GI 209 Constipation (&IBS) Flashcards
What nervous system supplies the large bowel? How does this work?
Enteric nervous system - works independently via programmed reflexes but activity is modified by the ANS
Where does the myenteric plexus sit and what does it control?
Between the longitudinal and circular muscles of the GIT system wall and controls the muscularis propria
What does the submucosal plexus control?
Muscularis mucosae
What does the parasympathetic nervous system do in the large intestine?
Increase motility, increase acid and glandular secretions via the vagus nerve and pelvic splanchnic nerves S2-S4
What does the sympathetic nervous system do in the large intestine?
decrease motility and glandular secretions, increases enzymes - via superior and inferior mesenteric ganglia
What does the somatic sensory system do in the large intestine?
Register pain via spinal ganglia
Where does absorption of FA’s, fluids and electrolytes occur in the large intestine alongside bacterial fermentation?
Ascending and transverse colon
What is the main way bowel contents get moved distally throughout the day?
Mass persistalsis 1-3x a day
What generally moves flatus and mixes up bowel contents?
Non-propulsive segmentation by circular muscle contractions - produces the segmented appearance of the large intestine
What blood vessels supply the colon and rectum?
Superior and inferior mesenteric vessles
What is persistalsis induced by hormonally in the gut?
5HT release from neuroendocrine cells in response to luminal distention
What is the internal rectal sphincter controlled by?
ANS - involuntary reflexes
What type of muscle makes up the external rectal sphincter?
Striated muscle
What factors maintain continence?
Sphincter tone Anorectal angle Intact central control Intact relfex pathways Renal capacity
What is the function of the descending bowel -> rectum?
Mostly as a reservoir and for defecation
Why can constipation lead to faecal impaction?
Because the stool remains in the bowel and more and more water is removed making it harder to pass until it can no longer be passed without medical or surgical intervention
What are some of the causes of reduced motility in the colon?
Hirschsprungs disease Paralytic ileus Stress Hypercalcaemia Constitutive
What is hirschsprungs disease?
Absent myenteric nerves in the distal colon - congenital abnormality
= Chronic obstruction and megacolon
What can cause a paralytic ileus?
Post abdominal surgery or hypokalaemia
What does stress reduce gut motility?
Action of sympathetic nerves on the ANS
Why does hypercalcaemia cause reduced gut motility?
Interferes with proper functioning of the neuromuscular junction
What drugs can cause constipation?
Opiates Antidepressants Anticholinergic drugs/effects Iron supplements Magnesium containing antacids 5HT3 receptor antagonists used to treat diarrhoea in IBS
What is a common general cause of constipation?
Lack of stool bulk
What is a colonic transit study?
Plastic rings ingested, none should be left on Xray at day 5
If they are scattered throughout colon = slow transit
If they are gathered in rectum = outflow obstruction
What will a barium enema show?
Obstructions
Megacolon/rectum
How would you exclude a defecation obstruction as a cause of constipation?
Defecating proctogram
What neurological causes may result in constipation?
MS
Peripheral neuropathy from diabetes
What is the 1st line treatment for constipation?
dietary advice - increase fibre and water in diet
What is the 2nd line treatment for constipation?
Pharmacological intervention
What is the 1st pharmacological agent used to help constipation?
Bulk-forming laxative e.g. fybogel to give mass to stool and stimulate peristalsis
What is the 2nd pharmacological agent to be used to help constipation?
Addition or switching to an osmotic laxative e.g. lactulose or macrogols (movicol)
How do osmotic laxatives work?
Are retained in the bowel so create a hyperosmolar environment meaning water is drawn into the bowel by osmosis
What is the 3rd pharmacological intervention for constipation?
Stimulant laxartive e.g.senna
What is the 4th pharmacological intervention for constipation?
Surdace wetting agent - e.g. docusate which reduces surface tension of the stool
What new drug can actively stimulate peristalsis?
Prucalopride - 5HT4 agonist
What are the three main surgical interventions for constipation?
Colectomy, antegrade colonic enema, sacral nerve stimulation
