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Urinary Bladder

What is the urinary bladder?
The urinary bladder is an organ for the temporary storage of urine formed by the kidneys. The capacity of the bladder to store urine is approximately 800 ml. in adults.

Where is the urinary bladder located?
The bladder is located immediately behind the pubic bones. The pubic bones are felt on the front of the pelvis. The bony projection on the front of the pelvis is the pubic symphysis, where both pubic bones from each side join together. The urinary bladder lies in the pelvis of the body. The ureters from the kidneys join the bladder on both its sides.

How can we describe the urinary bladder?
The urinary bladder is a strong muscular sac located in the pelvic cavity. Size and shape varies according to the amount of urine contained in the bladder. An empty bladder is pyramidal in shape. Its apex points downwards. The bladder has three surfaces:

  • The upper or superior surface
  • Two surfaces on the right and left sides of the body called as the infero-lateral surfaces. The upper surface bulges into the abdominal cavity when the bladder is full. The bladder also has a structure called as the neck, which is continuous with the apex and rests on the prostate gland in the males, which lies below it. At the point where the bladder meets the prostate in males, the smooth muscle fibers of the prostate are continuous with that of the bladder.
In females as there is absence of the prostate glands, the bladder lies at a slightly lower level in females than in males. The closeness of the bladder to the uterus in the females causes frequent pressure on the bladder during pregnancy leading top frequent urination during pregnancy. Internal structure of the urinary bladder Functionally the bladder is divided into the body, which is the major part of the bladder and the neck, which is the funnel shaped extension of the body. The neck opens into the urethra. The inside of the upper part of the urinary bladder is thrown into many folds when the bladder is empty. These folds disappear when the bladder is full. The narrow triangular part of the bladder contains smooth layer of muscle even if the bladder is empty. This part is called as the trigone. The muscular coat of the bladder is arranged in three layers of interlacing muscle fibers. It is known as the detrusor. This is the muscle that empties the bladder. The muscle coat at the neck thickens to form the internal sphincter of the bladder, which controls the opening of the bladder into the urethra. Functions of the bladder and the urination reflex When the bladder is full, the sensory nerves in the bladder wall send signals to the spinal cord. Signals are sent back to the bladder to make it squeeze and expel the urine out. The timing of this process can be regulated in adults and older children as the brain controls this process in them. While the bladder empties, the detrusor muscle of the bladder squeezes while the sphincter muscle relaxes, forcing urine out of the bladder into the urethra. This is called as the urination reflex. Voluntary control of the urination reflex is usually developed in the second or third year of life.