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
