Lower GI Flashcards
Diarrhoea - MOA
Rotavirus- damages small bowel villi.
Invasive bacteria - damage epithelium.
Adhesive enterotoxigenic bacteria - adhere to brush border, activate AC, increase cAMP leading to:
- Na+ and Cl- secretion followed by water
- inhibition of Na+ and Cl- absorption.
Diarrhoea may be secondary to….
ANITBIOTICS.
Superinfection
Alter GI flora (1kg bacteria)
Clings mucin associated with pseudomembraneous colitis
ORLISTAT.
Pancreatic lipase inhibitor
Causes fatty diarrhoea (steathorrhea)
MISOPROSTOL (labour inducer)
Via cAMP
PPIs
Infection
OTHER
Digoxin toxicity, acarbose, metformin, iron salts
Oral rehydration therapy. MOA
Effective mainstay therapy.
Solution of electrolytes lost of diarrhoea e.g. Diarolyte.
Must be isotonic
Glucose allows transport of Na via a symporter INTO gut cells, water follows
Anitbiotics use in diarrhoea
Most simple infections are viral and antibiotics are of little value.
Infection usually self limiting.
If microbiology identifies a causative bacteria then appropriate antibiotics may be used.
Ciprofloxacin often used empirically for travellers diarrhoea.
Anti motility agents - Opioids- Examples, use and MOA
E.g. Loperamide and Codeine
Loperamide - does not penetrate BBB, efficient enters healthy recycling so retained largely in gut.
Codeine - analgesic, constipation may be a side effect.
Used for symptomatic relief, increase quality of life.
In infection they may reduced clearance of infective organisms and possibly prolong the infection.
Reduce tone and peristaltic movements of GI muscle by inhibiting presynaptic ACh release……
Normally:
Presynaptic depolarisation, Ca influx into cell, ACh released to synapse, contraction of GI muscle.
Anti motility drugs:
Loperamide binds to presynaptic mu- receptors, inhibits AC, K+ efflux from cell, hyperpolarisation, no Ca influx, no release ACh, no stimulating of GI muscle
Overall….
Reduced motility and increases transit time
Promotes reabsorption of water
Alpha-2 adrenoceptor agonists - action
e.g. CLONIDINE
Cause the same effects as opioids but via alpha-2 receptors leading to constipation.
Anti motility agents - Anitmuscarinics
E.g. DICYCLOVERINE
Antagonise muscarinic receptors on GI muscle
(Which would otherwise by stimulated by ACh).
TCAs are also constipating as a side effect through antagonism of muscarinic receptors.
Constipation - Definition and Treatment
Altered bowel habit, less than 3 motions a week
Cause might be drug-induced:
Opioids/ TCAs/ Antimuscarinics/ Diuretics (dehydration)
Treat
Best approach is balanced diet with roughage
Failing diet treatment –> Drugs
Constipation - Laxatives (4)
OSMOTIC LAXATIVES
e.g. lactulose
Enters colon unchanged and concerted by bacteria to lactic and acetic acid, raise fluid volume osmotically.
MAGNESIUM
Osmotic effect
Mg2+ also releases CCK (cholecystokinin) which increases GI motility
BULKING AGENTS
Ispaghula, methyl cellulose
STIMULANT LAXATIVES
Senna extracts, enter colon and metabolised to anthracene derivatives, which stimulate GI activity
Danton: irritant
IBS - Defintion
Common, long standing disorder
Present for at least 12 weeks within 1 year
Pain, bloating, relieved by defecation
Episodes of diarrhoea/ constipation
High psychological association - Functional GI disorder
IBS treatment
Lactulose/ Loperamide for respective Sx
ANTISPASMODIC AGENTS
Antimuscarinics - inhibit parasympathetic activity
Mebeverine - direct relaxant of GI smooth muscle, probably acting as a phosphodiesterase inhibitor
TCA Amitriptyline Low dose widely used and effective Provides some pain relief Alters sensitivity of sensory nerves in low GIT
Define IBD
Inflammatory bowel disease Encompasses Crohn's and UC Distinct inflammatory condition, high morbidity, relapsing and remitting courses. Both cases, causes unclear, include: Genetics Microbial Environmental aetiologies
IBD Clinical Features
Diarrhoea Faecal incontinence Rectal bleeding/ bloody diarrhoea Passing of mucus Cramping pains Weight loss
Crohn’s is mouth to anus so…
Mouth ulcers
Anal skin tags
IBD - Complications
Crohn’s
Malabsorption leading to folate/ iron deficiencies
Iron deficiency anaemia
UC
Blood loss may also lead to iron deficiency anaemia
IBD - Non GI Associations
Arthritis
Iritis
Uveitis
Increased risk thromboembolism
