The arterial blood supply to each testis is provided by a testicular artery, a direct branch of the abdominal aorta arising caudal to the renal arteries. The testicular artery crosses the lateral abdominal wall and then passes ventrally through the inguinal canal [10]. As the testicular artery approaches the testis it begins to spiral, with the nearby tortuous pampiniform plexus of the testicular vein forming a vascular cone. This arterial/venous arrangement is an effective thermoregulatory apparatus [11].
An adequate blood supply to the penis and associated muscles is required for the processes of erection, ejaculation, and tissue maintenance. This comes by way of the internal iliac artery. The internal iliac artery is a direct continuation of the abdominal aorta at the entrance to the pelvic cavity. The umbilical artery, a branch of the internal iliac, supplies the ductus deferens and the bladder [4]. The prostatic artery leaves the internal iliac and supplies the prostate, vesicular glands, ductus deferens, ureter, and urethra [4]. As the internal iliac continues through the pelvic cavity it divides into the caudal gluteal and internal pudendal [10]. The internal pudendal gives off the ventral perineal artery and urethralis artery, and continues as the artery of the penis [10]. The artery of the penis gives off the artery of the bulb of the penis, which supplies the bulbospongiosus muscle and the cavernous spaces of the corpus spongiosum [12] (Figure 1.13). The deep artery of the penis is another branch of the artery of the penis that enters the crus of the penis and supplies the erectile tissue, the corpus cavernosum [12]. After the deep artery branches off, the artery of the penis continues as the dorsal artery of the penis which passes along the dorsal aspect of the penis toward the glans penis and prepuce. It is responsible for maintenance of penile tissue during quiescence [13].
Figure 1.13 Arterial supply to the penis: Ip = internal pudendal artery, Ab = artery of the bulb of the penis, Dpa = deep artery of the penis, Dn = dorsal nerve, Da = dorsal artery of the penis, Rp = retractor penis muscle, Sc = spermatic cord, Sf = sigmoid flexure.
Nervous Supply
The innervation of the external genitalia of the bull consists of the pudendal nerve and its branches. The pudendal nerve carries motor, sensory, and parasympathetic nerve fibers [4]. The pudendal nerve passes through the pelvic cavity medial to the sacrosciatic ligament and divides as it approaches the lesser ischiatic notch of the pelvis into proximal and distal cutaneous branches supplying the skin of the caudal hip and thigh [4, 8]. The pudendal nerve continues through the ischiorectal fossa, terminating in a preputial branch, a scrotal branch, and finally the dorsal nerve of the penis [6]. The pelvic nerve provides parasympathetic innervations from the sacral plexus [1]. The hypogastric nerve contributes sympathetic fibers from the caudal mesenteric plexus to the genital system [1] (Figure 1.14).
Figure 1.14 Nerves of the penis: Sc = sciatic nerve, Pu = pudendal nerve, Pc = proximal cutaneous branch of pudendal nerve Scl = sacrosciatic ligament, Stl = sacrotuberous ligament, R = rectum.
Accessory Glands
The accessory genital glands of the bull include the vesicular gland, ampulla of the ductus deferens, and prostate and bulbourethral glands (Figure 1.15). The bilateral vesicular gland is the largest accessory gland in the bull and contributes the greatest volume to the ejaculate. It is a lobated gland of firm consistency. It lies dorsal to the bladder and lateral to the ureter and ampulla of the ductus deferens [1]. The body of the prostate lies dorsal to the urethra between and caudal to the vesicular glands. The disseminate part of the prostate is concealed in the wall of the urethra and covered by the urethral muscle [1]. The ampulla, vesicular glands, and prostate all empty their contents into the urethra through the colliculus seminalis. The bilateral bulbourethral gland lies on each side of the median plane dorsal to the urethra; it is mostly covered by the bulbospongiosus muscle. Its duct opens into the urethral recess [1] (Figure 1.15). The urethral recess is a blind pouch that exits dorsally into the penile urethra at the level of the ischiatic arch. The presence of this structure makes it difficult to pass a catheter retrograde into the bladder.
Figure 1.15 Secondary sex glands: Am = ampulla, Vs = vesicular glands, P = prostate, Bu = bulbourethral gland, Ub = urinary bladder.
References
1 1 Nickel, R., Schummer, A., Seiferle, E., and Sack, W.O. (eds.) (1973). The Viscera of the Domestic Mammals. Berlin: Springer‐Verlag, xiv, p. 401.
2 2 Johnson, A., Gomes, W., and Vandemark, N. (1970). The Testis. New York;: Academic Press, v, illus. 3.
3 3 McGavin, M. and Zachary, J. (2007). Pathologic Basis of Veterinary Disease, 4e, 1476. St Louis, MO: Mosby Elsevier.
4 4 Schaller, O. and Constantinescu, G. (1992). Illustrated Veterinary Anatomical Nomenclature. Stuttgart: F. Enke Verlag, vi, p. 614.
5 5 Ross, M., Kaye, G., and Pawlina, W. (2003). Histology: A Text and Atlas, 4e, 875. Philadelphia: Lippincott Williams & Wilkins.
6 6 Mullins, K. and Saacke, R. (2003). Illustrated Anatomy of the Bovine Male and Female Reproductive Tracts: From Gross to Microscopic, 79. Columbia, MO: National Association of Animal Breeders.
7 7 Watson, J. (1964). Mechanism of erection and ejaculation in the bull and ram. Nature 204: 95–96.
8 8 Budras, K.‐D. (2003). Bovine Anatomy: An Illustrated Text, 138. Hannover, Germany: Schlütersche.
9 9 Ashdown, R. and Smith, J. (1969). The anatomy of the corpus cavernosum penis of the bull and its relationship to spiral deviation of the penis. J. Anat. 104: 153–160.
10 10 Schummer, A., Wilkens, H., Vollmerhaus, B., and Habermehl, K.‐H. (1981). The Circulatory System, the Skin, and the Cutaneous Organs of the Domestic Mammals, 158. Berlin: Springer‐Verlag.
11 11 Brito, L., Silva, A., Barbosa, R., and Kastelic, J. (2004). Testicular thermoregulation in Bos indicus, crossbred and Bos taurus bulls: relationship with scrotal, testicular vascular cone and testicular morphology, and effects on semen quality and sperm production. Theriogenology 61: 511–528.
12 12 Ashdown, R., Gilanpour, H., David, J., and Gibbs, C. (1979). Impotence in the bull. (2) Occlusion of the longitudinal canals of the corpus cavernosum penis. Vet. Rec. 104: 598–603.
13 13 Beckett, S., Wolfe, D., Bartels, J. et al. (1997). Blood flow to the corpus cavernosum penis in the bull and goat buck during penile quiescence. Theriogenology 48: 1061–1069.
2 Endocrine and Exocrine Function of the Bovine Testes
Peter L. Ryan1 and Federico G. Hoffmann2
1 College of Veterinary Medicine, Mississippi State University, Starkville, MS, USA
2 College of Agriculture and Life Sciences, Mississippi State University, Starkville, MS, USA
Introduction