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REPRODUCTION IN HUMANS

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REPRODUCTION IN HUMANS Powered By Docstoc
					REPRODUCTION IN HUMANS

      Formation of gametes
       A Spermatogenesis
          B Oogenesis
SPERMATOGENESIS
            Production of sperm
            Begins between ages
             of 11 to 15 and
             continues until death
            100 to 200 million
             sperm are made a day
SPERMATOGENESIS
            Each seminiferous tubule
             is surrounded by a layer of
             epithelium on which sit
             spermatogonia
            These divide by mitosis to
             form dipolid cells
            Some of these cells move
             towards the middle of the
             tubule becoming primary
             spermatocytes
SPERMATOGENESIS
            Primary spermatocytes
             then divide by
             meiosis.
            After first meiotic
             division two
             secondary
             spermatocytes are
             formed.
SPERMATOGENESIS
            Two or three days
             later the secondary
             spermatocytes
             undergo a second
             meiotic division to
             produce haploid
             spermatids.
SPERMATOGENESIS
            The spermatids mature
             over the next few
             weeks into
             spermatozoon.
            The whole process
             takes about 64 days.
SPERMATOGENESIS
            At all stages the
             developing sperm are
             supported and nourished
             by much larger non-
             dividing cells called
             Sertoli cells or nurse
             cells.
            The fully developed sperm
             are carried by a fluid
             released by the Sertoli
             cells.
OOGENESIS
             Each ovary weighs
              about 15g and
              contains many eggs at
              different stages of
              development.
             The process begins
              when a girl is still an
              embryo
Removing an ovarian cyst!
OOGENESIS
 5 or 6 weeks after zygote forms some cells
  in embryo ovary undergo mitosis to produce
  diploid oogonia
 By 24 weeks the embryo contains millions
  of oogonia
 From then until 6 weeks after birth the
  oogonia undergo a first meiotic division to
  form primary oocytes.
OOGENESIS
             They remain half way
              through this division
              for many years.
             Most of the primary
              oocytes disappear – by
              puberty about 400 000
              remain.
OOGENESIS
             As development
              recommences some of
              the surrounding ovary
              cells form the
              primordial follicle
              which later develops
              into the primary
              follicle
OOGENESIS
             At puberty hormones
              stimulate the primary
              follicle to become a
              secondary follicle
             One of these will
              develop each 28 days
              into an ovarian
              follicle containing the
              developing primary
              oocyte
OOGENESIS
             The meiotic division
              commenced as an
              embryo now
              completes.
             This results in a large
              secondary oocyte and
              a tiny polar body
OOGENESIS
             It is at this stage that
              the oocyte is released
              at the moment of
              ovulation.
             The meiotic division
              does not actually
              complete until after
              the sperm has entered
              it.

				
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