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Exercise 45
Physiology of
Reproduction
1
Meiosis
Gametes
 Haploid complement (n)
 Gametogenesis
 Process of gamete formation with the
reduction by half of the chromosome
number
 Homologous chromosome
 Carries genes for the same traits
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Meiosis
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Meiosis I
 Prophase
• 23 tetrads
• Homologues chromosomes
synapse
• Chiasmata or crossover
Meiosis
 Metaphase
 Anaphase
• Homologues separates
• Dyads stays together
 Telophase
• 2 cells with diploid number of
chromosomes
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Meiosis
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Meiosis II
 Prophase
• No chromosome replication
• Cells are diploid
 Metaphase
Meiosis
 Anaphase
• Breaks of the centromeres will result
each cell having one chromatid
• 4 daughter cells
• Crossover and the way in which the
homologues align on the spindle
equator during the first maturation
division introduces a great variability
in the resulting gametes
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Spermatogenesis
It is the male gamete formation
 Starts at puberty and continues
throughout life
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Spermatogenesis
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Spermatogenesis
Steps of sperm formation:
 Spermatogonia (2n)
 Stem cell
 Found in the seminiferous tubules
 It undergoes mitosis and forms one
primary spermatocyte and one
spermatogonium
 Phase regulated by FSH
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Spermatogenesis
Primary spermatocyte (2n)
 It undergoes to a growth phase
 It undergoes to meiosis I after the
growth phase and forms the
secondary spermatocyte
 Secondary spermatocyte (n)
 It undergoes meiosis II and produces
4 spermatids
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Spermatogenesis
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Spermatids (n)
 Nonfunctional gametes
 No motile
 They undergo spermiogenesis and
form the sperm
Spermatogenesis
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Sperm
 Motile
 Smaller than the spermatid
 Head of the sperm
• Contain the genetic material
• Acrosome
Spermiogenesis
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Spermatogenesis
 Midpiece
• Centriole that gives rise to the
filaments that forms the tail
• Mitochondria present
 Tail
• flagellum
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Spermatogenesis
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Sertoli cells
 Support cells responsible for sperm
nourishment
Oogenesis and ovarian
cycle
It is the female gamete formation
 Steps of the oogenesis:
 Before birth
 Oogonia
• Primitive stem cell
• it undergoes mitosis many times
• It grows in size and becomes a
primary oocyte
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Oogenesis and ovarian
cycle
 Primordial
follicles
• Capsule formed by a single layer
of squamouslike cells that
surround the primary oocyte
 At birth
 Oogonias no longer exists
 All cells are oocytes encapsulated by
a primordial follicle
 No more oocytes will be produced
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Oogenesis and ovarian
cycle
From birth to puberty
 Primary oocytes are quiescent
 From puberty and on
 Increase of FSH levels cause:
 Follicle
 One or more primordial follicles to
undergo maturation (every 28 days)
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Follicle
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Oogenesis and ovarian
cycle
 Formation
of primary follicle
• From the maturation of the primordial
follicle
• Follicle cells
• The epithelium changes from
squamous to simple cuboidal
• Many layers of cuboidal cells
• Granulosa
• It secrets estrogen
20• It contains the primary oocyte
Oogenesis and ovarian
cycle
 Secondary
follicle
• Follicle with several layers of
granulosa cells
• Presence of antrum
 Tertiary follicle (Graafian)
• Presence of granulosa cells
• Corona radiata
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Oogenesis and ovarian
cycle
• It is a mature follicle that continues
secreting increasing amounts of
estrogen
• It contains the secondary oocyte
• It expels the secondary oocyte
accompanied by the corona
radiata at the middle of the 28-day
cycle
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Oogenesis and ovarian
cycle
 Corpus
luteum
• It comes from the rupture Graafian
follicle
• It produces mainly progesterone
• If pregnancy does not occur it will
degenerate and will be replaced
by scar tissue
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Oogenesis and ovarian
cycle
 Corpus
albicans
• Scar tissue resulted from the
disintegration of the corpus luteum
 Oocyte
 Primary oocyte
 Meiosis I is completed forming one
secondary oocyte and one first polar
body
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Follicle
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Oogenesis
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Oogenesis and ovarian
cycle
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Secondary oocyte
 Large cell (contains most of the
cytoplasm of the primary oocyte)
 Haploid
 Arrested in metaphase of meiosis II
 It is expelled by the Graafian follicle
(ovulation)
 It is captured by the uterine tube
Oogenesis and ovarian
cycle
 If
penetrated by the sperm, it will
complete meiosis II and will produce
a large ovum and one small
secondary polar body
 Ovum
 Chromosomes of the ovum and
sperm will combine to form a diploid
cell
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Oogenesis and ovarian
cycle

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First polar body
 Small cell (almost no cytoplasm)
 Produced by the division of the
primary oocyte
 It will disintegrate
Secondary polar body
 Produced by the division of the
secondary oocyte
 It will also disintegrate
Oogenesis and ovarian
cycle
Hormonal cycle
 Beginning of the menstrual cycle
 FSH is the dominant hormone
 Low levels of LH
 Low levels of estrogen and
progesterone
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Oogenesis and ovarian
cycle
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Before ovulation
 Estrogen levels increase
 Progesterone level remain low
Ovulation
 Caused mainly by a peak of LH
After ovulation
 Estrogen levels decrease
 Progesterone levels increase
 FSH and LH levels decrease
Menstrual cycle
Controlled by ovarian hormones
 Menstrual phase
 Lasts 1-5 days
 Sloughing off of the functional layer
of the endometrium with bleeding
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Oogenesis and ovarian
cycle
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Proliferative phase
 From day 6-14
 Estrogen is the main hormone
 Ovarian follicle grows
 Endometrium thickens with
proliferation of its glands and blood
vessels
 Ovulation occur at day 14
Oogenesis and ovarian
cycle
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Secretory phase
 From day 15-28
 Progesterone produced by the
corpus luteum is the main hormone
 Endometrium thickens even more
with further proliferation and coiling
of the glands
 Uterus is getting ready for the
embryo implantation
Oogenesis and ovarian
cycle
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If no implantation occurs the corpus
luteum will deteriorate causing lack of
ovarian hormones that will cause
deterioration of the functional layer of
the endometrium
Menstrual cycle
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