Reproductive System Notes

The Reproductive System

Overview of Reproduction

Sexual reproduction involves the fusion of two haploid gametes (eggs and sperm) to form a diploid zygote. The reproductive system's primary role is to produce these gametes using specialized organs called gonads (ovaries and testes) and to facilitate their fusion between individuals.

Male Anatomy

External Anatomy (Penis and Scrotum)
  • Penis: Surrounds the urethra and delivers sperm into the vagina for fertilization.
  • Scrotum: Houses the testes, where sperm is produced and stored. It helps regulate temperature for optimal sperm development.
Internal Anatomy (Testes)
  • Lobules: Contain seminiferous tubules where sperm cells develop.
  • Seminiferous Tubules: Site of spermatogenesis.
  • Epididymis: The site of sperm maturation and storage. Sperm are stored until ejaculation.
Spermatogenesis
  • Begins at puberty and continues throughout life.
  • Produces 100-300 million sperm per day.
  • Spermatogonia (stem cells) are diploid, while sperm are haploid.
  • Spermatogonium undergoes asymmetric mitosis:
    • One daughter cell remains a spermatogonium.
    • The other becomes a primary spermatocyte and divides by meiosis.
Meiosis of Spermatogonia
  • After meiosis I, two daughter cells are haploid and called secondary spermatocytes.
  • Each secondary spermatocyte divides through meiosis II and forms two haploid spermatids.
  • Spermatids mature into sperm, which are released into the lumen of the seminiferous tubule, and stored in the epididymis.
Structure of Sperm
  • 85,000x smaller than oocytes.
  • Head:
    • Surrounded by an acrosome filled with lysosomal enzymes to penetrate the oocyte.
    • Contains the nucleus with the male's genetic material.
  • Mid-piece:
    • Connects to the head with a centriole.
    • Packed with mitochondria to provide energy for movement.
  • Tail:
    • Grows from the centriole in the "neck".
    • A flagellum that facilitates movement.
Anatomy for Semen Production
  • Seminal Vesicles: Site of sperm and semen mixing. Produce a fluid with large amounts of fructose.
  • Prostate Gland: Produces a milky fluid that protects sperm until they establish in the vagina, making semen alkaline and thick.
  • Bulbourethral (Cowper’s) Glands: Produce a pre-ejaculate that functions in lubrication and pH balance.
Sperm Transport
  • During ejaculation, sperm are pushed by smooth muscle contraction to the vas deferens.
  • Vasectomy: A surgical procedure where the vas deferens is cut to prevent sperm from being ejaculated.
  • The seminal vesicles produce fluid with large amounts of fructose.
  • Secreted to the prostate gland which makes semen alkaline and thick
  • Bulbourethral glands produce pre-ejaculate

Female Anatomy

Anatomy of the Vulva and Vagina
  • Labia Majora and Minora: Cover and protect the vaginal opening.
  • Clitoris: Highly innervated, similar to the glans penis.
  • Hymen: Not an indication of virginity.
  • Vagina: Extends from the cervix. A muscular canal about 10 cm in length.
    • Lactobacillus colonize the vagina and maintain an acidic environment to prevent infection.
Ovaries, Oviduct, and Uterus
  • Ovaries: Produce oocytes (eggs) and hormones.
    • Development of follicles that surround, protect, and nourish oocytes
  • Oviduct (Uterine Tubes): Transport oocytes from the ovary to the uterus.
  • Uterus: Hollow, thick-walled womb.
    • Endometrium: Inner layer, the mucosal lining where the embryo implants.
      • Stratum functionalis: Thickens and sheds during menstruation.
      • Stratum basalis: Regenerates the functionalis.
    • Cervix: The lower part of the uterus that connects to the vagina.
    • Vagina
Ovarian Cycle
  • Roughly a 28-day cycle with two main processes:
    • Oogenesis: The production of oocytes (gametes).
    • Folliculogenesis: Growth and development of ovarian follicles.
  • Three phases:
    • Follicular phase
    • Ovulation
    • Luteal phase
  • Correlated with, but not the same as the menstrual cycle.
Oogenesis
  • Diploid oogonia divide via mitosis to produce primary oocytes.
  • Meiosis of primary oocytes begins before birth but arrests in prophase I and is stored until puberty.
  • Primary oocyte divides by meiosis I and produces a secondary oocyte and a polar body.
  • Secondary oocyte leaves the ovary during ovulation for fertilization.
  • When sperm penetrates the secondary oocyte, meiosis II completes to produce one ovum and another polar body.
Folliculogenesis
  • Ovarian follicle = oocyte and supporting cells.
  • Theca cells work with granulosa cells to produce estrogen.
  • Oocyte secretes the zona pellucida, and follicular fluid pools around the oocyte.
  • One follicle continues to grow until ovulation when the secondary oocyte with granulosa cells is expelled from the ovary.
Hormonal Control of the Ovarian Cycle: Follicular Phase
  • FSH stimulates follicle growth, and LH stimulates granulosa and theca cells to produce estrogen.
  • The dominant follicle produces the most estrogen and signals negative feedback to "starve" other follicles.
Hormonal Control of the Ovarian Cycle: Ovulation
  • The dominant follicle produces even more estrogen, resulting in positive feedback, leading to more FSH and LH (LH surge, used to detect fertility).
  • LH stimulates meiosis of the primary oocyte and triggers proteases to break down the ovary wall.
  • Pressure from follicular fluid results in the expulsion of the oocyte.
Hormonal Control of the Ovarian Cycle: Luteal Phase
  • LH transforms the collapsed follicle into the corpus luteum.
  • Granulosa and theca cells in the corpus luteum produce progesterone, which triggers negative feedback and helps establish and maintain pregnancy.
  • If no pregnancy, the corpus luteum degrades and disintegrates.
Uterine Tubes and the Uterus
  • Uterine Tubes: Carry oocytes from the ovary to the uterus.
    • Ciliated cells "beat" in the direction of the uterus.
  • Uterus: Hollow, thick-walled womb.
    • Endometrium (inner layer, mucosal lining where the embryo implants):
      • Stratum functionalis: Thickens and sheds during menstruation.
      • Stratum basalis: Regenerates functionalis.
The Menstrual Cycle
  • Process by which the uterine lining is shed, rebuilds, and prepares for implantation of the embryo.
  • Three phases:
    • Menses
    • Proliferative
    • Secretory
  • Timing varies from 20-40 days (28-day average).
  • Day 1 is the first day of menses (period).
Menses Phase
  • Lasts approximately 5 days, but can be shorter or longer.
  • Triggered by a decline in progesterone at the end of the luteal phase.
  • Occurs during early days of the follicular phase when progesterone, FSH, and LH are low.
  • The stratum functionalis sloughs off.
Proliferative Phase
  • The endometrium begins to proliferate.
  • Occurs when granulosa and theca cells of the tertiary follicle produce estrogen.
  • The LH surge triggers ovulation and marks the end of the proliferative phase (usually around day 14).
Secretory Phase
  • High estrogen promotes uterine tube contraction to move the ovulated oocyte and decreases acidity.
  • Progesterone from the corpus luteum triggers the secretory phase.
  • Endometrial glands secrete a fluid rich in glycogen that nourishes the developing zygote.
  • Spiral arteries supply blood to the thickened endometrium.
  • If no embryo implants, estrogen and progesterone levels drop.
Coordinated Ovarian and Menstrual Cycles

The slide shows the relationship and synchronization of the ovarian cycle(follicular phase, ovulation and luteal phase) and the menstrual cycle (menses, proliferative, and secretory phase). Also the specific hormones and their fluctuation are connected.

Sex, Gender, and Appropriate Language

  • Gender: Cultural, not a biological classification. Includes pronouns, dress, behavior, femininity vs. masculinity.
  • Sex: Typically assigned at birth based on anatomy and chromosomes.
    • Anatomy:
      • Penis and testes (assigned male).
      • Vagina and ovaries (assigned female).
    • Chromosomes:
      • XY (assigned male).
      • XX (assigned female).
    • Hormones:
      • Testosterone (high production with testes).
      • Estrogen (high production with ovaries).
Sex is Not Binary
  • Intersex: Distinct from hermaphrodite (outdated, inaccurate, and offensive).
    • Not “fully male” or “fully female” genitalia.
    • Chromosomes:
      • XXY – “male”.
      • XYY – “male”.
      • XXX – “female”.
      • XO – “female”.
    • Hormones:
      • Ovaries and adrenal glands secrete testosterone.
      • Production and response vary dramatically based on a number of factors.
Sex Chromosomes in Humans
  • During the development of reproductive systems, the presence or absence of testosterone differentiates the tissue.
  • The Y chromosome includes genes that drive the production of testosterone (almost exclusively).
  • The X chromosome has many genes unrelated to the reproductive system.
Testosterone
  • Secreted by the testes to help the development of sex organs, increased production during puberty to initiate spermatogenesis.
  • Also secreted by ovaries and adrenal glands, maintains sex drive.
  • Negative feedback control mechanism with GnRH from the hypothalamus stimulating the release of FSH and LH by the anterior pituitary.
Embryonic Sex Development
  • The Y chromosome includes the SRY gene that begins the development of testes and suppresses the development of ovaries.
  • Testosterone influences bipotential cells.
    • Cells that could become the clitoris or glans penis will become the glans penis.
  • The uterus, uterine tubes, part of the vagina, epididymis, vas deferens, and seminal vesicles are not bipotential and form from either the Mϋllerian duct or Wolffian duct.
  • Anti-Mϋllerian hormone degrades the Mϋllerian duct, and testosterone stimulates the growth of the Wolffian duct.
Androgen Insensitivity
  • The gene for the androgen receptor is on the X chromosome.
  • About 1 in 10,000 people with XY chromosomes is born with a mutation in their androgen receptor gene that causes the receptor protein to be partially or completely insensitive to androgens.
  • Characteristics:
    • Female external genitalia.
    • Nonfunctional male internal genitalia.
    • Secondary sex characteristics typical of female.