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Exercise 45
Physiology of Reproduction
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Meiosis
GametesHaploid complement (n)
GametogenesisProcess of gamete formation with
the reduction by half of the chromosome number
Homologous chromosomeCarries genes for the same traits
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Meiosis
Meiosis IProphase
• 23 tetrads• Homologues chromosomes
synapse• Chiasmata or crossover
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Meiosis
MetaphaseAnaphase
• Homologues separates• Dyads stays together
Telophase• 2 cells with diploid number of
chromosomes
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Meiosis
Meiosis IIProphase
• No chromosome replication• Cells are diploid
Metaphase
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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 cellFound in the seminiferous tubulesIt 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 phaseIt 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
Spermatids (n)Nonfunctional gametesNo motileThey undergo spermiogenesis and
form the sperm
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Spermatogenesis
SpermMotile Smaller than the spermatidHead of the sperm
• Contain the genetic material • Acrosome
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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
Sertoli cellsSupport cells responsible for sperm
nourishment
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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 birthOogonias no longer existsAll cells are oocytes encapsulated by
a primordial follicleNo more oocytes will be produced
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Oogenesis and ovarian cycle
From birth to pubertyPrimary oocytes are quiescent
From puberty and onIncrease of FSH levels cause:FollicleOne 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• It contains the primary oocyte
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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
Secondary oocyteLarge cell (contains most of the
cytoplasm of the primary oocyte)HaploidArrested in metaphase of meiosis IIIt is expelled by the Graafian follicle
(ovulation)It is captured by the uterine tube
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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
OvumChromosomes of the ovum and
sperm will combine to form a diploid cell
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Oogenesis and ovarian cycle
First polar bodySmall cell (almost no cytoplasm)Produced by the division of the
primary oocyteIt will disintegrate
Secondary polar bodyProduced by the division of the
secondary oocyteIt will also disintegrate
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Oogenesis and ovarian cycle
Hormonal cycle Beginning of the menstrual cycle
FSH is the dominant hormoneLow levels of LHLow levels of estrogen and
progesterone
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Oogenesis and ovarian cycle Before ovulation
Estrogen levels increaseProgesterone level remain low
OvulationCaused mainly by a peak of LH
After ovulationEstrogen levels decreaseProgesterone levels increase FSH and LH levels decrease
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Menstrual cycle
Controlled by ovarian hormones Menstrual phase
Lasts 1-5 daysSloughing off of the functional layer
of the endometrium with bleeding
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Oogenesis and ovarian cycle
Proliferative phaseFrom day 6-14Estrogen is the main hormoneOvarian follicle growsEndometrium thickens with
proliferation of its glands and blood vessels
Ovulation occur at day 14
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Oogenesis and ovarian cycle Secretory phase
From day 15-28Progesterone produced by the
corpus luteum is the main hormoneEndometrium thickens even more
with further proliferation and coiling of the glands
Uterus is getting ready for the embryo implantation
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Oogenesis and ovarian cycle
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
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Menstrual cycle
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