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Blastocyst Embryonic Development - Anatomy & Physiology (view source)
Revision as of 14:06, 3 July 2008
, 14:06, 3 July 2008no edit summary
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* In the Ootid, male and female pronuclei along with the first and second polar bodies are present.
+* In the Ootid, male and female '''pronuclei''' along with the first and second '''polar bodies''' are present.
−* Fusion of male and female pronuclei to form a single diploid nucleus ('''Syngamy''')
+* Fusion of male and female pronuclei to form a single '''diploid nucleus''' ('''Syngamy''')
−* Zygote (diploid) undergoes mitotic divisions ('''cleavage''').
+* '''Zygote''' (diploid) undergoes mitotic divisions ('''cleavage''').
* Cleavage gives rise to daughter cells called '''Blastomeres'''.
* Cleavage gives rise to daughter cells called '''Blastomeres'''.
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* Cleavage divisions continue and the 4-celled Embryo gives rise to an 8-celled Embryo.
* Cleavage divisions continue and the 4-celled Embryo gives rise to an 8-celled Embryo.
* After the 8-celled stage, a ball of cells is formed. This stage is referred to as a '''Morula'''.
* 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:
−* Cells of the Morula continue to devide and a '''Blastocyst''' develops, consisting of:
** '''Inner Cell Mass''' (ICM)
** '''Inner Cell Mass''' (ICM)
** '''Blastocoele''' cavity
** '''Blastocoele''' cavity
** Single layer of '''Trophoblast''' cells
** 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 ''''hatches'''' from the '''Zona Pellucida'''.
+* Blastocyst continues mitosis.
−* Blastocyst free-floating within the Uterus.
+* 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.