Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The Urinary Ureters, Bladder and Urethra The Ureters The ureters are a pair of thin, muscular tubes that transport urine from the kidneys to the bladder. Beginning at the level of the second lumbar vertebra, the location of the ureters is retroperitoneal. Each ureter runs inferiorly and enters the posterolateral wall of the urinary bladder. This angle of entry is important, because it helps prevent urine from flowing back into the ureters when the bladder fills with urine. In addition, accumulating urine increases the internal pressure of the bladder, and this pressure compresses and seals the distal portion of the ureters. There are three layers in the ureter wall. The innermost mucosa lining contains transitional epithelium capable of stretching but is impermeable to urine. The ability to stretch allows the ureter wall to accommodate changing volumes of urine. The middle muscularis layer is composed of two layers of smooth muscle: an inner longitudinal layer and outer circular layer. In the lower third of the ureter, the muscularis has a third outer layer of longitudinal muscle fibers. The muscularis layer is responsible for the peristaltic contractions needed to move urine through the ureters and into the bladder. The external layer of the ureter wall, the adventitia, is made of fibrous connective tissue and helps anchor the ureter to the abdominal wall. When urine enters and distends the ureters, stretch receptors are stimulated. Reflexive action results in the contraction of the muscularis and, movement of the urine into the bladder. The power and frequency of peristalsis is directly related to the rate of urine formation. Although the ureters are innervated by both sympathetic and parasympathetic fibers, the nervous system does not appear to have major involvement in the transport of urine in these organs. The Urinary Bladder The urinary bladder is a hollow, collapsible muscular sac that serves as a temporary storage facility for urine. It is located in the pelvic cavity, just posterior to the pubic symphysis. In females, the bladder lies anterior to the vagina and inferior to the uterus. In males, it is immediately anterior to the rectum.Peritoneal folds hold the bladder in place. The bladder can hold up to about a liter of urine, although this amount varies from person to person. Despite its capacity to enlarge, an overfull bladder can burst but it is more likely that excess urine will leak out of the urethra. When empty, the bladder collapses into a pyramidal shape. When a small amount of urine accumulates, it is spherical. When a larger volume of urine accumulates, the bladder becomes pear-shaped and ascends in the abdominal cavity. There are three openings in the bladder: two for the ureters and one for the urethra. These openings frame a triangular region at the base of the bladder called the trigone. The bladder wall is made up of a mucosa with transitional epithelium, a submucosa, a thick muscularis called the detrusor muscle, and a fibrous adventitia. The adventitia is on the inferior surface only. In contrast, the peritoneum covers the superior surface. The detrusor muscle is composed of inner and outer layers of longitudinal smooth muscle fibers and an intermediate layer of circular muscle fibers. The Urethra The urethra is a small muscular tube that transports urine from the bladder out of the body. The urethra is five times longer in males (8 inches, 20 cm) than in females (1.6 inches, 4 cm). In males, the urethra is also part of the reproductive system, providing a passageway for semen as well as urine. The course of the urethra also differs between the sexes. In females, fibrous connective tissue binds it to the anterior vaginal wall, and its external urethral orifice (external opening) is located anterior to the vaginal opening and posterior to the clitoris. In males, the urethra is divided into three regions. The prostate surrounds the prostatic urethra. The membranous urethra passes through the urogenital diaphragm. The spongy urethraruns through the penis and ends at the external urethral orifice. At the bladder-urethra junction, the circular fibers of the bladder's detrusor muscle form the internal urethral sphincter. When urine is not draining from the bladder, this involuntary sphincter closes off the urethra to prevent the leakage of urine when you are not voiding. At the point where the urethra passes through the urogenital diaphragm, the external urethral sphincter, a skeletal muscle, surrounds it. The external sphincter is voluntarily controlled and is kept contracted until voiding. EXAMPLE Urinary Tract Infections Urinary tract infections (UTIs) are the most common type of bacterial infection. Women are predisposed to UTIs because their urethras are shorter than those of men. Moreover, the urethra's external opening in women is closer to the anus than it is in men. Over 50 percent of women will have a UTI at some point during their lifetime. Fecal bacteria such as Escherichia coli (E. coli) can easily travel up the urethra. This is why women should never wipe the anus in a forward direction after defecation. However, most UTIs in women occur as a result of sexual activity. During intercourse, bacteria from the external genital area and the vagina can be pushed up the short urethra toward the bladder. The use of spermicides actually increases the risk of UTIs, because spermicides kill bacteria that would otherwise help destroy infectious fecal bacteria in the vagina. Drinking plenty of water and urinating immediately after sexual activity can help prevent UTIs by flushing bacteria out of the urethra. Infection of the urethra (urethritis) can easily spread to the urinary bladder (cystitis) and sometimes to the kidneys (pyelitis or pyelonephritis). Symptoms of a UTI include pain during urination (dysuria), frequent urination or an urgent need to urinate, cloudiness or blood in the urine (hematuria), urine with a strong odor, nausea, and fever. Fortunately, most UTIs respond to antibiotics. Analgesics may also be prescribed to reduce discomfort. Unfortunately, having a UTI increases the chances of having subsequent UTIs. UTIs are also common in infants, particularly in uncircumcised male infants.