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CLINICAL APPLICATION NOTES
INTRODUCTION TO URODYNAMICS I: Lower Urinary Tract Anatomy and Physiology
Chemical and Electronic Control of the Micturition Reflex

The MICTURITION REFLEX is a two phase cycle that serves as a protective mechanism for the kidneys. It consists of the STORAGE (filling) PHASE and the EMPTYING PHASE. This reflex is uninhibited at birth, and we learn to inhibit (or control) it as we mature.
The ability to control the MICTURITION REFLEX is dependent upon three “systems” being intact. These are:

  1. NEURORECEPTORS in the detrusor muscle and bladder neck.
  2. PROPRIOCEPTIVE peripheral detrusor innervation.
The NEURO/SENSORY PATHWAY between the brain, spinal cord and bladder (the REFLEX and REGULATORY/SENSORY loops).
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Neuroreceptors

 

The NEURORECEPTORS that control the micturition reflex are PARASYMPATHETIC (cholinergic) and SYMPATHETIC (Alpha or Beta).

  • The PARASYMPATHETIC (cholinergic) receptors are throughout the “body” of the bladder, trigone and bladder neck.
  • The SYMPATHETIC (beta) receptors are throughout the bladder, more densely populating the “dome” and less dense in the trigone.
  • The SYMPATHETIC (alpha) receptors are densely located in the bladder neck (proximal urethra) and more sparsely populate the trigone.

Receptors During Storage

 

During the STORAGE phase,

1. Parasympathetic (cholinergic) receptors are inhibited, prohibiting detrusor muscle contraction.

2. Sympathetic receptors are stimulated, resulting in:

  • Relaxation of beta controlled detrusor muscle and increased stretch capacity of the bladder dome.
  • Contraction of the alpha controlled bladder neck.

Receptors During Emptying

 

During the EMPTYING phase,

1. Sympatheic receptors are inhibited, resulting in:

  • Cessation of the beta assisted stretch of detrusor muscle.
  • Relaxation of the alpha controlled bladder neck.

2. Parasympathetic (cholinergic) receptors are stimulated, strengthening the detrusor contraction

 

Intro to Urodynamics TOC
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