trophoblastic lacunae

Examples of trophoblastic lacunae in the following topics:

• Sinusoid Development

  • The invasion of endometrial sinusoids by the trophoblast allows maternal blood flow into the trophoblastic lacunae; this forms the uteroplacental blood circulation.

• Development of the Extraembryonic Coelom

  • It is located between Heuser's membrane and the trophoblast.
  • As development progresses, small lacunae begin to form within the extra-embryonic mesoderm that become larger and form the extra-embryonic coelom.
  • The chorionic plate is composed of an inner layer of somatopleuric mesoderm and an outer layer of trophoblast cells.
  • It consists of an extra-embryonic mesoderm and two layers of trophoblast and surrounds the embryo and other membranes.
  • Chorionic villi are at first small and nonvascular, and consist of only trophoblast, but they increase in size and branch.

• Trophoblast Development

  • Trophoblasts are the outer layer of cells that provide nutrients to the embryo and form part of the placenta.
  • This layer of trophoblasts is also collectively referred to as the trophoblast, or, after gastrulation, the trophectoderm, as it is then contiguous with the ectoderm of the embryo.
  • Cytotrophoblast in the tips of villi can differentiate into another type of trophoblast called the extravillous trophoblast.
  • Extravillous trophoblasts grow out from the placenta and penetrate into the decidualized uterus.
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• Blastocyst Formation

  • The blastocyst possesses an inner cell mass (ICM), or embryoblast, which subsequently forms the embryo, and an outer layer of cells, or trophoblast, which later forms the placenta.
  • The trophoblast surrounds the inner cell mass and a fluid-filled, blastocyst cavity known as the blastocoele or the blastocystic cavity.
  • The trophoblast combines with the maternal endometrium to form the placenta in eutherian mammals.
  • Before gastrulation, the cells of the trophoblast become differentiated into two strata.
  • The blastocyst possesses an inner cell mass from which the embryo will develop, and an outer layer of cells, called the trophoblast, which will eventually form the placenta.

• Implantation

  • The zona pellucida degenerates and decomposes, and is replaced by a layer of underlying cells called the trophoblast.
  • The trophoblast will give rise to the placenta after implantation.
  • During implantation, the trophoblast differentiates into two distinct layers: the inner cytotrophoblast, and the outer syncytiotrophoblast.
  • During implantation, extensions of the trophoblast, the syncytiotrophoblasts, embed within the endometrium and form chorionic villi.

• Postnatal Bone Growth

  • Zone of cell proliferation: Closer to the marrow cavity, chondrocytes in this region multiply and arrange themselves into longitudinal columns of flattened lacunae.
  • The walls of the matrix between the lacunae become very thin.
  • Minerals are deposited in the matrix between the columns of lacunae, but are not the permanent bone mineral deposits.
  • This acts as a temporary support for the cartilage that would otherwise be weakened due to the breakdown of the lacunae.
  • Zone of bone deposition (ossification): The walls between the lacunae break down and the chondrocytes die.

• Cleavage of the Zygote

  • However, they quickly become arranged into an outer or peripheral layer, the trophoblast, and an inner cell mass.
  • The trophoblast does not contribute to the formation of the embryo proper; the embryo develops from the inner cell mass .
  • Fluid collects between the trophoblast and the greater part of the inner cell mass, and thus the morula, is converted into the blastodermic vesicle (also called the blastocyst or blastula).
  • The inner cell mass remains in contact with the trophoblast at one pole of the ovum.

• Chorionic Villi and Placental Development

  • During the primary stage (the end of fourth week), the chorionic villi are small, nonvascular, and contain only the trophoblast.
  • During the secondary stage (the fifth week), the villi increase in size and ramify, while the mesoderm grows into them; at this point the villi contain trophoblast and mesoderm.
  • At this point, the villi contain trophoblast, mesoderm, and blood vessels.
  • The outer layer of the blastocyst becomes the trophoblast, which forms the outer layer of the placenta.

• Connective Tissues: Bone, Adipose, and Blood

  • Osteocytes are found in lacunae of the bone and assist in maintenance of the bone.
  • Small spaces between these circles are called lacunae.
  • Between the lacunae are microchannels called canaliculi; they connect the lacunae to aid diffusion between the cells .
  • Between the lamellae are cavities called lacunae.
  • Canaliculi are microchannels connecting the lacunae together.

• Cleavage, the Blastula Stage, and Gastrulation

  • Here the cells in the blastula arrange themselves in two layers: the inner cell mass and an outer layer called the trophoblast .
  • The trophoblast will contribute to the placenta and nourish the embryo.
  • The rearrangement of the cells in the mammalian blastula to two layers, the inner cell mass and the trophoblast, results in the formation of the blastocyst.