Читать книгу Bovine Reproduction - Группа авторов - Страница 216

The unique and interesting features contributing to extension and erection of the penis of the bull are well described [2, 3]. A brief summary of the process follows.

The fibroelastic ruminant penis is encased in the rigid tunica albuginea which encloses the erectile tissues of the corpus cavernosum penis (CCP). In the non‐erect state the penis is maintained within the prepuce and sheath by the traction of the retractor penis muscles, which insert on the ventral surface of the mid‐shaft of the penis at the distal bend of the sigmoid flexure. The proximal terminus of the CCP is the bulb of the penis, which divides laterally into two crura which are covered by the ischiocavernosus muscles at they attach to the bony pelvis at the ischiatic arch.

At the initiation of sexual arousal, the retractor penis muscles relax in synchrony with increased blood flow from the deep arteries of the penis into the crura, and the CCP fills with blood. The loss of muscle tension from the retractor muscles coupled with complete filling of the CCP initiates partial straightening of the sigmoid flexure. Contractions of the ischiocavernosus muscles compress the blood‐filled penile crura against the pelvis and occlude all vascular flow to and from the CCP, resulting in a closed hydraulic system. Further rhythmic contractions of the ischiocavernosus muscles increase the pressure of the blood contained within the crura and the CCP to produce the force necessary for full erection and extension of the penis. The pressure generated in the CCP far exceeds the arterial pressure of the circulatory system, reaching 14 000 mmHg (1.87 MPa) or higher at the time of peak erection in the bull [4].