Male and Female Reproductive Systems, Prenatal Development & Childbirth

Male Reproductive System

  • Function of Penis:
    • Urination
    • Injecting sperm into the female reproductive tract
  • Erectile Tissue: Engorges with blood to facilitate erection.
    • Root of penis: crus and bulb.
    • Corpora cavernosa.
    • Corpus spongiosum.
    • Glans penis: End of corpus spongiosum, covered by prepuce (unless circumcised).
  • Urethra: Passage for both urine and semen.
    • Prostatic urethra: Empties prostatic secretions into the urethra.
    • Membranous urethra: Extends through the muscular floor of the pelvis.
    • Spongy (penile) urethra: Passes through the penis.
  • Testes:
    • Divided into lobules containing:
      • Seminiferous tubules: Produce sperm.
      • Interstitial (Leydig) cells: Produce testosterone.
    • Located outside the body cavity in the scrotum.
      • Scrotum: Sac of skin and smooth muscle that holds the testes and maintains them at a slightly lower temperature, which is required for sperm development.
  • Epididymis: Sperm maturation (motility) and storage.
  • Ductus (vas) deferens: Carries sperm from the epididymis to the ejaculatory duct.
  • Descent of Testes:
    • Testes pass from the abdominal cavity through the inguinal canal into the scrotum.
    • Inguinal rings open through the aponeuroses of abdominal muscles, predisposing the area to herniation.
    • Cryptorchidism: Failure of one or both testes to descend, leading to abnormal sperm development.

Production of Gametes

  • Sperm and eggs are gametes (germ cells) and are haploid (n).
  • Cell divisions (mitosis and meiosis) produce gametes with half the number of chromosomes of somatic cells, which are diploid (2n).
  • Spermatogenesis Sequence:
    • Spermatogonia (2n): Undifferentiated.
    • Primary spermatocyte (2n): Undergoes meiosis I.
    • Secondary spermatocyte (n): Undergoes meiosis II.
    • Spermatids (n): Develop an acrosome and flagellum.
    • Sperm (n).
  • Testosterone:
    • Steroid hormone produced by Leydig cells in testes and some from the adrenal cortex.
    • Affects male reproductive capacity.
    • Determines the rate of sperm production by Sertoli (nurse) cells.
    • Forms the blood-testis barrier.
    • Controls growth of male reproductive tissues and development of secondary sexual characteristics (e.g., facial hair).
    • Stimulates aggression and sexual behavior.
    • Testosterone levels decrease slowly during aging but do not normally stop.
  • Sertoli Cells

Negative Feedback

  • Hormonal Regulation: Regulates testosterone and sperm production.
    • Hypothalamus: Secretes gonadotropin-releasing hormone (GnRH) that stimulates the release of gonadotropins (LH and FSH) from the anterior pituitary.
      • LH: Stimulates testosterone production by Leydig cells.
      • FSH: Enhances Sertoli cells to make sperm.
    • Negative feedback: Sertoli cells secrete inhibin to inhibit FSH secretion, maintaining a constant blood concentration of testosterone.
  • Route of Sperm:
    1. Seminiferous tubules of the testis.
    2. Epididymis.
    3. Ductus deferens.
    4. Seminal vesicle.
    5. Ejaculatory duct (prostate): Contains smooth muscle to force semen out during ejaculation.
    6. Penis (urethra).
  • Ejaculation: Forceful expulsion of semen from the urethra (caused by peristalsis).
    • The internal sphincter of the urinary bladder constricts, preventing semen and urine from mixing.

Accessory Glands

  • Produce semen (seminal fluid added to sperm) to help sperm survive.
    1. Seminal vesicles: Secrete fructose (energy for sperm) and most of the semen (60%).
    2. Prostate gland: Secretes watery alkaline fluid to raise vaginal pH and 30% of semen.
    3. Bulbourethral (Cowper’s) gland: Secretes lubricating mucus and 5% of semen.
    4. Mucus-secreting cells lining the urethra: Make the remaining 5% of semen.

Female Reproductive System

  • Mammary Glands:
    • breasts contain mammary glands for lactation (production of milk) to nourish the Infant
    • Modified sweat glands, part of the integumentary system.
    • Hormonal control:
      • Prolactin (anterior pituitary hormone): Stimulates milk production.
      • Oxytocin (posterior pituitary hormone): Stimulates contractions that eject milk.
    • Organs of milk production consist of glandular lobes and adipose tissue.
  • Vulva: The female external genitalia.
    • Labia majora and minora.
    • Clitoris: Organ of sexual arousal.
  • Vagina:
    • Organ of sexual intercourse (receptacle for penis).
    • Outlet for menstrual flow.
    • Birth canal.
    • Composed of muscular walls with a mucous membrane lining.
    • Produces lubricating fluids.
    • Secretions are acidic to prevent infection and entrance of foreign cells.
  • Female Reproductive System (Overview):
    • Cervix
    • Uterus
    • Oviduct (2)
    • Ovary (2)
  • Ligaments:
    • Broad ligament: Extension of the peritoneum that attaches to the uterus, uterine tubes, and ovaries.
    • Suspensory ligament: Connects ovaries to the peritoneum; contains ovarian arteries, veins, and nerves.
    • Ovarian ligament: Connects ovaries to the uterus; contains ovarian arteries, veins, and nerves.
  • Ovaries:
    • Site of oocytes (immature eggs), estrogen, and progesterone production.
    • Outer cortex: Contains follicles with oocytes.
    • Inner medulla: Contains blood vessels, nerves, and lymphatic vessels.
  • Ovulation and Fertilization:
    • 4th month fetus: ~ 5 million oogonia.
    • ~ 2 million oogonia begin meiosis I but stop at prophase I until puberty.
    • Puberty: A primary oocyte develops into a secondary oocyte.
    • Ovulation: Release of a secondary oocyte with the first polar body.
    • Fertilization: A sperm cell binds to the cell membrane of a secondary oocyte and enters the oocyte, triggering the oocyte to finish meiosis II and expel the last polar body.
    • The nuclei of the two cells fuse, and the new cell is called a zygote.
  • Oogenesis:
    • Primordial follicle: Primary oocyte + 1 layer of squamous granulosa cells (nourishment).
    • Primary follicle: FSH stimulates maturation; granulosa cells divide to produce zona pellucida.
    • Secondary follicle: Fluid-filled vesicles form.
    • Graafian (mature) follicle: Meiosis I completed producing a secondary oocyte and a polar body; fluid-filled vesicles become a single antrum; increasing estrogen causes a surge in LH resulting in ovulation.
    • Granulosa cells remain in the ovary and become the corpus luteum, which:
      • Secretes estrogen and progesterone if fertilization occurs or degenerates into corpus albicans if no fertilization.
  • Oviduct:
    • Also known as the fallopian tube or uterine tube.
    • Opens directly into the peritoneal cavity to receive the oocyte from the ovary.
    • Infundibulum with fimbriae extends from each tube to “catch” the oocyte when it is ovulated.
    • Fertilization occurs in the ampulla (upper third of oviduct and the widest part of oviduct).
    • The oviduct is lined with ciliated epithelium to lead the oocyte (or zygote) from the ovary to the uterus.
  • Uterus:
    • Hollow, pear-shaped organ where the fertilized egg grows and develops.
    • Divisions: fundus, body, and cervix.
    • Cervix: The narrow opening in the lower part of the uterus that permits sperm to enter the uterus and allows the fetus to exit during birth.
    • Layers:
      1. Endometrium: Supports fertilized egg; part of it sloughs off monthly during menstrual flow.
      2. Myometrium: Smooth muscle, expands during pregnancy, constricts during labor.
      3. Perimetrium: Outermost serous layer.
  • Menstrual Cycle:
    • Begins at puberty with “menarche” (first episode of menstruation) and continues until menopause (cessation of menstruation), except during pregnancy.
    • Cyclic changes in hormone levels produce the menstrual cycle, which cycles every 28 days.
    • Consists of two linked cycles:
      1. Ovarian cycle: FSH and LH regulate changes in the ovaries associated with oocyte maturation.
      2. Uterine cycle: Estrogen and progesterone regulate changes in the endometrial lining of the uterus.
  • Ovarian Cycle:
    • If fertilization and pregnancy occurs:
      • Chorion (embryonic tissue) secretes human chorionic gonadotropin (hCG).
      • hCG is detected by pregnancy tests.
      • hCG causes the corpus luteum to continue to produce estrogen and progesterone for another 9–10 weeks.
      • After 9–10 weeks, the placenta takes over progesterone and estrogen production.
      • High levels of estrogen and progesterone prevent ovulation during pregnancy.
  • Uterine Cycle:
    • Series of changes that occur in the endometrium as it prepares the uterus for the possible arrival of a fertilized egg.
      • Menstrual phase (Days 1–5): Estrogen and progesterone decrease, the endometrium degenerates, and menstruation occurs.
      • Proliferative (follicular) phase (Days 6–14): Estrogen and progesterone increase, the endometrium proliferates, and follicles mature.
        • Positive feedback: Increasing estrogen causes a surge in LH, which in turn causes ovulation.
      • Ovulation (Day 14).
      • Secretory (luteal) phase (Days 15–28): The corpus luteum produces progesterone and estrogen, the endometrium continues to proliferate, and uterine glands mature; the uterus is prepared to accept and nourish a fertilized egg.
        • Negative feedback: Steady levels of estrogen and progesterone inhibit LH and FSH release.

Prenatal Development & Childbirth

  • Prenatal Development (Overview):
    • Time period from conception to birth (three stages).
      1. Germinal period: First 2 weeks (Days 0 to 14) of development, including the formation of the primitive germ layers.
      2. Embryonic period: Second week to the end of the 8th week (Days 14-60), which includes the development of the organ systems.
      3. Fetal period: Lasts 32 weeks (Weeks 9 to ~ 40), which includes the growth and maturation of the organ systems (Day 60 becomes fetus).
  • Gamete Formation:
    • Oocyte and sperm in humans have the same number of chromosomes (23).
    • Sperms are formed in the testis in human males.
      • Ejaculate: may contain several hundred million sperm.
    • Oocytes are formed in the ovary in human females.
  • Fertilization:
    • Sperm move through the female reproductive tract to the oviduct (fallopian tube).
    • Sperm may reach the egg within hours to a day or more.
    • An oocyte can be fertilized up to 24 hours after ovulation.
    • Sperm may be viable for up to 5 days within the female reproductive tract.
    • One sperm penetrates egg and undergoes capacitation, releasing acrosomal enzymes to digest away follicular cells.
      • Acrosome: Enzyme in the sperm’s head to digest through the oocyte’s zona pellucida.
  • Cleavage:
    • Sperm and oocyte fuse to form a zygote.
    • Cleavage: Cell divisions of the embryo.
    • Morula: Solid ball of 12 or more cells.
      • About 5 days after fertilization, the morula consists of about 32 cells, and the blastocoel (fluid-filled cavity) starts to form in the center of the cells.
    • Blastocyst: Hollow sphere of cells that implants into the uterine wall.
  • Implantation:
    • 7 days after fertilization, the blastocyst implants in the uterus.
    • Trophoblast forms the placenta and membranes surrounding the embryo.
    • Inner Cell Mass (ICM) forms the embryo proper.
    • Syncytiotrophoblast (non-dividing, multinucleated cell) invades the endometrium of the uterus. It is “non-antigenic”.
  • Placenta Formation:
    • The placenta develops from the trophoblast.
    • Maternal blood vessels are digested by the syncytiotrophoblast, and lacunae are formed, which fill with maternal blood.
    • Cords of cytotrophoblast surround the lacunae and syncytiotrophoblast to produce chorionic villi.
    • The entire embryonic structure touching the maternal tissues is the chorion.
  • Gastrulation:
    • Gastrulation: Formation of three germ layers.
    • Embryonic disk – Ectoderm (which also forms the mesoderm) and endoderm.
      1. Ectoderm: Outer layer
        • Forms skin and nervous tissues.
      2. Mesoderm: Middle layer
        • Forms muscle, bone, blood vessels, and connective tissues.
      3. Endoderm: Inner layer
        • Forms linings of the digestive tract and many derivatives.
  • Ectoderm:
    • Forms the neural tube, which will become the central nervous system.
    • Amniotic cavity – contains amniotic fluid that surrounds and protects the baby.
    • Yolk Sac – forms between Weeks 5-10 and is eventually absorbed by the baby.
  • Tissue and Organ Development:
    • From the original 3 germ layers, all of the body tissues and organs develop.
    • Organogenesis: Major organ systems develop between 14 and 60 days after fertilization.
    • The embryo becomes a fetus approximately 60 days after fertilization, making the fetal period primarily a “growing phase”.
  • Aging of the Fetus:
    1. Clinical age – uses the mother’s last menstrual period to calculate the age of unborn child (Week 1-2: not pregnant).
    2. Postovulatory age – uses the timing of the developmental events (2 weeks less than the clinical age, Day 14: ovulation).
  • Gestation:
    • Time period between conception and birth.
      • Conception time is hard to determine.
      • Gestation age is calculated.
  • Parturition (Childbirth):
    • Mother:
      • Estrogens overcome the inhibitory effect of progesterone (on oxytocin binding).
      • Oxytocin is released and stimulates uterus contraction (positive feedback).
    • Fetus:
      • The adrenal cortex enlarges and releases cortisol prior to parturition (under the influence of the fetal hypothalamus).
    • Stages of Labor:
      1. First stage – Includes the onset of regular uterine contractions until the cervix dilates to the fetal head diameter.
      2. Second stage – Includes the time from the maximum cervical dilation until the baby exits the vagina.
      3. Third stage – Includes the expulsion of the placenta from the uterus.