Spermatids
The spermatids , referred to in the singular as spermatids or spermatids , are the smallest cells in the germinal epithelium ( epithelium spermatogenicum ) of most sexually reproducing tissue animals ( eumetazoa ). During spermatogenesis , they arise from second-order spermatocytes . In the further course of spermatogenesis, the so-called spermiohistogenesis , the spermatids mature into sperm .
Occurrence
The spermatids are located near the lumen of a testicular tubule ( tubuli seminiferi ).
Maturation process
Spermatids arise from the second meiosis of secondary spermatocytes. They have a haploid set of chromosomes . At the beginning of their maturation, the spermatids lie on the lumen of the tubular wall and have a rounded shape with a round nucleus . As they mature, they first migrate towards the basement membrane and then back to the tubular lumen. The spermatids do not divide further, but differentiate into mature elongated spermatids.
During ripening, three processes take place simultaneously: nuclear condensation, acrosome formation and the formation of the flagellum . With nuclear condensation, the caryoplasm (the content of the cell nucleus ) condenses to about a tenth of the original volume. The originally round cell nucleus takes on a paddle-like shape. The acrosome is the head cap of the later sperm. It is formed from the Golgi apparatus of the spermatids. The acrosome contains the enzyme acrosine (a serine protease ), which is important for fertilization . Acrosin causes the proteolysis of the glycoprotein glass skin ( zona pellucida ) of the egg cell . The flagellum is made up of two centrioles .
Once the nucleus, acrosome and flagellum structure are formed, the spermatids are released from the germinal epithelium. At this stage they are known as sperm or spermatozoa. Remnants of the cytoplasm of the spermatids remain in the germinal epithelium . The Sertoli cells break down these residues called residual bodies .
The spermatids are smaller than their precursor cells , the spermatocytes.
Individual evidence
- ^ HG Liebich: Functional histology of domestic mammals. Schattauer Verlag, 2004, ISBN 3-7945-2311-3 , p. 275.
- ↑ K. Steger et al.: Protamine as a prognostic factor for the success of a testicular sperm extraction (TESE). (PDF; 555 kB) In: Journal for Reproductive Medicine and Endocrinology. 2, 2005, pp. 13-17.
- ^ A b A. Benninghoff, D. Drenckhahn: Anatomie 1. Verlag Elsevier, Urban & Fischer, 2008, ISBN 978-3-437-42342-0 , pp. 806-807.
literature
- JCE Donner: Immunohistochemical studies on the development from testicular carcinoma in situ to seminoma. Dissertation . Justus Liebig University, Giessen 2003.