Chapter 1. Anatomy of the Genitourinary Tract

Urology deals with diseases and disorders of the male genitourinary tract, the female urinary tract, and the adrenal gland. These systems are illustrated in Figures 1–1 and 1–2.

Gross Appearance

Anatomy

Each kidney is capped by an adrenal gland, and both organs are enclosed within Gerota's (perirenal) fascia. Each adrenal weighs about 5 g. The right adrenal is triangular in shape; the left is more rounded and crescentic. Each gland is composed of a cortex, chiefly influenced by the pituitary gland, and a medulla derived from chromaffin tissue (Avisse et al, 2000; O'Donoghue et al, 2010).

Relations

Figure 1–2 shows the relation of the adrenals to other organs. The right adrenal lies between the liver and the vena cava. The left adrenal lies close to the aorta and is covered on its lower surface by the pancreas. The spleen lies superior and lateral to it.

Histology

The adrenal cortex, which makes up 90% of the mass, is composed of three distinct layers: the outer zona glomerulosa, the middle zona fasciculata, and the inner zona reticularis. The medulla lies centrally and is made up of polyhedral cells containing eosinophilic granular cytoplasm. These chromaffin cells are accompanied by ganglion and small round cells.

Blood Supply

Arterial

Each adrenal receives three arteries: one from the inferior phrenic artery, one from the aorta, and one from the renal artery.

Venous

Blood from the right adrenal is drained by a very short vein into the vena cava; the left adrenal vein terminates in the left renal vein.

Lymphatics

The lymphatic vessels accompany the suprarenal vein and drain into the lumbar lymph nodes.

Gross Appearance

Anatomy

The kidneys lie along the borders of the psoas muscles and are therefore obliquely placed. The position of the liver causes the right kidney to be lower than the left (Figures 1–2 and 1–3). The adult kidney weighs about 150 g each.

The kidneys are supported by the perirenal fat (which is enclosed in the perirenal fascia), the renal vascular pedicle, abdominal muscle tone, and the general bulk of the abdominal viscera (Rusinek et al, 2004). Variations in these factors permit variations in the degree of renal mobility. The average descent on inspiration or on assuming the upright position is 4–5 cm. Lack of mobility suggests abnormal fixation (eg, perinephritis), but extreme mobility is not necessarily pathologic.

On longitudinal section (Figure 1–4), the kidney is seen to be made up of an outer cortex, a central medulla, and the internal calices and pelvis. The cortex is homogeneous in appearance. Portions of it project toward the pelvis between the papillae and fornices and are called the columns of Bertin. The medulla consists of numerous pyramids formed by the converging collecting renal tubules, which drain into the minor calices at the tip of the papillae.

Relations

Figures 1–2 and 1–3 show the relations of the kidneys to adjacent organs and structures. Their intimacy with intraperitoneal organs and the autonomic innervation they share with these organs explain, in part, some of the gastrointestinal symptoms that accompany genitourinary disease (Glassberg, 2002).

Histology

Nephron

The functioning unit of the kidney is the nephron, which is composed of a tubule that has both secretory and excretory functions (Figure 1–4). The secretory portion is contained largely within the cortex and consists of a renal corpuscle and the secretory part of the renal tubule. The excretory portion of this duct lies in the medulla. The renal corpuscle is composed of the vascular glomerulus, which projects into Bowman's capsule, which, in turn, is continuous with the epithelium of the proximal convoluted tubule. The secretory portion of the renal tubule is made up of the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule.

The excretory portion of the nephron is the collecting tubule, which is continuous with the distal end of the ascending limb of the convoluted tubule. It empties its contents through the tip (papilla) of a pyramid into a minor calyx.

Supporting Tissue

The renal stroma is composed of loose connective tissue and contains blood vessels, capillaries, nerves, and lymphatics.

Blood Supply (Figures1–2, 1–4, and 1–5)

Arterial

Usually there is one renal artery, a branch of the aorta that enters the hilum of the kidney between the pelvis, which normally lies posteriorly, and the renal vein. It may branch before it reaches the kidney, and two or more separate arteries may be noted (Budhiraja et al, 2010). In duplication of the pelvis and ureter, it is common for each renal segment to have its own arterial supply.

The renal artery divides into anterior and posterior branches. The posterior branch supplies the midsegment of the posterior surface. The anterior branch supplies both upper and lower poles as well as the entire anterior surface. The renal arteries are all end arteries.

The renal artery further divides into interlobar arteries, which travel in the columns of Bertin (between the pyramids) and then arch along the base of the pyramids (arcuate arteries). These arteries then divide as interlobular arteries. From these vessels, smaller (afferent) branches pass to the glomeruli. From the glomerular tuft, efferent arterioles pass to the tubules in the stroma.

Venous

The renal veins are paired with the arteries, but any of them will drain the entire kidney if the others are tied off.

Although the renal artery and vein are usually the sole blood vessels of the kidney, accessory renal vessels are common and may be of clinical importance if they are so placed to compress the ureter, in which case hydronephrosis may result.

Nerve Supply

The renal nerves derived from the renal plexus accompany the renal vessels throughout the renal parenchyma.

Lymphatics

The lymphatics of the kidney drain into the lumbar lymph nodes.

Gross Appearance

Anatomy

Calices

The tips of the minor calices (8–12 in number) are indented by the projecting pyramids (Figure 1–4). These calices unite to form two or three major calices that join to form the renal pelvis (Sozen et al, 2008).

Renal Pelvis

The pelvis may be entirely intrarenal or partly intrarenal and partly extrarenal. Inferomedially, it tapers to join the ureter.

Ureter

The adult ureter is about 30 cm long, varying in direct relation to the height of the individual. It follows a rather smooth S curve. Areas that stones are often impacted are (1) at the ureteropelvic junction, (2) where the ureter crosses over the iliac vessels, and (3) where it courses through the bladder wall.

Relations

Calices

The calices are intrarenal and are intimately related to the renal parenchyma.

Renal Pelvis

If the pelvis is partly extrarenal, it lies along the lateral border of the psoas muscle and on the quadratus lumborum muscle; the renal vascular pedicle is just anterior to it. The left renal pelvis lies at the level of the first or second lumbar vertebra; the right pelvis is a little lower.

Ureter

On their course downward, the ureters lie on the psoas muscles, pass medially to the sacroiliac joints, and then swing laterally near the ischial spines before passing medially to penetrate the base of the bladder (Figure 1–2). In females, the uterine arteries are closely related to the juxtavesical portion of the ureters. The ureters are covered by the posterior peritoneum; their lowermost portions are closely attached to it, while the juxtavesical portions are embedded in vascular retroperitoneal fat (Koff, 2008).

The vasa deferentia, as they leave the internal inguinal rings, sweep over the lateral pelvic walls anterior to the ureters (Figure 1–6). They lie medial to the latter before joining the seminal vesicle and penetrating the base of the prostate to become the ejaculatory ducts.

Histology (Figure 1–4)

The walls of the calices, pelvis, and ureters are composed of transitional cell epithelium under which lies loose connective tissue (lamina propria). External to these are a mixture of helical and longitudinal smooth muscle fibers. They are not arranged in definite layers. The outermost adventitial coat is composed of fibrous connective tissue.

Blood Supply

Arterial

The renal calices, pelvis, and upper ureters derive their blood supply from the renal arteries; the midureter is fed by the internal spermatic (or ovarian) arteries. The lowermost portion of the ureter is served by branches from the common iliac, internal iliac (hypogastric), and vesical arteries.

Venous

The veins of the renal calices, pelvis, and ureters are paired with the arteries.

Lymphatics

The lymphatics of the upper portions of the ureters as well as those from the pelvis and calices enter the lumbar lymph nodes. The lymphatics of the midureter pass to the internal iliac (hypogastric) and common iliac lymph nodes; the lower ureteral lymphatics empty into the vesical and hypogastric lymph nodes.

Gross Appearance

The bladder is a hollow muscular organ that serves as a reservoir for urine. In women, its posterior wall and dome are invaginated by the uterus. The adult bladder normally has a capacity of 400–500 mL.

Anatomy

When empty, the adult bladder lies behind the pubic symphysis and is largely a pelvic organ. In infants and children, it is situated higher (Berrocal et al, 2002). When it is full, it rises well above the symphysis and can readily be palpated or percussed. When overdistended, as in acute or chronic urinary retention, it may cause the lower abdomen to bulge visibly.

Extending from the dome of the bladder to the umbilicus is a fibrous cord, the median umbilical ligament, which represents the obliterated urachus. The ureters enter the bladder posteroinferiorly in an oblique manner and at these points are about 5 cm apart (Figure 1–6). The orifices, situated at the extremities of the crescent-shaped interureteric ridge that forms the proximal border of the trigone, are about 2.5 cm apart. The trigone occupies the area between the ridge and the bladder neck.

The internal sphincter, or bladder neck, is not a true circular sphincter but a thickening formed by interlaced and converging muscle fibers of the detrusor as they pass distally to become the smooth musculature of the urethra.

Relations

In males, the bladder is related posteriorly to the seminal vesicles, vasa deferentia, ureters, and rectum (Figures 1–7 and 1–8). In females, the uterus and vagina are interposed between the bladder and rectum (Figure 1–9). The dome and posterior surfaces are covered by peritoneum; hence, in this area, the bladder is closely related to the small intestine and sigmoid colon. In both males and females, the bladder is related to the posterior surface of the pubic symphysis, and, when distended, it is in contact with the lower abdominal wall.

Histology (Figure 1–10)

The mucosa of the bladder is composed of transitional epithelium. Beneath it is a well-developed submucosal layer formed largely of connective and elastic tissues. External to the submucosa is the detrusor muscle that is made up of a mixture of smooth muscle fibers arranged at random in a longitudinal, circular, and spiral manner without any layer formation or specific orientation except close to the internal meatus, where the detrusor muscle assumes three definite layers: inner longitudinal, middle circular, and outer longitudinal (John et al, 2001).

Blood Supply

Arterial

The bladder is supplied by the superior, middle, and inferior vesical arteries, which arise from the anterior trunk of the internal iliac (hypogastric) artery, and by smaller branches from the obturator and inferior gluteal arteries. In females, the uterine and vaginal arteries also send branches to the bladder.

Venous

Surrounding the bladder is a rich plexus of veins that ultimately empties into the internal iliac (hypogastric) veins.

Nerve Supply

The bladder receives innervation from sympathetic and parasympathetic nervous systems. The sensory afferent of the bladder originates from both subepithelial nerve endings and nerve fibers between detrusor muscle bundles (Andersson, 2010; Birder et al, 2010; McCloskey, 2010).

Lymphatics

The lymphatics of the bladder drain into the vesical, external iliac, internal iliac (hypogastric), and common iliac lymph nodes.

Gross Appearance

Anatomy

The prostate is a fibromuscular and glandular organ lying just inferior to the bladder (Figures 1–6 and 1–7). The normal prostate weighs about 20 g and contains the posterior urethra, which is about 2.5 cm in length. It is supported anteriorly by the puboprostatic ligaments and inferiorly by the urogenital diaphragm (Figure 1–6). The prostate is perforated posteriorly by the ejaculatory ducts, which pass obliquely to empty through the verumontanum on the floor of the prostatic urethra just proximal to the striated external urinary sphincter (Figure 1–11).

According to the classification of Lowsley, the prostate consists of five lobes: anterior, posterior, median, right lateral, and left lateral. This classification is often used in cystourethroscopic examinations. After a comprehensive analysis of 500 prostates, McNeal (1981) divides the prostate into four zones: peripheral zone, central zone (surrounds the ejaculatory ducts), transitional zone (surrounds the urethra), and anterior fibromuscular zone (Myers et al, 2010) (Figure 1–12). The segment of urethra that traverses the prostate gland is the prostatic urethra. It is lined by an inner longitudinal layer of muscle (continuous with a similar layer of the vesical wall). Incorporated within the prostate gland is an abundant amount of smooth musculature derived primarily from the external longitudinal bladder musculature. This musculature represents the true smooth involuntary sphincter of the posterior urethra in males.

Relations

The prostate gland lies behind the pubic symphysis. Located closely to the posterosuperior surface are the vasa deferentia and seminal vesicles (Figure 1–7). Posteriorly, the prostate is separated from the rectum by the two layers of Denonvilliers' fascia, serosal rudiments of the pouch of Douglas, which once extended to the urogenital diaphragm (Raychaudhuri and Cahill, 2008) (Figure 1–8).

Histology (Figure 1–10)

The prostate consists of a thin fibrous capsule under which are circularly oriented smooth muscle fibers and collagenous tissue that surrounds the urethra (involuntary sphincter). Deep in this layer lies the prostatic stroma, composed of connective tissues and smooth muscle fibers in which are embedded the epithelial glands. These glands drain into the major excretory ducts (about 25 in number), which open chiefly on the floor of the urethra between the verumontanum and the vesical neck. Just beneath the transitional epithelium of the prostatic urethra lie the periurethral glands.

Blood Supply

Arterial

The arterial supply to the prostate is derived from the inferior vesical, internal pudendal, and middle rectal (hemorrhoidal) arteries.

Venous

The veins from the prostate drain into the periprostatic plexus, which has connections with the deep dorsal vein of the penis and the internal iliac (hypogastric) veins.

Nerve Supply

The prostate gland receives a rich innervation from the sympathetic and parasympathetic nerves of the inferior hypogastric plexus.

Lymphatics

The lymphatics from the prostate drain into the internal iliac (hypogastric), sacral, vesical, and external iliac lymph nodes (Saokar et al, 2010).

Gross Appearance

The seminal vesicles lie just cephalic to the prostate under the base of the bladder (Figures 1–6 and 1–7). They are about 6 cm long and quite soft. Each vesicle joins its corresponding vas deferens to form the ejaculatory duct (Kim et al, 2009). The ureters lie medial to each, and the rectum is contiguous with their posterior surfaces.

Histology

The mucous membrane is pseudostratified. The submucosa consists of dense connective tissue covered by a thin layer of muscle that in turn is encapsulated by connective tissue.

Blood Supply

The blood supply is similar to that of the prostate gland.

Nerve Supply

The nerve supply is mainly from the sympathetic nerve plexus.

Lymphatics

The lymphatics of the seminal vesicles are those that serve the prostate.

Gross Appearance

The two spermatic cords extend from the internal inguinal rings through the inguinal canals to the testicles (Figure 1–7). Each cord contains the vas deferens, the internal and external spermatic arteries, the artery of the vas, the venous pampiniform plexus (which forms the spermatic vein superiorly), lymph vessels, and nerves (Jen et al, 1999). All of the preceding are enclosed in investing layers of thin fascia. A few fibers of the cremaster muscle insert on the cords in the inguinal canal (Bhosale et al, 2008; Kim et al, 2009).

Histology

The fascia covering the cord is formed of loose connective tissue that supports arteries, veins, nerve, and lymphatics. The vas deferens is a small, thick-walled tube consisting of an internal mucosa and submucosa surrounded by three well-defined layers of smooth muscle encased in a covering of fibrous tissue. Above the testes, this tube is straight. Its proximal 4 cm tends to be convoluted.

Blood Supply

Arterial

The external spermatic artery, a branch of the inferior epigastric, supplies the fascial coverings of the cord. The internal spermatic artery passes through the cord on its way to the testis. The deferential artery is close to the vas.

Venous

The veins from the testis and the coverings of the spermatic cord form the pampiniform plexus, which, at the internal inguinal ring, unites to form the spermatic vein.

Lymphatics

The lymphatics from the spermatic cord empty into the external iliac lymph nodes.

Gross Appearance

Anatomy

The upper portion of the epididymis (globus major) is connected to the testis by numerous efferent ducts from the testis (Figure 1–7). The epididymis consists of a markedly coiled duct that, at its lower pole (globus minor), is continuous with the vas deferens. An appendix of the epididymis is often seen on its upper pole; this is a cystic body that in some cases is pedunculated, but in others, it is sessile.

Relations

The epididymis lies posterolateral to the testis and is nearest to the testis at its upper pole. Its lower pole is connected to the testis by fibrous tissue. The vas lies posteromedial to the epididymis.

Histology

The epididymis is covered by serosa. The ductus epididymidis is lined by pseudostratified columnar epithelium throughout its length.

Blood Supply

Arterial

The arterial supply to the epididymis comes from the internal spermatic artery and the artery of the vas (deferential artery).

Venous

The venous blood drains into the pampiniform plexus, which becomes the spermatic vein.

Lymphatics

The lymphatics drain into the external iliac and internal iliac (hypogastric) lymph nodes.

Gross Appearance

Anatomy

The average testicle measures about 4 × 3 × 2.5 cm (Figure 1–7). It has a dense fascial covering called the tunica albuginea testis, which, posteriorly, is invaginated somewhat into the body of the testis to form the mediastinum testis. This fibrous mediastinum sends fibrous septa into the testis, thus separating it into about 250 lobules.

The testis is covered anteriorly and laterally by the visceral layer of the serous tunica vaginalis, which is continuous with the parietal layer that separates the testis from the scrotal wall (Bidarkar and Hutson, 2005). Small amount of fluid normally exists within the tunica vaginalis sac. At the upper pole of the testis is the appendix testis, a small pedunculated or sessile body similar in appearance to the appendix of the epididymis.

Relations

The testis is closely attached posterolaterally to the epididymis, particularly at its upper and lower poles (Klonisch et al, 2004).

Histology (Figure 1–7)

Each lobule contains one to four markedly convoluted seminiferous tubules, each of which is about 60 cm long. These ducts converge at the mediastinum testis, where they connect with the efferent ducts that drain into the epididymis.

The seminiferous tubule has a basement membrane containing connective and elastic tissue. This supports the seminiferous cells that are of two types: (1) Sertoli (supporting) cells and (2) spermatogenic cells. The stroma between the seminiferous tubules contains connective tissue in which the interstitial Leydig cells are located.

Blood Supply

The blood supply to the testes is closely associated with that to the kidneys because of the common embryologic origin of the two organs.

Arterial

The arteries to the testes (internal spermatics) arise from the aorta just below the renal arteries and course through the spermatic cords to the testes, where they anastomose with the arteries of the vasa deferentia that branch off from the internal iliac (hypogastric) artery.

Venous

The blood from the testis returns in the pampiniform plexus of the spermatic cord. At the internal inguinal ring, the pampiniform plexus forms the spermatic vein.

The right spermatic vein enters the vena cava just below the right renal vein; the left spermatic vein empties into the left renal vein.

Lymphatics

The lymphatic vessels from the testes pass to the lumbar lymph nodes, which in turn are connected to the mediastinal nodes.

Gross Appearance

Beneath the corrugated skin of the scrotum lies the dartos muscle. Deep to this are the three fascial layers derived from the abdominal wall at the time of testicular descent. Beneath these is the parietal layer of the tunica vaginalis (Kim et al, 2007).

The scrotum is divided into two sacs by a septum of connective tissue. The scrotum not only supports the testes but also, by relaxation or contraction of its muscular layer, helps to regulate their temperature.

Histology

The dartos muscle, under the skin of the scrotum, is unstriated. The deeper layer is made up of connective tissue.

Blood Supply

Arterial

The arteries to the scrotum arise from the femoral, internal pudendal, and inferior epigastric arteries.

Venous

The veins are paired with the arteries.

Lymphatics

The lymphatics drain into the superficial inguinal and subinguinal lymph nodes.

Gross Appearance

The penis is composed of two corpora cavernosa and the corpus spongiosum, which contains the urethra. The corpus spongiosum enlarges distally and caps the glans penis. Each corpus is enclosed in a fascial sheath (tunica albuginea), and all are surrounded by a thick fibrous envelope known as Buck's fascia. A covering of skin, devoid of fat, is loosely applied about these bodies. The prepuce forms a hood over the glans.

Beneath the skin of the penis (and scrotum) and extending from the base of the glans to the urogenital diaphragm is Colles' fascia, which is continuous with Scarpa's fascia of the lower abdominal wall (Figure 1–8).

The proximal ends of the corpora cavernosa are attached to the pelvic bones just anterior to the ischial tuberosities. The ischiocavernosus muscles insert to the lateral surface of the tunica albuginea at the proximal corpora cavernosa. Occupying a depression of their ventral surface in the midline is the corpus spongiosum, which is connected proximally to the undersurface of the urogenital diaphragm, through which emerges the membranous urethra. This portion of the corpus spongiosum is surrounded by the bulbospongiosus muscle.

The suspensory ligament of the penis arises from the linea alba and pubic symphysis and inserts into the fascial covering of the corpora cavernosa.

Histology

Corpora and Glans Penis

The corpora cavernosa, the corpus spongiosum, and the glans penis are composed of smooth muscles, intracavernosal struts (corpus cavernosum only), and endothelium-lined sinusoids. The sympathetic and parasympathetic (continuing neuronal nitric oxide synthase) nerve terminals are often seen around the vessels and near the smooth muscles.

Urethra

The urethral mucosa that traverses the glans penis is formed of squamous epithelium. Proximal to this, the mucosa is transitional in type. Underneath the mucosa is the submucosa that contains connective and elastic tissue and smooth muscle. In the submucosa are the numerous glands of Littre, whose ducts connect with the urethral lumen. The urethra is surrounded by the vascular corpus spongiosum and the glans penis.

Blood Supply

Arterial

The penis and urethra are supplied by the internal pudendal arteries. Each artery divides into a cavernous artery of the penis (which supplies the corpora cavernosa), a dorsal artery of the penis, and the bulbourethral artery. These branches supply the corpus spongiosum, the glans penis, and the urethra. Accessory pudendal arteries originate from inferior vesical, obturator, or other arteries may also supply the penis.

Venous

The superficial dorsal vein lies external to Buck's fascia and drains to the saphenous vein. The deep dorsal vein is placed beneath Buck's fascia and lies between the dorsal arteries. The cavernous veins drain the crura of the penis. These veins connect with the pudendal plexus that drains into the internal pudendal vein and periprostatic plexus.

Lymphatics

Lymphatic drainage from the skin of the penis is to the superficial inguinal and subinguinal lymph nodes. The lymphatics from the glans penis pass to the subinguinal and external iliac nodes. The lymphatics from the proximal urethra drain into the internal iliac (hypogastric) and common iliac lymph nodes (Wood and Angermeier, 2010).

Gross Appearance

The adult female urethra is about 4 cm long and 8 mm in diameter. It is slightly curved and lies beneath the pubic symphysis just anterior to the vagina.

Histology

The epithelial lining of the female urethra is squamous in its distal portion and pseudostratified or transitional in the remainder. The submucosa is made up of connective and elastic tissues and spongy venous spaces. Embedded in it are many periurethral glands, which are most numerous distally; the largest of these are the periurethral glands of Skene that open on the floor of the urethra just inside the meatus.

External to the submucosa is a longitudinal layer of smooth muscle continuous with the inner longitudinal layer of the bladder wall. Surrounding this is a heavy layer of circular smooth muscle fibers extending from the external vesical muscular layer. This constitutes the involuntary urethral sphincter. External to this is the circular striated (voluntary) sphincter surrounding the middle third of the urethra. The smooth and striated muscles within the midurethra constitute the external urethral sphincter (Ashton-Miller and Delancey, 2009; Thor and de Groat, 2010).

Blood Supply

The arterial supply to the female urethra is derived from the inferior vesical, vaginal, and internal pudendal arteries. Blood from the urethra drains into the internal pudendal veins.

Lymphatics

Lymphatic drainage from the external portion of the urethra is to the inguinal and subinguinal lymph nodes. Drainage from the deep urethra is into the internal iliac (hypogastric) lymph nodes.

Adrenals

Kidneys

Calices, Renal Pelvis, and Ureter

Bladder

Prostate Gland

Spermatic Cord and Seminal Vesicles

Testis, Scrotum, and Penis

Female Urethra