Endo-Repro L13 Male 2 Flashcards
Spermatogenesis
- Mitotic proliferation → spermatogonia
- Meiotic division → Primary spermatocyte
- Spermiogenesis → round serpmatid – elongated spermatazoa
Spermiation
Releasing sperm from Sertoli cell
Spermatogenesis within seminiferous tubule epithelium: Definition
Process by which Type A dark spermatogonia (the main stem cell in the seminiferous tubule) form spermatozoa.
Spermatogenesis within seminiferous tubule epithelium: Involves three stages
- Mitotic proliferation to (Type A light is converted to Type B) produce large reservoir of identical cells (spermatogonia proliferate and form primary spermatocytes).
- Meiotic division to give rise to haploid gametes and increase genetic diversity (primary spermatocytes undergo meiosis to form spermatids)
- Spermiogenesis or cytoplasmic remodelling to produce specialised germ cells (spermatids form spermatozoa).
Type B
Committed cell to spermatogenesis
Type A Dark
Stem cell replaces sperm
Type A light
Transformed SC = divide to form Type B
Stages of spermatogenesis:
- Type A: Spermatogonium (Dark) converted to Spermatogonium
a. Some divide to replenish pool of Type A Dark (replaces pool) - Type A: Spermatogonium (light) is converted to a Type B spermatogonium (committed to differentiate).
Spermatocytogenesis:
Primary spermatocyte formed and undergoes meiosis.
- Primary spermatocyte converted to secondary spermatocyte
- Forms a spermatid converted into a spermatozoon
Dynamics of spermatogenesis:
- Highly organised process: temporally and spatially to ensure a continual production of sperm
- Whole process (Type A dark to spermatozoon) takes about 64 days in the human)
- In a given area, Type A dark spermatogonia initiate a new wave of spermatogenesis every 16 days.
- It is a long process therefore the epithelium will contain four successive batches (cohorts) of cells progressing through spermatogenesis at any one time
- The progression of these four batches is highly organised, and each patch of epithelium goes through a 16-day cycle recognised by particular cell associations.
- To avoid cyclic sperm production, adjacent patches of seminiferous epithelium initiate spermatogenesis at different times (i.e. they are not synchronised).
Spermiogenesis:
- Formation of Acrosome, flagellum and mid-piece.
- Loss of excess cytoplasm
a. Form acrosome (head)
b. Cap formation
c. Form midpiece (mitochondria)
Roles of Sertoli cells:
- Under FSH regulation
- Provides physical and metabolic support for developing spermatizia
- Form the blood-testis barrier (prevents autoimmunity and toxic damage)
- Secrete anti-lymphocytic factors – protection.
- Resorb leftovers from spermiogenesis
- Secrete and maintain ion composition of seminiferous tubular fluid.
- Secrete inhibin
- Make androgen binding protein
- Involved in steroid conversion (e.g. convert testosterone to DHT).
Spermatogenesis is dependent upon
Both pituitary gonadotrophins (i.e. LH and FSH)
LH targets
Leydig cells to maintain testosterone secretion
FSH targets Sertoli cells to
Maintain their function
Feedback regulation of LH is
Via testosterone