Basic Physiology of Micturition and Defecation reflexes.

1. Micturition &
Defecation
Reflexes
Dr. Aniket Shilwant
BAMS. MD (Ayurveda Physiology)

2. Introduction to Micturition
▪ A process by which urine is voided from the urinary bladder.
▪ It is a reflex process.
▪ In grown up children and adults, it can be controlled voluntarily to some extent by the
support of Skeletal muscles.
▪ Micturition is executed by functional anatomy and nerve supply of Urinary Bladder.

3. Functional anatomy of Urinary Bladder
▪ Triangular hollow organ
▪ Location – Lower Abdomen Parts – Body & Neck Walls – Anterior & Posterior
▪ Internally –
Special Smooth Muscle
Detrusor muscle, Tripple layered – IL, MC, OL
Lined by multiple folded Mucous membrane - Rugae.
▪ Posterior wall – Trigone
▪ Upper two corners – Ureter openings, Lower narrow part – Neck, opens into Urethra
▪ Guarded by Internal Urethral Sphincter

4. Urethra
Male Urethra serves both functions - Urinary and Reproductive.
Female urethra only urinary function

5. Male Urethra
Length – 20cm long
Route – Origin from Urinary Bladder to Prostrate Gland below bladder and then to Penis.
Throughout its length, the urethra has mucus glands called Glands of Littre.
Male urethra is divided into three parts:
1. Prostatic urethra
Prostatic fluid and Seminal Fluid
2. Membranous urethra
From base of the prostate gland through urogenital diaphragm up to bulb of urethra.
3. Spongy urethra
Also known as cavernous urethra. Surrounded by corpus spongiosum of penis.
Bulbourethral Glands, also known as – Cowpers Glands

6. Female Urethra
▪ Narrower and shorter than male urethra.
▪ Length – About 3.5 to 4 cm long.
▪ Route – Origin from bladder traverses through urogenital diaphragm and runs along
anterior wall of vagina and terminates at external orifice of urethra, located between
clitoris and vaginal opening

7. Urethral Sphincters
1. Internal Urethral sphincter
Location – Between neck of the bladder and upper end of urethra.
It is made up of smooth muscle fibers and formed by thickening of detrusor muscle.
It is innervated by autonomic nerve fibers. This sphincter closes the urethra when bladder is emptied.
2. External Urethral sphincter
Location – In the urogenital diaphragm.
This sphincter is made up of circular skeletal muscle fibers.
It is innervated by somatic nerve fibers.

8. Nerve Supply
Urinary bladder and Internal sphincter –
▪ Sympathetic ANS –
1. L1, L2 – Hypogastric Ganglion – Hypogastric N – Detrusor Muscle and Internal Sphincter
2. Function – Relaxation of Detrusor muscle & Constriction of Internal Sphincter – Bladder Filling.
3. Sympathetic Nerve – Nerve of Filling
▪ Parasympathetic ANS –
1. Pelvic N or Nervus Erigens – S1, S2, S3 – Hypogastric Ganglion – Hypogastric N – Detrusor
Muscle and Internal Sphincter
2. Pelvic nerve carries impulses from Stretch receptors over the wall of bladder.
3. Function – Contraction of Detrusor muscle & Relaxation of Internal Sphincter – Bladder Emptying
4. Parasympathetic Nerve – Nerve of Emptying / Micturition

9. Nerve Supply
External sphincter –
▪ Somatic nerve fibers – Pudendal nerve – S2, S3, S4
▪ Function – Maintains Tonic contraction of Skeletal muscle fibers of external sphincter
▪ External sphincter remains constricted always
▪ During Micturition – Nerve is inhibited
▪ Relaxation of External sphincter – Voiding of Urine

10. Nuclear Centers for Micturition
▪ Lower centers –
▪ Spinal centers – Sacral and Lumbar segments.
▪ Spinal centers regulated by Higher centers.
▪ Higher centers –
▪ Inhibitory centers – Midbrain and Cerebral Cortex
▪ Facilitatory centers – Pons

11. Filling of Urinary Bladder
Stretch Receptors –
Stimulation
Afferent Impulses –
Pelvic Nerve
Sacral Segments
Efferent Impulses –
Pelvic Nerve
Detrusor Muscle - Contraction
Internal Sphincter – Relaxation
Stretch Receptors –
Stimulation
Afferent Impulses –
Pelvic Nerve
Pudendal Nerve –
Inhibition
External Sphincter –
Relaxation
Voiding of Urine
Urine flow into Urethra

12. Introduction to Defecation
▪ Voiding of feces is known as defecation.
▪ Feces is formed in the large intestine and stored in sigmoid colon.
▪ Expelled outside body through Anus, with proper urge and an appropriate stimulus.
▪ In absence of urge or stimulus, expulsion is prevented by tonic constriction of Anal
sphincters.

13. Defecation Reflex
▪ Mass movement drives the feces into sigmoid or pelvic colon.
▪ Sigmoid colon – Storage of feces
▪ Urge for Defecation –
▪ Only when feces enters Rectum by bulk mass movement.
▪ Intra-Rectal Pressure – 20 – 25cm of H2O
▪ Stimulus for Defecation differs from person to person.

14. Act of Defecation
▪ Preceded by Voluntary efforts
▪ Relaxation of External sphincters
▪ Compression of Abdominal contents & thus abdominal muscles
▪ Appropriate Posture
▪ Initially Rectum empty – Initiates when feces comes to rectum due to Mass movement –
Contraction of Rectum – Relaxation of Internal and External Anal Sphincters

15. Anal Sphincters
Internal Anal Sphincter
▪ Smooth muscle
▪ Parasympathetic Nerve – Pelvic Nerve
External Anal Sphincter
▪ Skeletal muscle
▪ Somatic Nerve – Pudendal Nerve
▪ Pudendal Nerve – Keeps External Anal Sphincter always constricted
▪ Inhibition of Pudendal Nerve – Relaxation of Sphincter

16. Mass movement of feces to
Rectum
Distension of Rectum
Stretch Receptors –
Stimulation
Afferent impulses – Pelvic
Nerve
Spinal centers - Sacral
segments
Efferent impulses – Pelvic
Nerve
Descending – Sigmoid – Rectum
– Strong contraction
Internal Anal Sphincter –
Relaxation
Pudendal Nerve –
Inhibition
External Anal Sphincter –
Relaxation

17. Resources
▪ Textbook of Medical Physiology – Guyton & Hall
▪ Ganong’s review of Medical Physiology
▪ Essentials of Medical Physiology – Sembulingam
▪ Images – Internet

18. Dr. Aniket A. Shilwant
Associate Professor, Sharir Kriya Dept.
GJPIASR, CVM University, New Vidyanagar, Anand
ayuraniket18@gmail.com
Thank You All !!!