Exam 5 Review:  Chapter 27 Seminiferous Tubules

seminiferous tubules - Any of two or three twisted, curved ducts in each lobule of the testis in which spermatozoa develop; they are lined by epithelial cells including spermatogonial stem cells, which undergo mitosis, followed by meiosis, to produce the sperm cells, and supportive sustentacular cells; they empty into the straight tubules and rete testis.

See also THE MALE REPRODUCTIVE SYSTEM.

spermatogenesis - The long (~70 days) and complex process within the seminiferous tubules of the testes, in which an elaborate succession of distinct cell types are generated by mitotic and meiotic divisions; in the initial stage, diploid spermatogonia repeatedly divide by mitosis, giving rise to diploid primary spermatocytes, which in turn undergo the first meiotic division I, leading to haploid secondary spermatocytes; secondary spermatocytes undergo the second meiotic division II, leading to round spermatids, which elongate during the spermiogenesis process to form elongated spermatids and finally differentiate into mature spermatozoa, by condensation of the chromatin, with the substitution of histones with protamines in DNA supercoiling, and the formation of the acrosome, flagellum, and the other sperm organelles; the progression moves from the periphery to the center of the seminiferous tubule and is regulated by androgens.

spermatogenic cells = spermatogonia - Any of the diploid stem cells of the male gonads, the testes, located at the periphery of the seminiferous tubules, which are the progenitors of spermatocytes; they repeatedly divide by mitosis, giving rise to diploid primary spermatocytes, which in turn undergo the first meiotic division I, leading to haploid secondary spermatocytes; secondary spermatocytes undergo the second meiotic division II, leading to round spermatids, which elongate during the spermiogenesis process to form elongated spermatids and finally differentiate into mature spermatozoa.

sperm cell = spermatozoon - The mature male gamete, a tiny haploid cell with a head, body, and tail, produced by meiosis in the process of spermatogenesis in the seminiferous tubules of the testes, and which moves to the epididymus outside the testes for maturation (capacitation) and storage; after activation by seminal fluid and the stimulation of flagellar motility provided during the process of ejaculation, it is capable of fertilizing an egg = ovum.

sustentacular cells = Sertoli Cells - Any of the tall columnar, striated, supportive cells of the seminiferous tubules of the testis, to which spermatids attach for nourishment during spermatogenesis; they provide the appropriate microenvinonment for sperm differentiation, phagocytize degenerate sperm and form the blood-testis barrier; these cells also contribute to the blood-testis barrier; they are regulated by testosterone.

blood testis barrier - The physical (epithelial) and physiological membrane formed from interlocking processes of sustentacular cells, which separates the diploid spermatogonial stem cells from the interior of the seminiferous tubules, and, therefore, the developing sperm cells, from the interstitial tissues and blood stream of the testes; it is responsible for maintaining the unique microenvironment conducive to spermatogenesis; it also prevents the immune system from detecting, responding* to, and destroying the maturing sperm cells.  [*Note:  Because no sperm cells are present during fetal life, they are not screened by the developing immune system, and, therefore, elaborate some protein (surface markers, antigens) which would be treated as foreign by the immune system.]

interstitial endocrinocytes = Leydig cells = interstitial cells of Leydig - The endocrine cells located in the interstitial tissues, between the seminiferous tubules, of the testes, which produce and secrete the steroid androgens, testosterone, etc.; they are regulated by LH = ICTH from the anterior pituitary.

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