Describe the gross anatomy, innervation and applied importance of the urinary bladder. Add a note on autonomous bladder.

Gross Anatomy of the Urinary Bladder

The urinary bladder is a hollow, distensible muscular organ located in the pelvic cavity, posterior to the pubic symphysis. It’s roughly pyramidal in shape when empty and ovoid when full.

Parts of the Urinary Bladder

• Apex: Points superiorly, beyond the pubic crest.
• Body: The main central portion.
• Base: The posterior part, where the ureters enter and the urethra exits.
• Neck: The funnel-shaped distal portion leading into the urethra.
• Trigone: A triangular area defined by the openings of the two ureters and the internal urethral orifice. It remains relatively fixed during bladder filling.

Relations of the Urinary Bladder

The bladder has important relationships with surrounding structures:

• Anterior: Pubic bones and rectus abdominis muscle.
• Posterior: Rectum (in males), vagina (in females), and seminal vesicles (in males).
• Lateral: Obturator internus muscles and pelvic fascia.

Layers of the Urinary Bladder Wall

The bladder wall consists of four layers:

• Mucosa: Transitional epithelium, allowing for stretching. Forms rugae when empty.
• Submucosa: Dense irregular connective tissue.
• Muscularis (Detrusor Muscle): Three layers of smooth muscle responsible for bladder contraction.
• Serosa/Adventitia: Superior surface covered by peritoneum (serosa); inferior and lateral surfaces have adventitia.

Innervation of the Urinary Bladder

The bladder’s innervation is complex, involving parasympathetic, sympathetic, and somatic nerves.

Parasympathetic Innervation (S2-S4)

Primarily responsible for bladder contraction. Pelvic splanchnic nerves carry preganglionic fibers to intramural ganglia within the bladder wall. Postganglionic fibers innervate the detrusor muscle, causing it to contract and the internal urethral sphincter to relax.

Sympathetic Innervation (L2-L4)

Primarily responsible for bladder relaxation and storage. Hypogastric plexus carries preganglionic fibers to sympathetic ganglia. Postganglionic fibers innervate the detrusor muscle, causing relaxation, and the internal urethral sphincter, causing contraction.

Somatic Innervation (S2-S4)

Controls the external urethral sphincter via the pudendal nerve, providing voluntary control of urination.

Applied Importance of the Urinary Bladder

Several clinical conditions affect the urinary bladder:

• Cystitis: Inflammation of the bladder, often caused by bacterial infection.
• Bladder Cancer: Most common type is transitional cell carcinoma.
• Urinary Incontinence: Involuntary leakage of urine. Stress incontinence (weak pelvic floor muscles) and urge incontinence (overactive bladder) are common types.
• Neurogenic Bladder: Bladder dysfunction due to neurological damage (discussed further below).
• Bladder Outlet Obstruction (BOO): Blockage at the bladder neck or urethra, often due to benign prostatic hyperplasia (BPH) in men.

Autonomous Bladder (Neurogenic Bladder)

An autonomous bladder, also known as a neurogenic bladder, results from disruption of the normal neurological control of the bladder. This can occur due to spinal cord injury, stroke, multiple sclerosis, diabetes, or other neurological conditions.

Types of Neurogenic Bladder:

• Reflex Bladder: Involuntary bladder contractions occur due to spinal cord injury below the sacral level. Patients may experience incontinence.
• Flaccid Bladder: Loss of both sensation and contraction due to spinal cord injury at or above the sacral level. Requires intermittent catheterization.
• Uninhibited Bladder: Loss of inhibitory control, leading to frequent, urgent urination.

Management: Treatment options include intermittent catheterization, medications to control bladder contractions, and, in some cases, surgical interventions.