Corpus: Urinary bladder

The urinary bladder is an expandable hollow organ located in the pelvis, primarily responsible for storing urine. Together with the urethra, it forms the lower urinary tract.

The urinary bladder is situated in the lesser pelvis and is partially covered by peritoneum on its cranial and dorsocranial sides, particularly around the apex and part of the body (corpus vesicae). The bladder is anatomically divided into several regions:

• Apex of bladder: The cranioventral tip of the bladder, covered by peritoneum.
• Body of bladder: The main body of the bladder.
• Fundus of bladder: The base of the bladder, where the urethra emerges at the tip of the vesical trigone in the internal urethral orifice (ostium urethrae internum). This area is bounded cranially by the plica interureterica, a mucosal fold between the ureteral openings.
• Vesical neck: The funnel-shaped neck of the bladder leading into the urethra.

The ureters open laterally into the bladder and run intramurally for about 2 cm, forming mucosal prominences (columnae uretericae) that are visible from the inside. The ureteral openings are known as ureterostia or ostia ureterum and are connected by the plica interureterica.

The bladder is surrounded by loose connective tissue called the paracystium and is held in position by the pelvic floor and various ligamentous peritoneal duplications, including:

• Lateral ligament of bladder
• Median ligament of bladder
• Round ligament of bladder

These ligaments continue as part of the parietal peritoneum to the umbilicus after leaving the pelvis. Additionally, muscle-ligament apparatuses support the bladder's position:

• Pubovesical ligament (or pubovesical muscle) and puboprostatic ligament (or puboprostatic muscle)
• Rectourethralis muscle
• Vesicovaginalis muscle (in females) or Vesicoprostaticus muscle (in males)

2.1. Innervation

The bladder receives its innervation from branches of the sympathetic nervous system (Th12 - L2) and parasympathetic nervous system (S2 - S4). These fibres form a nerve plexus within the bladder wall known as the vesical plexus.

2.2. Arterial supply

The arterial supply to the bladder comes from the superior vesical artery (from the umbilical artery) and the inferior vesical artery (from the internal iliac artery). Additional supply can come from the middle rectal artery and the internal pudendal artery.

2.3. Venous outflow

Venous drainage from the bladder wall occurs through the vesical venous plexus, which drains into the internal iliac vein.

The bladder is covered by peritoneum on its cranial and dorsocranial sides. It is positioned ventrally to the pubic symphysis and caudally to the fascia of the levator ani muscle.

The bladder lumen is lined with transitional epithelium (urothelium), beneath which lies the lamina propria or submucosa, consisting of loose connective tissue with collagen and elastic fibres, and a dense capillary plexus. The tunica muscularis, located beneath the submucosa, is composed of smooth muscle layers that form the detrusor muscle, responsible for bladder contraction during urination. The outermost layer is the tunica adventitia, which connects the bladder to surrounding structures. At the apex, the muscle layer is covered by a tunica serosa, part of the peritoneum.

The bladder functions as a reservoir for urine, capable of holding approximately 500 ml of fluid. Stretch receptors in the bladder wall trigger the urge to urinate as the bladder fills. The maximum bladder capacity ranges from 900 to 1500 ml, depending on body size.

The bladder can be affected by various pathologies, including urinary retention, which may lead to bladder dilation and incomplete emptying. Bladder infections, particularly in women, can lead to cystitis, often caused by ascending bacteria through the urethra.

7.1. Diagnostics

Diagnostic methods for bladder evaluation include:

• Endoscopy (cystoscopy)
• Imaging techniques:
  • Ultrasound (first choice)
  • X-ray with contrast
  • Micturating cystourethrography (MCU)
  • Excretory urography
  • MRI
  • CT
• Functional tests:
  • Uroflowmetry
  • Flow EMG
  • Cystomanometry

Laboratory diagnostics (urine status) provide further indications of pathological changes.

7.2. Diseases

Diseases of the urinary bladder include cystitis and urothelial carcinoma. Cystitis is an inflammation of the bladder, often resulting from bacterial infection. Urothelial carcinoma is a type of bladder cancer that originates from the urothelium, the bladder's inner lining. This type of cancer is associated with various risk factors, including smoking and chronic inflammation.