Fig.:Summary of hormonal control of male reproductive systemHypothalamus
secretes GnRHAnterior pituitary
secretes FSH and LHFSH LHSertoli
cellsTestes
(Local)Leydig's
cellsTestosteroneTestosteroneStimulate
spermatogenesisInhibinReproductive tract
and other organs
respond to testosterone(Only FSH) (Only LH)Inhibits GnRH and LH productionGametogenesis in males
• The process of formation of male gametes i.e., sperms is
called spermatogenesis.
• It occurs in the seminiferous tubules of the testes. The
seminiferous tubules are lined by germinal epithelium and
Sertoli cells.
• The germinal epithelium consists largely of cuboidal primary
or primordial germ cells.
Fig.:T. S. of Seminiferous tubuleCytoplasmic
bridges
Early
spermatidsInterstitial cellsBasal laminaSpermiogenesis
MeiosisLate spermatidsFibroblastSecondary spermatocytesPrimary spermatocyte
SpermatogoniumCapillaryCapillarySertoli
cell
Sertoli
cellFormation of spermatids
• Multiplication phase: The undifferentiated germ cells,
divide mitotically again and again for a specified number of
division cycles to form large number of spermatogonia.
• Growth phase : Each spermatogonium actively grows to
a larger primary spermatocyte by obtaining nourishment
from the nursing cells. The phenomenon of formation
of primary spermatocytes from spermatogonia, is called
spermatocytogenesis.
• Maturation phase : Each primary spermatocyte increases
markedly in size and undergoes the first meiotic or reductional
division to form two secondary spermatocytes. Each of
which contains haploid set of (23 in humans) chromosomes.
Each secondary spermatocyte undergoes the second
meiotic or equational division to form spermatids. Thus,
each primary spermatocyte, containing 46 chromosomes,
produces four spermatids, each having 23 chromosomes.
Formation of spermatozoa
• The transformation of spermatids into spermatozoa is called
spermiogenesis or spermateleosis or differentiation
phase.
• The different changes occurring during spermiogenesis are:
(i) Formation of acrosome by Golgi apparatus. The latter
then degenerates.
(ii) Elongation and condensation of nucleus.
(iii) Separation of centrioles.
(iv) Formation of axial filament from distal centriole.
(v) Development of mitochondrial spiral around upper parts
of axial filament.
(vi) Formation of flagellum.
• The entire process of spermatogenesis, from primary
spermatocytes to mature spermatozoa (sperms) takes
approximately 64 days in man. The normal human male
manufactures nearly 30 million sperms per day. a very
high rate of sperm production appears to be necessary to
overcome the odds against internal fertilisation.Fig.:Stages in spermatogenesisMitotic divisionsMitotic divisionsMitotic divisionsMeiosis IMeiosis IISpermatogoniumPrimary spermatocyteSecondary spermatocyteEarly spermatidSperm2n2n2nn nnnn nn n n nPrimordial germ cells in embryoDifferentiationSpermatogonial stem cell