Q.Describe the process of spermatogenesis, including its hormonal control.

[!TLDR]

Spermatogonia divide mitotically and then, via meiosis I and II, give haploid spermatids, which undergo spermiogenesis into motile sperm; the whole process is driven by GnRH, LH, FSH and testosterone.

[!ANSWER]

Spermatogonium -> (mitosis) -> primary spermatocyte -> (meiosis I) -> secondary spermatocyte -> (meiosis II) -> spermatid -> (spermiogenesis) -> spermatozoon; regulated by GnRH -> LH/FSH -> testosterone (Leydig cells) + Sertoli-cell support.

Spermatogenesis proceeds in three phases. In the multiplicative phase, spermatogonia lying against the tubule's basement membrane divide mitotically; some remain spermatogonia, replenishing the stem-cell pool, while others enlarge into primary spermatocytes. In the meiotic phase, each primary spermatocyte completes meiosis I to give two secondary spermatocytes, which rapidly complete meiosis II to give four haploid spermatids in total from each original primary spermatocyte. In the transformation phase (spermiogenesis), each rounded spermatid is remodelled -- an acrosomal cap forms over a condensed nucleus (the head), mitochondria form a helical sheath around a new flagellum (the middle piece), and surplus cytoplasm is shed -- producing a mature, motile spermatozoon, which is then released into the tubule lumen by spermiation. Hormonal control runs along the hypothalamus-pituitary-testis axis: GnRH from the hypothalamus stimulates the anterior pituitary to release LH, which stimulates Leydig cells to secrete testosterone, and FSH, which acts on Sertoli cells to support the germ cells (via androgen-binding protein and other factors); testosterone acts both systemically and locally to sustain spermatogenesis, while Sertoli-cell inhibin feeds back on the pituitary to limit further FSH release.

[!ANSWER]

Spermatogonium -> (mitosis) -> primary spermatocyte -> (meiosis I) -> secondary spermatocyte -> (meiosis II) -> spermatid -> (spermiogenesis) -> spermatozoon; regulated by GnRH -> LH/FSH -> testosterone (Leydig cells) + Sertoli-cell support.

Present the cellular sequence first (spermatogonium through to spermatozoon, naming each division), then present the hormonal axis that drives it (GnRH -> LH/FSH -> testosterone/Sertoli support) as a separate, second part of the answer.

Saying each primary spermatocyte produces only two sperm -- meiosis I and meiosis II together produce four haploid spermatids (and ultimately four sperm) from a single primary spermatocyte, not two.