Human Reproduction
Spermatogenesis
Spermatogenesis
• Sperm production begins during
puberty and is stimulated by the
release of hormones
– Sperm production is controlled by the
hypothalamus and ant. Pituitary through
negative feedback
Spermatogenesis
•Hypothalamus releases gonadotropin
releasing hormone (GnRH) which
triggers ant. pit. To release FSH and LH
•FSH triggers seminiferous tubules to
produce sperm
•LH triggers testosterone production by
Leydig cells (interstitial cells) which
increases sperm production
Testosterone
• Produced by interstitial cells in the
Testes
– Also responsible for Secondary sex chars.
•Voice Deepens
•Body Hair
•Strengthening of muscles
•Sex drive
Hormonal control
Spermatogenesis:
The making of sperm
• Seminiferous tubules in the testes are the site
of sperm cell production
– Lumen of tubules is lined with spermatogonia
• 46 chromosomes
• Undergo mitosis to form primary spermatocytes
– primary spermatocytes undergo meiosis to
produce secondary spermatocytes
(46 Chromosomes *) and eventually
spermatids (23 chromosomes)
– One primary spermatocyte will
eventually produce four
sperm cells
Spermatogenesis
• Spermatogenesis occurs at the onset
of puberty
– Several hundred million produced/day
– Formation of a mature sperm cell takes
about 70 – 80 days
• Sperm cells mature in the epididymis
• Develop flagella and begin to swim within 4
days
Spermatogenesis
Mature Sperm
Human Reproduction
Oogenesis
Oogenesis
• All follicles are produced in the ovaries
during the first during the 1st six months
of fetal development
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–
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Max. of 7 million produced
2 million left at birth
400,000 at onset on puberty
Approx. 400-500 mature ova develop and
are released during the reproductive
years
Oogenesis
• Follicles consist of two types of cells:
– Primary oocyte
– Granulosa cells
• Clusters of these cells are called
primordial follicles
– Granulosa provide nutrients, chemical
signals, and protection for the developing
follicle
Oogenesis
• 6-20 primary follicles begin to mature
each month
• Only one follicle fully matures and is
released from one ovary each month
during reproductive years
Ovulation
• The ovum is released out of the ovary
and will move into the fallopian tube
• Remaining follicular cells change and
become the corpus luteum
– Secretes progesterone and estrogen
• If ovum remains unfertilized, corpus
luteum degenerates and new cycle
will begin
Hormonal control
• Cyclic process in females (continuous
in males)
• Hypothalamus secretes GnRH
• Stimulates LH and FSH in ant. Pit.
• Effects of LH and FSH on ovaries varies
during the cycle
The Ovarian Cycle
• 28 days long, divided into 3 phases
– Follicular phase (12 days)
– Luteal phase (11 days)
– Menstrual phase (approx. 5 days)