The prostatic urethra as a Venturi effect urine-jet pump to drain prostatic fluid.

Several experiments show that prostatic fluid is continuously produced and it is drained from the prostate during urination and ejaculation. The mechanism which causes prostatic fluid to drain from the prostatic acini during urination is currently unclear. Also in current opinion such structures of the prostatic urethra as the urethral crest and the colliculus seminalis have no apparent functional significance. This article describes a mechanism for the draining of the prostatic acini that involves these prostatic urethral structures. It is hypothesized that the prostatic urethra works as a pump using the Venturi effect, in which urine is the carrying or motive liquid during voiding, in order to drain prostatic fluid (the carried liquid) from the acini. The urethral crest and the colliculus seminalis take part in controlling flow rates and liquid pressures for this pump to be effective. The calculated estimation of a pressure drop in the region of the colliculus seminalis during micturition was obtained using morphometric and uroflowmetric data and was used to confirm this hypothesis of prostatic acini drainage. As a consequence of this, a previously unknown function for these intra-prostatic urethral structures is described.