Ureter, Bladder & Urethra

THE URETER

The Ureter, Urinary bladder & UrethraThe ureter is a paired tube – like organ, which conveys the urine from the renal pelvis into the bladder. The length of the ureter is about 30-35cm. the ureter lies behind the peritoneum. The ureter has three parts: abdominal, pelvic and intramural. The abdominal part (pars abdominalis) is situated on the major psoas muscle and forms a flexure, medially faced. At its origin, the right ureter is covered with duodenum, the left ureter with the duodeno – jejunal flexure. The ovarian (testicular) artery and vena, parietal peritoneum are situated in front of the abdominal part of the ureter. On the border line (at the place where the abdominal part transforms into the pelvis), the right ureter passes behind the root of the mesentery, the left one – behind the sigmoid mesocolon of the sigmoid colon.

The pelvic part (pars pelvica) of the ureter forms the flexure, facing laterally. In the pelvic cavity the ureter is situated in front of the internal iliac artery and medial to the obturator artery and vein. In females, the pelvic part of the ureter lies behind the ovary, near the uterine artery; the it goes around the lateral aspect of the uterus neck and, in front of the vagina, reaches the bladder. In males, the pelvic part of the ureter goes outwards to the vas deferens, crosses it, and continue downwards to the seminal vesicle reaches the bladder. The intramural part (pars intramuralis) of the ureter runs obliquely through the wall of the bladder. There are three narrowings within the ureter. The gap of the ureter narrows (to 3mm in the diameter) in the region of its origin, in the place where the ureter transforms from the abdominal to the pelvic part and where the ureter reaches the bladder.

The wall of the ureter is composed of mucosa with a submucosa layer, muscular layer and adventitia. The mucous membrane presents deep longitudinal folds, which provide the ureter the ability to extend. The mucous membrane is covered with transitional epithelium, situated on the basement membrane. The proper mucosa contains vessels and nerves, lymphoid elements, excreting ducts of the glands, mast cells and other cells.

Besides vessels and nerves, the wall, especially in the alveolar in the lower part of the ureter, contains the secretory section of the alveolar – tubular mucous glands. The muscular layer, on a level with the upper half of the ureter, consists of two thin layers of smooth myocytes. The fibre of myocytes of the internal layer have a longitudinal direction, myocytes of the external layer have a circular one. Thin internal longitudinal, middle circular and the external longitudinal fibres of myocytes represent the muscular layer of the ureter lower part. Outwards the ureter is covered with a fibrous coat.

Innervation: from the renal, ureteric and inferior hypogastric plexuses. Parasympathetic innervation of the upper part of the ureter comes from the vagus nerves (through the renal plexus); the lower part is innervated from the pelvic splanchnic nerves.

Blood supply: the upper part of the ureter – ureteric branches is supplied from the renal, ovarian, testicular arteries. The middle part – the ureteric branches are supplied from the abdominal aorta, common and internal iliac arteries. The lower part the ureteric branches are supplied from the middle rectal and inferior vesicle arteries.

Venous outflow: ovarian (testicle) and internal iliac veins.

Lymph outflow: lumbar and internal iliac lymph nodes

THE URINARY BLADDER

The bladder (vesica urinaria) – is a non-paired hollow organ, which is situated in the pelvic cavity. The bladder is a reservoir for the urine, which enters the bladder via the ureters and leaves it via the urethra. The form of the distended bladder is close to a ball. The capacity of an adult bladder is about 250-500ml. The anterior – superior part of the bladder is called an apex (apex vesicae). The apex without any visible boarder transforms into an ectatic part – the body of the bladder (corpus vesicae), which goes down and back and forms the fundus (fundus, vesicae). The inferior narrowed part is called the neck of the bladder (collum vesicae).

The anterior surface of the bladder is separated from the internal surface of the pubic symphysis by the diffused fatty tissue (retro – pubic pool). Between the inferior part of the bladder and pubic symphysis there are the suspensor ligament and muscles (pubovesicalis), which help to fixate of the bladder. The posterior surface of the bladder in males is situated to the front of the rectum and is separated from it by a recto-vesical pouch (excavation rectovesicalis). In females the uterus is situated behind the bladder, between them there is a vesico – uterine pouch (excavation vesicouterina). Below the posterior surface the bladder is attached to the anterior wall the of the vagina, the fundus is attached to the urogenital diaphragm. The inferior – lateral surfaces of the bladder in males are in the relationship with the levator ani muscle. The superior surface of the bladder is attached to the loops of the small intestine. The fibres of the pubo-prostatic ligament are situated between the bladder and the prostate. The fibres of the rectovesicalis go from the bladder to the rectum with reference to the peritoneum. The distended bladder is situated mesoperitoneally, the empty – retroperitoneally. The wall of the bladder is consisted of the mucosa, submucosa, muscular and fibrous (partly by peritoneum) layer. The mucosa of the empty or normally filled bladder forms a significant number of variously directed folds. The folds become smooth when the bladder is substantially filled. The folds of the mucosa are absent in the anterior region of the fundus of the bladder and in the region of its trigone. The fold between the ureters forms the base of the bladder’s trigone (trigonum vesicae), this fold connects the mouths of the left and the right ureters.

The apex of the triangular corresponds to the beginning of the urethra. The epithelial layer and the proper mucous layer represent the mucosa of the bladder. The cells of the epithelium, which covers the mucosa of the empty bladder, are cyclic. The epithelial cells of the distended bladder are flattened. They are connected by close contacts. There are alveolar – tubular glands, nerves, vessels, and lymphoid structures in the thick part of the proper mucous layer. The lower part of submucosa of the bladder is well – developed, but it is absent in the region of the trigonum. The muscular coat is presented by three interlaced layers (detrusor muscle, m. detrusor vesicae).

The internal and external, longitudinal and middle circular layers of smooth myocytes are distinguished. Interlacing of the muscular fibres promotes contraction of their walls in the process of urine excretion, pushing the urine into the urethra. The circular layer of the muscular coat is the most developed. Fibres of the internal muscular layer of the bladder surround the mouths of the ureters. The contraction of these fibres and oblique direction of the terminal section of the ureter prevent the back flow of the urine. In the region of the internal opening of the urethral the circular layer forms the internal (involuntary) sphincter. During micturition the musculature of the internal and external (which is situated within the thickness of the perineum) sphincters weakens, the muscles of the walls of the bladder contract. The external coat of the bladder on the superior – posterior and partly on the lateral surfaces is formed by peritoneum, on the other surfaces – by a fibrous coat.

Innervation: sympathetic – from the inferior hypogastrical plexuses, parasympathetic – by pelvic splanchnic nerves.

Arteries: the apex and body of the bladder receive blood from the superior vesicle arteries (from umbilical arteries), the fundus and lateral walls of the bladder – from the inferior vesicle arteries (from internal iliac arteries).

Venous outflow: the venous plexus of the bladder, the vesical veins, (tributaries of the internal iliac veins).

Lymph outflow: the internal iliac lymph nodes.

URETHRA

The female urethra (urethra feminia) – is a non-paired hollow tube, which excretes the urine from the bladder. The famle urethra begins with its internal urethral orifice (ostium urethrae internum) from the region of the apex of the bladder trigone. It finishes with the external urethral orifice (ostium urethrae externum) of the urethra in the vestibule of the vagina. The urethra is a tube about 2.5 – 3.5 cm long, 0.8 – 1.2 cm in diameter. It is fused with the anterior wall of the vagina and passes through the urogenital diaphragm.

The walls of the female urethra are composed of the mucosa and muscular coats. The mucosa forms longitudinal folds. The most developed fold of the mucosa of the posterior wall of the urethra is the urethral crest (crista urethralis). There are deep recesses (urethral lacunae) in the mucosa. The mucosa is covered with epithelium, which is situated on the basement membrane. To the outside of the basement membrane there is the proper layer of the mucosa, which contains vessels, nerves, and alveolar – tubular mucous galnds of the urethra. The muscular coat contains the internal longitudinal and external circular layers. The circular layer of myocytes fuses with the muscular coat of the urethra, forming the internal, involuntary sphincter (sphincter urethrae internus). At the place, where the urethra passes through the urogenital diaphragm of the perineum, fibres of striated muscles, which form the external voluntary sphincter, surround the urethra.

Innervation of the female urethra: sympathetic – coeliac plexuses, and parasympathetic – branches of the pelvic nerves.

Blood supply: the internal pudendal artery (from the internal iliac artery).

Lymph outflow: superficial inguinal nodes.