Physiology of Ejaculation

Abstract

The human sexual response can be described as a cycle formed by successive distinct, although intimately connected, phases. These are desire, excitation, orgasm, and resolution. In the human male, the orgasm phase actually refers to ejaculation and the intense pleasurable feeling that normally accompanies it. A correct ejaculatory response in human male engaged in sexual intercourse with a female partner is obligatory, although not sufficient, for reproduction. A correct ejaculation can be defined as forceful propulsion of seminal fluid out of the body through the urethral meatus (antegrade ejaculation). Ejaculation consists of the synchronized succession of physiological events that form two distinct phases: emission and expulsion. Emission corresponds to the secretion of the different components of the seminal fluid from accessory sex glands and testes. The composition of the seminal fluid is complex and contains, besides spermatozoa, a variety of enzymes, sugars, lipids, oligo-elements, and other substances. This mixture provides spermatozoa with a ­nutritive and protective milieu promoting their survival and movement during their run through the female reproductive tract to the ovule. The seminal secretions are secreted in a specific sequence into the posterior urethra via phasic contractions of the glands and the relative ducts. This is followed by seminal expulsion, which occurs in the form of intense rhythmic contractions of pelvi–perineal striated muscles. Concluding the ejaculatory response and marking the sexual climax, arises orgasm, a complex neuropsychophysiological process that translates in intense cerebral discharge but also whole-body physiological changes. The orgasmic response is intimately connected to the ejaculatory response but this will not be addressed here as another chapter is dedicated to this aspect of the male sexual response. It is nevertheless of crucial importance to state that orgasm can occur without ejaculation in certain conditions like after radical prostatectomy or after lesion of the sympathetic innervation to the seminal tract following retro-peritoneal lymph node dissection in testicular cancer.