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Adult Years > Nausea, Vomiting and Gut Motility > Flashcards

Nausea, Vomiting and Gut Motility Flashcards

1
Q

Describe the reflex mechanism of vomiting.

A
  • Defence response.
  • Emetic stimuli:
    • In blood or intestine, OR
    • Neuronal input from GI tract, labyrinth and CNS
  • Central neural regulation of vomiting is controlled by 2 separate units both in the medulla:
    • Vomiting (emetic) centre
    • Chemoreceptor Trigger Zone (CTZ)
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2
Q

Describe the vomiting centre.

A
  • Collection of multiple sensory, motor and control nuclei.
  • Mainly in the medullary and pontine reticular formation, also extending into the spinal cord.
  • Receive nerve impulses from both vagal and sympathetic afferent nerve firbes.
  • Responds to the incoming signals to coordinate emesis.
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3
Q

Describe the Chemoreceptor Trigger Zone (CTZ).

A
  • CTZ is the area called the postrema in the floor of the 4th ventricle.
  • CTZ is sensitive to chemical stimuli and is the main site of action of many emetic and antiemeti drugs.
  • The CTZ is also concerned with the mediation of motion sickness.
  • Motion sickness is caused by certain kinds of movement and the origin of the stimuli is primarily the vestibular apparatus.
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4
Q

Which are the main neurotransmitters involved in stimulating the vomiting centre?

A
  • Acetylcholine
  • Histamine
  • 5-HT
  • Dopamine
  • Substance P
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5
Q

Give an overview of the control of vomiting.

A
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6
Q

What are the triggers of nausea / vomiting?

A
  • Stimulation of the sensory nerve endings in the stomach and duodenum.
  • Stimulation of the vagal sensory endings in the pharynx.
  • Drugs (in particular cancer chemotherapy, opioids, GA, digoxin) or endogenous emetic substances.
  • Disturbances of the vestibular apparatus.
  • Various stimuli of the sensory nerves of the heart and viscera.
  • A rise in ICP.
  • Nauseating smells, repulsive sights, emotional factors.
  • Eneocrine factors.
  • Migraine.
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7
Q

Describe the stages of vomiting.

A
  • Nausea:
    • ​Feeling of wanting to vomit
    • Associated with autonomic effects: salivation / pallor / sweating.
    • Often pro-drome of vomiting.
  • Retching:
    • ​Strong involuntary effort to vomit.
    • Unproductive.
  • Vomiting:
    • ​Expulsion of gastric contents through the mouth.
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8
Q

What are the types of vomiting?

A
  • Projectile vomiting
    • Suggestive of gastric outlet or upper GI obstruction.
  • Haematemesis
    • Vomiting fresh or altered blood (‘coffee grounds’)
      • E.g. oesophageal varices, bleeding gastric ulcer.
  • Early-morning
    • E.g. pregnancy, alcohol dependence, some metabolic disorders (uraemia).
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9
Q

What are the types of anti-emetic?

What are their sites of action?

A
  • Antimuscarinics (M1)
  • Antihistamines (H1)
  • Dopamine antagonists (D2)
  • 5HT3 antagonists
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10
Q

Describe the action of anti-muscarinics (M1 receptors).

A
  • Muscarinic receptor antagonists.
  • Blockade of muscarinic receptor-mediated impulses from the labyrinth and from visceral afferents.
  • For example:
    • Hyoscine hydrobromide (scopolamine hydrobromide) - useful in motion sickness.
    • Comes as patch as well as tablets - practical!
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11
Q

What are the antimuscarinic side effects?

A
  • Dry mouth
  • Blurred vision
  • Increased intraocular pressure
  • Hot and flushed skin
  • Dry skin
  • Bradycardia followed by tachycardia, palpitations and arrhythmias.
  • Difficulty with micturition - urinary retention.
  • Constipation
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12
Q

Describe the action of antihistamines.

Give some examples.

A
  • H1 histamine receptor antagonists.
  • Useful in numerous causes of nausea and vomiting; including motion sickness and stomach irritants.
  • Side effect profiles vary. E.g. drowsiness and anti-muscarinic effects.
  • Examples:
    • ​Cinnarizine
    • Cyclizine
    • Promethazine
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13
Q

Describe the action of dopamine (D2) receptor antagonists.

A
  • Act centrally as dopamine antagonists.
  • For example:
    • The phenothiazines are related drugs. These are also classed as neuroepileptics / antipsyhotics. Examples:
      • Chlorpromazine
      • Prochlorperazine
    • Domperidone
    • Metoclopramide
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14
Q

Describe the action of 5HT3 agonists.

Give an example.

A
  • Block 5HT3 receptors.
  • Prime site of action is CTZ.
  • Particularly useful in managing nausea and vomiting in patients receiving cytotoxics, radiation therapy and in postoperative nausea and vomiting.
  • Side effects of headaches and GI upsets relatively uncommon.
  • Example:
    • Ondansetron (contraindication - congenital long QT syndrome).
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15
Q

Describe the control of the gut.

A
  • GI function os controlled by a combination of hormonal and neuronal factors.
  • Parasympathetic nerves increase activity of the enteric nervous system (increase smooth muscle tone, promote sphincter relaxation); sympathetic inhibits (opposite).
  • GI hormones exert effects on target cells, including:
    • Secretin
    • Gastrin
    • Cholecystokinin
    • Somatostatin
    • Motilin
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16
Q

Describe the nervous system of the GI tract.

A
  • The GI tract has its own nervous system from oesophagus to anus.
  • Myenteric plexus (outer plexus) and submucosal plexus (inner plexus).
  • Myenteric stimulation
    • ​Increased tone of gut wall
    • Increased strength of contractions
    • Increased rate of contraction
    • Inhibits pyloric, iliocaecal and lower oesophageal sphincters.
  • Submucosal stimulation
    • ​Controls functions of the inner wall. For example, local secretion and absorption, contraction of submucosal muscle.
17
Q

What are the layers of smooth muscle in the GI tract from outer to inner?

A
  1. Serosa
  2. Longitudinal smooth muscle
  3. Circular smooth muscle
  4. Submucosa
  5. Mucosa (with muscularis mucosae deep within)
  • These layers are responsible for motor functions:
    • Propulsion (peristalsis)
    • Mixing (peristalsis + local constrictive contractions)
18
Q

Describe the use of laxatives in a patient presenting with constipation.

What are the 5 types of laxative?

A
  • Before prescribing ensure the peoblem is constipation.
  • Check what is normal for the patient.
  • Try to reverse the cause, including diet and lifestyle changes.
  • Types
    • ​Bulk-forming laxatives
    • Stimulant laxatives
    • Faecal softeners
    • Osmotic laxatives
    • Peripheral opioid-receptor antagonists
19
Q

Give examples of each type of laxative.

A
  • Bulk - Ispaghula husk
  • Stimulant - Senna
  • Softener - Docusate
  • Osmotic - Lactulose
  • Peripheral opioid receptor antagonist - Methylnaltrexone bromide
20
Q

What are the indications, contraindications and side effects for each type of laxative?

  • Bulk
  • Stimulant
  • Softener
  • Osmotic
  • Peripheral opioid receptor antagonist
A
21
Q

Describe the treatment of acute diarrhoea.

A
  • Diarrhoea involves both an increase in the motility of the GI tract and a decrease in the absorption of fluid and thus a loss of electrolytes.
  • Approaches for treatment of ACUTE diarrhoea:
  1. ​​​Maintnance of fluid and electrolyte balance (oral rehydration preparation).
  2. Antimotility drugs.
  3. Antispasmodics (reduce smooth muscle tone). Examples - Hyoscine butylbromide (buscopan), Mebeverine.
  4. Occasionally antibacterial agent is indicated, for example in the case of systemic bacterial infection, campylobacter enteritis, shigellosis and salmonellosis.
22
Q

What is the action of buscopan?

What are the indications, contraindications and side effects?

A
  • Antimuscarinic, relaxes intestinal spasm.
  • Indicated for GI/GU spasm, irritable bowel and acute spasm.
  • Also in palliative care (excess respiratory secretions and bowel colic).
  • Contraindications: if IM/IV/SC, tachycardia.
  • Side effects: skin reactions, dyspnoea, mydriasis.
23
Q

What are the treatment options for chronic diarrhoea?

A
  • Antimotility agents: loperamide (imodium).
  • Bulk forming drugs (conversely useful in controlling diarrhoea associated with diverticular disease): ispaghula.
  • (Opioids).
  • Adsorbents (nb. not for acute diarrhoea): kaolin.
24
Q

What is the action of Loperamide?

What are its indications, contraindications and side effects?

A
  • µ-opioid receptor agnoist. Inhibits peristalsis.
  • Indications: symptomatic treatment of acute diarrhoea, chronic diarrhoea, faecal incontinence and pain of bowel colic in palliative care.
  • Contraindications: active UC, antiobiotic-associated colitis, conditions where risk of abdominal distension / risk of peristalsis is inhibited.
  • Side-effects: GI disorder, headache, nausea.
25
Q

Describe how laxatives work in the treatment of constipation.

A

Adult Years (27 decks)

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