Spermatogenesis

• Spermatogenesis


  Spermatogonia are transformed to mature spermatozoa in the seminiferous epithelium of the testis
• Spermatogenesis


  The sequence of events by which spermatogonia are transformed to mature spermatozoa in the seminiferous epithelium of the testis
• Spermatogenesis begins at puberty, is dormant in seminiferous tubules since fetal period, and continues into old age
• Sperm can be detected in the morning urine of boys after the 15th year of pubertal changes and occasionally earlier
• Fertility in boys


  Reached by 13 years of age but full fertility is gained at 14-16 years of age
• Spermatogenesis


  Formation of mature spermatozoa from male primitive germ cells which line the seminiferous tubules of the testis
• Each cycle of spermatogenesis takes 64-80 days
• Spermatogenesis


  • Arranged from the basal lamina toward the lumen of the seminiferous tubules in the order of increasing maturity
  • Can be divided into 3 phases: Spermatocytogenesis, Meiosis, Spermiogenesis
• Spermatocytogenesis


  Proliferative phase
• Meiosis


  Production of haploid gamete
• Spermiogenesis


  Metamorphosis of spermatids into spermatozoa
• Spermiation


  Shedding of spermatozoa into the lumen of the seminiferous tubule for transport
• At birth, germ cells in the male infant present in the sex cords of the testis are surrounded by supporting cells (Sertoli cells)
• Spermatogenesis

  1. Primordial germ cell divides to give spermatogonia

  2. Spermatogonia gives rise to 1st spermatocyte

  3. 1st spermatocyte by 1st meiotic division gives 2nd spermatocyte

  4. 2nd spermatocyte in meiosis I gives haploid spermatids
• Overall result of spermatogenesis

  • Cell proliferation
  • Maintenance of a reserve germ cell population
  • Reduction in chromosome number
  • Genetic variation through meiosis
  • Shaping of the spermatids into spermatozoa
• Spermatogenic cycle

  Quantitating the effect of drugs, hormones, nutrition factors
• Functions of Sertoli Cell


  • Remove excess cytoplasm from developing spermatid
  • Move spermatids toward the lumen of the seminiferous tubules-ectoplasmic specializations
  • Nurture and mediate maturation of spermatids
  • Segregate groups of developing gametes
  • Secrete fluid to transport sperm in reproductive tract
  • Secrete hormones and other factors
• Sertoli cell


  Supports, protects, nurtures the germ cells and regulates spermatogenesis
• Functions of Sertoli cell

  • Inhibin (inhibits FSH production)
  • Estrogen (inhibits GnRH production)
  • Androgen binding protein (promotes spermatogenesis)
• Spermiogenesis


  1. Nucleus condenses

  2. Flagellum develops

  3. Spermatid elongates

  4. Acrosome formed from Golgi body

  5. Mitochondria aggregate around base of forming flagellum

  6. Mitochondria fuse to form supermitochondrion

  7. Most of cytoplasm is shed and phagocytosed by Sertoli cell
• Spermatozoa


  • Developed in the testis and are present in enormous numbers in the seminal fluid
  • Each consists of a small but greatly modified cell with a head, neck, connecting piece or body, and a tail
• Spermatozoon


  • Anterior two-thirds is covered by head-cap, a cap-like, saccular organelle containing enzymes which disperse the corona radiata and penetrate the Zona Pellucida during fertilization
  • About 50-60um in length, free swimming actively motile, consisting mainly of head and the tail
  • Tail consists of 3 segments: middle, principal and end piece, providing motility for the sperm to the site of fertilization
  • Middle piece of the tail contains mitochondria that provide ATP for activity
• Gene implicated in spermatogenesis is Bcl-2
• Y chromosome is essential for normal spermatogenesis
• Sperm Transport


  1. Spermatozoa in the seminiferous tubules are neither motile nor fertile

  2. Both properties are acquired during passage through the epididymis

  3. Spermatozoa are mainly stored in the ampulla of the vas deferens

  4. During ejaculation, spermatozoa pass from the vas to the prostatic urethra, where it mixes with alkaline secretions of the prostate and the seminal vesicles

  5. Spermatozoa are best motile in alkaline medium
• The most important factor in sperm transport is the speed of spermatozoa, which is 1-4mm/min, and 30-60 minutes after coitus, the spermatozoa travel through the uterine cavity and the fallopian tubes with great rapidity such that spermatozoa can be aspirated from the pouch of Douglas 30-60 minutes after artificial insemination
• Maturation


  Testis-spermatogonium-m1-1°spermatocyte-m2-2°spermatocyte-spermatids-spermatozoon
• Sperm Transport


  Sperm are transported passively from the seminiferous tubules to the epididymis where they become finally mature and mobile