Exam 5 Review:  Chapter 27 Spermatogenesis

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.

spermiogenesis - That portion of the process of spermatogenesis during which the transformation of an imature spermatid into a mature spermatozoon occurs; during the process the round spermatid, derived from a secondary spermatocyte by meiotic division II, forms an elongated spermatid and then transforms into a mature spermatozoon 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; it is regulated by testosterone.

spermiation - The normal continual discharge of spermatozoa from the sustentacular cells into the lumen of the seminiferous tubules and then from the testis through the straight tubules and rete testis into the epididymus; it is regulated by testosterone.

primary spermatocytes - The diploid cells within the seminiferous tubules, derived by mitosis from spermatogonial stem cells, which undergoe meiosis to form two haploid secondary spermatocytes, which in turn divide, completing meiosis, to form the four haploid spermatids.

secondary spermatocytes - The pairs of haploid cells within the seminiferous tubules, derived by meiosis I from a primary spermatocyte, which undergoe meiosis II to form the four haploid spermatids.

spermatid - One of the haploid cells within the seminiferous tubules which are formed by division of the secondary spermatocytes and which differentiate by spermiogenesis into spermatozoa.

(sperm) head - The anterior enlarged, oval, part of a sperm consisting of the acrosome and the haploid nucleus, surrounded by cell membrane.

acrosome - The membrane bound vesicle at the tip of the head of the sperm which contains proteolytic enzymes, e.g., hyaluronidase, which have the capacity to digest the outer coat of the egg = ovum to allow the sperm to inject its haploid sperm nucleus into the egg = ovum at fertilization.

(sperm) midpiece - The short, tapering part of a sperm, at the juncture of the head and the tail, consisting of mitochondria for ATP production and the base of the flagellum, surrounded by cell membrane.

(sperm) tail - The thin posterior part of a sperm consisting of the middle portion, midpiece, and the terminal flagellum, surrounded by cell membrane.

flagellum - The special cell organelle consisting of microtubules in a 9 + 2 array, surrounded by cell membrane, which beat in a back-and-forth motion, powered by ATP hydrolysis, to achieve movement; the flagellar motion of sperm cells does not begin until ejaculation when contact with regulatory substances in seminal fluid trigger the action.

Sketch and label:

3.  a sperm cell = spermatozoan.

7. a cross-section of the seminiferous tubule illustrating the stages of spermatogenesis.