CHAPTER I 



77?^ Two Components of Semen: 

 Spermatozoa and Seminal Plasma 



Spermatozoa. Spermatogenesis and sperm 'ripening'. Sperm transport in 

 the female reproductive tract and 'capacitation'. Structural and chemical 

 characteristics of the sperm-head, middle-piece and tail. 



Seminal plasma. Secretory function of male accessory glands. Prostatic 

 secretion. Seminal vesicle secretion. Physiological significance of seminal 

 plasma. Prostaglandin, vesiglandin, and certain other pharmacodynamic- 

 ally active substances. Coagulation and liquefaction. 



'Whole semen' as ejaculated, generally appears as a viscous, creamy, 

 slightly yellowish or greyish fluid, and consists of spermatozoa or 

 'sperm', suspended in the fluid medium, called seminal plasma; its 

 composition depends in the first place, on the proportion of sperm 

 and plasma, and is further determined by the size, storage capacity, 

 and secretory output of several different organs which comprise the 

 male reproductive tract. The volume of the ejaculate and the con- 

 centration of spermatozoa or the 'sperm density' in ejaculated semen, 

 vary widely from one species to another, as seen from Table 1. A 

 single ram ejaculate for instance, amounts to 0-7-2 ml. only, but is 

 distinguished by a very high sperm density, 2-5 million per f.i\. 

 semen; when subjected to high-speed centrifugation, ram semen 

 separates, on the average, into about two-thirds of seminal plasma 

 and one-third of firmly packed sperm. Boar semen ejaculates on the 

 other hand, may reach a volume of as much as 500 ml; this is not 

 due to spermatozoa, but to the seminal plasma generated in very 

 capacious accessory organs (Plate III); a sperm density not exceed- 

 ing 100,000 cells //^l. is quite usual for boars, and even lower sperm 

 densities would still be regarded as normal. In man, the average 

 volume of a single ejaculate is about 3 ml., but the sperm density 

 is frequently less than 100,000 cells///!., so that only a small portion 

 of the ejaculate, much less than 10%, is represented by the sperm 

 and the rest is seminal plasma. 



1 



