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gastrointestinal Flashcards

1
Q

how is the enteric system controlled neuronally and hormonally

A

neuronal control:
myenteric plexus
meissners plexus
pns
sns

hormonal:
gastrin/somatostatin
histamine
prostoglandins e2 and i2

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2
Q

what is gastric juice made of

A

juice:
pepsinogens
acid (HCL)
intrinsic factor

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3
Q

what cells are in da stomach lining

A

cells:
parietal cells: gastric acid
peptic cells (chief): pepsinogen (protease precursor)
mucous cells: mucus and bicarbonate to protect stomach lining
D cells: produces somatostatin (inhibits acid secretion)
G cells: produces gastrin (stimulates acid secretion)

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4
Q

describe the mechanism of parietal cell acid secretion

A

Co2 from blood capillaries react with h2o to produce H2CO3 and this reaction is catalysed by carbonic anhydrase
H2CO3 then ionizes into H+ and HCO3-.
H+ cells are secreted by H+-K+ ATPase transporter (k+ into cell H+ out)
Hco3- is absorbed back into the blood via the HCO3- CL- antiporter (HCO3- into blood Cl- into cell)
cl- is effluxed into the stomach lumen to combine with H+ to make HCL
some KCl and NaCl is also produced

parietal cells can respond to gastrin (cck2 receptors), histamine (H2 receptors), acH (m3) (enhances acid secretion)
and prostoglandins E2 and I2 (inhibits acid secretion)

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5
Q

differentiate between direct and indirect pathway of parietal cell stimulation

A

direct: acH gastrin and histamine stimulate triggering H+ release into lumen
indirect: Ach and gastrin stimulate enterochromaffin like (ecl) cells leading them to release histamine which acts on parietal cells

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6
Q

what are the causes of dyspepsia (indigestion)

A
  1. Peptic ulceration
    due to Helicobacter pylori infection or long use of NSAID’s
  2. Gastro-oesophageal Reflux disease (GERD)
    Bile secretions into stomach
  3. Zollinger Ellison Syndrome (gastrin secreting tumour)

4.Gastritis (Inflammation) (can lead to ulcers)
Spicy foods
Alcohol

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7
Q

what can ulcers lead to

A

Can lead to erosion of mucous lining (duodenal gastric or oesophageal)
Damage the protective layers
Leads to excessive bleeding

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8
Q

describe the use of antacids and alginates for dyspepsia

A

symptom relief.

antiacids Increase gastric pH >4 and inhibits action of pepsin ex: aluminium hydroxide and magnesium hydroxide
sodium bicarbonate aluminium bicarbonate
mg bicarbonate
side effx: Nausea, Vomiting, Hypophosphatemia, Chalky taste, Constipation, Abdominal cramping. Diarrhoea, Electrolyte imbalance

alginates: Alginic acid combines with saliva to form a viscous foam
Floats on gastric contents and protects oesophagus

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9
Q

describe the use of antibiotics for dyspepsia

A

2 antibiotics given with PPI or H2 antagonist for eradication if H. pylori present (amoxicillin/clarithromycin/metronidazole)

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10
Q

describe the use of H2 antagonists for dyspepsia

A

symptom relief
H2 antagonists ex: ranitidine
Block Histamine activation of H2 receptors on parietal cells
H2 receptors are coupled to cAMP to activate proton pump action
Reduce gastric acid secretion
side effects:Headache, Anxiety, Depression, Dizziness, Cardiovascular effects, Thromocytopenia

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11
Q

describe the use of PPI for dyspepsia

A

symtpom relief.
ppi (irreversibly inhibit H+/k+ atpase)
Activated in acidic environments
Inhibition of >90% HCl secretion: can lead to achlordiya (absence of acid)
ex: omeprazole lansoprazole
side effects: Headaches, Abdominal pain, Diarrhoea, Nausea, Vomiting, Constipation, Flatulence, Vitamin B12 deficiency, Osteoporosis

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12
Q

describe the use of potassium competitive agents for dyspepsia

A

symptom relief
Potassium competitive acid blockers (binds to potassium H+/k+ is symporter needs both to bind) ex: vanoprazan
side effects: Naopharyngitis, Fall, Confusion, Diarrhoea, Upper Respiratory tract inflammation, Eczema, Constipation, Back pain

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13
Q

describe the use of cytoprotective agents for dyspepsia

A

symtpom relief
cytoprotective agents (stimulate mucus production and enhance blood flow to lining of GI) ex: Misoprostol Sucralfate
side efx: Diarrhoea, abdominal pain, headache, constipation

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14
Q

list emetic stimulti and what drugs can be used

A

Bacterial or viral infection

Pregnancy : 5HT3 antagonist in CTZ and GI ex: ondansteron granisteron metoclopramide

Chemicals in blood ex: toxins/drugs
from things like chemo : 5HT3 antagonist (CTZ GI) ex: ondansteron granisteron metoclopramide
D2 dopamine antagonist (CTZ GI) ex: prochloroperazine, tiethylperazine, domepridone, metoclopramide, phentothiazines
NK1 antagonist (GI) ex: aprepitant
cannabinoid agonist (vomitting center) ex: dronabinol (unclear mechanism)
from drugs: D2 dopamine antagonist (CTZ GI)
ex: prochloroperazine, tiethylperazine, domepridone, metoclopramide, phentothiazines

Motion sickness: antihistamine H1 antagonist acts on vestibular nuclei
ex: diphenhydramine dimenhydrinate /cinnarizine, cyclizine, promethazine
some histamine analogues are H1 partial agonists h3 antagonists used in vertigo ex: betahistine (increases blood flow to ear?)

chronic idiopathic nausea and cyclic vomitting: tricyclic antidepressant
ex: amitriptyline and nortriptyline

also: anti muscarinic ex: hyoscine
Act on vomiting centre and vestibular apparatus
Highly effective but adverse side effects limit their usefulness

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15
Q

How do NSAID’s cause damage to stomach

A

NSAID’s inhibit both COX-1 and 2. Cox 1 enzyme produces prostanoids that have gastric protective effects and COX 2 enzyme produces prostanoids that have a role in inflammation.
to prevent this damaging side effect NSAID can be given with cytoprotective agents such as misoprostol which bind to prostanoid receptors that block gastric H+ secretions

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16
Q

describe the process of vomitting

A

triggers:
1. higher cortical centres (memory fear taste sight smell or pain)
2. GI tract (surgery toxins Gastroparesis( paralysis of the stomach))
3. vestibular (motion sickness and middle ear surgery)
4. act directly on CTZ (hypotension hypoxia drugs (anaesthetic opioids chemo))

emetic agonists give neuronal input to chemoreceptor trigger zone which goes to the vomiting centre to trigger vomiting (muscarinic histaminic dopamine opiod NK-1 from CTZ to VC) (5HT3 from GI to CTZ)

17
Q

what do drugs for the lower GI tract treat

A

Constipation
(reduced bowel movements) can be due to low fibre but can be induced from drugs like opioids diuretics anti-muscarinic or TCA)

Irritable bowel syndrome
long term condition with pain bloating and cycles of diarrhoea and constipation does not involve inflammation or any structural damage
cause unkown: abnormal gastrointestinal motility, visceral hypersensitivity, altered gut-brain communication, (genetics) and psychological factors like stress anxiety depression

Inflammatory bowel disease
conditions that cause chronic inflammation ex: chrons disease or ulcerative colitis. can lead to pain and blood in stools and persistant diarrhoea caused by genetics and immune system

Diarrhoea
passing of frequent watery/soft stools. can be life threatening and lead to chronic dehydration. acute diarrhoea can be linked to bacterial or viral infections

18
Q

describe the treatment of constipation

A
  1. Laxatives
    a. osmotic: retain fluid in GI lumen to soften faeces
    ex: lactulose enters colon and converted by bacteria to lactic and acetic acid which cause inward osmotic pressure
    b. Bulk: increase volume of non absorbable solid residue
    ex: methylcellulose
    c. stimulating purgatives: increase contraction of GI smooth muscle. metabolised to active components inside colon
    ex: bisacodyl, sodium picosulphate
  2. drugs that alter GI motility (non purgative)
    enhance gastric peristalsis by acting on pre synaptic receptors to alter release of Ach from pns terminals
    ex: domperidone (d2 antagonist)
    metoclopramide (d2 and at higher doses 5ht3 antagonist)
    prucalopride (5HT4 agonist)
  3. Fecal softeners
    docusate sodium
19
Q

Describe the treatment for IBS

A

lactulose and loperamide to reduce symptoms of diarrhoea/constipation
anti spasmodic ex: anti muscarinic mebeverine
TCA like amitriptyline/ SSRI like citalopram to alter sensitivity of sensory nerves for pain relief

20
Q

describe the treatment for IBD

A

anti inflammatory
immunosupressant actions

5-aminosalicylates: release 5-aminosalicylate to inhibit leukotriene and prostanoid formation. it scavenges for free radicals and reduces neutrophil chemotaxis. ex: sulpasalazine, mesalazine
immunosupressants: ex: azathioprine, ciclosporin, methotrexate infliximab (monoclonal antibody for TNF alpha
corticosteroids ex: budesonide (poorly absorbed less side effx)

21
Q

what are the types of infections that can cause diarrhoea

A

rotavirus: damages small intestine villi
Invasive bacteria: damages epithelium layer
campylobacter: releases toxins that damage mucosa
adhesive enterotoxigenic bacteria:
adhere to brush border release cholera toxin that travels inside the cell. which activates adenylyl cyclase increasing camp and increasing Cl- Na+ secretion into lumen (water follows)

22
Q

give examples for causes of drug induced diarrhoea

A
  1. antibiotics (esp broad spectrum)
    (alter intestinal flora which prevent colonization by harmful bacteria by competing for nutrients and producing antimicrobial substances)
  2. orlistat
    blocks pancreatic lipase giving rise to oily diarrhoea (fat breakdown prevented)
  3. Misoprostol
    used to treat ulcers, increase mucosa and bicarbonate production reducing acidity of stomach
  4. PPI’s
    reduce gastric acid secretion which can lead to an increase in risk of infections
23
Q

what is the treatment strategy for diarrhoea

A
  1. oral rehydration
    solution of electrolytes water and glucose (promotes sodium reuptake via glucose symporter, water also reabsorbed)
  2. anti motility drugs
    a. opiates ex: LOPERAMIDE
    activate presynaptic U opioid heteroreceptors to decrease acH release (decreased contractions increased transit time to promote water reabsorption)
    b. muscarinic antagonists ex: low dose atropine or dicycloverine
    inhibit post junctional muscarinic receptors
    -both can have side effx of constipation)
  3. absorbents ex: kaolin, pectin, chalk, charcoal, Magnesium aluminum silcate
    reduce impacts of toxins by providing protective coating

for bacteria such as cholera vaccine is also available and better sanitisation and access to clean water is important
4. antibiotics

other: Bismuth subsalicylate
Antidiarrheal Effect: Bismuth subsalicylate has mild antibacterial properties. also Bulks up stool and reduces fluidity and frequency
Antacid Effect: Bismuth subsalicylate can help neutralize excess stomach acid
Protective Coating: Bismuth subsalicylate forms a protective coating on the stomach lining

drugs and diseases (36 decks)

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