The Reproductive System

I. Anatomy of the Male Reproductive System

A. Macroscopic Anatomy Diagram

B. Scrotum and Testes (Testicles)

• Testes Diagram
  • Suspended in sac-like scrotum
  • Testis is surrounded by two tunics: tunic vaginalis derived from peritneum (two layers with a cavity) and tunica albuginea (inner tunica) which extends inward dividing testi into lobules
  • Each lobule contains one to four seminiferous tubules (site of sperm production) that converge, forming the tubulus rectus
  • Sperm is brought, via tubulus rectus, into the rete testis (tubular network) then out into efferent ductules that leads to the epididymis.
  • Viable sperm production occurs three degrees below core body temperature, therefore suspended testi outside abdominopelvic cavity
  • Sperm travel via a duct system: epididymis, ductus deferens, and urethra
• Scrotum (scrotal sac)  Diagram
  • Subdivided by a midline septum into two compartments each containing testi
  • Contains two sets of muscles controlling temperature and affecting sperm production
    
  • dartos muscle - smooth muscle controlling surface area
  • cremaster muscle - skeletal muscle controlling ascension and descension of scrotal sac
    
  • Vascular supply: testicular arteries and pampiniform plexus (veins) that absorb heat from arterial blood.
  • Scrotal sac structures (encased in spermatic cord):
    • spermatic cord (external spermatic fascia)
    • cremaster muscle
      
    • internal spermatic fascia
    • autonomic nerve fibers
    • arteries and pampiniform plexus
    • tunic vaginalis
    • tunica albuginea
    • epididymis

C. Epididymis Diagram

• Storage site of non-motile sperm, twenty feet long, divided into superior head (receives immature sperm via efferent tubules) and posterolateral body and tail
• The epididymis contains stereocilia (non-motile microvilli) absorb excess fluid and passes nutrients to sperm
• Twenty day trip via the body, sperm mature and become motile
• During ejaculation, smooth muscle expels sperm into ductus deferens.

D. Ductus (vas) deferens Diagram

• One and a half feet long, runs upward from the epididymis into the pelvic cavity along bladder posteriorly, then downward to form enlarged terminus (ampulla)
• Sperm is dumped into ejaculatory duct via smooth muscle peristaltic waves.

E. Urethra  Diagram

• Serves as urinary and accessory reproductive system, conveys urine and semen to tip of penis
• Composed of three regions: (1) prostatic urethra, (2) membranous urethra (urogenital diaphragm), and (3) spongy urethra.

F. Accessory glands (seminal vesicles, bulbourethral (cowpers), and prostate) Diagram

• Seminal vesicle - secretes viscous alkaline fluid (60% os semen volume) containing fructose, ascorbic acid, and prostaglandins
• Prostate - encircles upper part of urethra and is composed of tubuloalveolar glands surrounded by smooth muscle
  • Prostatic secretion is 33% of semen volume and contains enzymes and other chemicals involved in sperm activation.
  • Sperm and seminal fluid mix in ejaculatory duct of prostate
• Bulbourethral gland - inferior to prostate, it produces clear mucus that may neutralize any acidic urine residue.

G. Penis

• Consists of root (bulb and crus/crura of penis) and shaft, ending in the glans penis.
• Internal structure: Diagram
  • Spongy and external urethral tissue
  • Corpora (erectile tissue) - (2) corpora cavernosa and (1) corpus spongiosum

H. Semen

• 2-5ml of semen ejaculated
• 50-130 million sperm per milliliter
• Sperm and accessory gland secretions:
  • Fructose = cellular fuel
  • Prostaglandins = decrease viscosity of mucus of cervix and reverses peristalsis in uterus
  • Relaxin = enhances sperm motility
  • Alkaline chemicals = neutralizes acidic vagina
  • Seminalplasmin = bacteriostatic agent
  • Fibrinogen = clots/coagulates sperm
  • Fibrinolysin = liquifies sperm

II. Physiology of the Male Reproductive System

A. Erection

• Arterioles supplying blood to the erectile tissue are usually constricted
• Sexual excitement causes a parasympathetic reflex that promotes nitrous oxide release locally
• Nitrous oxide relaxes vascular smooth muscle, causing the arterioles to dilate, which allows the erectile tissue to fill with blood
• Expansion of the corpora cavernosa compresses thier drainage veins, retarding blood outflow and maintaining engorgement

B. Ejaculation

• Impulses provoking erection reach a critical level and then a spinal reflex is initiated
• Sympathetic impulse sent to penis to:
  • Contract reproductive ducts and accessory glands
  • Constrict bladder muscles
  • Contract bulbospongiouses muscles of the penis, propelling semen 200 inches/sec

C. Spermatogenesis

• Spermatogonium
  • Stem cells of basal lamina of seminiferous tubules
  • Undergo mitosis to produce two daughter cells - one that remains to produce more stem cells and another that undergoes meiosis and produces sperm
• Meiosis Diagram
  • Two divisions (Meoisis I and Meiosis II) and four phases
  • Meiosis I
    • Chromosomes already replicated from interphase
    • Prophase I - homologus pairs of chromosomes synapse (forming a tetrad) and crossing over (exchange of genetic material) occurs
    • Metaphase I - tetrads line up
    • Anaphase I - homologous chromosomes separate
    • Telophase I - cytokinesis occurs, forming two daughter cells that are diploid in amount of DNA but haploid in chromosomal number
    • Interkinesis - preparation of Meiosis II
  • Meiosis II
    • Same events as mitosis except that chromosomes are not replicated before the process
  • Spermatogenesis Diagram - (meiosis I) spermatogoinium ro spermatocytes → (meiosis II) spermatids to spermatozoa

III. Hormonal Regulation of Male Reproductive Function Diagram

• Gonadotropic releasing hormone, produced in the hypothalamus, is released and promotes the adenohypophysis to produce and secrete follicle stimulating hormone (FSH) and luteinizing hormone (LH)
• Luteinizing hormone stimulates interstitial cells of testi to produce testosterone which is sent to sustentacular cells to stimulate spermatogenesis
• Follicle stimulating hormone is sent directly to sustentacular cells and promote spermatogenesis
• Hormone production and circulation is directly controlled by both the extent of concentration (decrease/increase) of hormones circulation and the production of the hormone inhibin which inhibits FSH and LH production.

IV. Anatomy of the Female Reproductive System

A. Macroscopic Anatomy Diagram

B. Ovaries

• Gamete-producing organ - produces egg or ova
• Endocrine organ - produces estrogens (estradiol, estrone, and estriol) and progesterone
• Two ovaries flank uterus and held in place by ligaments:
  • Ovarian - anchors ovary medially to uterus
  • Suspensory - anchors ovary laterally to pelvis wall
  • Mesovarium - anchors ovary between uterus and pelvis wall
  • Mesosalpinx - anchors uterine and ovary (together)
  • Mesometrium - distributes vascular supply
  • Broad = mesovarium + mesosalpinx + mesometrium
• Ovary surrounded by tunica albuginea covered by germinal epithelium
• Blood is supplied via suspensory ligament to mesovarium into ovary
• 40,000 ovarian follicles (develop into ova) found in ovaries
• Follicle development: Diagram
  • Primordial follicle (one layer of squamal, thecal, cells around oocyte)
  • Primary follicle (outer layer of thecal cells & 1 or more inner layers of cuboidal, granulosa, cells)
  • Secondary follicle (fluid-filled space appears between granulosa cells --> forms antrum)
  • Vesicular (graafian) follicle (oocyte sits on a stalk of granulosa cells at one side of antrum)
  • Ovulation (of ova)
  • Corpus luteum ( thecal and granulosal cells)

C. Uterus and Vagina Diagram

• Uterus is located in pelvic region, anterior to rectum, posterosuperior to the bladder, and receives, retains, and nourishes fertilized egg. Structures: fundus, body, lumen, isthmus, cervix
• Uterine tubes extend from ovary to superiolateral region of uterus
• Tube structure:
  • Fimbriae = finger-like projections of infundibulum
  • Infundibulum = opening of oviducts
  • Ampulla = curved structure, distal end
  • Isthmus = narrow constricted region toward uterus
    
• Uterine wall structure:
  • Perimetrium - serous membrane, outermost layer (composed of visceral peritoneum)
  • Myometrium - middle smooth muscle layer
  • Endometrium - simple columnar layer, site of embryo development
    • Endometrium is composed of two layers (strata): Diagram
      • Stratum functionalis - responds to cyclic changes in hormone levels and can be shed during menstruation
      • Stratum basalis - forms new stratum functionalis
• Uterine wall vascular supply:
  
  • Uterine artery -- arcuate -- radial -- straight -- spiral
  • Spiral undergoes regeneration/degeneration and spasms cause shedding of functionalis layer
  • Also extensive venous network with sinusoidal enlargements
• Vagina is a thin-walled but highly distensible tube 8-10 inches long containing three caots:
  • Outer adventitia
  • Muscularis
  • Inner mucosa containing ridges or rugae

V. Physiology of the Female Reproductive System

A. Oogenesis

• Production of female gametes
• During fetal period oogonia (stem cells) multiply by mitosis
• Oogonia transformed into primordial oocytes (marked by one layer of cells suurounding the oocyte)
• Primary oocyte begin the first meiotic division BUT stop at prophase I
• Puberty initiates the continuation of oogenesis and fertilization by sperm causes second meiotic division to occur
  
• Meoisis I results in two daughter cells: a large cell called a secondary oocyte and a small cell called a first polar body
• Meiosis II results in four cells: the secondary oocyte when penetrated by sperm divides into and ovum and a second polar body and the first polar body divides into two more polar bodies
  

B. Ovarian Cycle (three phases)  Diagram

i. Follicular Phase

• Day 1-10 follicle growth
• Primordial follicle activated and squamous-like cells become cuboidal cells, forming primary follicle with granulosa cells surrounded by thecal cells
• Follicle grows in size by granulosa cell division
• Granulosa and thecal cells cooperate to produce estrogens (thecal, androgens and granulosa, estrogen)
• Granulosa cells secrete a glycoprotein substance that forms transparent membrane (zona pellucida) around oocyte
• Liquid accumulates around granulosa cells forming an antrum
• Primary follicle matures into secondary follicle
• The antrum expands and granulosa cells around oocyte (cells called corona radiata) become isolated on a stalk - the secondary follicle is now called a vesicular (graafian) follicle.

ii. Ovulatory

• Day 11-14 follicle growth and ovulation
• The antrum swells, the ovary well at site of ballooning ruptures and expels secondary oocyte (ovulation)
  
• Usually one follicle is expelled at a time and all other follicles undergo atresia (cell degradation/reabsorption).

iii. Luteal

• Day 14-28 corpus luteum activity
• Ruptured follicle collapses and thecal and granulosa cells form corpus luteum (endocrine gland) that secretes progesterone and some estrogen
• If pregnancy does not occur, corpus luteum becomes the corpus albicans which starts to degenerate

C. Menstrual Cycle Diagram

i. Menstrual phase

• Days 1-5
• Uterus sheds stratum functionalis, causing bleeding and menstrual flow
• By day 5 growing ovarian follicles are starting to produce more estrogen

ii. Proliferative phase

• Days 6-14
• Estrogen levels rise
• Stratum functionalis is rebuilt
• Day 14 LH levels climax and promote ovulation and corpus luteum development

iii. Secretory phase

• Days 15-28
• Corpus luteum produces progesterone

D. Homones Diagram