Scrotum and Testes (Testicles)

  • Testes
  • Suspended in sac-like scrotum
  • Testis is surrounded by two tunics: tunic vaginalis derived from peritoneum (two layers with a cavity) and tunica albuginea (inner tunica) which extends inward dividing testis into lobules
  • 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)
  • Subdivided by a midline septum into two compartments each containing testi
  • Contains two sets of muscles (dartos muscle, smooth muscle and cremaster muscle, skeletal muscle) that control scrotal surface area (thus temperature).
  • 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 (elevates the testes)
  • autonomic nerve fibers
  • arteries and pampiniform plexus
  • tunic vaginalis
  • tunica albuginea
  • epididymis

C. Epididymis

  • Twenty day trip via the body, sperm mature and become motile
  • During ejaculation, smooth muscle expels sperm into ductus deferens.

D. Ductus (vas) deferens

  • Site of vasectomy
  • Sperm is dumped into ejaculatory duct via smooth muscle peristaltic waves.

E. Urethra

  • 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)

  • Seminal vesicle - secretes viscous alkaline fluid (60% of semen volume) containing fructose, ascorbic acid, and prostaglandins
  • Prostate - encircles upper part of urethra
  • 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:
  • 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
  • Seminalplasmin = bacteriostatic agent
  • 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 their 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
  • Contract bulbospongiouses muscles of the penis, propelling semen 200 inches/sec

C. Spermatogenesis

  • Spermatogonium
  • Stem cells of seminiferous tubules
  • Undergo mitosis to produce two daughter cells - one that remains to produce more stem cells and another that undergoes meiosis reduction division) and produces sperm
  • Spermatogenesis
  • spermatogonium → (meiosis I) spermatocytes → (meiosis II) spermatids to spermatozoa (4 are produced)
  • Haploid (n)= 23
  • Diploid (2n)= 46

III.Hormonal Regulation of Male Reproductive Function

  • 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 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.

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:
  • Primordial follicle (one layer of squamal, thecal, cells around oocyte)
  • Primary follicle
  • 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

  • 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
  • Uterine wall vascular supply:
  • Uterine artery
  • Vagina is a thin-walled but highly distensible tube 8-10 inches long containing three caots:

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 surrounding the oocyte)
  • Primary oocyte begin the first meiotic division.
  • Puberty initiates the continuation of oogenesis
  • 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)

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

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

i. Menstrual phase

  • Days 1-5
  • Uterus sheds stratum functionalis (layer of endometrium), 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