BIO reproductive system

• Male reproductive structures

  • External genitalia
  • Internal genitalia
• Reproductive system

  Only system not essential to sustaining life
• Gonads produce gametes
• Male gametes are sperm
• External genitalia

  • Penis contains erectile tissue, deposits sperm into vagina of female
  • Urethra conducts semen to exterior
  • Scrotum surrounds testes
• Internal genitalia

  • Ductus deferens conducts sperm between epididymis and prostate
  • Seminal gland secretes fluid making up much volume of semen
  • Prostate secretes fluid and enzymes
  • Bulbo-urethral gland secretes fluids that lubricate tip of penis
  • Epididymis is the site of sperm maturation
  • Testis produces sperm and hormones
• Sperm transport

  1. Ducts, glands, and related structures of the scrotum and testes

  2. Path of sperm: Testis to the epididymis, along the ductus deferens, then along the ejaculatory duct to the urethra
• Accessory organs

  • Secrete various fluids into the reproductive tract
  • Seminal glands, prostate, and bulbo-urethral glands secrete various fluids into ejaculatory duct and urethra
  • Urethra passes through the penis to exit the body
• The testes

  • 5 cm long; 3 cm wide; 2.5 cm thick
  • Each weighs 10–15 g
  • Form inside the body cavity adjacent to the kidneys
  • Connective tissue bands do not elongate as fetus grows
  • Relative position of testes changes as body enlarges
  • Late in fetal development, connective tissue band contracts, pulls each testis through abdominal musculature into the scrotum
• Scrotum and associated structures

  • Scrotal cavities house the testes
  • Scrotal septum separates right and left cavities
  • Dartos muscle elevates testes and wrinkles scrotal surface
  • Cremaster muscle contracts to pull testes closer to body during sexual arousal or when exposed to cold temperature
  • Spermatic cords extend through the inguinal canals between testes and abdominopelvic cavity
• Superficial inguinal ring

  • Entrance to the inguinal canal
• Inguinal canal

  • Extends from the inguinal ring to the scrotal cavity
  • Presence of spermatic cords creates weak points in the abdominal wall, leading to inguinal hernias
• Internal organization of the testes

  • Tunica vaginalis is a serous membrane that lines the scrotal cavity and reduces friction
  • Tunica albuginea is a tough, fibrous capsule that covers the testis and is continuous with septa subdividing testes into lobules
  • Seminiferous tubules are coiled tubules within lobules, the site of sperm production
  • Myoid cells contract to transport sperm through tubule
  • Rete testis is a maze of passageways where seminiferous tubules merge into straight tubules then rete testes
  • Efferent ductules are 15–20 tubes connecting the rete testis to the epididymis
• Spermatogenesis occurs in the testes and produces mature sperm
• Spermatogenesis (sperm production)

  Involves three processes: Mitosis and cell division, Meiosis, Sperm formation and structure
• Daughter cells

  Contain 23 pairs of chromosomes, called diploid
• Seminiferous tubules

  Stem cells undergo mitosis
• Meiosis

  1. Special form of cell division involved in gamete production

  2. Two cycles of cell division (meiosis I and II)

  3. Produces four haploid cells, each with 23 individual chromosomes

  4. Synapsis: Corresponding material and paternal chromosomes associate to form 23 chromosome pair. Set of four chromatids is called a tetrad
• Spermiogenesis

  Differentiation of immature male gametes into physically mature spermatozoa
• Mitosis of spermatogonium

  Spermatogonia are stem cells in the seminiferous tubules that go through mitosis to form two daughter cells
• Meiosis I

  Each primary spermatocyte begins with 46 chromosomes diploid. Daughter cells produced are called secondary spermatocytes, each containing 23 chromosomes haploid with each chromosome having a pair of duplicate chromatids
• Meiosis II

  Secondary spermatocytes divide to produce spermatids, each containing 23 chromosomes. Each primary spermatocyte produces four spermatids
• Spermiogenesis

  Physical maturation of sperm. Each spermatid matures into a single sperm
• Meiosis and early spermiogenesis occur within the seminiferous tubules
• Structure of a sperm

  • Lacks most organelles and intracellular structures to reduce size and mass
  • Acrosome contains enzymes essential to fertilization
  • Head contains nucleus with densely packed chromosomes
  • Neck contains centrioles and microtubules
  • Middle piece contains mitochondria for ATP production
  • Tail (flagellum) is a whiplike organelle that moves the sperm
• Seminiferous tubules are tightly coiled within lobules, sites of spermatogenesis, and spermatogenesis and spermiogenesis together take 9 weeks
• The male reproductive tract receives secretions from the seminal, prostate, and bulbo-urethral glands
• Activation of sperm

  Sperm released from testes are physically mature but immobile and incapable of fertilizing an oocyte. Capacitation is the process enabling sperm to become motile and fully functional
• Male reproductive tract and glands

  • Ampulla: Expanded distal portion of ductus deferens
  • Ejaculatory duct: Carries fluid from seminal gland and ampulla to urethra
  • Epididymis: Coiled tube bound to posterior border of each testis, lined with pseudostratified columnar epithelium, sperm undergo functional maturation here
• Epididymis

  • Start of the male reproductive tract
  • Coiled tube bound to posterior border of each testis
  • Lined with pseudostratified columnar epithelium
  • Has long stereocilia that increase surface area
  • Sperm undergo functional maturation here
• Regions of the epididymis

  • Head - Receives spermatozoa from efferent ductules
  • Body - Extends inferiorly along the posterior surface of the testis
  • Tail - Starts near the inferior border of the testis, Number of coils decreases, Connects with the ductus deferens
• Ductus deferens (or vas deferens)

  • 40–45 cm (160–16 in.) long
  • Passes through inguinal canal as part of spermatic cord
  • Transports sperm from the epididymis
  • Can store sperm for several months in a state of suspended animation
• Seminal glands (seminal vesicles)

  • Sandwiched between the posterior wall of the urinary bladder and the rectum
  • Secretion ejected by smooth muscle lining gland, Stimulates flagellum movement in sperm, First step of capacitation
  • Produce ~60 percent of semen volume
• Components of semen

  • Sperm and seminal fluid
  • Fluid is a combination of secretions from: Seminal glands, Nurse cells, Epididymis, Prostate, Bulbo-urethral glands
  • ~2–5 mL of semen are released in a typical ejaculation
• Prostate

  • Encircles the proximal urethra as it leaves the bladder
  • Produces 20–30 percent of semen volume
  • Secretions contain seminal plasmin, Antibiotic that may help prevent urinary tract infections in males
• Bulbo-urethral glands (Cowper’s glands)

  • Located at the base of the penis
  • Duct of each gland empties into the urethra
  • Secrete thick, alkaline mucus, Helps neutralize acids in the urethra, Also lubricates the tip of the penis
• The penis conducts urine and semen to the exterior
• Functions of the penis

  • Conducts urine to the exterior
  • Introduces semen into the female’s vagina during sexual intercourse
• Regions and structures of the penis

  • Root of the penis - Fixed portion that attaches the penis to the body wall just inferior to the pubic symphysis
  • Body (or shaft) of the penis - Tubular, movable portion of the organ
  • Glans penis (head) - Expanded distal end that surrounds the external urethral orifice, Neck of glans - Narrow portion between the shaft and the glans
• Erectile tissue

  • Three-dimensional network with vascular spaces
  • In the resting state, arterial branches are constricted, and muscular partitions are tense (restricts blood flow into the erectile tissue)
  • Corpora cavernosa (singular, corpus cavernosum) - Two cylindrical masses on the anterior/dorsal surface of the penis
  • Corpus spongiosum - Surrounds the penile urethra, Expands at the tip of the penis to form the glans