Embryology

Defintions

Embryogenesis - formation of body structures and organs

Embryonic period - time period from fertilization to earliest stages of organogenesis

Fetal period - time period between the embryonic period and parturition in which organs grow and begin to function

Fertilization - union of two haploid gametes to form a diploid zygote

Clevage - series of mitotic division increasing in cell number, but not cell size

Blastomere - daughter cells formed by mitotic divisions of a large zygote

Morula - compacted zygote created in late clevage; solid ball of blastomeres within a zona pellucida (pluripotent stem cells)

Holoblastic clevage - the egg divides into seperate blastometes (whole cell divides)

Meroblastic clevage - incomplete clevage; only a portion of the egg divides due to large yolk

Cell differentiation - result of cell expressing some genes and suppressing others within a common genome

Blastulation - process that a morula (pluripotent stem cell) will undergo; beginning of cell differentiation

Outer blastomere - becomes flattened and develops the capacity to secrete fluid (trophoblasts)

Inner blastomeres - from gap junctions to maximize intercellular communication (inner cell mass; embryoblasts)

Blastocyst - consists of a large number of blastomeres arranged to form a hollow, fluid-filled, spherical, or cylindrical structure

Gastrulation - Begins with a blastocyst and the formation of the embryonic disc; inner cell mass begins to differentiate (hypoblasts and epiblasts)

Embryonic disc - group of thickened cells (made by embryoblasts) that degrades trophoblast cells overlaying the inner cell mass layers

Primitive streak - forms as cell growth creates a pair of ridges seperated by a depression on the epiblast surface

Notes

Embryogenesis requires cell division and differentiation (proliferation and specialization); produces variety of cell types and extracellular bodily products

Fertilization ends with the initiation of mitosis (clevage)

Fusion of a spermatozoon with an oocyte takes place in the uterine tube near the ovary, binds to glycoprotein on the zona pellucida surrounding the oocyte - spermatozoon releases degradative enzymes that denatures the zona pellucida allows the sperm to penetrate the barrier - oocyte cancels its membrane potential and denatures its zona pellucida, preventing additional sperm fusion

Cells in the center of a morula will differentiate, as opposed to cells in the surface

Cell differentation occurs due to different protein/peptide (secretory products, enzymes, and channels/pumps) production

During the separation of the trophoblasts and the inner cell mass, the zona pellucida will begin to degrade

Eventually blastocyst attaches to or implants within the uterine wall

Only after the degradation of the zona pellucida

Morphogenic process that give rise to the three primary germ layers: Ectoderm, mesoderm, and endoderm

Trophoblast cells overlaying the inner cell mass degenerate

Inner cell mass cells proliferate, break loose, and migrate to form the endoderm

Trophoblast cells overlaying the inner cell mass layers begins to degenerate due to the increase in cells below

The hypoblast cells will detach from the epiblast cells and form the yolk sac.

Which will later become the gastrointestinal tract