Continence and voidance

Question 1

Anal sphincters

Answer 1

Internal = smooth muscle, ANS
External = striated muscle, somatic

Question 2

Anal canal structure

Answer 2

Longitudinal folds called anal columns

Network of veins

Question 3

Enteric NS plexuses

Answer 3

Myenteric (auerbachs) = between muscle layers
Submucosal (meissners) = in submucosa layer
can function alone, however can be modulated by sym/parasym

Question 4

Neurotransmitters of ENS

Answer 4

PNS = ACh, acts at M receptors to increase motility 
ANS = NA, acts at alpha and beta receptors, inhibits smooth muscle

Question 5

Innervation of the distal gut

Answer 5

Parasym = S1-4, pelvic nerves, promote defamation and motility
Sym = L1-3, mesenteric and pelvic plexuses, promotes continence and contraction of internal sphincter 
Somatic = pudendal nerves, innervate external anal sphincter

Question 6

Process of defecation

Answer 6

Stimulus = distension of the rectum
Short reflex = activation of nerves (myenteric plexus) in sigmoid colon, increases local peristalsis, moves towards rectum and acts as positive feedback loop
Long reflex = stimulates parasym motor neurons in sacral spinal cord, pelvic nerves, increase in peristalsis in the large intestine, mass movement. pelvic nerves causes relaxation of pelvic sphincter
Voluntary relaxation of external sphincter required to defecate

Question 7

Internal sphincter control

Answer 7

Contract = NA bind to alpha 1
Relax =isoprenaline/salbutamol bind to alpha receptors, Gs, relaxation
ACh. carbachol cause relaxation through NO production

Question 8

Urinary tract innervation

Answer 8

Parasym = pelvic nerve, S2-3, stimulate detrusor smooth muscle, M3 receptors, emptying 
Sym = hypogastric nerve, release NA, inhibit detrusor muscle and stimulates internal sphincter 
Somatic = pudendal nerve from S2-4, stimulate external sphincter, ACh

Question 9

Empty bladder mechanisms

Answer 9

Low level of pelvic nerve firing from visceral afferent
Stimulate hypogastric nerve through thoracic/lumbar
Activates SNS, constrict smooth muscle sphincter and keeps bladder relaxed
brain signals to activate hypogastric and inhibit pelvic

Question 10

Micturition

Answer 10

High level of visceral afferent firing
Inhibit hypogastric and pudendal, stimulate pelvic nerve (via micturition centre and brain signals spinal cord)
Inactivate sympathetic and somatic, activate parasym
causes sphincter to relax and bladder wall to contract

Question 11

Treatment for incontinence from overactive bladder

Answer 11

Muscarinic antagonisti

blocks parasym

Question 12

Treatment for outflow obstruction

Answer 12

Alpha 1 antagonists

Question 13

function of rectum

Answer 13

expandable organ, temporary storage of faeces

movement of faeces into the rectum promotes urge to defecate

Question 14

defecation signals entering the spinal cord also stimulate

Answer 14

taking a deep breath
closure of glottis
contraction of abdominal wall muscles

Question 15

factors controlling continence

Answer 15

consistency of stool
delivery of colonic content to the rectum
renal capacity and compliance 
anorectal sensation 
function of the anal sphincter mechanism

Question 16

pharmacology for internal anal sphincter

Answer 16

decreases IAS tone: NO donors, calcium channel blockers, sildenafil, bethanecol
increases IAS tone: alpha adrenoreceptor agonist

Question 17

voiding reflex

Answer 17

activate stretch receptors
back to spinal cord
activates inter neurones
activates pelvic efferent 
contraction of urinary bladder