FUNGSI MIKSI

Proses miksiPengisian ( filling )Pengosongan ( storage )

Laplace's equationLaplace's equation states that there is a direct relationship between wall tension and intravesical pressure and bladder size. T is tension, P is intravesical pressure, R is bladder radius, and d is wall thickness. During bladder filling, Pves is relatively constant. With a fully distended bladder, d, because of its relative thinness, is ignored relative to the other parameters unless a hypertrophied wall exists. Thus, T=P R/2 approximates tension in the full normal bladder

THE URINARY BLADDER The bladder performs several important functions. First, it must store a socially adequate volume of urine. The bladder wall must be able to stretch and rearrange itself to allow an increase in bladder volume without significant rise in pressure. In other words, the bladder wall must be extremely compliant.

Second, the smooth muscle and intrinsic nerves have to be protected from exposure to urine by the urothelium, which itself must also expand readily during filling. Third, bladder emptying requires synchronous activation of all the smooth muscle, because if only part of the wall contracted, the uncontracted compliant areas would stretch and prevent the increase in pressure necessary for urine to be expelled through the urethra. This is the problem often seen in an elderly man with benign prostatic hyperplasia who develops urinary retention and a bladder diverticulum.

Smooth Muscle There are several universal characteristics of smooth muscle:

Smooth muscle consists of a sheet containing many small, spindle-shaped cells linked together at specific junctions. Smooth muscle cells contain actin and myosin, but these proteins are not arranged in a regular sarcomere pattern. Instead, each smooth muscle cell consists of a more variable matrix of contractile proteins that is attached to the plasma membrane at the junctional complexes between neighboring cells.

Smooth muscle maintains a steady level of tension that can be modulated by circulating hormones, by local factors such as nitric oxide, or by activity in the autonomic nerves.

Smooth muscle is more adaptable than skeletal muscle and is able to adjust its length over a much wider range than skeletal muscle.

Based on the assumption of a spherical bladder, the circumference of a 400-ml capacity bladder is approximately 30 cm. If the bladder empties to a residual urine volume of 10 ml, the circumference would be only 8 cm. To accomplish this feat, the detrusor would have a change in muscle length of 75%. If the bladder were to be made of skeletal muscle instead, the maximum length change would be only about 30%. The maximum "skeletal muscle bladder" emptying would be only 70% of its contents, leaving a residual urine of 120 ml. Thus, the bladder requires the unique property of smooth muscle to accomplish its job. What is assumed to be the stronger skeletal muscle is not up to the job of bladder emptying

Smooth Muscle There are several universal characteristics of smooth muscle

Smooth muscle consists of a sheet containing many small, spindle-shaped cells linked together at specific junctions. Smooth muscle cells contain actin and myosin, but these proteins are not arranged in a regular sarcomere pattern. Instead, each smooth muscle cell consists of a more variable matrix of contractile proteins that is attached to the plasma membrane at the junctional complexes between neighboring cells.

Smooth muscle maintains a steady level of tension that can be modulated by circulating hormones, by local factors such as nitric oxide, or by activity in the autonomic nerves. Smooth muscle is more adaptable than skeletal muscle and is able to adjust its length over a much wider range than skeletal muscle.