Embryology
Lecture -2-
12/10/2015
Male gametogenesis
Spermatogenesis & Spermiogenesis
spermatogenesis
#Maturation of sperm begins at puberty.
Spermatogenesis: includes all of the events by
which spermatogonia are transformed into
spermatozoa.
At birth, germ cells in the male infant can be
recognized in the sex cords of the testis as
large, pale cells surrounded by supporting cells.
Supporting cells
which are derived from the
surface epithelium of the gland in the same
manner as follicular cells, become
Sertoli cells.
Shortly before puberty, the sex cords acquire a lumen &
become ^ seminiferous tubules.
At about ^ same time, PGCs give rise to spermatogonial
stem cells. At regular intervals, cells emerge from this
stem cell population to form type A spermatogonia, &
their production mark ^ initiation of spermatogenesis.
Type A cells undergo a limited no. of mitotic divisions to
form clones of cells, ^ last cell division produces type B
spermatogonia, which then divide to form primary
spermatocytes.
Primary spermatocytes then enter a prolonged prophase
(22 days) followed by rapid completion of meiosis I
&formation of secondary spermatocytes. During the
second meiotic division, these cells immediately begin to
form haploid spermatids.
During all these events (stem cell to spermatid), cytokinesis
is incomplete, so that successive cell generations are
joined by cytoplasmic bridges until individual sperm are
separated from residual bodies.
Spermatogonia & spermatids remains embedded in deep
recesses of Sertoli cells throughout their development.
In this manner, Sertoli cells :
#support & protect the germ cells
#participate in their nutrition
#assist in the release of mature spermatozoa.
• Spermatogenesis is regulated by LH production by the
pituitary gland. LH binds to receptors on Leydig cells &
stimulates testesterone production, which in turn binds to
sertoli cells to promote spermatogenesis.
• Follicle-stimulating hormone (FSH) is also essential
because its binding to Sertoli cells stimulates testicular
fluid production & synthesis of intracellular androgen
receptor proteins.
Spermiogenesis
• The series of changes resulting in the transformation of
spermatids into spermatozoa is spermiogenesis.
• These changes include:
1-formation of acrosome, which covers half of ^ nuclear
surface & contains enzymes to assist in penetration of ^
egg & its surrounding layers during fertilization.
2- condensation of the nucleus.
3- formation of neck, middle piece, & tail.
4- shedding of most of the cytoplasm as residual bodies
that are phagocytized by Sertoli cells.
• In humans, the time required for a spermatogonium to
develop into a mature spermatozoon is approximately 74
days,& approximately 300 million sperm cells are
produced daily.
• When fully formed, spermatozoa enter the lumen of
seminiferous tubules. From there, they are pushed
toward the epididymis by contractile elements in the wall
of the seminiferous tubules. Although initially only slightly
motile, spermatozoa obtain full motility in the epididymis
