Reproductive System
Reproduction
–Depends on union of male and female gametes to form new individual
–Male and female reproductive systems designed to enable union of
genetic material
Anatomy: gonads, reproductive tract, and accessory sex glands
Gonads: primary reproductive organs - testes and ovaries
Functions of mature gonads:
• Gametogenesis: spermatozoa; ova
• Secreting sex hormones
– Testosterone in males
– Oestrogen and progesterone in females
Although males have more androgens and females have more
oestrogens and progesterone, all these hormones are found in both sexes
Hypothalamus and Pituitary
synthesis
TRH
CRH
GnRH
PRH PIH GHRH SS
+
Blood
oxytocin
ADH
TSH
ACTH
FSH
-
+
-
vessels
LH prolactin
GH
storage and secretion
breast
kidney
adrenal
thyroid
uterus blood vessels
cortex
gonads
breast
many
tissues
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Male Reproductive Function
• Functions
– Production of sperm (spermatogenesis)
– Delivery of sperm to female
• Male gonads
– Testes
• Sperm-producing organs
• Suspended outside abdominal tract (temperature)
• Accessory sex glands
• Seminal vesicles, prostate gland, bulbourethral glands
– Secretions conducive to sperm viability
– Male gonads
– 250-300 compartments
– Seminiferous tubules
• Sperm production
Leydig cells (interstitial cells)
• Synthesise and secrete testosterone
Sertoli cells (epithelial cells)
• Support sperm development
• Contained within seminiferous tubules
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Spermatogenesis
• Results in many highly specialized, mobile sperm
• Undifferentiated diploid primordial germ cells
(spermatogonia) are converted into haploid spermatozoa
(sperm)
• Three major stages
– Mitotic proliferation
– Meiosis
– Packaging (of cell elements; spermiogenesis)
Spermatozoa
Remain closely associated with Sertoli cells throughout development
Head - Consists primarily of the
nucleus (contains DNA)
Acrosome
–Enzyme-filled vesicle that caps
tip of the head
–Used to penetrate ovum
–Formed by endoplasmic
reticulum and Golgi complex
before these organelles are
discarded
Midpiece - Area where
mitochondria are concentrated
Tail - Provides mobility for
spermatozoan
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Spermatogenesis
Sperm Maturation
– Spermatozoa released into lumen
of seminiferous tubules
• Immotile
• 20 days
– Move to epididymis by peristaltic contractions and flow
of lumenal fluid
• Acquire motility
– Move to vas deferens by peristalsis
• Remain in vas deferens until ejaculation
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Spermatogenesis
Functions of Sertoli cells
–
–
–
–
Form blood-testes barrier
Provide nourishment
Phagocytic function
Secrete seminiferous tubule fluid which flushes released
sperm from tubule into epididymis for storage and
additional processing
– Secrete androgen-binding protein (ensures high levels of
testosterone in fluid)
– Site of action to control spermatogenesis
• Release inhibin
• Acts in negative-feedback fashion to regulate FSH secretion
Location and Functions of the Components of the Male
Reproductive System
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Hormonal Regulation of Reproductive Function in Males
Testosterone limits its own secretion by negative feedback
Acts on hypothalamus and the anterior pituitary, thereby
decreasing secretion of GnRH, FSH and LH.
Sertoli cells also secrete inhibin: suppresses release of FSH
but not LH
Blood Levels of Sex Hormones in Males
– Fairly constant on short term basis
– Prepubescent – low blood levels
– Puberty and adulthood – high blood levels
Testosterone acts
as a paracrine, working
with FSH to stimulate
spermatogenesis
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Characteristics of Female Reproductive System
Cyclic changes in activity
-Menstrual cycle
Restricted periods of fertility
-Ovulation
Limited gamete production
-Pool established at birth
Ovaries
Primary female reproductive organs
• Produce ova (oogenesis)
• Secrete female sex hormones
Oestrogen
» Essential for ova maturation and release
» Establishment of female secondary sexual
characteristics
» Essential for transport of sperm in oviduct
» Contributes to breast development in
anticipation of lactation
Progesterone
» Important in preparing suitable environment for
nourishing a developing embryo/fetus
» Contributes to ability of breasts to produce milk
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Oogenesis
Oogonia
– Undifferentiated primordial germ cells in fetal ovaries
– Divide mitotically to give rise to 6 - 7 million oogonia by
fifth month of gestation
– During last part of fetal life begin early steps of first
meiotic division but do not complete it
– Now known as primary oocytes
– Contain diploid number of 46 replicated chromosomes
– Remain in meiotic arrest for years until prepared for ovulation
Oogenesis
Primary oocyte: surrounded by single layer of granulosa cells
– Oocyte + granulosa cells → primary follicle
Primary follicle
– After development starts - two possible fates
• Reach maturity and ovulate
• Degenerate to form scar tissue (atresia)
Between puberty and menopause
– Follicles develop into secondary (antral) follicles on cyclic basis
Just before ovulation
– Primary oocyte completes first meiotic division:
– First polar body & secondary oocyte
– Ovulated
– Sperm entry triggers second meiotic division which produces
» Secondary polar body (haploid)
» Mature haploid ovum which unites with haploid sperm
cell during fertilization
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Oogenesis
Oogenesis
• Identical steps of
chromosome
replication and
division during
gamete production
in both sexes
– Timing and end
result are very
different
Spermatogenesis
Oogenesis
Accomplished within
two months
Take anywhere from
12 to 50 years to
complete on cyclic
basis from onset of
puberty until
menopause
Postpubertal male can
produce several
hundred million sperm
each day
Female born with
limited, largely
nonrenewable
supply of germ cells
Each primary
spermatocyte yields
four equally viable
spermatozoa
Each primary oocyte
yields only one
cytoplasm-rich ovum
and three
cytoplasm-poor
polar bodies that
disintegrate
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