation of embryonic disc from days 12-15
-Names after area attached (pagos-fixed)
Down syndrome-trisomy 21
- Slanted palpebral fissures, epicanthal folds, flat nasal bridge
- Protruding tongue
- Mental deficiency
- CHD
- Simian crease
- macroglossia
- slanted palpebral fissures,
- epicanthal folds,
- flat nasal bridge,
- Protruding tongue ,
- Most common chromosomal abnormality in children
- 1-2/1000 live births
- 80% of cases due to maternal non-disjunction and Robertsonian Translocation
- Risk of non-disjunction increases with maternal age
Edward syndrome-trisomy 18
- Micrognathia
- Clenched fists
- Rocker bottom feet
- Short sternum
- Narrow pelvis
- VSD
- Mental deficiency
- Growth retardation
- 1/7000 live births
- Death by 2 weeks of age
- Robertsonian Translocation
-Patau syndrome – trisomy 13
- Mental deficiency
- Growth retardation
- Bilateral cleft lip/palate
- Malformed ears
- CNS malformations
- Omphalocele – intestines coming out of abdomen
-1/29,000 live births
-Death typically before 1 yr of age
-Robertsonian Translocation
and nondisjunction
-Bilateral cleft lip/palate - Malformed ears
- CNS malformations
- Omphalocele
Ectoderm
- Gives rise to: o Epidermis and its derived structures: hair, nails & sweat glands o Nervous tissue – brain and SC o Lining of mouth o Tooth structures
Endoderm
- Gives rise to:
o Lining of pharynx
o Respiratory tract
o GI tract
Mesoderm
- Gives rise to: o Most of muscles o Bones o Connective tissues o Blood vessels o Heart o blood
Teratogen- factors
- Heredity – abnormal genes (e.g. trisomies)
- Chemicals and drugs (e.g. thalidomide)
- Alcohol
- Abnormally high hormone levels
- Vitamins (A)
- Irradiation (e.g. X-Rays, fallout etc.)
Thalidomide
- claimed to cure “anxiety, insomnia, gastritis, and tension”.[3] Afterwards it was used against nausea and to alleviate morning sickness in pregnant women.
- Caused limb deformities
