The Reproductive System Flashcards

Female Reproductive System

Major Structures

• Ovaries: Female gonads responsible for oogenesis (gamete production) and hormone production (estrogen and progesterone).
• Uterine/Fallopian Tubes: Connect ovaries to the uterus, serve as a passageway for sperm, and are the site of fertilization. Composed of the isthmus, ampulla, and infundibulum with fimbriae.
• Uterus: A hollow, thick-walled organ that houses the developing fetus and is the site of menstruation. It has three layers:
  • Perimetrium (outer serosa)
  • Myometrium (middle smooth muscle)
  • Endometrium (inner mucosa that sheds monthly if pregnancy does not occur)
• Cervix: The distal region of the uterus, separating it from the vagina, involved in mucus production and facilitates childbirth.
• Vagina: Passageway for childbirth and menstrual flow with an acidic environment to repel infection and sperm.
• External Genitalia:
  • Clitoris
  • Labia minora
  • Labia majora
• Mammary Glands: Branched glands (modified sweat glands) composed of ducts surrounded by connective tissue and fat, arranged into lobes culminating at the nipple; lobes contain milk-producing lobules.

Functions

• Gamete production (oogenesis)
• Hormone production (estrogen, progesterone, inhibin, and relaxin)
• Reception and transport of sperm
• Housing fertilized ovum, maintaining pregnancy, and providing a passageway for childbirth
• Lactation (synthesis, secretion, and ejection of milk)

Male Reproductive System

Major Structures

• Testes: Male gonads responsible for spermatogenesis (gamete production) and testosterone production.
• Epididymis: Receives and is the site of functional maturation of sperm.
• Ductus/Vas Deferens: Transports ejaculated sperm.
• Accessory Glands:
  • Seminal Vesicles: Secrete fluid to aid in sperm motility (approx. 65% of semen).
  • Prostate: Secretes fluid to provide energy for sperm (approx. 30% of semen).
  • Bulbourethral Glands: Secrete thick alkaline fluid for sperm protection (less than 1% of semen).
• External Genitalia
  • Penis
  • Urethra
  • Scrotum

Functions

• Gamete production (spermatogenesis)
• Maturation, storage, transport, and protection of sperm
• Hormone production (testosterone)

Anatomy of the Testes

• Lobules: Compartments within the testes.
• Seminiferous Tubules: Highly coiled tubes within lobules, the specific site of spermatogenesis.
  • Spermatogenic Cells: Cells at various stages of spermatogenesis.
  • Sertoli Cells: Supporting cells spanning from the basement membrane to the lumen.
• Leydig Cells: Located between seminiferous tubules; produce testosterone.

Male Reproductive Ductal System

• Epididymis: Receives physically mature sperm from seminiferous tubules; site of functional maturation (motility development) taking 12-16 days.
• Ductus/Vas Deferens: Receives mature sperm from the epididymis; transports ejaculated sperm via peristalsis.
• Urethra: Passageway for both urine and semen.

Semen

• Composition: Mixture of sperm (approx. 4%) and glandular secretions (approx. 96%).
• Functions:
  • Contains nutrients and chemicals for sperm protection, activation, and movement.
  • Contains prostaglandins to reduce viscosity of cervical mucus.
  • Alkaline pH to neutralize the acidic environment of the female reproductive tract.
  • Ability to suppress the immune response of the female reproductive tract.
  • Coagulation factors to allow adherence to vaginal walls.

Oogenesis (Females)

• Sequence of events (mitosis and meiosis I & II) leading to mature gametes (ova or secondary oocytes).
• Not a continuous process; development pauses before birth (as primary oocytes) and resumes at puberty.
• One primary oocyte is selected to complete development each monthly cycle after puberty begins.
• Oogenesis begins in fetal life; a female has a lifetime supply of primary oocytes at birth.
• Process starts with one oogonium and results in one ovum (secondary oocyte).
• Oocytes are housed within a follicle (supportive cells) for nourishment and protection until ovulation.
• Ova contain 23 chromosomes.
• Oogenesis continues until there are no more ova left to ovulate (menopause).

Spermatogenesis (Males)

• Sequence of events (mitosis and meiosis I & II) leading to mature gametes (sperm).
• Occurs within the seminiferous tubules.
• Depends on testosterone production.
• Takes approximately 64 days.
• Approximately 300 million new sperm are produced daily.
• Begins at puberty and continues throughout life until death (production and quality decline with age).
• Process starts with a spermatogonium and results in four physically mature sperm (spermatozoa).
• Spermiogenesis occurs in the final stage, resulting in the characteristic shape of sperm.
• Sperm contain 23 chromosomes.

Female Ovarian & Uterine Reproductive Cycles

• Cyclic changes to the uterine endometrial lining (uterine cycle) in response to changes in the ovary (ovarian cycle).
• Occurs in females of reproductive age who are not pregnant.
• Ovarian cycle phases: Pre-ovulatory, Ovulation, Post-ovulatory.
• Uterine cycle phases: Menstrual, Proliferative, Secretory.
• Menstruation begins if fertilization does not occur (shedding of the topmost layer of endometrium).
• Reproductive cycle length varies, but textbooks use 28 days as a reference.

Key Concepts

• Hormonal control
  • Gonadotropic hormones from the anterior pituitary.
  • Ovarian hormones from the ovaries.
• Follicular changes during the ovarian cycle (follicles are oocytes + supportive cells).
• Endometrial changes during the uterine cycle.

Hormones of the Female Reproductive Cycle

Gonadotropic Hormones

• Secreted by the anterior pituitary in response to Gonadotropin-releasing hormone (GnRH) from the hypothalamus.
  • Luteinizing hormone (LH):
    • Surge causes ovulation of ovum from follicle.
    • Surge causes formation of corpus luteum.
  • Follicle-stimulating hormone (FSH):
    • Stimulates follicle development.

Ovarian Hormones

• Secreted by structures within the ovary.
  • Estrogen:
    • Secreted by follicles.
    • Secreted by corpus luteum.
  • Progesterone:
    • Secreted by the corpus luteum.
• Both hormones act on the endometrial lining of the uterus.

Phases of the Cycle

Pre-Ovulatory Phase

• Follicular Changes:
  • FSH acts on the primary follicle (primary oocyte + supportive cells), which develops into a secondary follicle.
  • Continued FSH secretion causes maturation of secondary follicle into a tertiary follicle (mature follicle).
  • Maturing follicle secretes estrogen.
• Endometrial Changes:
  • Estrogen causes thickening of the recently shed layer of the endometrium (shedding occurred during menstruation).

Ovulation Phase

• Follicular Changes:
  • LH levels surge, causing rupture of mature follicle and release of ovum from the ovary.
  • Remaining follicular cells start to develop into corpus luteum.
• Endometrial Changes:
  • No major changes to the endometrium; still thickening in response to high levels of estrogen.

Post-Ovulatory Phase – No Implantation

• Follicular Changes:
  • Remaining follicular cells develop into the corpus luteum, which secretes both estrogen and progesterone.
  • If a fertilized ovum does NOT implant, the corpus luteum degenerates into the corpus albicans (cessation of estrogen and progesterone secretion).
• Endometrial Changes:
  • In response to estrogen and progesterone, the endometrium further thickens and increases blood supply.
  • If no implantation occurs and there is cessation of estrogen and progesterone secretion, the topmost layer of the endometrium degenerates and sheds (menstrual phase).

Post-Ovulatory Phase – Successful Implantation

• If fertilization is successful and the embryo implants into the uterine wall, the corpus luteum does not degenerate into corpus albicans.
• The embryo secretes human chorionic gonadotropin (hCG) – which mimics LH – to keep the corpus luteum alive until the placenta develops.
• Pregnancy is maintained, and both monthly ovarian and uterine cycles cease.

Fertility Across the Lifespan