The Urinary
Bladder
Function
The Urinary Bladder stores urine and forces it into the urethra for excretion from the
body.
Structure
The urinary bladder is a hollow, distensible, muscular organ. It is
somewhat spherical, but the pressure of the surrounding organs causes its
shape to become altered. When the bladder is empty, the inner wall
retracts into many folds, but as it is filled with urine, the wall expands
and becomes smoother. The wall of the urinary bladder consists of four
layers. The inner layer, or mucous coat, is several thicknesses of
epithelial cells. The second layer, or submucous layer, is made up of
connective tissue and contains many elastic fibers. The third layer, or
muscular coat, is primarilly made up of coarse bundles of smooth muscle
fibers. These muscles in the muscular coat are interlaced to form the
detrusor muscle. The portion of the detrusor muscle around the neck of
the bladder forms an internal urethral sphincter, which controls excretion
of urine. The outer layer, or serous coat, is made of the parietal
peritoneum. However, this layer occurs only on the upper surface of the
urinary bladder, and elsewhere, the outer coat is composed of fibrous
connective tissue.