L4.2.1: Spermatogenesis

• Spermatogenesis

  ● Development of sperm.

  ○ Formation of 4 daughter cells.

  ● Happens at the Seminiferous Tubules. Specifically, in the wall of a seminiferous tubule.

  ○ Found in the lobules in the testes.

  ● Influence of Sperm Production

  ○ The Endocrine System, via the pituitary gland.
• SEMINIFEROUS TUBULES

  ● Parts of the Seminiferous Tubules

  ○ Lumen

  ■ The internal structure.

  ○ Wall

  ■ The external structure

  ■ The site of spermatogenesis.

  ■ Where primary germ layers are located: The spermatogonium
• Stages

  • Spermatocytogenesis
  • Rounded immature sperm cells undergo successive mitotic and meiotic divisions
  • Spermiogenesis
  • Metamorphic change from spermatid to spermatozoa
• PROCESS OF SPERMATOGENESIS

  [1] Start with the spermatogonium.

  ● A stem cell w/ two types: Type A and Type B
• Type A

  ● Remains at the basement membrane as a stem cell.

  ● Ensures the creation of type B (through mitotic division)

  ● Diploid cell (2n) – 48
• Type B

  ● A product of mitosis of Type A.

  ● Will move towards the tubule lumen.

  ● Recall: lumen is the central area of a seminiferous tubule.

  ● Diploid cell (2n) – 48
• PROCESS OF SPERMATOGENESIS

  [2] Type B will undergo spermatogenesis, which is divided into

  two events:

  ❖ Meiosis (Spermatocytogenesis) — Cell division. Starts during prophase I:

  ➢ Result: Primary Spermatocyte

  ➢ 1 cell; diploid (2n)

  ● Meiosis I completed.

  ○ Result: Secondary Spermatocytes

  ○ 2 cells; haploid (n) each

  ● Meiosis II completed.

  ○ Result: Early Spermatids

  ○ 4 cells; haploid (n) each

  ○ Non-motile

  ○ Yields 92 chromosomes for all 4 early spermatids (23 chromosomes each).
• PROCESS OF SPERMATOGENESIS

  [2] Spermiogenesis

  ➢ The series of sperm transformations.

  ■ From circular to pointed structure of sperm cells.

  ➢ Formation of motility structure.

  ➢ No change in chromosomal quality, but rather,

  changes in characteristics.

  ➢ Early spermatids to Late Spermatids

  ➢ Late spermatids to Sperm
• PROCESS OF SPERMATOGENESIS

  [3] The sperm will now be ejected to the lumen of seminiferous tubules.
• Spermatids

  ● Will undergo spermiogenesis to become a sperm cell (spermatozoa)