Early Embryogenesis Flashcards
embryo
organism in early stages of development
conceptus
product of conception
conceptus includes
- embryo during early embryonic stage
- embryo and extra embryonic membranes during preimplantation stage
- fetus and placenta during post-attachment phase
Fetus
A potential offspring that is still within the uterus but is
generally recognizable as a member of a given species
mesoderm
- surrounds the yolk sac and developing allantois
- growing mesoderm pushes against trophectoderm to create the amniotic folds
allantois
collects embryonic wastes
purpose of amniotic fluid
protects embryo or fetus from mechanical perturbation or forces
amnion consists of
trophectoderm and mesoderm
yolk sac forms when
primative embryo completes growth
extraembryotic membranes of pre-attachment embryo consist of:
- yolk sac
- chorion
- amnion
- allantois
yolk sac develops from
primitive endoderm
chorion and amnion both develop from
trophoblast, primitive endoderm, and mesoderm
amnion develops from
trophoblast, primitive
conceptus expansion in cows/bovines occurs through
the continuous production
(hyperplasia) of trophoblasts
conceptus expansion in pigs occurs through
cellular reorganization and remodeling
purpose of conceptus expansion in pig
provides each
conceptus a mechanism to cover the uterine surface
purpose of conceptus expansion in bovines
permits the conceptus to
extend its placental membranes
throughout the uterus and block the
contralateral horn synthesis of
PGF2𝝰 to prevent luteolysis.
equine conceptus (in comparison to others)
remains spherical, doesn’t elongate
intrauterine migration and spacing occurs in
pig
purpose of intrauterine migration and spacing
- to provide space for embryo development and placentation
- to cover the endometrial surface
process of intrauterine migration and spacing
- Embryos spend 2 to 3 days in the proximal portion of the uterine horns,
before becoming more evenly distributed throughout the uterus. - Conceptuses migrate within and between the uterine horns to become
regularly spaced within the uterus. - Establishment of pregnancy requires at least two embryos in each
uterine horn - Modulated by peristaltic contractions of the myometrium stimulated by
the developing conceptus
steps of conceptus expansion
1) spherical
2) tubular
3) filament
Shedding of the zona pellucida allows for
expansion of the spherical blastocyst,
after that time it may migrate and transition from a spherical to tubular and
filamentous form (domestic animals) or remain spherical prior to implantation
(mare, rodents, human)
Periods of Prenatal Development
- Period of ovum or early embryo (culminates with attachment of blastocyst)
- period of embryo (culminates with organogenesis)
- period of fetus (cumulates with birth)
cleavage
series of rapid cell divisions that result in the formation of morula
importance of conceptus Expansion in Bovines
allows conceptus to extend throughout uterus and thus block the synthesis of PGF2a in the contralateral horn (preventing luteolysis)
extra embryonic membranes of pre-attachment embryo consist of
Yolk sac (develops from primitive endoderm)
Chorion (develops from trophoblast, the primitive endoderm and mesoderm)
Amnion (develops from trophoblast, the primitive endoderm and mesoderm)
Allantois (a diverticulum of the hind gut)
During the pre-attachment period, the zone pellucida sheds and then…
the spherical blastocyst is able to expand so that it can either:
- migrate to a tubular/filamentous form (domestic animals)
- or remain spherical (mares rodents, humans)
- or immediately implant within the uterine wall (rodents)
period between zona hatching and implantation in ruminants (cows and sheep/ewes)
1) zona hatching
2) CONCEPTUS ELONGATION
3) implantation
period between zona hatching and implantation in horses
1) zona hatching
2) TRANSUTERINE MIGRATION
3) Implantation
During Symetric Cleavage (cell division) bastomeres…
bastomeres polarize along the axis of cell contact, forming:
- outward, apical domains
- inward facing basolateral domains
During Asymmetrical Cleavage (cell division) blastomeres…
blastomeres that divide parellel to the axis produce: 2 outside polar cells
blastomers that divide perpendicular to the axis produce: one outside polar cell, and one non-polar inside cell
overall, asymetrical cell division (cleavage) produces…
two populations of cells:
- outside, polar cells
- inside, nonpolar cells
assymetric division occurs during
- growth between 8-16 cells
- growth between 16-32 cells
compaction is
an increase in intracellular adhesion
process of compaction
bastomeres flatten upon each other to maximize their baso-lateral contact areas
the process of polarization leads to
the formation of two distinct domains within the cell: apical—enriched with polarity-related proteins, microvilli, dynamic microtubules, and actin; and baso-lateral where more stable acetylated microtubules are localized
define zygotic genome activation
Transcription of mRNA coded by the zygotic genome, so essentially the transition from maternal to zygotic transcripts
Morula
solid ball of cells resulting from division of a fertilized ovum, and from which a blastula is formed
action of estrogen in oviduct
increased: fluid volume and cillilary activity, muscle contraction= promotes embryo transport
Progesterone in Oviduct
decreased: fluid volume, cilliary acivity, muscle relaxation= decreases embryo transport
histology of uterus
1) serosa
2) mucularis
3) endometrium
Histotroph
Endometrial glands that produce/or selectively transport a complex array of proteins and related substances such as: (enzymes, growth factors, cytokines, lymphokines, hormones, transport proteins, sugars, amino acids, water, and other nutrients)
that affect trophectoderm development and function
Blastulation
The process by which the morula becomes a blastocyst which is
characterized by having a fluid-filled cavity called the blastocoel
- Formation of cell junctions: Tight junctions form between the outer cells of the morula; Gap junctions form between the inner cells
- Formation of the blastocoele
- Segregation of cell lineages
Blastocoel Formation
Cavitation: Microlumens are formed in the intercellular spaces within the embryo by exocytosis of vesicles or vacuoles from the basal membrane of the outer cells. Sodium ions are actively transported across the outer cell layer through transmembrane pumps. The differential sodium ion concentration generates an osmotic gradient that enables fluid to be pumped into the embryo, enlarging and coalescing the microlumens into a single cavity.
Segregation of Cell Lineages
Key stage during which major cell lineages of the
embryo and its extraembryonic membranes are formed
Steps invovled in segregating cell lineages
The first lineage decision: segregation of the trophectoderm
(teal color) and inner cell mass (tan color)
The second lineage decision: segregation of inner cell mass
into primitive endoderm/hypoblast (red) and epiblast (yellow)
