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Renin Angiotensin Mechanism.

Micturition Reflex.

 

Introduction.

  • Micturition is the process by which the urine stored in the urinary bladder is excreted out of the body.

  • In simple terms “Micturition” is the scientific name of the process of urination.

  • It is the result of involuntary and voluntary opening of internal and external urethral sphincters.

  • When the bladder is filled with urine around 150ml there is an urge to urinate, while it can be easily ignored.

  • When the bladder is filled by urine around 300-400 ml the urge to urinate becomes hard to ignore which results in opening of both the urethral sphincters causing excretion of the urine.

  • The nerves which play an important role are;

    • Pelvic nerve.

    • Pudendal nerve

    • Hypogastric nerve.

  • The receptors from which actions are initiated are,

    • B3 receptors (causes relaxation of detrusor muscles in bladder wall)

    • M3 receptors (causes contraction of detrusor muscles in bladder wall)

    • Nicotinic receptors (causes contraction of muscles of external urethral sphincter)

  • The process of micturition involves following steps;

    • On filling of the urinary bladder, the stretch receptors in the bladder get activated.

    • Stretch receptors send faster impulses to the sacral micturition center located in the sacral region.

    • The impulses are then relayed to “Pons' ' in the brain which activates parasympathetic nerves which cause contraction of detrusor muscles through M3 receptors.

    • Internal urethral sphincter opens involuntarily following contraction of the bladder.

    • External urethral sphincter is guarded by skeletal muscle which is relaxed by voluntary control causing voiding (urination).

    • When we are controlling the urination we are actually firing the “Pudendal Nerve” which causes contraction of the external urethral sphincter.

Commonly Asked Question.

  1. Write a short note on “Micturition Reflex”.
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