REVIEW OF NORMAL HISTOLOGY OF THE LOWER URINARY TRACT “QUICK REVIEW”
The outflow of the kidneys (renal pelvis, ureters, bladder, and urethra) comprises the lower urinary tract (Figure 14-1). The basic histology is that all are lined by urothelium (transitional epithelium), which covers a connective tissue layer of lamina propria, a variably thick layer of smooth muscle (muscularis propria), and adventitia (Figure 14-2). Urothelium is specialized epithelium that is multilayered with large surface superficial cells (umbrella cells), which can change shape as the bladder dilates and contracts. These contain specialized cell junctions that are resistant to permeation by urine. Beneath this are five to six layers of smaller urothelial cells. The muscularis propria is well developed in the bladder. Coordinated contraction of this muscle (detrusor muscle) helps in emptying the bladder. Muscle is less prominent in the ureters and the urethra. The distal urethra is lined by squamous epithelium, which is in continuity with the squamous epithelium of the external genitalia. Both the male urethra and female urethra contain mucinous glands in their walls.
Gross image of kidneys, ureters, and bladder. Kidneys are shown in coronal section. The bladder has been opened to show oblique ureteral openings in the posterolateral wall. The neck of the bladder and the urethral opening are visible at the bottom of the figure.
Photomicrograph of normal urothelium. Arrow indicates umbrella cell layer of urothelium epithelium. Line “A” indicates urothelium, and line “B” indicates lamina propria. The muscularis propria is not shown.
REVIEW OF LOWER URINARY TRACT AND NORMAL MALE GU DEVELOPMENT
The lower urinary tract develops from the anterior part of the cloaca. In early fetal development, this area of the cloaca becomes the urogenital sinus, and develops into the fetal urinary bladder, proximal urethra, and the urachus. The distal urethra develops from the urogenital membrane, and the proximal and distal structures fuse. The urachus is a temporary structure that connects to the umbilicus. The urachus involutes in later fetal life. The ureters develop as lateral buds from the bladder, grow cranially, and induce the formation of the kidney from the metanephric blastema.
Development of the male genital system is complex. The testes begin as intraabdominal organs, from the genital ridges in the coelomic cavity. The genital ridges contain primordial germ cells that have migrated there from the yolk sac. Testes develop from this mixture of tissues, and they migrate from their intraabdominal location into the inguinal canal and eventually the scrotum. During development in the abdomen, testes connect with their outflow tracts derived from Wolffian ducts. These develop into the epididymis and vas deferens. The external male genitalia develop from the genital tubercle and the anterior urogenital sinus. The presence of testosterone allows development of these primordial ...