Flashcards in Session 13 - Shitting 'n Sickness Deck (62)
What is management of peptic ulcer if due to h.pylori
H2 antagonist - Cimetidine
What are four defensive aspects of the gastric mucosa
Cell replication and restitution
Mucous membrane barrier
What are the three main agressive factors of the gastric mucosa
Outline the phases of control of gastric secretion
- Sensory stimulus and act of swallowing stimulates Ach release, stimulating parietal cells
- Distension, further stimulating Ach release
- Buffering of stomach acid stimulates gastrin release
- Small peptides cause upregulation of gastrin
- CCK and GIP released once chyme enters duodenum, which inhibit gastrin.
- Low pH also inhibits gastrin
Outline the plexi of the enteric nervous system (four), including where they can be found
o Auerbach’s Plexus
Between circular and longitudinal muscle layers
o Meissner’s Plexus
o Henle’s Plexus
Circular muscle adjacent to submucosa
o Cajal’s Plexus
Circular muscle adjacent to longitudinal muscle
How do the plexi control the GI tract?
Together these autonomic gonglionated plexi control the functioning of the GI tract through complex local reflex connections between sensory neurones, smooth muscle, mucosa and blood vessels.
Extrinsic parasympathetic fibres from the vagus are excitatory, extrinsic sympathetic fibres are inhibitory.
What are the three main reflexes of the GI tract
o Intestino-intestinal inhibitory reflex
Distension of one intestinal segment causes complete intestinal inhibition (Peristalsis)
o Anointestinal Inhibitory Reflex
Distension of anus causes intestinal inhibition
o Gastrocolic and Duodenocolic Reflexes
Stimulates motility after material has entered the stomach or duodenum
What are laxatives used for?
To hasten transit time in the gut and encourage defecation. Laxatives are used to relieve constipation and to clear the bowel prior to medical and surgical procedures.
What is the best regulator of frequency and volume of stool?
What are four different types of laxatives?
o Bulk Laxatives
o Faecal Softeners
o Osmotic Laxatives
o Irritant / Stimulant Laxatives
What would you give in soft faeces constipation
What would you give in history or DRE hard faeces
What is the indication for a bulk laxative?
Constipation, particularly when hard stools are present
What are four contraindications for bulk laxatives?
Intestinal obstruction (Adhesions, ulceration)
What is the mechanism of action for bulk laxatives?
Increases the volume of the non-absorbable solid residue in the gut, distending the colon and stimulating peristaltic movement.
Give three ADRs of bulk laxatives
What is necessary for the patient to do while taking bulk laxatives?
Have a normal fluid intake
Give a type of faecal softener
Glycerol (given as suppository
Give four indications for faecal softeners
What group should faecal softeners not be used on/
Children less than 3
What is the mech of action of faecal softeners?
Lubricate and softens stools
What is the mechanism of action of an osmotic laxative?
Increase water content of the bowel via osmosis
Lactulose – Disaccharide (galactose/fructose) that cannot be hydrolysed by digestive enzymes. The fermentation of lactulose by colonic bacteria gives acetic and lactic acid. This has an osmotic effect
Name an osmotic laxative
What are the indications for osmotic laxatives?
Lactulose - Liver failure (reduced production of ammonia)
What is the main contraindication for osmotic laxative?
Give four adverse drug reactions?
Caution required to prevent intestinal obstruction
How quickly do magnesium and sodium (osmotic laxatives) work?
Quickly and severly, so should be reserved for resistant constipation if urgent relief is required
What is the mechanism of action of irritant laxatives?
Increase gastrointestinal peristalsis and water and electrolyte secretion by the mucosa. Possibly by excitation of sensory enteric nerves.
What are the indications for osmotic laxatives?
Constipation and bowel evacuation prior to medical/surgical procedures
What are the contraindications for osmotic laxatives?
What are two ADRs to stimulant laxatives?
How can stimulant laxative abuse be detected?
Melanosis coli (pigmentation of the bowel wall)
What is diarrhoe?
The passage of frequent, liquid stools
What are some causes of diarrhoea?
Infections, toxins, drugs, chronic disease and anxiety
Name an anti-motility anti-diarrhoeal
Give a contraindication for an anti-motilitity anti-diarrhoeal
Inflammatory Bowel Disease - Toxic Megacolon
What is the mechanism of action of anti-motility anti-diarrhoeals
Act on opioid receptors in the bowel
Reduce motility (increase time for fluid reabsorption)
Increase anal tone and reduce sensory defecation reflex
Give some ADRs of anti-motility anti-diarrhoeals
Nausea, vomiting, abdominal cramps, constipation drowsiness
What is spesh about imodium?
40 times more potent than Morphine as an antidiarrhoeal agent, and penetrates the CNS poorly
What are bulk forming anti-diarroeals used for?
IBS and ileostomy
What are some contraindications for bulk forming antidiarrhoeals?
What is a mechanism of action fo bulk forming anti-diarrhoeals
A relatively small amount of faecal fluid (10-20ml) influences composition. Bulk forming antidiarrhoeals absorb this fluid
What are four symptoms of IBS?
o Abdominal Pain
o Alteration of Bowel Habits
What is used to treat IBS?
Mebeverine which has a direct decreasing effect on colonic hypermotility
Outline the process of vomiting
o Pyloric sphincter closes while the cardia and oesophagus relax
o Gastric contents propelled by contraction of abdominal wall and diaphragm
o Glottis closes with elevation of soft palate, preventing entry of vomit into the trachea and Nasopharynx
If vomiting is due to alcohol, or patient has a cranial nerve lesion they are at a higher risk of aspiration as this does not work properly
Name four stimulating factors for vomiting
Meds, toxins, pain
- Smell, touch
- Raised ICP
- Stretching of the stomach
What does external stimulation act on to stimulate vomiting?
Postrema (floor of 4th ventricle) which acts on medullary centre -> Medullary centre releases Ach, histamine and serotonin which causes emesis
How does spinning round and round cause vomiting?
Causes dysfunction of vestibular apparatus, which released Ach + Histamine -> Medullar centre, Ach, histamine, serotonin -> Emesis
Give four ways you can prevent vomiting
Histamine receptor antagonists
What are two key indications for dopamine receptor antagonists?
Especially induced by L-DOPA or dopamine agonists
What is the mech of action for dopamine antagonists?
Acts on the Postrema on the floor of the 4th ventricle
Acts on the stomach to increase the rate of gastric emptying
What are two key ADRs for dopamine receptor antagonists?
Stimulates prolactin release
Metoclopramide – extra-pyramidal reactions (dystonia) occur in 1%, therefore is avoided in Parkinson’s disease
What is the main indication for serotonin antagonists?
In high doses in radiation sickness, chemotherapy sickness, post operatively
What is the main mechanisms of action for serotonin antagonists?
5-HT is released into the gut, reducing Vagus activity, therefore effective at deactivating the vomiting centre (the Postrema on the floor of the 4th ventricle)
Blocks Serotonin receptors in Chemoreceptor Trigger Zone
What are three ADRs of serotonin antagonists?
Headaches, constipation, flushing
How can serotonin antagonist effects be amplified?
Dose of corticosteroid
What are anti-muscarinincs used for?
What some ADRs of anti-muscarinics?
Systemic anti-cholinergic effects, bradycardia
What are histamine receptor antagonists used for?
Acute nausea and vomiting
What is a contraindication for histamine antagonists
What are two ADR of histamine receptor antagonists?
Can cause QT prolongation
Crosses the BBB - Sedative effect