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HUMAN
REPRODUCTIONG A M E TO G E N E S I S , M E N S T R U A L C Y C L E A N D
F E R T I L I Z AT I O N
BY
I N D E R J I T S I N G H
P G T B I O L O G Y
K V S E C TO R 3 1 C H A N D I G A R H
• Gametogenesis: the process of formation of male and female gamete.
• Formation of male gamete in human is known as spermatogenesis and formation of
female gamete is known as oogenesis.
• # Spermatogenesis: -
• Formation of spermatozoa in the testis; the process starts at puberty.
• In testis, the immature male germ cells (spermatogonia) produce sperms by
spermatogenesis that begins at puberty.
• The spermatogonia (sing. spermatogonium) present on the inside wall of seminiferous
tubules multiply by mitotic division and increase in numbers.
• Each spermatogonium is diploid and contains 46 chromosomes.
• Some of the spermatogonia called primary spermatocytes periodically undergo meiosis.
• A primary spermatocyte completes the first meiotic division (reduction division) leading
to formation of two equal, haploid cells called secondary spermatocytes, which have only
23 chromosomes each.
• The secondary spermatocytes undergo the second meiotic division to produce four equal,
haploid spermatids.
• The spermatids are transformed into spermatozoa (sperms) by the process called
spermiogenesis.
• After spermiogenesis, sperm heads become embedded in the Sertoli cells, and are finally
released from the seminiferous tubules by the process called Spermiation.
Schematic representation of SpermatogenesisDiagrammatic sectional view of a seminiferous
tubule (enlarged)
Spermatogenesis:
-
HORMONAL CONTROL OF SPERMATOGENESIS
SPERMIOGENESIS AND
SPERMATOZOON STRUCTURE
Structure of a
sperm
• # Oogenesis: -
• Process of formation of female gametes or ova in ovary.
• Oogenesis is initiated during the embryonic development stage when a couple of
gamete mother cells (oogonia) are formed within each fetal ovary; no more oogonia are
formed and added after birth.
• These cells start division and enter into prophase-I of the meiotic division and get
temporarily arrested at that stage, called primary oocytes.
• Each primary oocyte then gets surrounded by a layer of granulosa cells and then called
the primary follicle.
• A large number of these follicles degenerate during the phase from birth to puberty.
• Therefore, at puberty only 60,000-80,000 primary follicles are left in each ovary.
• The primary follicles get surrounded by more layers of granulosa cells and a new theca
and called secondary follicles.
• The secondary follicle soon transforms into a tertiary follicle which is characterised by a
fluid filled cavity called antrum. The theca layer is organised into an inner theca interna
and an outer theca externa.
• the primary oocyte within the tertiary follicle grows in size and completes its first meiotic
division. It is an unequal division resulting in the formation of a large haploid secondary
oocyte and a tiny first polar body.
• The tertiary follicle further changes into the mature follicle or Graafian follicle.
• The secondary oocyte forms a new membrane called zona pellucida
surrounding it. The Graafian follicle now ruptures to release the secondary
oocyte (ovum) from the ovary by the process called ovulation.
• The secondary oocyte starts its second meiotic division but it is suspended
in metaphase II, until a sperms enters it.
Diagrammatic Section view of ovary
Schematic representation of Oogenesis
HORMONAL CONTROL OF
OOGENESIS
# MENSTRUAL CYCLE: -
• The reproductive cycle in the female primates (e.g. monkeys, apes and human beings) is
called menstrual cycle.
• The first menstruation begins at puberty and is called menarche.
• In human females, menstruation is repeated at an average interval of about 28/29 days,
and the cycle of events starting from one menstruation till the next one is called the
menstrual cycle.
• One ovum is released (ovulation) during the middle of each menstrual cycle. The major
events of the menstrual cycle are: -
• i) Menstrual Phase: -
• Cycle starts with this phase and menstrual flow (menstruation) lasts for 3-5 days.
Diagrammatic presentation of various events during a menstrual
cycle
• Results due to break down of endometrial lining of uterus and its blood vessels, along
with unfertilized ovum.
• ii) Follicular Phase/ Proliferative Phase: -
• the primary follicles in the ovary grow to become a fully mature Graafian follicle.
• simultaneously the endometrium of uterus regenerates through proliferation of its cells.
• These changes are due to an increased level of pituitary hormones, FSH and LH and
ovarian hormone, estrogen.
• FSH controls the follicular phase; it stimulates the growth of follicles and secretion of
estrogen by the growing follicles.
• Both LH and FSH attain a peak level in the middle of cycle (about 14th day).
• iii) Ovulatory Phase: -
• The peak level of LH (called LH surge) induces the rupture of the mature Graafian follicle
and thereby release of secondary oocytes (ovum); this process is called ovulation.
• iv) Luteal Phase/ Secretory Phase: -
• Ruptured follicle is transformed into corpus luteum.
• It secretes large quantities of progesterone’s.
• Endometrium thickens further and their glands secrete a fluid in the uterus.
• In the absence of the fertilization, corpus luteum degenerates and this causes
disintegration of the endometrium leading to menstruation.
• Ceasing of the menstrual cycle is known as menopause at the age of about 45-50 years.
Ovum surrounded by few sperms
# Fertilization: -
• During copulation (coitus) semen is released by the penis into the vagina (insemination).
• The motile sperms swim rapidly, pass through the cervix, enter into the uterus and finally
reach the junction of the isthmus and ampulla (ampullary-isthmic junction) of the
fallopian tube.
• The ovum released by the ovary is also transported to the ampullary-isthmic junction
where fertilisation takes place.
• The process of fusion of a sperm with an ovum is called fertilisation.
• During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum
and induces changes in the membrane that block the entry of additional sperms.
• The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum
through the zona pellucida and the plasma membrane.
• This induces the completion of the meiotic division of the secondary oocyte. The second
meiotic division is also unequal and results in the formation of a second polar body and a
haploid ovum (ootid).
• Soon the haploid nucleus of the sperms and that of the ovum fuse together to form a
diploid zygote.
• Thanks………………

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3. human reproduction gametogenesis and menstrual cycle

  • 1. HUMAN REPRODUCTIONG A M E TO G E N E S I S , M E N S T R U A L C Y C L E A N D F E R T I L I Z AT I O N BY I N D E R J I T S I N G H P G T B I O L O G Y K V S E C TO R 3 1 C H A N D I G A R H
  • 2. • Gametogenesis: the process of formation of male and female gamete. • Formation of male gamete in human is known as spermatogenesis and formation of female gamete is known as oogenesis. • # Spermatogenesis: - • Formation of spermatozoa in the testis; the process starts at puberty. • In testis, the immature male germ cells (spermatogonia) produce sperms by spermatogenesis that begins at puberty. • The spermatogonia (sing. spermatogonium) present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers. • Each spermatogonium is diploid and contains 46 chromosomes.
  • 3. • Some of the spermatogonia called primary spermatocytes periodically undergo meiosis. • A primary spermatocyte completes the first meiotic division (reduction division) leading to formation of two equal, haploid cells called secondary spermatocytes, which have only 23 chromosomes each. • The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids. • The spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis. • After spermiogenesis, sperm heads become embedded in the Sertoli cells, and are finally released from the seminiferous tubules by the process called Spermiation.
  • 4. Schematic representation of SpermatogenesisDiagrammatic sectional view of a seminiferous tubule (enlarged) Spermatogenesis: -
  • 5. HORMONAL CONTROL OF SPERMATOGENESIS
  • 8. • # Oogenesis: - • Process of formation of female gametes or ova in ovary. • Oogenesis is initiated during the embryonic development stage when a couple of gamete mother cells (oogonia) are formed within each fetal ovary; no more oogonia are formed and added after birth. • These cells start division and enter into prophase-I of the meiotic division and get temporarily arrested at that stage, called primary oocytes. • Each primary oocyte then gets surrounded by a layer of granulosa cells and then called the primary follicle. • A large number of these follicles degenerate during the phase from birth to puberty.
  • 9. • Therefore, at puberty only 60,000-80,000 primary follicles are left in each ovary. • The primary follicles get surrounded by more layers of granulosa cells and a new theca and called secondary follicles. • The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum. The theca layer is organised into an inner theca interna and an outer theca externa. • the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. It is an unequal division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body. • The tertiary follicle further changes into the mature follicle or Graafian follicle.
  • 10. • The secondary oocyte forms a new membrane called zona pellucida surrounding it. The Graafian follicle now ruptures to release the secondary oocyte (ovum) from the ovary by the process called ovulation. • The secondary oocyte starts its second meiotic division but it is suspended in metaphase II, until a sperms enters it. Diagrammatic Section view of ovary
  • 13. # MENSTRUAL CYCLE: - • The reproductive cycle in the female primates (e.g. monkeys, apes and human beings) is called menstrual cycle. • The first menstruation begins at puberty and is called menarche. • In human females, menstruation is repeated at an average interval of about 28/29 days, and the cycle of events starting from one menstruation till the next one is called the menstrual cycle. • One ovum is released (ovulation) during the middle of each menstrual cycle. The major events of the menstrual cycle are: - • i) Menstrual Phase: - • Cycle starts with this phase and menstrual flow (menstruation) lasts for 3-5 days.
  • 14. Diagrammatic presentation of various events during a menstrual cycle
  • 15. • Results due to break down of endometrial lining of uterus and its blood vessels, along with unfertilized ovum. • ii) Follicular Phase/ Proliferative Phase: - • the primary follicles in the ovary grow to become a fully mature Graafian follicle. • simultaneously the endometrium of uterus regenerates through proliferation of its cells. • These changes are due to an increased level of pituitary hormones, FSH and LH and ovarian hormone, estrogen. • FSH controls the follicular phase; it stimulates the growth of follicles and secretion of estrogen by the growing follicles. • Both LH and FSH attain a peak level in the middle of cycle (about 14th day).
  • 16. • iii) Ovulatory Phase: - • The peak level of LH (called LH surge) induces the rupture of the mature Graafian follicle and thereby release of secondary oocytes (ovum); this process is called ovulation. • iv) Luteal Phase/ Secretory Phase: - • Ruptured follicle is transformed into corpus luteum. • It secretes large quantities of progesterone’s. • Endometrium thickens further and their glands secrete a fluid in the uterus. • In the absence of the fertilization, corpus luteum degenerates and this causes disintegration of the endometrium leading to menstruation. • Ceasing of the menstrual cycle is known as menopause at the age of about 45-50 years.
  • 17. Ovum surrounded by few sperms # Fertilization: -
  • 18. • During copulation (coitus) semen is released by the penis into the vagina (insemination). • The motile sperms swim rapidly, pass through the cervix, enter into the uterus and finally reach the junction of the isthmus and ampulla (ampullary-isthmic junction) of the fallopian tube. • The ovum released by the ovary is also transported to the ampullary-isthmic junction where fertilisation takes place. • The process of fusion of a sperm with an ovum is called fertilisation. • During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane that block the entry of additional sperms. • The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane. • This induces the completion of the meiotic division of the secondary oocyte. The second meiotic division is also unequal and results in the formation of a second polar body and a haploid ovum (ootid). • Soon the haploid nucleus of the sperms and that of the ovum fuse together to form a diploid zygote.