Reproduction Systems Lecture

• Reproductive systems


  Designed to provide for the continuation of life
• Sexual reproduction


  Process by which genetic information is passed from generation to generation
• Gametogenesis


  • Form male and female gametes
• Primary sex organs (gonads)

  • Produce gametes and sex hormones
• Accessory structures


  • Include ducts, glands and external genitalia
• Primary sex organ - testes


  Accessory ducts - epididymus, ductus (vas) deferens, ejaculatory duct, urethra
• Accessory glands


  Seminal vesicles, prostate gland, bulbourethral glands
• Figure 28.1a


  • Textbook: Tortora, Gerard J. and B. Derrickson. 2021 Principles of Anatomy and Physiology (16th Edition). John Wiley & Sons Inc.
• Testes


  • Paired oval glands (5 cm long, 2.5 cm diameter)
  • Located in scrotum: pouch of skin and subcutaneous tissue outside abdominal cavity
  • Cooler temperature in scrotum by at least 3 degrees below body temp. (~ 34°C) is needed to produce viable sperm
  • Involves dartos and cremaster muscles of scrotum
  • Tunica albuginea is a fibrous capsule surrounding the testes that divides the testes into > 250 lobules
  • Each lobule contains 1-4 highly coiled seminiferous tubules where sperm are produced
• Seminiferous tubules


  • 2 types of cells: Spermatogenic cells - give rise to sperm, Sertoli (sustentacular) cells - nourish, protect and support spermatogenic cells
  • Between tubules are Leydig (interstitial) cells which produce testosterone
• Sertoli (Sustentacular) Cells


  • Large cells that extend from the basement membrane of tubule to lumen
  • Tight junctions join Sertoli cells
  • Form blood – testis barrier
  • Substances from blood must pass thru Sertoli cells before they reach developing sperm
  • Prevents an immune response against spermatogenic cell's surface antigens which are "foreign" to immune system (as immune system develops before puberty)
• Function of Sertoli cells

  • Nourish spermatocytes, spermatids + sperm
  • Phagocytize excess spermatid cytoplasm
  • Control movements of spermatogenic cells
  • Control release of sperm into lumen
  • Produce fluid for sperm transport
  • Regulate effects of FSH and testosterone
  • Secrete hormone – inhibin (inhibits FSH release)
  • Secrete androgen – binding protein into lumen → binds testosterone therefore keep it high for final stages of spermatogenesis
• Spermatogenesis


  1. Occurs in seminiferous tubules

  2. Takes about 64-72 days

  3. Starts from outer wall of tubule towards lumen

  4. Spermatogonia (stem cells that are 2N and remain dormant until puberty) divide by mitosis giving rise to type A and B spermatogonia

  5. Type A cells remain at basement membrane as a reservoir of cells for future cell division

  6. Type B cells grow and move toward lumen, called primary spermatocytes
• Spermiogenesis


  1. Spermatids are small, round cells close to lumen and undergo spermiogenesis to become spermatozoa – shed cytoplasm

  2. Spermatozoa has 3 parts: 1. head – has nucleus and acrosome, 2. midpiece – contains mitochondria, 3. tail – is a flagellum

  3. Sperm are released into lumen of seminiferous tubule
• Hormonal Control of the Testis


  1. At puberty, hypothalamus increases secretion of gonadotropin-releasing hormone

  2. Stimulates anterior pituitary to release LH and FSH

  3. FSH stimulates Sertoli cells to release androgen binding protein

  4. LH stimulates Leydig cells to release testosterone

  5. Combined effect is to stimulate spermatogenesis
• Testosterone


  • Promotes development of male secondary sex characteristics
  • Before birth: stimulates male development of reproductive systems ducts + descent of testis; development of external genitalia
  • At puberty: enlargement of male sex organs + development of secondary sex characteristics (facial/chest hair, enlarged larynx for deep voice, bones/muscles ↑ in size and mass)
• Inhibin


  A hormone released by the Sertoli cells which suppresses the production of FSH once spermatogenesis has progressed
• Pathway of Sperm


  1. From seminiferous tubules (#1), sperm enter straight tubules (#2)

  2. Next, enter network of ducts, rete testis (#3), to move into coiled efferent ducts in the epididymis (#4)

  3. Epididymis (#5) lies on surface of testes - takes about 20 days to travel, site of sperm storage and maturation, are expelled during ejaculation into ductus (vas) deferens (#6)

  4. Spermatic cord consists of the ductus deferens, blood vessels and nerves
• Pathway of Sperm (continued)

  1. Ductus deferens is a muscular tube that passes into pelvic cavity, ends behind urinary bladder, enlarges to form ampulla

  2. Ampulla joins with the duct of the seminal vesicle to form the short ejaculatory duct (#7)

  3. Ejaculatory duct enters prostate gland and empties into urethra (#8)

  4. Urethra extends from bladder to tip of penis
• Penis


  • Contains 3 cylindrical masses of erectile tissue: blood sinuses lined by endothelial cells surrounded by smooth muscle and elastic CT
  • Corpora cavernosa (two lateral masses)
  • Corpus spongiosum (midventral mass containing the spongy urethra)
  • Erection = enlargement and stiffening of penis
  • Ejaculation = sympathetic reflex, close urethra at base of bladder
• Accessory Glands


  • Seminal Vesicles (2) - produce viscous alkaline fluid, adds ~ 60% of seminal fluid, released into ejaculatory ducts
  • Prostate Gland (1) - surrounds urethra below bladder, adds ~ 35% of seminal fluid, slightly acidic secretion, empties into prostatic urethra
  • Bulbourethral Glands (2) - produce thick clear mucus prior to ejaculation, alkaline secretion, lubricates end of penis and lining of urethra, about 5% of fluid volume, released into spongy urethra
• Semen


  • Mixture of sperm and seminal fluid
  • About 2-5 ml released per ejaculation
  • Contains about 100 million sperm/ml (if # below 20 million sperm/ml considered infertile)
  • pH is 7.2-7.7
• Seminal Fluid Functions


  • Provide sperm with a transport medium
  • Provide sperm with nutrients
  • Neutralizes acidity of male urethra and female vagina
  • Contains an antibiotic to destroy bacteria in semen and lower female reproductive tract
• Figure 28.9a


  • Textbook: Tortora, Gerard J. and B. Derrickson. 2021 Principles of Anatomy and Physiology (16th Edition). John Wiley & Sons Inc.
• Primary sex organ - ovaries


  Accessory ducts - uterine tubes (oviducts), uterus, vagina
• Ovaries


  • Paired almond-shaped organ, held in place by broad, ovarian and suspensory ligaments
  • Surrounded by tunica albuginea covered by germinal epithelium
  • Ovary has cortex and medulla - outer cortex contains ovarian follicles, inner medulla contains loose CT, blood vessels, lymph vessels and nerves
• Oogenesis


  1. Occurs in ovarian follicles in cortex of ovary

  2. Takes years to complete

  3. Oogonia (2N) are formed in fetus, divide by mitosis to form primary oocytes (2N)

  4. Primary oocytes (2N) are arrested in prophase I of meiosis until puberty, a primary oocyte is surrounded by a layer of follicle cells and is called a primordial follicle

  5. At puberty, secretion of FSH results in primordial follicle becoming a primary follicle, follicle cells grow and become granulosa cells, granulosa cells produce estrogen, fluid-filled cavity (antrum) forms and becomes a secondary follicle

  6. Primary oocyte completes meiosis I and gives rise to a large secondary oocyte (n) and first polar body, becomes a mature Graafian follicle that is ovulated
• Ovulation


  1. Graafian follicle migrates to ovary surface

  2. LH triggers ovulation and follicle ruptures

  3. Secondary oocyte is released into pelvic cavity and swept into oviduct

  4. Fertilization takes place in the oviduct
• Oogenesis


  • Process that occurs in ovarian follicles in cortex of ovary
  • Takes years to complete
• Oogenesis


  1. Oogonia (2N) are formed in fetus

  2. Oogonia divide by mitosis to form primary oocytes (2N)

  3. Primary oocytes (2N) are arrested in prophase I of meiosis until puberty

  4. Primary oocyte is surrounded by a layer of follicle cells and is called a primordial follicle
• Oogenesis at puberty


  1. Secretion of FSH results in primordial follicle becoming a primary follicle

  2. Follicle cells grow and become granulosa cells

  3. Granulosa cells produce estrogen

  4. Fluid-filled cavity (antrum) forms and becomes a secondary follicle

  5. Primary oocyte completes meiosis I and gives rise to a large secondary oocyte (n) and first polar body

  6. Becomes a mature Graafian follicle that is ovulated
• Ovulation


  1. Graafian follicle migrates to ovary surface

  2. LH triggers ovulation and follicle ruptures

  3. Secondary oocyte is released into pelvic cavity and swept into oviduct

  4. Fertilization takes place in the oviduct

  5. Secondary oocyte will only complete meiosis II if fertilization occurs

  6. Produces large ovum and second polar body

  7. Nuclei of sperm cell and ovum unite to form a diploid zygote that begins to undergo cell divisions

  8. Remainder of ruptured follicle becomes corpus luteum within ovary which will secrete the hormones progesterone and estrogen
• Oogenesis begins before birth
• If fertilization does not occur, corpus luteum degenerates and becomes the corpus albicans
• Once corpus luteum degenerates, estrogen and progesterone hormone levels decrease and FSH and LH will restart cycle
• Pathway of Oocyte


  1. Secondary oocyte is drawn into funnel-shaped infundibulum of oviduct by action of fimbriae

  2. Takes 4 days to travel oviduct, helped by cilia and peristalsis

  3. Fertilization occurs in the oviduct

  4. Unless fertilized within first 24 hours after ovulation oocyte degenerates

  5. A fertilized egg arrives at the uterus 6-7 days after ovulation
• Uterus


  • Has a fundus, body, cervix
  • Receives fertilized ovum
  • Protects and nourishes embryo
  • Wall has 3 layers: outer perimetrium, thick middle myometrium of 3 layers of smooth muscle, inner endometrium with a superficial functional layer and a deeper basal layer
• Inner Endometrium


  • Highly vascularized
  • Contains numerous uterine glands that secrete nutritious glycogen into uterine cavity to sustain embryo until it implants
  • Divided into functional layer that sloughs off during menstruation, and basal layer that gives rise to a new functional layer after menstruation
• Vagina


  • Extends from cervix to external genitalia
  • Passageway for infant, discharge of menstrual fluid and receives semen
  • Lined with non-keratinized stratified squamous epithelium for protection from abrasion
  • Contains stores of glycogen - produces organic acids (acidic pH)
  • Cervix mucosal cells produce mucus that can block cervical canal when not fertile (impedes sperm) and blocks spread of bacteria
• Female Reproductive Cycle


  1. Ovarian cycle - events involved in maturation of an oocyte

  2. Menstrual (Uterine) cycle - events that prepare uterine endometrium to receive a fertilized ovum

  3. Cycle is about 28 days