Efficiency of spermatogenesis: a comparative approach

Efficiency of spermatogenesis is the estimated number of spermatozoa produc ed per day pergram of testicular parenchyma. Spermatogenesis is the process of cell division and cell differentiation by which spermatozoa are produce d in testes. Efficiency of spermatogenesis is influenced by species differe nces in the numerical density of germ cell nuclei and in the life span of t hese cells. Activities of spermatogonia, spermatocytes, and spermatids part ition spermatogenesis into three major divisions (spermatocytogenesis, meio sis, and spermiogenesis, respectively). Spermatocytogenesis involves mitoti c germ cell division to produce stem cells and primary spermatocytes. Meios is involves duplication of chromosomes, exchange of genetic material, and t wo cell divisions that reduce the chromosome number and yield four spermati ds, In spermiogenesis, spherical spermatids differentiate into mature sperm atids which are released in the lumen of seminiferous tubules as spermatozo a. Spermatogenesis and germ cell degeneration can be quantified from number s of germ cells in various developmental steps throughout spermatogenesis. Germ cell degeneration occurs throughout spermatogenesis; however, the grea test impact occurs during spermatocytogenesis and meiosis. There are specie s and seasonal influences on the developmental steps in spermatogenesis at which germ cell degeneration occurs. Number of Sertoli cells, amount of smo oth endoplasmic reticulum of Leydig cells, and the number of missing genera tions of germ cells within the spermatogenic stage of the cycle influence e fficiency of spermatogenesis. Efficiency of spermatogenesis is influenced t o the amount of germ cell degeneration, pubertal development, season of the year, and aging of humans and animals. (C) 2000 Published by Elsevier Scie nce B.V. All rights reserved.