The process of spermatogenesis is induced by

The correct option is FSH.

To understand why Follicle-Stimulating Hormone (FSH) is the hormone responsible for inducing spermatogenesis, let us break down the endocrine regulation of the male reproductive system step-by-step:

1. What is Spermatogenesis?
Spermatogenesis is the biological process by which diploid spermatogonia (undifferentiated male germ cells) undergo division and differentiation to produce mature, haploid spermatozoa (sperm cells) within the seminiferous tubules of the testes.

2. The Role of the Hypothalamic-Pituitary-Gonadal (HPG) Axis:
The entire process of sperm production is tightly regulated by hormones traveling along the HPG axis:
- The hypothalamus releases Gonadotropin-Releasing Hormone (GnRH).
- GnRH stimulates the anterior pituitary gland to secrete two primary gonadotropins: Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH).

3. Specific Action of FSH in Spermatogenesis:
- FSH binds specifically to its receptors located on the Sertoli cells, which are the "nurse" cells found inside the seminiferous tubules.
- Once stimulated by FSH, Sertoli cells mature and secrete key factors necessary for spermatogenesis, including androgen-binding protein (ABP) and nutrients that support developing sperm cells.
- ABP helps concentrate testosterone (produced by Leydig cells under the influence of LH) inside the seminiferous tubules, maintaining the high local levels of androgen required for spermatids to mature.

4. Analyzing the Other Options:
- TSH (Thyroid-Stimulating Hormone): Stimulates the thyroid gland to produce thyroid hormones (T₃ and T₄), regulating metabolism.
- MSH (Melanocyte-Stimulating Hormone): Stimulates the production and release of melanin by melanocytes in skin and hair.
- ACTH (Adrenocorticotropic Hormone): Stimulates the adrenal cortex to release glucocorticoids (such as cortisol) in response to stress.

Therefore, among the choices provided, FSH is the specific hormone that directly stimulates Sertoli cells to initiate and support the process of spermatogenesis.