Male Reproductive System

• Sexual Reproduction


  • Combine genes from two parents
  • Union of two gametes to form a zygote (fertilized egg)
• Male gametes


  Sperm (spermatozoon)
• Female gametes


  Egg (ovum)
• Sex chromosomes


  Male = XY, Female = XX
• Primary sex organs


  • Gonads (testes and ovaries)
• Secondary sex organs


  • Internal genitalia (pelvic cavity)
  • External genitalia (perineum)
• Scrotum


  • Skin with fascia and muscle
  • Contains two testes
  • Maintains testes at lower than body temp
  • Necessary for sperm production
• Dartos muscle


  • Smooth muscle that wrinkles skin, pulls closer to body
• Cremaster muscles


  • Skeletal muscle that elevates testes, pulls closer to body
• Pampiniform plexus


  • Absorbs arterial heat
• Testes


  • Location of sperm production
  • 2 tunics (Tunica vaginalis and Tunica albuginea)
  • Septa divide testes into lobules
  • Lobules have 1-4 seminiferous tubules that make sperm
  • Interstitial endocrine cells (Leydig cells) secrete androgens (testosterone!)
• Spermatic cord


  • Contains ductus deferens, blood supply, lymphatics, autonomic & visceral sensory nervous innervation
• Spermatogenesis


  Sequence of events in seminiferous tubules that produce male gametes (sperm)
• Spermatogenesis starts at puberty (~14 years old) and continues daily, producing ~400 million sperm daily
• Gametes


  Have haploid chromosome number (n = 23), only one member of the homologous pair is present
• Somatic cells


  Have diploid chromosome number (2n = 46), 23 PAIRS of homologous chromosomes
• Interphase (prior to cell division)


  1. Uncoiled chromosome duplicates

  2. Uncoiled strings called chromatin

  3. Chromatin will eventually coil into condensed form with 2 sister chromatids
• Chromosome


  2 sister chromatids
• Meiosis I


  1. Interphase: Chromosome replicates

  2. Prophase I: Chromatin coils, condense = 2 sister chromatids, Homologous partners form a "buttoned together" PAIR (tetrad), Crossover occurs

  3. Metaphase I: Tetrads randomly line up at cell equator

  4. Anaphase I: Tetrads split apart, paired sister chromatids split, each go to opposite end of cell

  5. Telophase I: Cell splits apart
• At the end of Meiosis I, daughter cells have a haploid chromosome number (still united sister chromatids are considered a single chromosome) but twice the DNA per chromosome
• Meiosis II


  1. Mirrors meiosis I EXCEPT chromosomes do not replicate prior to division

  2. Sister chromatids of two daughter cells are split equally between 4 (new) daughter cells
• Gametes have a haploid chromosome number (n), somatic cells have a diploid chromosome number (2n)
• Before Interphase: 46 chromosomes, 46 chromatids

  After Interphase: 46 chromosomes, 92 chromatids

  After Meiosis I: 23 chromosomes, 46 chromatids

  After Meiosis II: 23 chromosomes, 23 chromatids
• Spermatogenesis is the production of sperm
• Spermatogenesis


  Production of sperm
• Seminiferous tubules of the testes


  • Spermatogenic cells
• Spermatogonia


  Stem cells in outermost tubule cells
• Spermatogenesis


  1. Mitotic division of spermatogonia

  2. Type A daughter cell remains in situ and continues mitotic division, remains A germ cell

  3. Type B daughter cell pushed towards lumen and becomes primary spermatocyte

  4. Primary spermatocytes undergo meiosis I to produce 2 haploid secondary spermatocytes

  5. Secondary spermatocytes undergo meiosis II to produce 4 spermatids
• Spermatids still not quite a sperm cell
• Spermatogenesis and Sperm

  1. Spermatogonia give rise to primary spermatocytes (2n)

  2. Primary spermatocytes undergo meiosis I to produce secondary spermatocytes (n)

  3. Secondary spermatocytes undergo meiosis II to produce spermatids (n)

  4. Spermiogenesis produces spermatozoa (sperm)
• Spermatozoa (sperm)


  • Head with flattened nucleus (genetic storage)
  • Acrosome
  • Tail (flagellum) (locomotor apparatus)
  • Midpiece with mitochondria (ATP)
• Nurse cells


  • Also called supporting cells, sustenocytes, sertoli cells
  • Connected by tight junctions to form blood-testis barrier
  • Support sperm, regulate nutrients/hormones/toxins, remove waste
• Sperm pathway from testes to epididymis

  1. Seminiferous tubules

  2. Straight tubule

  3. Rete testis

  4. Efferent ductules

  5. Epididymis (where sperm mature and are stored)
• Hypothalamic–Pituitary–Gonadal axis (HPG axis)


  • Hypothalamus releases GnRH
  • Anterior pituitary releases FSH and LH
  • FSH enhances spermatogenesis
  • LH stimulates interstitial cells to secrete testosterone
• Penis


  • Root (anchored to body)
  • Crura (crus) + bulb
  • Shaft (unattached)
  • Glans penis (enlarged tip)
  • Smegma
  • Prepuce (foreskin)
• Erectile tissue


  3 erectile bodies surrounded by dense fibrous connective tissue sheaths
• Semen


  • Milky, white, alkaline fluid (pH 7.2-8.0)
  • Contains sperm and secretions from accessory glands
  • Function is transport medium for sperm
  • Volume is 2-5 mL/ejaculation with 100+ million sperm
• After puberty mitotic division of spermatogonia leads to Type A and Type B cells
• Deepest part of seminiferous tubules is the lumen
• Spermatids elongate, shed cytoplasm, form tail, and become sperm