What is the urinary bladder?

What it is

• The urinary bladder is a musculomembranous sac which acts as a reservoir for the urine; and as its size, position, and relations vary according to the amount of fluid it contains, it is necessary to study it as it appears ( a ) when empty, and ( b ) when distended. ) In both conditions the position of the bladder varies with the condition of the rectum, being pushed upward and forward when the rectum is distended. The Empty Bladder.
• —When hardened in situ, the empty bladder has the form of a flattened tetrahedron, with its vertex tilted forward. It presents a fundus, a vertex, a superior and an inferior surface. The fundus is triangular in shape, and is directed downward and backward toward the rectum, from which it is separated by the rectovesical fascia, the vesiculæ seminales, and the terminal portions of the ductus deferentes.
• The vertex is directed forward toward the upper part of the symphysis pubis, and from it the middle umbilical ligament is continued upward on the back of the anterior abdominal wall to the umbilicus. The peritoneum is carried by it from the vertex of the bladder on to the abdominal wall to form the middle umbilical fold.
• The superior surface is triangular, bounded on either side by a lateral border which separates it from the inferior surface, and behind by a posterior border, represented by a line joining the two ureters, which intervenes between it and the fundus. The lateral borders extend from the ureters to the vertex, and from them the peritoneum is carried to the walls of the pelvis. On either side of the bladder the peritoneum shows a depression, named the paravesical fossa .
• The superior surface is directed upward, is covered by peritoneum, and is in relation with the sigmoid colon and some of the coils of the small intestine.
• When the bladder is empty and firmly contracted, this surface is convex and the lateral and posterior borders are rounded; whereas if the bladder be relaxed it is concave, and the interior of the viscus, as seen in a median sagittal section, presents the appearance of a V-shaped slit with a shorter posterior and a longer anterior limb—the apex of the V corresponding with the internal orifice of the urethra.