What organ is the bladder

The bladder of an adult is located in the front of the pelvis and is connected to the pubic symphysis. The posterior parts are the seminal vesicles, the ampulla of the vas deferens, and the rectum. The back part of a woman is the uterus and vagina. The bladder neck is adjacent to the prostate in men and to the urogenital diaphragm in women. There is a membrane covering the bladder, which is adjacent to the small intestine in men and the uterus in women. The bladder of a newborn is located higher than that of an adult, and most of it is inside the abdominal cavity.

What is the bladder?

When the bladder is empty, the tip of the bladder does not exceed the upper edge of the pubic symphysis. When the bladder is full, the tip of the bladder rises above the pubic symphysis. At this time, the peritoneum of the anterior abdominal wall folded toward the bladder also moves upward, making the anterior and lower wall of the bladder directly attached to the anterior abdominal wall. At this time, bladder puncture or bladder surgery above the pubic symphysis can avoid damaging the peritoneum and disturbing the peritoneal cavity. The bladder of a newborn is located higher than that of an adult, and most of it is located in the abdominal cavity. As age increases and the pelvis develops, the position of the bladder gradually descends and reaches the adult position around puberty. In the elderly, the pelvic floor muscles are relaxed and the bladder is located lower.

The structure of the bladder

The bladder is a cone-shaped sac-like muscular organ located in the front of the pelvic cavity. The adult bladder is located in the pelvis and is an organ that stores urine. The infant's bladder is higher and located in the abdomen, with its neck close to the upper edge of the pubic symphysis. By the age of 20, the bladder gradually descends into the pelvis due to the expansion of the pubic bone, the evolution of the role of the sacrum, and the tilt and depth of the pelvis. When empty, the bladder is cone-shaped. When full, it becomes oval in shape, with the top rising above the pubic bone. The adult bladder capacity is 300 to 500 ml of urine. There is a triangular area on the inner surface of the bladder base, called the bladder triangle, which is located between the line connecting the two ureteral orifices and the internal urethral orifice. At the lower part of the bladder, there is the internal opening of the urethra, and the two posterior upper corners of the bladder triangle are where the ureters open.

Bladder wall

The bladder wall is composed of three layers of tissue: the mucosa, muscularis, and adventitia. The muscular layer is composed of smooth muscle fibers, called the detrusor. The contraction of the detrusor increases the pressure inside the bladder and forces urine to be discharged from the urethra. There is a thick circular muscle at the junction of the bladder and urethra, which forms the internal urethral sphincter. The contraction of the sphincter closes the internal opening of the urethra, preventing urine from leaking out of the bladder.

The bladder wall is divided into four layers: the serosa, muscle, submucosa, and mucosa.

Serosa: The serosa is a honeycomb fatty tissue that surrounds the posterior and superior sides and top of the bladder.

Muscle layer: ① Detrusor muscle: Detrusor muscle is the general term for the bladder wall muscles, which are composed of smooth muscle. It is divided into three layers: the inner and outer layers are longitudinal muscles, and the middle layer is circular muscles. The circular muscle is the thickest and strongest. ② Bladder trigone muscle: The trigone muscle is the muscle tissue outside the bladder wall layer. It originates from the longitudinal muscle fibers of the ureter and spreads out inward, downward, and forward in a fan-like manner. The part that extends inward and combines with the opposite side muscle to form the interureteric ridge, which extends downward and forward to the posterior urethra and is the Bell muscle. There is another group of left and right muscle fibers that cross in the center of the triangle to become the bottom muscle of the triangle.

Mucosal layer: The mucosal layer is a very thin layer of transitional epithelial tissue, which is continuous with the ureter and urethral mucosa. The mucosa is very smooth in the triangular area because it is closely connected to the underlying muscles, but it has prominent folds in other areas, which disappear when the bladder is full. The mucosal layer contains glandular tissue, especially in the bladder neck and trigone.

The submucosal layer only exists in the area outside the triangle. It is a loose tissue with rich blood vessels and elasticity. It tightly connects the mucosa and muscle layer to each other.