spermatider

Spermatider are haploid male germ cells formed during spermatogenesis in the testes of most animals. They arise from secondary spermatocytes after the second meiotic division, and in humans each primary spermatocyte yields four spermatids. In the seminiferous tubules, spermatids are initially round and remain connected by cytoplasmic bridges while Sertoli cells provide nourishment and structural support.

During spermiogenesis, spermatids transform into spermatozoa. The nuclear chromatin condenses and becomes highly compact; an acrosomal cap forms over the anterior nucleus; the flagellum develops from the centriolar complex; mitochondria reorganize to form the midpiece around the axoneme; most cytoplasm is discarded as a residual body and phagocytosed by Sertoli cells. The cells elongate and differentiate into mature spermatozoa, though they are not yet released into the lumen at this stage.

Mature spermatozoa are released into the lumen of the seminiferous tubules during spermiation and subsequently travel through the male reproductive tract, where they acquire motility and fertilizing ability. Spermatids themselves are not typically motile or fertilization-competent until completion of spermiogenesis.

The process is regulated by hormones and the local testicular environment and is organized in a cyclical manner within the seminiferous epithelium. In humans, spermatids carry a haploid set of 23 chromosomes.