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I./1.1.: Structural description of the kidney and the urinary passages
The human uropoetic system comprises the paired kidneys, the organs of urinary drainage (ureters), the urinary bladder for temporary storage of urine and, finally, the terminal tubular conduit of urinary passages (urethra).
In adults, the kidneys are paired bean-shaped organs situated in the retroperitoneal space on either side of the lumbar spine. The lower pole of left kidney lies in the level of lumbar vertebra 3, the medially directed hilum being in the level of lumbar vertebra 1, whereas the upper pole reaches the upper edge of thoracic vertebra 12. The right kidney is displaced downward by the liver. The kidneys are fixated to the body wall by an external fascial sheath and an adipose capsule. Immediately attached to the smooth outer surface, the renal capsule (capsula fibrosa) is a connective tissue tunic, also extending via the hilum deep into the interior of the kidney, the renal sinus containing yellow adipose tissue.
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1. fotó: A bal vese in situ – Pápai Zsolt, Molnár Attila és Balogh Attila
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2. fotó: A jobb vese helyzete – Pápai Zsolt, Molnár Attila és Balogh Attila
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3. fotó: A vesék – Molnár Attila és Balogh Attila
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The ground substance of kidney is divided into 10-18 renal lobes. Each lobe can be subdivided into outer cortex and inner medulla. Excretion of urine is carried out by the structural and functional units of the kidneys' ground substance: nephrons. The latter comprise the renal corpuscle and the adjoining uriniferous tubules: proximal and distal convoluted tubules, loop of Henle and connecting tubule (tubulus reuniens). The excreted urine will be accumulated in the initial part of uriniferous passages, in the cavity of minor and major renal calyces. The human kidney contains 7-14 minor calyces, which drain into 2-3 major calyces passing urine via the renal pelvis into the ureter.
A slightly flattened tubular organ of 4-7 mm diameter and 25-30 cm length, the ureter passes urine from the renal pelvis to the urinary bladder. Along its course, two main portions (abdominal and pelvic) can be distinguished. The abdominal portion emerges from the renal pelvis, and it courses retroperitoneally in front of the psoas major muscle in a caudal direction, undercrossing the gonadal vessels (ovarian or testicular arteries and veins). Then it dips into the pelvis, overcrossing the common iliac arteries, followed by undercrossing of the uterine artery (in the female) or the vas deferens (in the male).
The ureters penetrate the posterior caudal wall of the bladder (fundus vesicae urinariae) diagonally, in dorsoventral and lateromedial direction. Their orifice gets blocked with increasing distension of the filling bladder, thereby preventing reflux of urine into the ureter. Mucosa of the ureter is composed of transitional epithelium (urothelium), a continuation of similar epithelial lining of the renal calices and pelvis. Peristalsis generated in the smooth mucle layers of ureteric wall (outer and inner longitudinal and an intermediate circular) drives the passage of urine between the kidneys and the bladder.
Temporary storage site for urine, the urinary bladder is a lemon-shaped organ situated subperitoneally behind the pubic symphysis. In empty state, its diameter is 3-4 cm. The wall of the bladder consists of mucosa (lined by urothelium) inside, and a meshwork of smooth muscle bundles outside. The mucosa of the distended bladder is flat, whereas it is thrown up in folds in the contracted state. In a triangular area near the base (trigonum vesicae) the mucosa appears smooth. This region does not participate in distension and the mucosa is firmly adherent. The ureteric orifices are situated at the posterior edge of the trigone, whilst its anterior tip continues in the urethra. An upward bulging part of the bladder (apex or vertex), connected through a connective tissue ligament (median umbilical ligament) to the navel, represents the remnant of urachus (obliterated cavity of allantois).
The female urethra is short (2.5-4 cm) and it opens between the labia minora immediately in front of the vagina. Emerging from the lower end of vesical trigone, the female urethra begins with an ostium urethrae internum (internal orifice) and it ends 2-3 cm behind the glans clitoridis with an ostium urethrae externum (external orifice). Its wall is surrounded by muscular sphincters (musculus sphincter vesicae et urethrae). The male urethra is longer (20-25 cm) and, having passed through the prostate and penis, it opens on the glans penis.
Four portions of the male urethra can be distinguished: intramural (narrow initial part embedded in the bladder wall, with the internal urethral orifice); prostatic (perforating the gland); membranous (perforating the pelvic floor and surrounded by the urethral sphincter); and spongy (penile urethra) (in the corpus spongiosum and the navicular fossa of glans penis, ending in the external urethral orifice.
The epithelial lining of the urethra displays high degree of variability in both genders; urothelium followed by pseudostratified or stratified columnar epithelia and finally stratified squamous epithelium are characteristic for the upper, intermediate or terminal portions, respectively.
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