Difference between revisions of "Blastocyst Embryonic Development - Anatomy & Physiology"
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| − | + | == Pre-Implantation Development == | |
| − | == Pre-Implantation Development | + | [[Image:Blastocyst.jpg|thumb|right|300px|Blastocyst - Courtesy of Wikimedia Commons]] |
| + | * 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. | ||
| + | |||
| + | |||
| + | |||
| + | [[Category:Pregnancy and Parturition]][[Category:Developmental Biology]] | ||
Revision as of 14:24, 7 December 2010
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.