Difference between revisions of "Blastocyst Embryonic Development - Anatomy & Physiology"
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[[Image:Blastocyst.gif|thumb|right|300px|Blastocyst - Courtesy of Wikimedia Commons]] | [[Image:Blastocyst.gif|thumb|right|300px|Blastocyst - Courtesy of Wikimedia Commons]] | ||
* The sperm enters the the oocyte forming the ootid. | * The sperm enters the the oocyte forming the ootid. | ||
| − | * In the | + | * In the ootid, male and female '''pronuclei''' along with the first and second '''polar bodies''' are present. |
| − | * Fusion of the male and female pronuclei results in a single '''diploid nucleus''' (''' | + | * Fusion of the male and female pronuclei results in a single '''diploid nucleus''' ('''syngamy''') |
* The '''zona pellucida''' then becomes an imprenetrable layer that prevents polyspermy and so polyploidy. | * The '''zona pellucida''' then becomes an imprenetrable layer that prevents polyspermy and so polyploidy. | ||
* '''Zygote''' (diploid) undergoes mitotic divisions ('''cleavage'''). | * '''Zygote''' (diploid) undergoes mitotic divisions ('''cleavage'''). | ||
| − | * Cleavage gives rise to daughter cells called ''' | + | * Cleavage gives rise to daughter cells called '''blastomeres'''. |
| − | * Cleavage divisions continue and the 4-celled | + | * Cleavage divisions continue and the 4-celled embryo gives rise to an 8-celled embryo. |
* These cells are totipotent and divide asynchronously. | * These cells are totipotent and divide asynchronously. | ||
| − | * After the 8-celled stage, a ball of cells is formed. This stage is referred to as a ''' | + | * After the 8-celled stage, a ball of cells is formed. This stage is referred to as a '''morula'''. |
| − | * '''Tight junctions''' form between outer cells of the | + | * '''Tight junctions''' form between outer cells of the morula. |
| − | * '''Gap junctions''' form between inner cells of the | + | * '''Gap junctions''' form between inner cells of the morula. |
| − | * Thus, two groups of cells are created within the | + | * Thus, two groups of cells are created within the morula. |
| − | * Outer cells pump | + | * Outer cells pump sodium into the intracellular spaces and water follows osmotically. |
| − | * Fluid begins to accumulate within the | + | * Fluid begins to accumulate within the morula. |
| − | * Cells of the | + | * Cells of the morula continue to divide and a '''blastocyst''' develops, consisting of: |
| − | ** '''Inner | + | ** '''Inner cell mass''' (ICM) |
** '''Blastocoele''' cavity | ** '''Blastocoele''' cavity | ||
| − | ** Single layer of ''' | + | ** Single layer of '''trophoblast''' cells |
| − | * As fluid accumulates, the outer cells become flattened and a cavity known as the | + | * As fluid accumulates, the outer cells become flattened and a cavity known as the blastocoele is formed. |
| − | * Gap junctions connecting the inner cells of the | + | * Gap junctions connecting the inner cells of the morula enable them to polarise as a group. |
| − | * As a result, two separate cellular components emerge - the | + | * As a result, two separate cellular components emerge - the inner cell mass and the trophoblasts. |
Revision as of 14:05, 13 August 2009
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Pre-Implantation Development
- The sperm enters the the oocyte forming the ootid.
- In the ootid, male and female pronuclei along with the first and second polar bodies are present.
- Fusion of the male and female pronuclei results in a single diploid nucleus (syngamy)
- The zona pellucida then becomes an imprenetrable layer that prevents polyspermy and so polyploidy.
- Zygote (diploid) undergoes mitotic divisions (cleavage).
- Cleavage gives rise to daughter cells called blastomeres.
- Cleavage divisions continue and the 4-celled embryo gives rise to an 8-celled embryo.
- These cells are totipotent and divide asynchronously.
- After the 8-celled stage, a ball of cells is formed. This stage is referred to as a morula.
- Tight junctions form between outer cells of the morula.
- Gap junctions form between inner cells of the morula.
- Thus, two groups of cells are created within the morula.
- Outer cells pump sodium into the intracellular spaces and water follows osmotically.
- Fluid begins to accumulate within the morula.
- Cells of the morula continue to divide and a blastocyst develops, consisting of:
- Inner cell mass (ICM)
- Blastocoele cavity
- Single layer of trophoblast cells
- As fluid accumulates, the outer cells become flattened and a cavity known as the blastocoele is formed.
- Gap junctions connecting the inner cells of the morula enable them to polarise as a group.
- As a result, two separate cellular components emerge - the inner cell mass and the trophoblasts.
- Blastocyst continues mitosis.
- Fluid accumulates to fill the Blastocoele and pressure within the embryo increases.
- Concurrent with growth and fluid accumulation is the production of proteolytic enzymes by Trophoblastic cells.
- Enzymes weaken the Zona Pellucida.
- Blastocyst begins to contract and relax causing intermittent pressure pulses on the Zona Pellucida.
- Zona Pellucida ruptures with the development of a small fissure just large enough for the Blastocyst to squeeze out.
- Blastocyst 'hatches' from the Zona Pellucida.
- Rodent,Dog,Cat,Primate: 8 days after fertilization
- Ungulates: 12 days after fertilization.
- Blastocyst free-floating within the Uterus, totally dependent on the Uterine environment for survival.