embryonic disk

Examples of embryonic disk in the following topics:

• Amnion Development

  • Its floor consists of the prismatic ectoderm of the embryonic disk.
  • The continuity between the roof and the floor is established at the margin of the embryonic disk.
  • This fluid increases in quantity, causing the amnion to expand and ultimately to adhere to the inner surface of the chorion so that the extra-embryonic part of the coelom is obliterated.

• Bilaminar Embryonic Disc Development

  • The floor of the amniotic cavity is formed by the embryonic disc.
  • The floor of the amniotic cavity is formed by the embryonic disc, which is composed of a layer of prismatic cells and the embryonic ectoderm.
  • In humans, the formation of the embryonic disc occurs after implantation and prior to embryonic folding (between about day 14 to day 21 post-fertilization).
  • The embryonic disc forms during early development.
  • Simultaneously, morphological changes ocur in the embryoblast that result in the formation of a flat, almost circular bilaminar plate of cells--the embryonic disk--which includes the epiblast and the hypoblast.

• Blastocyst Formation

  • The blastocyst forms early in embryonic development and has two layers that form the embryo and placenta.
  • The embryoblast is the source of embryonic stem cells and gives rise to all later structures of the adult organism.
  • The floor of this cavity is formed by the embryonic disk, which is composed of a layer of prismatic cells called the embryonic ectoderm.

• Prenatal Brain Development

  • There are three stages of prenatal development: germinal, embryonic, and fetal.
  • The first trimester ends with the end of the embryonic stage, the second trimester ends at week 20, and the third trimester ends at birth.
  • The embryonic stage lasts from implantation (2 weeks) until week 8 of pregnancy.
  • During the first week of the embryonic period, the embryonic disk separates into three layers: the ectoderm, mesoderm, and endoderm.

• Vertical Structure

  • We have assumed that the disk is thin.
  • The pressure gradient in the disk must resist the vertical component of gravity.
  • This is essentially assuming that the disk is isothermal vertically.
  • The relative thickness of the disk remains nearly constant with radius if only internal heating is important in a vertically isothermal disk.
  • To go further we need an estimate of the density of the disk.

• Development of the Extraembryonic Coelom

  • The extra-embryonic coelom is a cavity that contains the chorion.
  • As development progresses, small lacunae begin to form within the extra-embryonic mesoderm that become larger and form the extra-embryonic coelom.
  • The extra-embryonic mesoderm is divided into two layers: the extra-embryonic splanchnopleuric mesoderm, which lies adjacent to Heuser's membrane around the outside of the primitive yolk sac; and the extra-embryonic somatopleuric mesoderm, which lies adjacent to the cytotrophoblast layer of the embryo.
  • The extra-embryonic coelomic cavity is also called the chorionic cavity—it is enclosed by the chorionic plate.
  • It consists of an extra-embryonic mesoderm and two layers of trophoblast and surrounds the embryo and other membranes.

• Emission

  • If we assume that the energy is radiated through the surface we find that the flux per unit area is half this value (two surfaces) and that the total luminosity of the disk is
  • If one assumes that the disk radiates locally as a blackbody, the spectrum is simply the sum of the various blackbodies (the so-called multi-temperature disk model).

• Development of Nervous Tissue

  • In vertebrates, landmarks of embryonic neural development include the birth and differentiation of neurons from stem cell precursors, the migration of immature neurons from their birthplaces in the embryo to their final positions, outgrowth of axons from neurons and guidance of the motile growth cone through the embryo towards postsynaptic partners, the generation of synapses between these axons and their postsynaptic partners, and finally the lifelong changes in synapses which are thought to underlie learning and memory.
  • The gastrula has the shape of a disk with three layers of cells, an inner layer called the endoderm, which gives rise to the lining of most internal organs, a middle layer called the mesoderm, which gives rise to the bones and muscles, and an outer layer called the ectoderm, which gives rise to the skin and nervous system.

• Accretion Disks

  • Understanding the production of ejecta is beyond our scope, but examining the transport of angular momentum through a rotating disk of material is not once we add an additional ingredient to our analysis, viscosity.
  • Around this radius, the accretion flow must make a transition between a spherical inflow and a disk.
  • Unfortunately, natural estimates for the microscopic viscosity of astrophysical gas are too small by many orders of magnitude to account for the structure of accretion disks.
  • It is likely that accretion disks are turbulent magnifying the effects of small-scale viscosity to larger scales.

• Problems

  • This is a simplified model for an accretion disk.
  • Let's divide the accretion disk into a series of rings each of mass $M$.
  • What and where is the peak temperature of the disk?
  • What and where is the minimum temperature of the disk?
  • Sketch the spectrum from the accretion disk on a log-log plot.