Anatomy of the Internal Genitalia

The most important feature in the anatomy of the internal genitalia of Camelidae is the absence of seminal vesicles.^{(3, 5, 6, 9, 23, 24, 30, 38, 56, 69)}

In the dromedary, the internal genitalia comprises the pelvic portion of the urethra and the accessory sex gland. The accessory sex glands in the dromedary are: the ampullae, the prostate, the bulbourethral, and the urethral (cowpers) glands. The size and weight of all glands are affected significantly by the age of the animal but tend to reach a maximum at 10.5 to 15 years.⁽³⁾ This is especially true for the ampullae and the bulbourethral glands.⁽³⁾ In one study, the respective weights of the ampullae, prostate, and bulbourethral glands were 3.0, 2.0, and 3.6 g for animals between 4.5 and 6 years of age and 4.2, 16.1, and 4.9 g for animals age 10.5 to 15 years. The overall average weights were 3.9, 14.1, and 4.5 g for these glands respectively.^{(3, 24)} Other authors have reported slightly higher weights for the accessory sex glands in the dromedary but the same trend toward increased size until 15 years of age.⁽⁸⁾ Size and weight of the accessory sex glands are also affected by season. Maximum glands weight is recorded during the breeding season (spring and winter) and the minimum values are recorded during summer.^{(3, 5, 6, 56)} This is concomitant with the increased activity and weight of the testis which suggests that the activity of the accessory sex gland is regulated by androgen secretion from the testis.^{(2, 25, 34-37, 47, 54, 78)}

In the South American camelidae, the only accessory sex glands described in the literature as significant are the bulbourethral glands and the prostate.^{(9, 30, 38)}

The prostate

Macroanatomy

The prostate is the largest and the only palpable gland in the dromedary. In adult animals, it measures 4 x 5 cm and consists of two parts - the body of the prostate (corpus prostatae) situated dorsally and the disseminated part (pars disseminata) located ventrally and overlying the prostatic urethra.^{(6, 19, 24)} The body of the prostate (corpus prostatae) is entirely intrapelvic, being situated on the dorsal aspect of the urethra and over the neck of the urinary bladder. It is discoid in shape, soft and grayish in color (Figure 1.24). The cranial two thirds of the gland are almost free and the caudal third is fused with the prostatic urethra.⁽⁶⁾

The parenchyma of the prostate is delineated by a thin band originating from the internal aspect of the urethral muscle, thus forming a disseminate portion confined mainly to the prostatic urethra.

Caudally it becomes continuous with the glandular pelvic urethra. The prostate opens into the colliculus seminalis with two main and 15 to 20 minor prostatic ducts (Figure 1.25).^{(6, 65)}

In the llama and alpaca, the prostate is usually described as a small gland (3x3x2 cm) firmly attached to the dorsolateral aspect of the pelvic urethra near the trigone of the bladder.^{(9, 30, 64)}

Histology

The prostate consists of a lobulated glandular parenchyma and interstitial connective tissue contained within a thin fibromuscular capsule (Figure 1.26). The interstitial connective tissue is abundant and rich in smooth muscle which often encircles the lobules. Each lobule consists of tubuloalveolar secretory units with a distinct basement membrane. The epithelium of the secretory units consists of a simple columnar cell lining averaging 17 µm in height which is alternated in a few places by small cuboidal cells. Inactive glands are lined with cuboidal epithelium devoid of granules whereas the active epithelium shows tall cells with parabasal nuclei and a richly granulated cytoplasm (Figure 1.27). The main ducts are lined with a transitional epithelium.⁽⁶⁾

The glandular parenchyma of the pars disseminata is surrounded by a striated muscle layer on all sides except dorsally where there is a dense fibromuscular band. Thin fibromuscular trabeculae extend into the parenchyma, which consists of a few lobules. The secretory units are similar to those of the body of the prostate. A few lobules are observed in the lamina propria of the urethra. Most of the units have narrow lumina and are lined with columnar or pyramidal cells.⁽⁶⁾
 

The bulbourethral gland

Macroanatomy

The two bulbourethral glands are located on the dorsolateral aspect of the pelvic urethra, above the ischial arch and about 10 cm caudal to the corpus prostatae. They are difficult to visualize because they are partly covered by the bulbocavemosus muscle. The glands are separated by a thick interglandular septum and open individually on each side of the urethra by a duct lodged in U-shaped fossa formed by a fold of the mucous membrane.⁽⁶⁾ In the llama and alpaca, the bulbourethral glands are similarly located. They are oval in shape and measure 2 cm in diameter.^{(30. 64)}

Histology

The glands are covered externally by striated muscle and internally by a thick capsule. The parenchyma is lobulated and consists of compound tubulo-alveolar secretory end-pieces supported by abundant reticular fibers. These secretory units have been classified into 3 types (A, B and C) according to the nature of their epithelial lining, representing different degrees of secretory activity. The epithelium of Type A secretory units is simple, tall, pyramidal or columnar with basal flat nuclei and markedly condensed chromatin, and the cytoplasm is basophilic. The height of the epithelium is variable, but averages 21 µm. Type B units are found in isolated lobules, or scattered among Type A units. They are smaller and more dense than type A and lined with a simple cuboidal epithelium and a pale eosinophilic cytoplasm. Type C units are intermediary between types A and B and their epithelial lining presents a mixture of both types in different proportion.⁽⁶⁾ It is possible that the transition of the epithelium from cuboidal to tall columnar reflects the increased secretory activity of the gland.

The alveo-tubular secretory units end with primary ducts with wide branching lumen, lined with simple columnar epithelium similar to that of Type A units. The epithelium becomes transitional as the primary ducts enter the main duct which opens into the pelvic urethra and through which the secretions of the bulbourethral glands are forced into the urethra by contractions of the muscle fibers surrounding the glands.⁽⁶⁾

Effect of age and season

In the mature dromedary, the weight and size of the bulbo-urethral glands are affected by the season. During the breeding (rutting) season, these glands become enlarged, and are lined by an epithelium predominantly of type A showing a high secretory activity.^{(5, 6, 56)} The proportion of glands in the parenchyma showing activity decreases during the inactive period. However, complete inactivity is never observed in the glands of the dromedary.⁽⁶⁾

The ampullae

Macroanatomy

The ductus deferens emerges into the abdominal cavity from the internal inguinal ring. It runs between the superficial and deep layers of the urogenital fold, dorsal to the urinary bladder and medial to the ureters (Figure 1.24). The initial part of the ductus deferens is small in diameter and very tortuous. The ductus deferens becomes markedly thick and forms the ampulla (ampulla ductus deferentis) as it approches the pelvic urethra. The ampulla averages 18 cm in length most of which is visible. Its terminal part follows is embeded in a deep groove located on the ventral surface of the coipus prostatae. The ampulla becomes narrow at this level and pierces the dorsal wall of the prostatic urethra, to open internally on the colliculus seminalis.^{(6, 65)}

Histology

The mucosa of the ductus deferens is folded and lined with a pseudo-stratified columnar epithelium. The lumen contains numerous spermatozoa, degenerating cells and a homogeneous eosinophilic material. The mucosa is supported by abundant elastic fibers. The submucosa is glandular, consisting of peripheral, central and submucosal tubular glands which open directly into the lumen of the ductus deferens (Figure 1.28). The interstitial tissue is mainly fibroelastic, but a few smooth muscle fibers are also present.⁽⁶⁾

The peripheral glands are large and present a wide lumen lined with tall, slender, columnar cells and a few basal cells. The columnar cells of the epithelial lining have a brush border averaging 15 µm in height. The nuclei are spherical and occupy the basal cytoplasm and contain nucleoli. The cytoplasm presents acidophilic material concentrated mainly in the supranuclear region. The lumen contains globular bodies and a few spermatozoa (Figures 1.28 and 1.29).⁽⁶⁾

The central and submucosal glands are comparatively small and possess narrow lumina. They are lined with low columnar epithelium (10µm). The cytoplasm occasionally contains acidophilic granules.

The ampullary glands decrease in thickness as the ductus deferens approaches the corpus prostatae. The epithelial lining becomes simple columnar at this region.

The tunica muscularis in the non-glandular portion of the ductus deferens consists of a thick, circular, smooth muscle layer with longitudinal smooth muscle bundles disposed peripherally. In the glandular portion, the tunica muscularis is thin and arranged into an inner circular layer of loose smooth fibers and an outer layer with irregularly disposed fibers.⁽⁶⁾

Peripheral ampullary glands are wider than the central and submucosal glands. It has been suggested that these glands may play the role of a sperm reserve before ejaculation.⁽⁶⁾

The urethral glands

The pelvic urethra is thick and flattened dorsoventrally, averaging 13 cm in length in adult dromedaries and is almost entirely glandular. Urethral glands (glandulae urethrales, littre glands) are located just behind the body of the prostate and extend to the level of the urethral bulb. These glands open into the urethral lumen just caudal to the colliculus seminalis via numerous ducts. The urethral glands and the urethra are surrounded by thick striated muscles laterally and ventrally, and by a dense fibromuscular layer dorsally. The glandular parenchyma is lobulated and consists of dense tubular secretory units which are lined by a simple tall pyramidal epithelium (13 µm). The main ducts are lined with transitional epithelium. A few tubules and ducts are always seen beneath the urethral mucosa.⁽⁶⁾ The pelvic urethra and the bulbourethral glands are richly enervated. These nerves are probably responsible for the contraction of the muscle and expulsion of glandular secretion.⁽⁶⁾

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