Spermatogenesis
Spermatogenesis
- Spermatogenesis comprises cell division and differentiation processes that produce sperm cells.
- Takes place in the seminiferous tubules of the testes.
- Requires sustentacular cell stimulation from FSH and testosterone (discussed in detail, elsewhere).
- Takes approximately 64 days.
Stages:
Spermatocytogenesis
- Mitotic divisions create spermatocytes.
- Meiotic divisions create spermatids.
Spermiogensis
- Spermatids differentiate to become sperm (aka, spermatozoa).
Spermination
- Occurs when the sperm disassociate from the sustentacular cell and enter the lumen of the seminiferous tubule.
- From here, sperm cells travel to the epididymis for storage and maturation.
Cell Divisions:
Spermatogonium
- Primordial stem cells from which the sperms originate.
- Undergoes mitosis and creates two cell types:
- A replication of itself
- Another that is committed to passing through spermatogenesis = a spermatocyte.
Primary spermatocyte
- Primary spermatocyte undergoes meiosis I to create two daughter cells: secondary spermatocytes
Secondary spermatocytes
- Undergo meiosis II, which produces spermatids.
Spermatids
- Undergo spermiogenesis to form immature sperm; during this time, the cells develop but no longer divide.
Early sperm
- Enveloped in the cytoplasmic processes of the sustentacular cells.
- Have tails, which extend towards the lumen.
- Cytoplasm is concentrated towards one end, the head.
- Are released via spermination into the lumen of the seminiferous tubule.
Maturation:
- Full maturation and motility are not achieved until after ejaculation.
- Uterine tubule fluids within the female reproductive tract triggers capacitation (further maturation), which prepares the sperm for fertilization.
Anatomy of a sperm cell:
Head
- Comprises the cell nucleus covered by the acrosome; the acrosome contains enzymes that facilitate joining of sperm and ovum at fertilization.
Midpiece
- Comprises mitochondria, which provide the energy for sperm motility.
Tail
- Produces flagellar movements ("back and forth" movements) that enable the sperm to "swim" upon ejaculation.
Clinical Correlation:
- Sperm cells must be able to move through the female reproductive tract for conception to occur; if they cannot, a man may be infertile despite normal sperm count.
- Poor motility may stem from stress, excessive heat, drug effects, and dietary inefficiencies.