Male Genitalia - The Pelvis and Reproductive Organs

The Pelvis and Reproductive Organs

4.5 Male Genitalia

Goal: You should be able to identify the major male reproductive structures includ- ing the testes and their adnexa, penis, prepuce (sheath), and accessory sex glands.

These structures are examined in breeding

Box 4.3

The peritoneal pouch determines the caudal extent of the peritoneum. Vaginal and rectal tears caudal to these pouches carry favorable prognosis compared to tears involving the pouches and therefore the peritoneum and the possibility of peritonitis.

Rectovaginal fistula is a complication of dystocia that results from a difficult birth when a malpresented or oversized calf tears through the rectovaginal septum (perineal body), a musculofibrous tissue that separates the rectum from the vagina.

soundness examination (BSE) of bulls. At the end of this unit watch video 11.

The male genitalia comprise paired testes and their adnexa, penis, prepuce, and accessory sex glands.

4.5.1 Penis

Goal: Know that male ruminants have a fibroelastic penis compared to the muscu- locavernous type of penis of the equine.

Dogs have bone (os penis) incorporated in the distal part of the corpus cavernous penis. Bulls, bucks (billy), and rams have no bone in their penises.

Identify the corpus cavernosum penis (CCP), corpus spongiosum penis (CSP), and tunica albuginea (TA) penis sur- rounding the CCP. Identify the sigmoid flexure and its proximal and distal bends.

Note the post‐scrotal position of the sigmoid flexure in small and large male ruminants. Identify the urethral process in the bull and small ruminants. Know where the penis has a weak TA that could

rupture from increased blood pressure in the CCP.

Understand that a major contributor to the thinness of the TA on the inside of the distal bend is the stretching when the sigmoid flexure straightens upon erection, similar to a glove thinning if you pull it tight over your finger.

Identify regions where the urethral diameter becomes small (potential location for urethral calculi). Understand the importance of the dorsal nerve of the penis, the size of the testis, physical condi- tions, and accessory sex glands in BSE in bulls.

The penis of male ruminants is of the fibroe- lastic type. It is rigid in a non‐erect state. It is characterized by the presence of a sigmoid flexure and well‐developed retractor penis (Figure 4.4). The penis is topographically divided into root, body, and glans (Figure 4.4). Clinically sound anatomy of the penis is very important for bull breeding soundness and must be examined for any bruises and injuries.

Sigmoid flexure of penis Retractor penis m.

Prostate gland Vesicular glands

Ductus deferens

Testis Glans penis

Bulb of penis Left crus of penis (cut) Urinary

bladder

1 2

Sigmoid flexure:

1. Proximal bend 2. Distal bend

Urethralis m.

Prepuce (opened)

Bull Glans

Body

Root

Figure 4.4 Isolated urogenital tract of the bull (urinary bladder, penis, accessory sex glands, and testis). Note the pre‐scrotal position of the sigmoid flexure. Keep this location in mind when palpating the sigmoid flexure in the live animal. 1 and 2, the proximal and distal bends of the sigmoid flexure, respectively (review the clinical significance of the sigmoid flexure in Box 4.6).

4.5.1.1 Root of the Penis and Cavernous Tissue

The root of the penis is composed of two lateral (left and right) crura and a midline located bulb of the penis. The crura attach the root of the penis to the left and right ischiatic tuberosities (pins) on the os coxae.

The penis is also attached to the ischial arch and pelvic symphysis by a pair of collagenous

sheets known as the suspensory ligament of the penis (Figure 4.5). There is no need to dissect this ligament.

Each crus is composed of cavernous tissue CCP, surrounded by a layer of dense collagenous connective tissue, TA penis. A short ischiocavernosus muscle covers each crus (Figure 4.5).

The bulb of the penis is the enlarged middle portion of the root. The bulb is an

Vesicular gland

Body of the prostate Bulbourethral gland

Sigmoid flexure of the penis (proximal bend) Ductus deferens Testicular vessels

Ampulla of ductus deferens

Bulbospongiosus m.

Ischiocavernosus m.

Superficial inguinal lymph nodes

Sigmoid flexure of the penis (distal bend) Retractor penis m.

Urethralis m.

Bull

Corpus cavernosum

Corpus spongiosum

Urethra Tunica

albuginea

Deep vein of the penis

Bull

(a)

(b)

Figure 4.5 (a) Schematic illustration of the reproductive tract of the bull in situ. Note the location of the superficial inguinal lymph nodes which are also known as scrotal lymph nodes. They drain the scrotum, prepuce, and penis but not the testes. Star, suspensory ligament of the penis (bilateral). (b) Cross‐section of the bovine penis at the level of the sigmoid flexure.

expansion of the proximal end of the CSP.

This expansion is covered by the bulbospon- giosus muscle (Figure 4.4). Study the structures that make up the root of the penis with the help of Figures 4.4 and 4.5.

The body of the penis is the region between the root and the glans (Figure 4.4).

It characterized by the presence of an S‐

shaped sigmoid flexure, a clinically important feature. In the non‐erect penis, the sigmoid flexure is situated caudal to the neck of the scrotum (post‐scrotal position).

The post‐scrotal location of the sigmoid flexure in the bull is different from that in the boar where the sigmoid flexure has a pre‐

scrotal position. In boars, the testicles have a perineal position, whereas in ruminants the testicles are vertically suspended below the pelvic floor.

4.5.1.2 Free Part of the Penis and Glans Penis

The free part of the penis and the glans are the regions of the penis distal to the attachment of the internal lamina of the prepuce (Figure 4.6b). The glans is most proximal enlarge- ment at the tip of the penis (Figures 4.4, 4.6a,b, and 4.7a-b). It asymmetrical in shape. Push the prepuce backward to expose the free part of the penis and glans penis (Figure 4.7a,b).

A shallow ridge of skin along the ventral surface of the free part of the penis is called the raphe of the penis (Figure 4.7b). The raphe of the penis is a thickening of the tunica albuginea on the midventral line of the free part of the penis. It extends from the preputial fornix to the tip of the glans on the right side (Figure 4.7b).

Note that in small male ruminants (rams and bucks), the glans has a long urethral pro- cess that extends a few centimeters beyond the glans. In contrast, the bull urethral process does not extend beyond the glans (Figure 4.7b). The external urethral orifice is located at the tip of the urethral process.

4.5.1.3 Retractor Penis Muscle

The retractor penis comprises well‐

developed, paired smooth muscles that are

separated at their origin but come together at their insertion on the ventral surface of the distal bend of the sigmoid flexure and beyond (Figures 4.4 and 4.5a).

The retractor penis muscle originates from the caudal vertebrae dorsally, pass on each side of the external anal sphincter muscle (where a few fibers from external and internal sphincter muscles are added), and inserts distally at the ventral surface of the distal bend of the sigmoid flexure in small ruminants. In the bull, the muscle continues distally to insert on the free part of the penis.

The retractor penis muscle is innervated by sympathetic fibers that are thought to travel through the caudal, rectal, or deep per- oneal nerves to reach the muscle. Relaxation of the retractor penis muscle is essential for attainment of full erection and straightening of the sigmoid flexure.

Make cross‐sections of the body of the penis proximal and distal to the sigmoid flexure and compare the size of the urethral lumen in the two cross‐sections. Note that the ure- thra is narrower at the distal bend than its diameter in cross‐sections proximal to the sigmoid flexure. In general, the sigmoid flex- ure of the penis is a typical site for obstruc- tion by urinary calculi, especially at the distal bend.

The penile urethra runs on the mid‐ ventral urethral groove of the penis. It is surrounded by CSP. Identify the CCP and CSP on cross‐

sections of the body of the penis (Figure 4.5b).

4.5.1.4 Apical Ligament

Identify the apical ligament on the dorsum of the distal portion of the penis of the bull (Figure 4.6). The apical ligament typically arises from the dorsal midline of the TA approximately 8 inches from the penile tip (Figure 4.6b). The fibers are shorter but more firmly attached on the left and longer and more easily undermined on the right side.

Defects of the length, strength, or attachment of the apical ligament can lead to path- ological penile deviations.

Male goats and sheep have apical ligaments but, unlike the single apical ligament of the

Prepuce (internal

lamina) Apical Glans penis

ligament

Bull Apical ligament: bull

Dorsal view

Left lateral view

Right lateral view

Skin of penis (reflected)

Glans penis

Apical ligament

Penile urethra

(a)

(b)

Figure 4.6 (a) Right lateral, left lateral, and dorsal views of the apical ligament in the penis of the bull. Source:

adapted from Garrett, P.D. (1988) Guide to Ruminant Anatomy Based on the Dissection of the Goat, Iowa State University Press. (b) Dissection of the apical ligament on the dorsum of the bull penis: right lateral view. The apical ligament is a feature of the tunica albuginea covering corpus cavernosum penis (CCP). It arises distal to sigmoid flexure from the dorsal midline and left side, with thinner fibers on the left side (a).

Box 4.4

Abnormalities in the strength of the apical ligament can cause spiral, ventral, and S‐shaped deviations of the penis. The ligament can be dissected out and reinforced surgically. Two surgical procedures have been described:

(i) apical ligament splitting and interweaving, and (ii) fascia lata autographing. Sexual rest for 2 months is recommended.

The apical ligament can be used to facilitate extraction and handling of the penis during some surgeries (e.g., preputial injuries such as pro lapse abscesses, papilloma, persistent frenulum, and fractured penis). Typically, the penis is extended and grasped with a gauze pad. A penetrating towel forceps is placed deep to the dorsal apical ligament in the area proximal to the glans penis.

Free part

of penis Glans

(a)

Opened prepuce (internal lamina) Preputial cavity

Bull

Buck

Ram

Glans penis

Urethral process Glans

penis

Urethral process Prepuce (internal lamina)

Raphe of the penis

External urethral orifice

(b)

Figure 4.7 (a) The free part and glans of the penis: right lateral view. The right lateral wall of the prepuce is transected longitudinally and removed to expose the preputial cavity and the free part of the penis.

(b) The glans penis in the bull and small male ruminants (buck and ram): right lateral view. Note the extension of the urethral process beyond the glans in the penis of small ruminants (2-4 cm). The internal lamina of the prepuce is peeled backward.

bull’s penis, these animals have two lateral ligaments situated on each side of the apex of the penis with no outward connection over the dorsal surface of the penis. Do not attempt to dissect these ligaments.

4.5.1.5 Dorsal Nerve of the Penis

Identify the dorsal nerve, artery, and vein of the penis coursing distally on each side of the dorsal wall of the penis (all are paired structures) (Figure 4.8).

Sigmoid flexure of penis Retractor penis m.

Testis reflected

dorsally Left and right

dorsal nerves of the penis

Scrotum (opened) Superficial inguinal (or scrotal) lymph node

Genitofemoral n. External

pudendal a.

Bull

Figure 4.8 In situ dissection of the bull reproductive tract showing the dorsal nerves of a bull penis and the sigmoid flexure.

The dorsal nerve of the penis is a branch (continuation) of the pudendal nerve. The nerve supplies important sensory fibers to the glans penis. The integrity of pudendal nerve is critical for breeding soundness of the bull and its ability to inseminate a cow (Box 4.5).

4.5.2 Male Urethra

The male urethra is technically divided into pelvic urethra (within the pelvic cavity) and penile urethra (within the penis). It trans- ports urine from the urinary bladder to the exterior. The urethra is a potential site for calculi deposition and bacterial infections.

As discussed earlier, the urinary bladder is located within the pelvic cavity when is empty. It extends further cranial in the abdomen when distended.

Box 4.5

The dorsal nerve of the penis can be blocked on the exterior dorsal wall of the penis.

Alternatively, the pudendal nerve can also be blocked inside the pelvic cavity along the inner surface of the sacrosciatic ligament or as it crosses the ischiatic arch. Pudendal nerve block leads to relaxation of the penis and hence facilitates clinical examination.

Box 4.6

Penile sigmoid flexure

In the bull, the dorsal surface of the distal bend of the sigmoid flexure is a frequent site for penile rupture and hematoma, an emer- gency condition that typically requires surgical intervention. This condition is a common injury in breeding bulls during mating when there is a sudden bend of an erect penis during breeding. A serious injury left unattended can lead to hematoma, infection, and possible retirement of the affected bull.

The sigmoid flexure is also a frequent site for calculi (obstructive urolithiasis), especially in

young male pet ruminants (bucks and rams) that have been castrated at young age for marketing. The condition can also be secondary to feeding pet goats special diets. For example, hay containing high amounts of oxalates promotes oxalate stone formation. Similarly, a diet composed of high amounts of calcium‐containing grains, legumes, or clover hay promotes the formation of calcium carbonate calculi.

The urethral process in small male ruminants can also be a potential site for urolith obstruction (obstructive material formed from mucus, proteins, and minerals).

Make a mid‐ventral incision on the ventral wall of the bladder and locate the openings of the ureters inside the bladder cavity. Note that the ureters tunnel for short distance inside the dorsal wall of the bladder before they open inside the urinary bladder. This helps prevent backflow of the urine to the kid- neys when the urinary bladder is full.

Make a note of the relationship of the ure- ters and ductus deferens. Note that the left and right ductus deferens course from the inguinal canal and pass caudally and dorsally to reach the roof of the bladder. Here they course medial (i.e., below) to the ureters. Because of this rela- tionship, it is recommended that you avoid excessive pulling of the ductus deferens in cas- tration procedures. Forceful pull on the ductus deferens could result in tearing of the ureters, a disastrous outcome.

The triangular area on the inner dorsal wall of the neck of the urinary bladder defined by the two openings of the ureters in the bladder and opening of the bladder into the urethra is called the trigone of the blad- der (Figure 4.9a,b).

The male urethra forms a dorsal recess or diverticulum deep to the bulb of the penis (the area between the left and right crus of the penis). The diverticulum can be demon- strated by making a vertical cut through the midline of the bulb of the penis down to the lumen of the urethra.

Note the dorsal recess formed at the junction of the pelvic and penile urethra in the most proximal part of your cut. Insert the tip of your

probe in the lumen of the proximal penile urethra and move it dorsally until the tip of the probe becomes trapped in the recess at the point where the penile urethra turns cranially toward the pelvis to become the pelvic urethra.

Note the clinical significance of the dorsal urethral recess in male ruminants (Box 4.7).

4.5.3 Prepuce

You should be able to identify the external and internal laminae of the prepuce, prepu- tial orifice, preputial cavity, and free part of the penis. Clinicians call the prepuce “the sheath.” With the help of Figures 4.7(a) and 4.9(c), identify these parts.

The prepuce consists of an external prepu- tial lamina (has hair; Figure 4.9c) and internal preputial lamina (without hair; Figure 4.7a).

The external lamina is continuous with the skin of the abdomen. The internal lamina of the prepuce lines the preputial cavity in the non‐erect state. The preputial cavity houses the free part of the penis (Figure 4.7a).

The preputial orifice (opening at the junction of the external and internal laminae) is surrounded by preputial hair ring (Figure 4.9c).

Clinically, preputial injuries are common especially during breeding seasons (e.g., preputial lacerations and preputial prolapse).

Box 4.7

The presence of the dorsal urethral diverticulum and the sigmoid flexure make it difficult to catheterize a male ruminant.

Box 4.8

Persistent frenulum

Separation of the internal lamina of the prepuce from the free part of the penis occurs at puberty.

Failure of this process, when the internal lamina remains attached to the free part of the penis, is known as persistent frenulum. Persistent frenulum causes the penis to bend and prevent full extraction of the penis during erection.

Persistent frenulum is a heritable condition.

Penile hair ring

Hair at the preputial orifice occasionally becomes entrapped, forming a tight ring around the penis in bulls. It can be source of serious penile and preputial injuries. Hair rings occur in young bulls exhibiting homosexual behavior when they mount each other.

4.5.4 Superficial Inguinal (Scrotal) Lymph Nodes

The superficial inguinal lymph nodes (also called scrotal or mammary lymph nodes)

are located on each side of the body of the penis above the sigmoid flexure (Figure 4.8) or above the base of the udder in the female.

In the male, they drain the scrotum, prepuce,

Openings of left and right ureters

Trigone of the bladder

Pelvic urethra Pelvic urethra

Neck ot the bladder Opening of left ureter Left ureter

(a)

(b)

(c)

Prepuce

(sheath) – external lamina Testis

Figure 4.9 (a) Schematic illustration of a longitudinal section of the urinary bladder to show an opening of the ureter on the craniodorsal surface of the urinary bladder. (b) Schematic illustration of the inner dorsal surface (roof) of the urinary bladder showing the trigone of the bladder: ventral view. (c) The testes and prepuce (external lamina) of the bull: left lateral view. Note the vertically suspended (pendulous) testicles.

Rudimentary teats may be present on the scrotum. The external lamina of the prepuce is very long and extends from the scrotum to the umbilicus. Note the preputial hair ring around the external preputial orifice. The external lamina is continuous with the skin of the abdominal wall dorsally.

and penis but not the testis. Lymph from the testicles is drained through independent lymphatic vessels coursing within the sper- matic cord. In the female, these nodes drain the udder and skin of the medial thigh region.

Lymph from both the superficial inguinal lymph nodes and the testicles drain into the medial iliac lymphocenter. This center is located at the terminal branches of the abdominal aorta.

4.5.5 Blood Supply to the Pelvic Viscera and Male Genitalia

In ruminants, the penis receives blood from the artery of the penis, a terminal branch of the internal pudendal artery (Figure 4.10a).

The arterial distribution of blood to the penis in male ruminants is similar to that of the dog but differs from that of the stallion.

At the root of the penis, the artery of the penis terminates by giving rise to the artery of the bulb of the penis (supplying the bulb and CSP), the deep artery of the penis (supplying the CCP), and dorsal artery of the penis (supply the glans and prepuce).

The dorsal artery of the penis follows the dorsal vein and dorsal nerve of the penis.

Using a sagittal section of the pelvis, follow the terminal branches of the aorta. Note that the aorta gives rise to two external iliac arteries and then terminates by trifurcating into two internal iliac arteries and a median sacral. The internal iliac artery is relatively very long in ruminants when compared with the equine species.

In female ruminants, the umbilical artery, a branch of the internal iliac artery, gives the clinically important uterine artery. Beyond the umbilical artery, the internal iliac gives the vaginal artery and terminates close to the lesser ischiatic foramen by dividing into cau- dal gluteal artery (passes outside the pelvis through the lesser ischiatic foramen) and internal pudendal artery which courses toward the vulva in the female or the penis in the male (Figure 4.10). Note that the internal pudendal artery and pudendal nerve makes

an “X” intersection close to the pelvic outlet (Figure 4.10).

Identify the internal iliac artery and its terminal branches, internal pudendal and caudal gluteal arteries.

Because of time constrains and the com- plexity of this area of the pelvis, your instruc- tor may opt to use a prosection for a quick demonstration of the major blood vessels and nerves. Understand that many of the vessels (e.g., prostatic, iliolumbar, obturator) have no clinical significance in ruminants. Ask your instructor which vessels and nerves you need to identify. Check the lab ID list at the end of this chapter for more details.

4.5.6 Testes

Goal: Identify testicular layers from superficial to deep (skin–tunica dartos, sper- matic fascia–parietal vagina tunic–vaginal cavity and visceral vaginal tunic). Do not cut into the tunica albuginea testis which forms the testicular capsule deep to the visceral vaginal tunic. Identify the scrotal septum that separates left and right testes.

Identify the ligaments of the testis (proper ligament of the testis and ligament of the tail of the epididymis) and understand the process of thermoregula- tion and testicular descent.

Study the location of the testis in situ and its relation to the sigmoid flexure of the penis. Identify the pampiniform plexus, the mesoductus deferens, and mesorchium. Identify the head, body, and tail of the epididymis.

A bull with larger testicular circumference is desirable for breeding as the size of the testis is positively correlated to sperm production.

Measurement of testicular diameter is part of BSE for bull selection.

Start by studying the testicular layers.

Identification of testicular layers is important when performing castration. Remove one testicle for close in vitro inspection.

Using a sharp scalpel, cut through the skin and peel the testis out of the scrotal sac. Using

Dalam dokumen Boook Guide to Ruminant Anatomy Dissection and Clinical Aspects pdf (Halaman 157-171)