 Dear students, in this topic, we shall discuss the role of testes as endocrine tissue. You know that testes are male gonads, which are primarily involved in spermatogenesis. In addition to this function, they also act as endocrine tissue and produce two major types or groups of male sex hormones. These hormones include inhibits and androgens, which are the male reproductive hormones. Dear students, in a cross-section, testes have two major parts. One, the semiferous tubules and number two, the interstitial tissue. The semiferous tubules are lined with two major types of cells. One are the germ cells, which are involved in spermatogenesis. The other type of cells are the sirtuli cells. These are the cells which function as endocrine cells. We shall discuss in detail the role of sirtuli cells as endocrine cells. Sirtuli cells synthesize and secrete a hormone inhibin. Inhibin is secreted on stimulation from androgens. It locally regulates the process of spermatogenesis and also involved in the downregulation of FSH hormone from the pituitary gland. The interstitial tissue lies between the semiferous tubules. It constitutes about 20% of the mass of testes. The endocrine cells present in the interstitial tissue are the leading cells. Leading cells are the cells which produce and secrete male sex hormones collectively called as endrogens. Androgens have three major hormones. The first and most important is testosterone. The second is dihydrotestosterone. The third is androesthenydeone. Testosterone is the primary male sex hormone. It is the most abundant of the three. Dihydrotestosterone is more active hormone in the target tissues. So most of the testosterone is converted into this form by the target cells. The third type of endrogens that is androesthenydeone is a weak endrogens. It is formed as an intermediate in the biosynthesis of testosterone. Dear students, now we shall discuss the details of secretion of testosterone. Testosterone is secreted when its concentration is lowered in the blood. It gives its signals to the hypothalamus which produces gunadotropin-releasing hormone in response to lower concentration of testosterone in the blood. This gunadotropin-releasing hormone promotes the release of FSH and leutinizing hormone from the anterior pituitary gland. These two hormones that is FSH and LH act on the leading cells of testis and stimulate the synthesis and release of testosterone. Dear students, when the level of testosterone in blood rises to a certain level, then it causes the production of inhibin hormone from the cell-to-line cells of testis. This inhibin along with the testosterone provide a negative feedback to the hypothalamus which decreases the synthesis and release of gunadotropin-releasing hormone that decrease results in decrease in the secretion of FSH and LH by pituitary and ultimately it results in decrease in the production and release of testosterone.