Early Embryogenesis and Maternal Recognition of Pregnancy

terms

syngamy: fusion of the male and female pronuclei

after this the zygote becomes an embryo

embryo has not acquired an anatomical form that is readily recognizable in appearance as a member of the specific species

embryo: an organism in the early stages of development

fetus: a potential offsprings that is still within the uterus, but is generally recognizable as a member of a given species

conceptus: product of conception

the embryo during the early embryonic stage

embryo and extraembryonic membranes during the preimplantation stage

the fetus and placenta during the post-attachment phase

four steps the need to happen before the embryo can attach to the uterus

hatching of the blastocyst from the zona pellucida

maternal recognition of pregnancy

Development within the confines of the zona pellucida

formation of the extraembryonic membranes

ootid: when male and female pronuclei can be observed, the cell

one of the largest single cells in the body and is characterized by having an enormous cytoplasmic volume relative to nuclear volume

blasomeres: first cleavage division generates a two celled embryo

totipotent: used to describe the ability of a single cell (blastomere) to give rise to a complete, fully formed individual

morula: when a solid ball of cells is formed and individual blastomeres can no longer be counted accurately, the early embryo

hatching of the blastosyt is governed by three forces

Production of enzymes by the trophoblastic cells

contraction of the blastocyst

growth and fluid accumulation within the blastocyst

development of the extraembryonic membranes represents an "explosion" of embryonic tissue growth prior to attachment

the extraembryonic membranes of the preattachment embryo consist of the

chorion

amnion

yolk sac

allantios

extraembryonic membranes: dramatic growth of the conceptus is due largely to the development of a set of membranes

allantois: fluid-filled sac that collects liquid waste from the embryo

allantochorion: fetal contribution to the placenta and will provide the surface for attachments to the endometrium

in most species, the conceptus must provide a timely biochemical signal or the preganacy will terminate

maternal recognition of pregnancy must occur prior to luteolysis

a successful pregnancy requires maintenance of high blood progesterone concentrations

embryo transfer technology provides avenues for reproductive and genetic enhancement

embryo transfers require set of procedures that allows removal of pre-attachment embryos from the reproductive tract of a donor female and transfers them into the reproductive tract of a recipient female

advantages of embryo transfer are

circumvention of seasonal reproduction

enhanced generation of offspring in monotonous species

assisted reproduction for infertility in humans

enhanced reproductive potential of endangered species

enhanced genetic diversity across a wide geographical region (ship embryos rather than animals)

successful embryo transfer involves

recovery of embryos from the donor

maintenance of viable embryos in vitro

artificial insemination of the donor female

transfer of embryos to recipient females

superovulation (hyperstimulation of the ovaries) of the donor

synchronizing the cycles of donors and reciepients

superovulation results from hyperstimulation of the ovaries with gonadotropins

superovulation: treatment of a female with gonadotropins (typically FSH) to increase the number of oocytes that are selected to become dominant follicles and the ovulate

recovery of oocytes from ovaries can be accomplished by

surgically exposing the ovary and aspirating follicles

non-surgically aspirating follicles utilizing ultrasonography

aspirating follicles postmortem in an abattoir

recovery of embryos from the donor females may be accomplished in several wasy

recovery of embryos from the oviduct requires surgery in all spaces

oocytes can be recovery directly from the ovary using aspiration with a hypodermic needle

embryo viability must be maintained in vitro

in order for embryos to be transferred successfully into recipient females they must be stored in an environment that maintains viability

embryos can be frozen successfully for long term storage

transfer of embryos can be accomplished surgically or non-surgically

zona pellucida is an important component of the early embryo

embryo transfer procedures have become very successful