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Unit 10 > Week 5: Defecation and Micturition > Flashcards

Week 5: Defecation and Micturition Flashcards

1
Q

What gross anatomical part of the sympathetic nervous system is involved in defecation and micturition?

A

SNS has thoracolumbar outflow (t1 to L2)
Specifically lumbar splanchnic (L1,2,3) which becomes the hypogastric nerve travelling through the inferior hypogastric plexus to become pelvic nerves

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2
Q

What is the gross anatomy of the parasympathetic nervous system involved in defecation and microturition?

A

PNS has cranioscaral outflow
In this scenario - sacral spinal nerves are involved - form pelvic splanchnic nerves which travel through the inferior hypogastric plexus to form pelvic nerves.

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3
Q

What is the ganglionic transmission like in the sympathetic nervous system?

A

Preganglionic release ACh
Post ganglionic release noraderenaline, adrenalin or Ach (eccrine sweat glands or in junctional receptors)
The effect depends on the receptor

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4
Q

What is the ganglion transmission like in parasympathetic nervous system?

A

Preganglionic release ACh
Post ganglioninc ACh
The cell receptor tends to be muscurinic

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5
Q

Where are the two intramural plexus of the enteric nervous system located?

A

Myenteric - between longitudinal and circular smooth muscle in muscuris external
Submucosal - deep to the circular smooth muscle (this is smaller than the myenteric)

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6
Q

How do the myenteric and submucosal plexus initiate communication with the CNS?

A

Via sensory afferents.

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7
Q

Where are the preganglionic fibres, ganglions and postganglionic fibres of the parasympathetic nervous system found in the gut?

A

Preganglionic:
Vagus (CNX) in midgut and forgeut
Pelvic splanchin S2-4 in hindgut.

Ganglions - found in both the myenteric and submucosal plexus

Postganglionic fibres - found in ENS

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8
Q

Where are the preganglionic fibres, ganglions and postganglionic fibres of the sympathetic nervous system found in the gut?

A

Preganglionic fibres - originate from lateral horn of spinal cord from T1 to L2

Ganglion - prevertebral splanchnic ganglion

Postganglionic - ENS plexus

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9
Q

What sensory innervation is present in the gut?

A

Visceral afferents can communicate with the CNS
Pain - via parasympathetic (lower GIT) or sympathetic (upper GIT)
Distenstion - parasympathetic
Enter the spinal cord via the dorsal nerve roots into the grey horn of the spinal cord.

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10
Q

What are the different functions that the enteric nervous system can effect?

A

Smooth muscle
Gland secretion
Endocrine function
Blood vessels.

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11
Q

What are the different movements in peristalsis?

A

Haustral contractions - slower
Mass movement - faster

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12
Q

What is different about the anatomy of the internal and external anal sphincter?

A

internal - smooth muscle, autonomic control - ENS
External - skeletal muscle, somatic control - pudendal nerve

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13
Q

What are the effects of sympathetic control over defecation?

A

Rectal smooth muscle is relaxed - no defecation
Internal sphincter is under tonic contraction

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14
Q

What are the reflex pathways in the defecation reflex?

A

Urge to defecate appears when stretch receptors are activated
Unconscious control=
intrinsic pathway - activates myenteric plexus and imitates local peristalsis
Extrinsic pathway - activates parasympathetic input to further stumlate peristalsis and cause internal anal sphincter relaxation
Voluntary control=
When social acceptable - relaxation of external anal sphincter and the pubrorectalise via the pudendal nerve allows defecation. Postponed if this does not occur

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15
Q

What is the intrinsic reflex in defecatino?

A

Stimulus - distention in rectum activates stretch receptors in rectal wall
Causes local activation of myenteric plexus - causes smooth muscle to contract in the sigmoid colon and rectum
Response - weak peristalis causing feaces to table distally towards the rectum

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16
Q

What is the extrinsic reflex in defecation?

A

distention in the sigmoid colon and rectum activates stretch receptors in the wall.
Activates sensory afferents - relay and terminate in the spinal cord and activate parasympathetic nerves (S2-S4)
Causes strong peristalsis causing feaces to travel distally to rectum and relaxation of the internal anal sphincter.

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17
Q

What is the role of voluntary input in defecation?

A

Inhibition of the external anal sphincter via the pudendal nerve (s2-s4) causes relaxation of the striated muscle of the sphincter

Pubrectalis relxes

Valsalva manoeuvre - close glottis, deep inhalation, contraction of abdominal muscles.

18
Q

What is the role of pubrectalis in faecal continence?

A

Part of pelvic floor
Forms a sling around the anal rectal junction - must relax to allow defecation

19
Q

What are some common causes of faecal incontinence?

A

Youth - not yet toilet trained, need to be trained to develop voluntary control which then normally persists for the rest of the adult life

Temporarly loss may occur in diahorrea for large stool volume

Other causes: childbirth, nerve injury or surgery, causa equina syndrome

20
Q

How does a spinal cord injury present affect the defecation reflex?

A

Loss of sensory afferents to cerebral cortex so..
Loss of voluntary motor function

Short arc intrinsic reflex normally remains intact

Long arc parasympathetic reflex may or may not be intact. Is lost if injury is below or at L1 level as sensory afferents no longer able to reach L1.

21
Q

What is reflex bowel damage?

A

Damage to the spinal cord above T12/L1 (UMN)
results in a los of bowel sensation
loss of descending control from the brain
Defecation reflex still intact
Sphincters still have tone

22
Q

What is a flaccid bowel damage?

A

Damage belwo T12/L1 (LMN)
Loss of bowel sensation
Loss of descending control from the brain
Loss of defecation reflex
Loss of reflex tone of sphincters.

23
Q

What are the different sections of the male urethra?

A

The prostatic urethra - in the prostate gland
The membranous urethera - travels through pelvic floor
The penil urethra - after gone through the pelvic floor to terminal

24
Q

What somatic nerve gives control over the defecation and micturition reflex?

A

Pudendal nerve (s2,3,4)

25
Q

What afferent nerves are involved in the pelvis for the defecation and micturition reflex?

A

Afferent nerves follow the autonomic nerves
Mainly the parasympathetic

26
Q

What is the pain line?

A

The peritoneal line (where peritoneum stops covering organs)
Above this line pain afferents tend to travel with sympathetic nerves
below this line pain afferents tend to travel with parasympathetic nerves

27
Q

What receptors are effected in the bladder by nerves affecting micturition?

A

Pelvic nerve (PNS) affects M3 receptors by releasing Ach - in bladder wall
Hypogastric nerves releases Noradrenaline to affect Beta 3 receptors in the bladder wall and Alpha 1 receptors int he urethra
Pudendal nerve (somatic) releases ACh to effect nicotinic receptors on the external urethral sphincter contained within the urogenital diaphragm around the urethra.

28
Q

What is the role of sympathetic nerves in micturition?

A

Relaxes detrusor muscle - allows volume of bladder to increase (beta 3 receptors)
Contract internal urethral sphincter - prevents leakage (alpha 1 receptors)

29
Q

What is the role of the parasympathetic nerves in micturition?

A

Contract detrusor muscle - decrease volume of the bladder
Contract urethral muscle - cause expulsion of urine

30
Q

What is the role of somatic nerves in micturition?

A

Contracts externa urethral sphincter
Contracts levator ani
Prevent urination

Lack of stimulation causes alternative

31
Q

What is the mechanism of the guarding reflex in micturition?

A

Low-level vesical afferent firing during storage
Stimulates sympathetic outflow in hypogastric nerve - causes the bladder to relax and internal urethral sphincter to contract - this enables the bladder to fill correctly.
Visceral afferent fibres increase pudendal outflow to the external urethral sphincter so contracts
Pontine storage centre - also increase external urethral activity

This prevents urination

32
Q

What is the mechanism of the micturition reflex?

A

Bladder stretch cause intense afferent firing which activates the spinobulbospinal reflex
- afferent fibres active relay neurone in the periaqueduct grey (PAG) in pons
- stimulates parasympathetic outflow causing bladder (detrusal) and urethral smooth muscle to relax
- inhibition of sympathetic (hypogastric nerve) and pudendal outflow (external urethral sphincter relax)

33
Q

What voluntary factors can contribute to micturition?

A

Pudendal nerve - inhibition - relaxation of external urethral sphincter
Laryngeal closed airway/glottis
Deep breath in to retain air in thorax - increases thoracic pressure
Contract abdominal muscles - increase intra-abdominal pressure
This aids defecation, micturition and child birth.

34
Q

Why do we not urinate uncontrollably?

A

Element of somatic control develops in childhood
Sacral afferent inputs communicate with PAG in pons then many area in brain including insula and cingulate cortex - ensures socially acceptable
Leads to sacral efferent output that can control urination.

35
Q

What are the two different spinal cord injury presentations on the bladder?

A

Automatic bladder
Atonic bladder

36
Q

How does spinal cord injury result in automatic bladder?

A

Upper motor neuron lesion (above sacrum) - affects afferents and efferent to the CNS
Micturition in initially blocked and cathetrisation needed
Eventually alternative reflex in established
Loss of bladder sensation
Emptying controlled by bladder reflex (enteric, parasympathetic and sympathetic - depending on height of lesion)

37
Q

How does spinal cord injury result in atonic bladder?

A

Lower motor neuron lesion (at sacrum)
Loss of sensory input
loss of micturition reflex
leads to overflow incontinence - unable to empty bladder fully leads to leakage which may or may not be expected.

38
Q

What are the blue labels?

A

Anal column
Anal sinus
Anal valve

39
Q

What are the yellow labels?

A

Deep superficial and subcutaneous
External anal sphincter

40
Q

What are the red labels?

A

Pectinate line
Anocutanoues line

41
Q

What is the black label?

A

Internal anal sphincter

42
Q

What is the purple label?

A

Pelvic floor/Levator ani
Illiococcygeus
Puborectalis

Unit 10 (37 decks)

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