11.1 Lower Urinary Tract

Lower Urinary Tract Overview

• The lower urinary tract (LUT) is responsible for urinary storage, voiding, and protection from infection.
• It comprises the bladder and urethra.
• The LUT is controlled by a complex neural system in the lower pelvis.
• The micturition cycle alternates between storage and voiding phases. Storage takes up 98% of the time.

Learning Objectives

• Define the lower urinary tract and its functions.
• Describe the urinary sphincter unit.
• Illustrate the neural control of the LUT.
• Explain the micturition cycle.

Key Concepts and Definitions

• Lower Urinary Tract (LUT): Composed of the bladder and urethra, responsible for urine storage, voiding, and protection from infection.
• Micturition: The process of voiding urine from the bladder.
• Detrusor Muscle: The smooth muscle of the bladder wall that contracts to void urine.
• Internal Urethral Sphincter: An involuntary smooth muscle sphincter at the bladder neck.
• External Urethral Sphincter: A voluntary striated muscle sphincter controlling urine release from the bladder.

Clinical Applications

• Case Study: A patient with detrusor overactivity experiences incontinence due to difficulty deferring the urge to void.
• Diagnostic Approach: Urodynamic testing assesses coordination between detrusor contraction and sphincter relaxation.
• Treatment Options: May include behavioral training (bladder training) and medications (antimuscarinics).
• Complications/Management: Incomplete bladder emptying can lead to urinary retention and recurrent UTIs

Pathophysiology

• Pathway/Mechanism: The micturition cycle is controlled by central and peripheral nervous systems, switching between storage and voiding.
• Diagram: A diagram illustrating the roles of parasympathetic, sympathetic, and somatic control in the micturition cycle is needed.

Pharmacology

• Antimuscarinics: Reduce detrusor overactivity, used to treat overactive bladder.
• Beta-3 Adrenergic Agonists: Relax the detrusor muscle, promoting bladder filling and increasing storage capacity.

Differential Diagnosis

• Overactive Bladder: Urgency with or without incontinence, often due to detrusor overactivity.
• Stress Urinary Incontinence (SUI): Urine leakage during increased intra-abdominal pressure.
• Overflow Incontinence: Occurs when the bladder does not fully empty, leading to dribbling.

Investigations

• Urodynamic Testing: Measures bladder pressure, capacity, and function.
• Bladder Diary: Tracks voiding patterns to identify bladder function issues.
• Urinalysis: Examines urine to detect infections, hematuria, and other abnormalities.

Summary and Key Takeaways

• The LUT has two main functions: urine storage and voiding
• The micturition cycle involves a switch controlled by sympathetic, parasympathetic, and somatic nervous systems.
• Key muscles involved include the detrusor, internal and external urethral sphincters.