Blastula Stage in Embryonic Development

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Questions and Answers

Match the following terms with their description in mammalian development:

Morula = Structure without an internal cavity initially Blastocyst = Resulting structure after cavitation Inner cell mass = Layer that actively supports the trophoblast Trophoblast = Layer that secretes fluid to create a blastocoel

Match the following processes with their description in mammalian development:

Cavitation = Process of creating a blastocoel Differentiation = First event in mammalian development Implantation = Process of adhering to the uterus Cleavage = Process of cell division

Match the following structures with their function in mammalian development:

Zona pellucida = Prevents blastocyst from adhering to the oviduct Blastocoel = Fluid-filled cavity in the blastocyst Trophoblast = Layer that secretes proteins to divide inner cell mass Inner cell mass = Layer that supports the development of the embryo

Match the following terms with their description in mammalian development:

Ectopic pregnancy = Dangerous condition where embryo adheres to the oviduct Fertilization = Process of sperm fusion with an oocyte Cleavage = Process of cell division without significant growth Implantation = Process of adhering to the uterus Signup and view all the answers

Match the following cells with their function in mammalian development:

Trophoblast cells = Secrete fluid to create a blastocoel Inner cell mass cells = Actively support the trophoblast Oocytes = Ffuse with sperm to form a zygote Blastomeres = Represent the first differentiation event in mammalian development Signup and view all the answers

Match the following structures with their location in mammalian development:

Blastocoel = Fluid-filled cavity in the blastocyst Zona pellucida = Outer layer surrounding the embryo Inner cell mass = Layer positioned on one side of the trophoblast cells Oviduct = Tube where the embryo moves before implantation Signup and view all the answers

Match the following proteins with their function in mammalian development:

FGF4 = Causes trophoblast cells to divide Hormones = Supports the development of the embryo Enzymes = Breaks down nutrients for energy Proteins = Structural components of cells Signup and view all the answers

Match the following terms with their description in mammalian development:

One-cell embryo = Usually somewhat retracted from the zona pellucida Unfertilized oocyte = Fills the entire space inside the zona pellucida Blastocyst = Structure that expands within the zona pellucida Morula = Stage with 64 cells Signup and view all the answers

Match the following terms with their description in mammalian development:

Tubal pregnancy = Condition where the embryo adheres to the oviduct Uterus = Organ where the embryo implants Oviduct = Tube where the embryo moves before implantation Fetus = Developing embryo after implantation Signup and view all the answers

Match the following processes with their description in mammalian development:

Adhesion = Process of the embryo adhering to the uterus Cleavage = Process of cell division without significant growth Fusion = Process of sperm fusion with an oocyte Differentiation = Process of separating into distinct cell layers Signup and view all the answers

Study Notes

Blastula Stage

Begins at the 128-cell stage with all cells equal in size and slower micromere division.
Tight junctions form a seamless epithelial layer encircling the blastocoel.
The blastula remains one cell layer thick due to blastomere adhesion and water influx, expanding the blastocoel.
Cell cleavages are rapid and invariant until the 9th or 10th division, leading to a mid-blastula transition.
Synchrony in cell division ceases, new genes are expressed, and non-dividing cells develop cilia.

Morphological Changes in Blastula

Cells at the vegetal pole thicken to form the vegetal plate.
Animal half secrete a hatching enzyme that digests the fertilization envelope, allowing free-swimming.
A tuft of long, nonmotile cilia forms at the animal pole of the blastula.
The marginal zone, between area pellucida and area opaca, contains cells crucial for cell fate determination in early chick development.
Polyingression results in a primary hypoblast, more prominent at the posterior end of the embryo.

Embryonic Polarity

The primary hypoblast provides polarity to the embryo, influencing the future primitive streak through inductive interactions.
The bird's epiblast is equivalent to the animal hemisphere, while the hypoblast shares properties with the amphibian's vegetal hemisphere.

Mammalian Development

Early cleavage in mammals is characterized by equal holoblastic cleavage in isolecithal eggs.
Cleavage divisions in mammals are slow, with the first division taking up to 24 hours.
The first cleavage is a normal meridional division leading to a temporary 3-cell stage; rotation of the spindle can occur during the second cleavage.

Compaction and Morula Formation

At the 8-cell stage in mice, blastomeres undergo compaction, forming a tightly packed arrangement stabilized by tight junctions.
Gap junctions facilitate communication among compacted cells.
The blastocyst cavity forms as a result of internal fluid secretion during the transition from morula.

Inner Cell Mass and Trophoblast

The inner cell mass and trophoblast become distinct by the 64-cell stage, marking the first differentiation event crucial for uterine adhesion.
Trophoblast secretes fluid during cavitation to create the blastocoel, positioning the inner cell mass on one side.
The blastocyst forms, which is significant in mammalian cleavage and development.
Zona pellucida prevents premature adhesion of the expanding blastocyst to the oviduct, avoiding ectopic pregnancies.

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Description

Learn about the blastula stage of embryonic development, where all cells are the same size and united into a seamless epithelial sheet. Understand the role of tight junctions and the formation of the blastocoel. Test your knowledge of this critical stage in embryonic development.