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CHAPTER 22: THE REPRODUCTIVE SYSTEMS

VI.DEVELOPMENT DURING PREGNANCY

B.Formation of the Morula

See Fig 23.3 and Fig 23.4, page 943.

1.Cleavage = the early series of mitotic divisions of the zygote.

a.These divisions occur so rapidly, that the cells are unable to grow between divisions.  

b.The mass of successively smaller and smaller cells is still contained within the zona pellucida.

c.These small cells are called blastomeres.

2.First division = 36 hours = 2 cells.

3.Second division = 48 hours = 4 cells.

4.Morula = solid ball of 32 cells (resembles a raspberry); about 96 hours.

C.Formation of the Blastocyst:

Fig 23.4, page 943

1.Blastocyst = a hollow ball of cells surrounding a central cavity; about 5 days.

Further development will be discussed in Chapter 23.

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