**2. Prostate gland anatomy**

The prostate is a semioval bilobular exocrine gland that makes dorsal contact with the rectum, ventral with the pubic symphysis, lateral with the abdominal

wall, and cranial with the bladder; its position may present slight variations depending on the age of the dog. Up to 2 months of age, the prostate is located in the caudal portion of the abdominal cavity; from this age until the animal reaches sexual maturity, the prostate is located in the pelvic cavity. After sexual maturity is reached, it increases in size cranially extending into the abdominal cavity [1, 2].

The sulcus dividing the right and left prostate lobes can be palpated dorsally by rectal palpation. Each lobe is subdivided into lobules by trabeculae; these are being formed by composed tubuloalveolar glands, and the ducts of these glands flow into the urethra throughout all its circumference. The prostatic urethra (part of the pelvic urethra that passes through the prostate) crosses the prostatic parenchyma slightly dorsally to its center. In addition, the prostate is covered by a fibromuscular tissue capsule, the prostate capsule [1, 2]. The vas deferens enters the prostate through the cranio-dorsal surface, and each one in a lobe traverses its parenchyma making a caudoventral path ending up in the urethra by the *colliculus seminalis* [1, 2].

The vascularization of the prostate is mainly due to the prostatic artery that originates from the internal pudendal artery. The prostatic artery gives rise to the middle rectal artery that branches and penetrates the prostatic capsule through the dorsolateral surface, becoming subcapsular vessels, until later they enter the prostate to provide the necessary blood supply to the glandular tissue. Anastomoses occur between the prostatic vessels and the urethral, cranial rectal, and caudal arteries, complicating prostatectomy [1, 2].

A venous blood is drained from the prostate by the prostatic and urethral veins to the internal iliac vein. The prostatic lymph vessels drain into the iliac lymph nodes. Prostatic innervation occurs through the hypogastric nerve (sympathetic system), which presents a path similar to the prostatic artery and the pelvic nerve (parasympathetic system). Glandular secretion is increased by parasympathetic stimuli [1, 2].

### **3. Prostate gland histology**

The canine prostate is a morphologically homogeneous organ that does not differentiate into areas such as the human prostate and is mostly composed of secretory glandular tissue (**Figure 1**). The prostatic stroma that surrounds the prostatic urethra extends dorsally and ventrally to almost the limit of the prostate, whereas the lateral projections of the stroma are thinner. These stromal projections subdivide the prostate into several lobules of glandular epithelium. This epithelium is mostly columnar that modifies to cuboid within the ductal structures of

#### **Figure 1.**

*Canine normal prostate gland. Histological evaluation revealing a columnar epithelium distributed in one layer. The tissue stroma is composed by collagen fibers and fibroblasts. Hematoxylin and eosin (H&E) staining, 10×.*

**89**

*Anatomy, Histology, and Physiology of the Canine Prostate Gland*

the prostate; meanwhile the epithelium of the prostatic urethra may be cuboid or

*Immunohistochemical evaluation of high molecular weight cytokeratin (HMWC) in a canine normal prostate gland. It is possible to identify positive membranous staining (brown color) in the basal cells, forming a discontinuous basal cell layer. The luminal cells are negative for the HMWC (blue staining). Harris* 

*hematoxylin counterstaining, 3 3'-diaminobenzidine tetrahydrochloride (DAB), 10×.*

The prostatic urethra passes through the prostate gland, showing an urothelial (transitional) epithelium, and the prostatic ducts have connection with the prostatic urethra. Then, inflammatory cells infiltrating the prostatic stroma are common due to the constant antigenic stimulus related with ascended bacteria contamination of the urinary system. Thus, the prostatic stroma is composed by collagen fibers, fibroblast, smooth muscle (for prostatic contraction), and few mononuclear inflammatory cells. In dogs, the smooth muscle cells and the nerves are located in

The basal or reserve cells are located in the basal cell layer in a discontinuous distribution (**Figure 2**). Usually, the luminal epithelial cells are positive for cytokeratin 8/18, pan-cytokeratin, NKX3.1, PTEN, and AR [3]. On the other hand, basal cells are positive for cytokeratin 5, p63, and high molecular weight cytokeratins

The prostate is responsible for the production of most of the seminal plasma, which contains large amounts of proteins. One of the most studied proteins in humans, produced by both human and canine prostatic epithelia, is prostatespecific antigen (PSA) [6]. The kallikrein-3 (KLK 3) gene encodes the PSA protein in humans, and dog genome lacks KLK 3 gene. In dogs, kallikrein-2 (canine prostate-specific arginine esterase, (CPSE) is a PSA homolog enzyme belonging to the serine-protease class [6]. This protein is normally secreted into the lumen of the prostate ducts and does not come into contact with the bloodstream in a prostate under physiological conditions. However, when there is a lesion that disrupts the prostate architecture, this protein can be found in the blood and may be an indica-

Comparably to PSA, the canine prostate-specific arginine esterase (CPSE) is the most produced protein in the canine prostate and seems to be an alternative for the diagnosis of some prostatic conditions in dogs. Although the use of plasmatic markers as a diagnostic method for prostatic pathologies in human medicine is a

commonplace in veterinary medicine, it is not a reality [7, 8].

*DOI: http://dx.doi.org/10.5772/intechopen.81410*

columnar, simple, or stratified [5].

the peripheral region of this gland.

**4. Prostate gland physiology**

tor of a prostatic disease [7, 8].

(HMWC) [3].

**Figure 2.**

*Anatomy, Histology, and Physiology of the Canine Prostate Gland DOI: http://dx.doi.org/10.5772/intechopen.81410*

#### **Figure 2.**

*Veterinary Anatomy and Physiology*

wall, and cranial with the bladder; its position may present slight variations depending on the age of the dog. Up to 2 months of age, the prostate is located in the caudal portion of the abdominal cavity; from this age until the animal reaches sexual maturity, the prostate is located in the pelvic cavity. After sexual maturity is reached, it increases in size cranially extending into the abdominal cavity [1, 2]. The sulcus dividing the right and left prostate lobes can be palpated dorsally by rectal palpation. Each lobe is subdivided into lobules by trabeculae; these are being formed by composed tubuloalveolar glands, and the ducts of these glands flow into the urethra throughout all its circumference. The prostatic urethra (part of the pelvic urethra that passes through the prostate) crosses the prostatic parenchyma slightly dorsally to its center. In addition, the prostate is covered by a fibromuscular tissue capsule, the prostate capsule [1, 2]. The vas deferens enters the prostate through the cranio-dorsal surface, and each one in a lobe traverses its parenchyma making a

caudoventral path ending up in the urethra by the *colliculus seminalis* [1, 2].

arteries, complicating prostatectomy [1, 2].

The vascularization of the prostate is mainly due to the prostatic artery that originates from the internal pudendal artery. The prostatic artery gives rise to the middle rectal artery that branches and penetrates the prostatic capsule through the dorsolateral surface, becoming subcapsular vessels, until later they enter the prostate to provide the necessary blood supply to the glandular tissue. Anastomoses occur between the prostatic vessels and the urethral, cranial rectal, and caudal

A venous blood is drained from the prostate by the prostatic and urethral veins to the internal iliac vein. The prostatic lymph vessels drain into the iliac lymph nodes. Prostatic innervation occurs through the hypogastric nerve (sympathetic system), which presents a path similar to the prostatic artery and the pelvic nerve (parasympathetic system). Glandular secretion is increased by parasympathetic

The canine prostate is a morphologically homogeneous organ that does not differentiate into areas such as the human prostate and is mostly composed of secretory glandular tissue (**Figure 1**). The prostatic stroma that surrounds the prostatic urethra extends dorsally and ventrally to almost the limit of the prostate, whereas the lateral projections of the stroma are thinner. These stromal projections subdivide the prostate into several lobules of glandular epithelium. This epithelium is mostly columnar that modifies to cuboid within the ductal structures of

**88**

**Figure 1.**

stimuli [1, 2].

**3. Prostate gland histology**

*Canine normal prostate gland. Histological evaluation revealing a columnar epithelium distributed in one layer. The tissue stroma is composed by collagen fibers and fibroblasts. Hematoxylin and eosin (H&E) staining, 10×.*

*Immunohistochemical evaluation of high molecular weight cytokeratin (HMWC) in a canine normal prostate gland. It is possible to identify positive membranous staining (brown color) in the basal cells, forming a discontinuous basal cell layer. The luminal cells are negative for the HMWC (blue staining). Harris hematoxylin counterstaining, 3 3'-diaminobenzidine tetrahydrochloride (DAB), 10×.*

the prostate; meanwhile the epithelium of the prostatic urethra may be cuboid or columnar, simple, or stratified [5].

The prostatic urethra passes through the prostate gland, showing an urothelial (transitional) epithelium, and the prostatic ducts have connection with the prostatic urethra. Then, inflammatory cells infiltrating the prostatic stroma are common due to the constant antigenic stimulus related with ascended bacteria contamination of the urinary system. Thus, the prostatic stroma is composed by collagen fibers, fibroblast, smooth muscle (for prostatic contraction), and few mononuclear inflammatory cells. In dogs, the smooth muscle cells and the nerves are located in the peripheral region of this gland.

The basal or reserve cells are located in the basal cell layer in a discontinuous distribution (**Figure 2**). Usually, the luminal epithelial cells are positive for cytokeratin 8/18, pan-cytokeratin, NKX3.1, PTEN, and AR [3]. On the other hand, basal cells are positive for cytokeratin 5, p63, and high molecular weight cytokeratins (HMWC) [3].

## **4. Prostate gland physiology**

The prostate is responsible for the production of most of the seminal plasma, which contains large amounts of proteins. One of the most studied proteins in humans, produced by both human and canine prostatic epithelia, is prostatespecific antigen (PSA) [6]. The kallikrein-3 (KLK 3) gene encodes the PSA protein in humans, and dog genome lacks KLK 3 gene. In dogs, kallikrein-2 (canine prostate-specific arginine esterase, (CPSE) is a PSA homolog enzyme belonging to the serine-protease class [6]. This protein is normally secreted into the lumen of the prostate ducts and does not come into contact with the bloodstream in a prostate under physiological conditions. However, when there is a lesion that disrupts the prostate architecture, this protein can be found in the blood and may be an indicator of a prostatic disease [7, 8].

Comparably to PSA, the canine prostate-specific arginine esterase (CPSE) is the most produced protein in the canine prostate and seems to be an alternative for the diagnosis of some prostatic conditions in dogs. Although the use of plasmatic markers as a diagnostic method for prostatic pathologies in human medicine is a commonplace in veterinary medicine, it is not a reality [7, 8].

The prostate depends on the testosterone that is produced in the testicles and converted into dihydrotestosterone (DHT) by the enzyme 5α-reductase. It is known that without this hormonal stimulus, the prostate will decrease its secretory function and volume. Castrated dogs lack testosterone, and consequently DHT will lead the prostate to a state of atrophy [7]. Thus, the endocrine control of the prostate gland, mainly by testis, is well characterized. In male dogs, the testosterone is the most important circulating androgen, and CYP19 (aromatase) can be metabolized into an estradiol-17β. The estrogen can affect the prostate gland growth and differentiation. The role of androgen in prostatic development and pathological process is an understudied area.
