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• Meiosis in Males (Spermatogenesis)


  • Location: Occurs in the seminiferous tubules of the testes
  • Onset: Begins at puberty and continues throughout life
  • Outcome: Each diploid spermatogonium undergoes meiosis to produce four haploid sperm cells
  • Cytoplasmic Division: Equal division, resulting in four equally sized sperm cells
  • Frequency: Continuous process; millions of sperm are produced daily
  • Prophase I Duration: Relatively short, taking days to weeks
  • Completion: Meiosis is uninterrupted and progresses to completion with each cycle
• Meiosis in Females (Oogenesis)


  • Location: Occurs in the ovaries
  • Onset: Begins before birth; oogonia enter meiosis and become primary oocytes during fetal development
  • Outcome: Each diploid oogonium undergoes meiosis to produce one haploid ovum and three polar bodies (which typically degenerate)
  • Cytoplasmic Division: Unequal division, resulting in one large ovum and smaller polar bodies
  • Frequency: Cyclical process, with limited oocytes present at birth; typically, one ovum is produced per menstrual cycle
  • Prophase I Duration: Can last years; primary oocytes are arrested in prophase I until puberty
  • Completion: Meiosis is arrested twice, first at prophase I (until puberty) and again at metaphase II (until fertilisation)
• Meiosis in males and females exhibits similarities and differences in terms of location, timing, outcome, and process. In males, meiosis is a continuous process starting at puberty, producing four equal sperm cells from each diploid cell. In females, meiosis begins before birth and is characterised by two arrest points. This results in one ovum and three polar bodies from each diploid cell, with unequal cytoplasmic division. These differences are essential for the respective roles of sperm and eggs in reproduction.
• Follicle-stimulating hormone (FSH)

  Produced by: Anterior pituitary gland<|>Role: Initiates the growth and maturation of ovarian follicles
• Interaction of FSH

  1. Early Follicular Phase: FSH levels increase slightly, stimulating the development of several follicles, each containing an egg

  2. Mid-follicular phase: As the FSH level decreases, usually only one follicle continues to develop and begins secreting oestrogen
• Oestrogen


  Produced by: Growing ovarian follicles<|>Role: Regulates the menstrual cycle and prepares the endometrium for potential implantation; also affects breast tissue
• Interaction of Oestrogen

  1. Follicular Phase: Low oestrogen levels at the start cause the endometrium to break down and shed, leading to menstrual bleeding

  2. Mid Follicular Phase: The developing follicle produces increasing levels of oestrogen, promoting the thickening of the endometrium

  3. Late Follicular Phase: High oestrogen levels stimulate a surge in LH and FSH
• Luteinising Hormone (LH)

  Produced by: Anterior pituitary gland<|>Role: Triggers ovulation and the formation of the corpus luteum
• Interaction of LH

  1. Late Follicular Phase: High oestrogen levels cause an LH surge, leading to ovulation

  2. Ovulation: LH surge stimulates the release of the egg, usually 16 to 32 hours after the surge begins

  3. Post-Ovulation: LH supports the corpus luteum formation from the ruptured follicle
• Progesterone


  Produced by: Corpus luteum<|>Role: Prepares and maintains the endometrium for implantation and pregnancy
• Interaction of Progesterone

  1. Luteal Phase: Progesterone levels rise, promoting further thickening of the endometrium. Oestrogen levels are also high during this phase

  2. If No Pregnancy: Decreased levels of progesterone and oestrogen lead to the breakdown of the endometrium and menstrual bleeding

  3. If Pregnancy Occurs: The corpus luteum continues to produce progesterone to maintain the pregnancy
• Feedback Mechanisms

  1. Negative Feedback: Follicular Phase: Low levels of oestrogen and progesterone inhibit FSH

  2. Negative Feedback: Luteal Phase: High levels of progesterone and oestrogen inhibit FSH and LH

  3. Positive Feedback: Late Follicular Phase: High oestrogen levels stimulate an LH surge
• Phases of the Menstrual Cycle


  1. Follicular Phase: FSH stimulates the growth of multiple follicles, leading to increased oestrogen production

  2. Follicular Phase: Rising oestrogen levels initially inhibit FSH but later cause an LH surge

  3. Ovulation: The LH surge triggers the release of a mature egg

  4. Ovulation: During the surge, oestrogen levels decrease while progesterone levels begin to increase

  5. Luteal Phase: LH maintains the corpus luteum, which secretes progesterone and oestrogen

  6. Luteal Phase: High progesterone prepares the endometrium and inhibits further FSH and LH secretion

  7. Menstruation: If pregnancy does not occur, the corpus luteum degenerates

  8. Menstruation: Decreased progesterone and oestrogen levels lead to endometrial shedding and the start of a new cycle

  9. Pregnancy: If pregnancy occurs, the corpus luteum continues functioning, maintaining early pregnancy
• Mature Male Gametes (Sperm Cells)


  • Size: Microscopic, around 50-60 micrometres in length
  • Shape: Elongated and streamlined, with a distinct head, midpiece, and tail
• Components of Mature Male Gametes (Sperm Cells)


  • Head:
  • Nucleus: Contains tightly packed chromatin with 23 chromosomes (haploid)
  • Acrosome: A cap-like structure containing enzymes that penetrate the egg's outer layers during fertilisation
  • Midpiece: Contains numerous mitochondria that provide ATP for motility
  • Tail (Flagellum): A long, whip-like structure that propels the sperm forward, enabling it to swim towards the egg
• Mature Male Gametes (Sperm Cells)


  • Mobility: Highly motile, capable of swimming through the female reproductive tract to reach and fertilise the egg
  • Lifespan: Can survive up to 5 days within the female reproductive tract
• Mature Female Gametes (Oocytes)


  • Size: Approximately 100-120 micrometres in diameter
  • Shape: Round and relatively large compared to sperm, with a spherical shape
• Components of Mature Female Gametes (Oocytes)


  • Nucleus: Contains 23 chromosomes (haploid) surrounded by a large amount of cytoplasm
  • Cytoplasm: Rich in nutrients and organelles to support early embryonic development
  • Zona Pellucida: A thick glycoprotein layer surrounding the oocyte crucial for species-specific sperm binding and preventing polyspermy
  • Corona Radiata: A layer of follicular cells that provide additional support and protection to the oocyte
• Mature Female Gametes (Oocytes)


  • Mobility: Non-motile; relies on ciliary action and muscular contractions of the female reproductive tract for movement
  • Lifespan: Viable for about 24 hours after ovulation
• Luteinising Hormone (LH)


  Stimulates the testicles to produce testosterone, which is crucial for the production of sperm (spermatogenesis) and the development of male secondary sexual characteristics
• LH Levels in Males

  • Adults: LH levels are relatively stable
  • Children: LH levels are low in early childhood and gradually increase as puberty approaches, usually between ages six and eight
• Follicle Stimulating Hormone (FSH)


  Signals the testes to produce sperm, playing a direct role in spermatogenesis
• FSH Levels in Males

  • After puberty, FSH levels remain relatively constant, ensuring continuous sperm production
• LH in Females

  LH is critical for both sexual development and fertility in females<|>Contributes to sexual development in children<|>Regulates the menstrual cycle<|>Triggers ovulation, the release of an egg from the ovary<|>The surge in LH levels mid-cycle induces ovulation, which is essential for fertility
• FSH in Females

  FSH is essential for sexual development and fertility in females<|>Contributes to sexual development in children<|>Helps control the menstrual cycle<|>Stimulates the growth and maturation of ovarian follicles, preparing eggs for ovulation
• FSH Levels in Females

  • Follicular Phase: FSH levels rise at the beginning to promote follicle development
  • Ovulation: A decrease in FSH levels later in the follicular phase usually ensures the selection of a dominant follicle for ovulation
• LH in Males: Stimulates testosterone production, crucial for spermatogenesis and male secondary sexual characteristics
• FSH in Males: Directly stimulates sperm production, maintaining a constant level post-puberty for continuous spermatogenesis
• LH in Females: Regulates the menstrual cycle and triggers ovulation, essential for egg release and fertility
• FSH in Females: Controls the menstrual cycle by stimulating the growth of ovarian follicles, preparing eggs for ovulation and ensuring reproductive health
• Menstrual Cycle


  1. Follicular Phase

  2. Ovulation

  3. Luteal Phase
• Follicular Phase


  Hormonal Levels:<|>Oestrogen and Progesterone: Both levels are low at the start, causing the endometrium (uterine lining) to break down and shed, resulting in menstrual bleeding.<|>FSH: Levels increase as bleeding begins, promoting the development of ovarian follicles.<|>Follicle Development: As follicles develop, they start to produce oestrogen. One dominant follicle continues to mature and releases increasing amounts of oestrogen.<|>Endometrial Changes: Rising oestrogen levels help rebuild the endometrium in preparation for a potential pregnancy.
• Ovulation


  Hormonal Surge: LH and FSH: Levels surge, triggering the release of the mature egg from the dominant follicle.<|>Oestrogen and Progesterone: Oestrogen levels decrease slightly just before the LH surge. Progesterone levels begin to rise as ovulation occurs.<|>Egg Release: The surge in LH causes the follicle to release an egg (ovulation).
• Luteal Phase


  Hormonal Levels: LH and FSH: Levels decrease after ovulation.<|>Progesterone: Produced by the corpus luteum (the remnant of the ruptured follicle), levels rise significantly.<|>Oestrogen: Levels remain high, alongside progesterone.<|>Endometrial Changes: Progesterone, along with oestrogen, promotes the thickening and maintenance of the endometrium, preparing it for potential implantation of a fertilized egg.<|>Cycle Restart: If fertilization does not occur, the corpus luteum degenerates, leading to a drop in progesterone and oestrogen levels. The endometrium breaks down, leading to menstruation and the start of a new cycle.
• Ovarian Cycle


  1. First Half of the Cycle (Pre-Ovulation)

  2. Second Half of the Cycle (Post-Ovulation)
• Hormone Secretion

  Oestrogen and Progesterone: Ovaries secrete these hormones, which are crucial for reproductive development, menstruation, and secondary sexual characteristics such as breast development, body shape, and body hair.
• First Half of the Cycle (Pre-Ovulation)


  Oestrogen Production: Highest before ovulation, stimulating the growth and maturation of the ovarian follicles. Promotes the thickening of the endometrium and regulates FSH and LH levels through feedback mechanisms.
• Second Half of the Cycle (Post-Ovulation)


  Progesterone Production: Increases significantly during the luteal phase to prepare the uterus for a potential pregnancy. Maintains the endometrium, making it suitable for implantation of a fertilized egg.<|>Oestrogen: Continues to be produced at high levels to support the endometrial lining.
• Summary of Hormonal Roles

  • FSH: Promotes follicle development in the ovaries. Peaks during the follicular phase to initiate the growth of ovarian follicles.
  • LH: Triggers ovulation and the formation of the corpus luteum. Surge in LH is crucial for the release of the egg from the follicle.
  • Oestrogen: Produced by developing follicles. Stimulates the thickening of the endometrium. Regulates FSH and LH levels through feedback mechanisms. Important for secondary sexual characteristics.
  • Progesterone: Produced by the corpus luteum. Maintains and further thickens the endometrium post-ovulation. Prepares the uterus for a potential pregnancy.
• Hormonal Levels Immediately Before Ovulation

  1. Follicular Phase (Before Ovulation)

  2. Luteal Phase (After Ovulation)