The urinary bladder is located in the lower abdomen, and is a hollow capsule-shaped organ, occupying the space underneath the kidney and the front of the large intestine. Its upper end is connected to the kidney by the ureters; its lower end is connected to the urethra, which opens to the external genitalia. Among the five zang-viscera and six fu-viscera, it occupies the lowermost position. Here, the remainder of the water is gathered after metabolism occurs. Its main physiological function is to store and discharge the urine.
The joint activity of the lung, spleen, and kidney, transform the water-fluid into body fluid. It then supplies nutrients to the entire body. After metabolism occurs, the remaining body fluid is transported back to the kidney and urinary bladder, where it becomes stored urine. Once it amounts to a certain quantity, it is discharged voluntarily out of the urinary bladder by means of the transformative function of kidney-qi. Thus Chapter 8 in Plain Questions states: "The urinary bladder is a reservoir official who is in charge of the storage of body fluids and its discharge through the transformative function of the qi." If the transformative function is abnormal, it may fail to perform the opening and closing function, and dysuria or retention of urine results. Since the storage and excretion of urine is related to the preserving function and transformative function of kidney-qi, disorders of enuresis and incontinence of urine are often treated through the kidney.
The urinary bladder communicates with the natural world via the urethra, allowing for exogenous damp-heat evil to possibly invade the bladder. This is characterized by urgent urination, frequent micturition, and pain in micturition, etc.
In addition, urine is formed from the body fluids thereby the amount of urination and the amount of body fluids influence each other. Urime may increase in volume, leading to a greater volume of body fluids consumed, and thus to a syndrome of deficient body fluid. Conversely, when the body fluid is impaired, the volume of urine will decrease.
