The ureters serve as the pathway for the formed urine from the kidney to the bladder. The placement of each ureter is uniquely tailored so that it prevents backflow of the urine when the bladder is filled. Each ureter goes down behind the peritoneum and runs obliquely through the posterior bladder wall. With this placement, the increase in balder pressure triggers the closure of the distal ends of the ureters.
Tissue examination of the ureters reveals that its wall is composed of three layers. The epithelium found in the lining if the mucosa is continous with the bladder medially and by the kidney superiorly. The muscularis in the middle is made up of two sheets of smooth muscles. The internal smooth muscle sheet is a longitudinal layer and the external smooth muscle sheet is a circular layer. Typical fibrous connective tissue covers the adventitia or the external surface of the ureter.
Function of the Ureter
The main role the ureters play has to do with the transportation of urine. As urine enters the ureters, it becomes distended thereby stimulating the muscularis. As the muscularis is stimulated, it contracts and propels the urine towards the bladder. Although gravity plays a role, it alone cannot suffice the delivery of urine to the bladder.
The urinary bladder is where urine is temporarily stored. It is a muscular sac located retroperitoneally posterior to symphysis pubis. In makes, the prostate surrounds the neck of the bladder.
The urinary bladder has openings for both the urethra and the ureters. The triangular region outlined by connecting the three points constitutes the area known as the trigone. The trigone is important clinically because this is where infections tend to persist.
Function of the Urinary Bladder
The urinary bladder is uniquely made to store urine. It is distensible and collapsible, making it ideal for urine storage. When urine is excreted, the bladder collapses and thrown into folds known as rugae. As urine starts to build up again, the bladder now expands and the rugae disappears. With this unique mechanism, it allows the bladder to store more urine without the hazard of rising internal pressure. The bladder can hold about 800-1000ml of urine.
The stored urine in the urinary bladder drains through a muscular tube and conveys it out of the body. The thin-walled muscular tube is the urethra. The mucosal lining of the urethra changes according to its region. The epithelium is pseudostratified columnar, near the bladder it becomes transitional and as it approaches the opening it becomes protective stratified squamous.
The internal urethral sphincter is formed by the thickening of the detrusor smooth muscle. This sphincter helps keep the urethra closed and avoids leakage during voiding. This sphincter is uniquely because it opens during contraction and it closes during relaxation.
The external urethral sphincter is voluntarily controlled. It is formed of skeletal muscle and the muscle of the pelvic floor, known as the levator ani is also used as a voluntary contrictor of the urethra.