Pharmacology of the Large Intestine Flashcards
Constipation can be defined as what 3 things?
- Infrequent bowel movements (typically 3 times or less/ week).
- Difficulty during defecation.
- Sensation of incomplete bowel evacuation.
What is the name for severe constipation where faeces becomes stuck in the rectum? What can some symptoms of this be?
Faecal impaction
- Vomiting
- Very tender abdomen
- Paradoxical diarrhoea (where soft stool from the small intestine bypasses the impacted matter in the colon).
Which types on the Bristol Stool Chart indicate diarrhoea?
Types 1 and 2.
Weight loss, anaemia, and constipation may indicate which pathology?
Colon cancer.
Alternating diarrhoea and constipation in an otherwise healthy patients may suggest which pathology?
IBS
Painful defecation in patients may indicate which pathology?
Anorectal disease.
List 5 broad causes of constipation.
- Dietary
- Hormonal
- Anatomical
- Side effects of medication
- Illness or disorder
What are the 4 classes of drugs used to treat constipation?
- Bulk laxatives
- Osmotic laxatives
- Faecal softeners
- Stimulant purgatives
What are the 2 brands of bulk laxatives and what are their active ingredients?
- Citrucel - methylcellulose
2. Fybogel - ispaghula husk
How do bulk laxatives work?
By retaining fluid within the stool and increasing faecal mass, leading to stimulation of peristalsis. They also have stool-softening properties.
How do osmotic laxatives work?
Promote movement of fluid across the wall into the GI lumen, which accelerates transit and causes colonic distension, stimulating purgation.
Name 3 types of osmotic laxatives.
- Saline purgatives
- Macrogols
- Lactulose
What is the onset of action of saline purgatives? What are they mainly used for?
Rapid onset, 1-2 hours. Used for bowel prep prior to procedure.
What substance are Macrogols?
Inert polymers of ethylene glycol.
What substance is lactulose?
A semi-synthetic disaccharide of fructose and galactose.
How does lactulose work as an osmotic laxative?
- Lactulose is converted into its two component monosaccharides (fructose and galactose) by colonic bacteria.
- Fermentation yields lactic acid and acetic acid, which function as osmotic laxatives as they are not absorbed.
How do faecal softeners work?
They are anionic surfactants which lower the surface tension at the oil-water interface, allowing water or fats to enter the stool, causing faecal matter to soften.
Give 2 types of stimulant purgatives.
- Bisacodyl
2. Senna
How does Bisacodyl work and how is it administered usually?
Usually given as a suppository, it stimulates the rectal mucosa, resulting in mass movements and defecation in 15-30 minutes.
What is Senna made from?
Contains derivatives of anthracene combined with sugars to form glycosides.
What does Senna directly stimulate? What effect does this have? What effect does Senna have on the motility of the distal colon?
Senna stimulates the myenteric plexus, which decreases the frequency of haustral contractions, leading to softer stools due to decreased mixing.
Senna increases the frequency and force of mass movements, which moves stool towards the rectum.
Overuse of laxatives can lead to which condition?
Cathartic colon
What is a medical consequence of cathartic colon?
Fluid and electrolyte imbalance.
What are the 4 types of diarrhoea?
- Secretory diarrhoea
- Osmotic diarrhoea
- Motility-related diarrhoea
- Inflammatory diarrhoea
What are the 3 drug classes of anti-diarrhoeal agents?
- Oral rehydration therapy
- Anti-infective agents
- Anti-motility agents
What substance is oral rehydration therapy? How does it work?
An isotonic or hypotonic solution of glucose and sodium chloride.
It exploits the ability of glucose to enhance the absorption of Na+ and hence water.
Severe Campylobacter infections may require which antibiotics?
Erythromycin or Ciprofloxacin.
What is the active ingredient in Imodium?
Loperamide
How does Loperamide affect the circular and longitudinal smooth muscles of the intestines?
Increases activity of the circular smooth muscles
Decreases activity of the longitudinal smooth muscles
