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Ajman University of Science & TechnologyFaculty of Dentistryaculty of Dentistry

Histology & Cell Biology08 01 112

Dr Al Moutassem Billah Khairr. Al-Moutassem Billah Khair

Gametogenesis

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SpermatogenesisPrimordial germ cells ( 2n )

At the time of the birth, germ cells in male can be recognized in the sex cords of the testis as large, pale cells surrounded by supporting cells (epithelial cells),

which become Sertoli cells.

Shortly before puberty, the sex cords become the seminiferous tubules. At thesame time primordial germ cells give rise to:

Spermatogonia ( 2n )

Type A Type BMitosis

of stem cells (2n) Mitosis

the last division Type B

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Spermatogenesis

Primary spermatocytes ( 2n )Enter rolon ed ro hase 22 da sRapid completion of the 1st meiosis

Secondary spermatocytes ( 2n DNA )(23 double-structured chromosomes)

2nd meiosis

Spermatids ( 1n )( 1n DNA, 23 chromosomes )

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SpermatogenesisSpermatids ( 1n )

( 1n DNA, 23 chromosomes )

Spermiogenesis:The series of changes resulting inthe transformation of spermatidsinto spermatozoa:

*formation of the acrosome*condensation of the nucleus*formation of neck, middle piece

& tail*shedding of most of the cytoplasm

Spermatozoa ( 1n )

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Oogenesis

most of oogonia divide by mitosis

increase in number some differentiate intoof oogonia primary oocytes ( 2n ).

mon mme a e y, ey en erprophase of 1st meiosis.

5th 7th month cell death take place and the most of oogonia

have degenerated except for a few near the surface.

All surviving primary oocytes have entered the 1st meiosis &

most of them are surrounded by a layer of flat epithelial cells.

Primordial follicles 4n

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OogenesisPostnatal maturation

Near the time of birth, all primary oocytes (4n) have started prophaseof the 1st meiosis (diplotene) and remain in it & do not finish their

division before puberty is reached, because of OMIOMI (a substance secreted by follicular cells that stops the progress of meiosis).

[ 7X105 2X106 cells at birth ]

With the onset of puberty primary oocytes increase in size and flat

follicular cells cuboidal cells granulosa cells[ 4X105 cells at the beginning of puberty ]

Primary follicle

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OogenesisPrimary follicle

Granulosa cells & Oocyte Layer of glycoproteins ( Zona pellucida )

changes in epithelial cells

Secondary follicle

maturation of Primary oocyte

one reaches full maturity every 4 weeks(Ovarian cycle)

[ >500 primary oocytes will be ovulated in the reproductive lifetime of the female individual ]

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Oogenesis

2 daughter cells of unequal size, but each with

Secondary oocyte 1st Polar body2n DNA, 1n chromo. 2n DNA, 1n chromo.(most of cytoplasm) (none cytoplasm)

2nd meiosis without DNA replication

Secondary oocyte

(in metaphase, 2nd meiosis)

Fertilization

& polar body (1n) each with 23

single chromosomes

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Oogenesis

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Oogenesis

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Oogenesis