MIDTERMS

• Spermatogenic cycle

  A cycle of progressive stages occurring within a particular segment of the seminiferous tubules
• Spermatogenic wave


  The distance from one stage to another similar stage
• A spermatogenic cycle and wave can be observed along the length of the seminiferous tubules
• The seminiferous tubules is found inside the testis
• Spermatogenesis


  A sequential event by which the male undifferentiated germ cells (spermatogonia) are transformed into mature gametes called the spermatozoa
• Spermatogonia


  • All derived from the original primordial germ cells that were implanted in the embryonic genital ridge
  • All diploid and experience a constant, steady mitosis so that there will be a continuous supply of new cells available for sperm production
• Testes


  Male gonads where the production of viable male germ cells is initiated
• Parts of a generalized testis of vertebrate

  • Tunica albuginea
  • Interstitial cells or Leydig cells
  • Seminiferous tubules or tubuli contorti
• Seminiferous tubules

  • Basement membrane
  • Spermatogonia
  • Sertoli (Sustentacular) cells
  • Spermatogonia
  • Primary spermatocytes
  • Secondary spermatocytes
  • Spermatids
  • Spermatozoa
• Newly collected urine from a pregnant woman can stimulate spermatogenesis in a male frog
• The motile structures seen in the frog's urine are the sperm cells
• The number of stages in a spermatogenic cycle differs among species
• Humans have six stages (I-VI) in a cycle and it takes four 16-day cycles for a spermatogonium to be transformed into a spermatozoon
• Spermatogenic wave


  The progressive movements or the maturity of the cell from periphery going inside (lumen)
• Spermatogenesis occurs in overlapping waves which pass along the tubules of the testis so that the stages of spermatogenesis observed at any given level of a tubules will be different from those at another level
• The wave of spermatogenesis moves slowly
• Spermatogenic waves in the seminiferous tubule

  • Oldest wave (cells bordering the lumen of the tubule, comprised of maturing spermatozoa or metamorphosing spermatids)
  • Intermediate wave (cells in the middle layer of the tubular wall, intermediate, usually circular in shape)
  • Youngest wave (cells near the outer surface of the tubules, spermatogonia ready to undergo meiosis)
• At any one time, each specific segment of the tubule is in one stage of the cycle
• All the stages of one cycle can be seen taking place in sequence within a long segment of a tubule
• Testes or Testicles


  Glands in which the male reproductive cells are formed, lying one on each side in the scrotum
• Testis


  • Oval gland about one and a half inches long with its long axis directed downward, backward and inward
• 2 major functions of the testes

  • Producing sperm from stem cell spermatogonia (spermatogenesis)
  • Producing androgens, to maintain and regulate androgen mediated functions throughout the body
• Generalized vertebrate testis


  • Tunica albuginea (a strong fibrous coat that protects the seminiferous tubules)
• Rete testis


  A plexus of tubules into which the seminiferous tubes open
• Epididymis


  A soft body lying behind the testis, made up of a convoluted tube about 20 ft. long
• Vas deferens


  The continuation of the tube of the epididymis, starting at the globus minor and running up on the inner side of the epididymis to the external abdominal ring in the abdominal wall
• Frog testis structure


  • Oval body consisting of 2 kinds of epithelia: germinal epithelium (stratified epithelium lining the seminiferous tubules) and glandular epithelium
• Leydig cells/Interstitial cells


  Somatic cells located at the septula, responsible for the secretion of the male hormone testosterone
• Sertoli/Sustentacular cells


  Located at the basal layer of the germinal epithelium, function as nurse cells to nourish the developing sperm cells
• Cell types in the testis in order of development

  • Spermatogonia
  • Primary spermatocytes
  • Secondary spermatocytes
  • Spermatids
  • Mature spermatozoa
• Spermatogonium


  Considered as the ancestral cell for the spermatogonia
• Spermatocytogenesis


  The male form of gametocytogenesis involving stem cells dividing to replace themselves and produce a population of cells destined to become mature sperm
• Types of spermatogonia


  • Type A dark spermatogonia (Ad)
  • Type A pale spermatogonia (Ap)
  • Type B spermatogonia (B)
• Types of spermatogonia


  • Permatogonia (Ad), type A pale
  • Spermatogonia (Ap), type A pale
  • Type B spermatogonia
• Type Ad spermatogonia


  Also called "dark" spermatogonia, they maintain the population of spermatogonia
• Type Ad spermatogonia


  Divide to produce another type Ad spermatogonia and one type Ap spermatogonia
• Type Ap spermatogonia


  Also called "pale" spermatogonia, they repeatedly divide mitotically to produce identical cell clones linked by cytoplasmic bridges
• Type Ap spermatogonia


  Differentiate into type B spermatogonia when repeated division ceases
• Type B spermatogonia


  Undergo mitosis to produce diploid intermediate cells called primary spermatocytes
• For humans, the entire process of spermatogenesis takes 74 days, including the transport on the ductal system, it takes 3 months