Nausea, Vomiting, Pain

Question 1

Define:

1. Aversion
2. Nausea
3. Emesis/Vomiting
4. Retching

Answer 1

1. A strong dislike
2. Sensation of being unpleasant, and triggers aversion
3. Physical act of expelling contents of upper GIT
4. Making sound and movement of vomiting

Question 2

What is the relationship between nausea and vomiting?

Answer 2

Nausea and vomiting are produced by the same stimuli.

Nausea generally happens before vomiting, and can clear up before vomiting occurs. However, vomiting can occur without nausea.

Question 3

What are the stimuli that cause nausea and emesis? Which stimuli act as an advantage?

Answer 3

• GI infection
• Pregnancy
• IV drugs
• Excessive eating
• Poisoning
• Excessive alcohol
• Others being sick
• Obstruction of GIT

Question 4

How can Taste and Smell help protect against ingested toxins?

How can the Gastric and Upper GI afferents help protect against ingested toxins?

Answer 4

• Can prevent ingestion. We have a built-in dislike of bitter flavours and we learn from elders what is safe to eat.
• Can expel harmful agents before they’re absorbed. Associated with chemoreceptive cells that respond to a range of harmful chemicals. However, when these toxins haven’t been absorbed and are in the blood, they will still stimulate these receptors to cause emesis.

Question 5

How can Chemoreceptor Trigger Zone help protect against ingested toxins?

How can the Vestibular system help protect against ingested toxins?

How does learning and aversion help protect against ingested toxins?

Answer 5

• Is the AREA POSTREMA of the medulla where the BBB is leaky. Chemoreceptors can detect the toxins in the blood.
• Is a potent trigger for emesis. Poisoning produces aberrant activity in vestibular neural pathways. But this system can also trigger nausea + vomiting in response to un-natural motions.
• If we’ve had bad experiences, we’ll avoid repeating it, due to aversion. But, the aversion can create wrong associations.

Question 6

What are the anti-poison defences coordinated by? Where is it found?

Where does it receive warning signals from?

Answer 6

• Nucleus Tractus Solitarius (NTS) - found in medulla.

- Area Postrema, Vestibular system, Higher centres, Abdominal afferents.

Question 7

What does the NTS send fibres to during nausea? What does it cause? What’s its importance?

Answer 7

• Sends signals to higher centres to show the aversion/dislike memories to bring the sensation of nausea.
• NTS sends signals to the Hypothalamus = ↑ADH release - important as vomiting expels a lot of fluid.
• NTS sends signals to Autonomic system = ↑Salivation, Vasoconstriction in the GIT/skin, Sweating. Also causes changes Gut motility - protect against acid in mouth, prevent further absorption.

Question 8

Outline the phases of Emesis

Answer 8

1. Mixing and peristalsis:
   • Prevents toxins from being carried further through the system
2. Stomach relaxes:
   • Prepares stomach to receive additional contents
3. Giant retrograde contraction:
   • Sweeps up from mid-small intestine
   • Returns upper intestinal contents to stomach
4. Retching (Dry heaves):
   • Rapid contractions of abdominal muscles and diaphragm - produces waves of high pressure in abdomen
   • Compresses stomach but anti-reflux barriers intact so no expulsion
5. Vomiting (Emesis)
   • Oesophageal sphincters and crural diaphragm relax
   • Waves of contraction expel stomach contents

Question 9

What are the sensory afferents that detect nausea stimuli? What do they respond to?

What occurs with gut over-distension?

Answer 9

• Nociceptors - gut over-distension, inflammation, muscle spasms.
• Once the gut gets too large, afferent nerves around gut send high frequency signals to the brain = pain.

Question 10

What occurs with gut inflammation? What is the inflammation caused by?

Answer 10

Nociceptors respond to inflammatory mediators, as well as stretching of the gut wall - they carry out positive feedback by releasing more inflammatory mediators, making the nociceptors even more active.

Like over-distension, high frequency signals are sent to the brain when there’s too much inflammation.

Inflammation can be caused by injury, irritants, infection.

Question 11

Compare Somatic and Visceral pain

What is visceral-somatic convergence?

LOOK AT DIAGRAM!

Answer 11

• Somatic pain is precisely localised.
  Visceral pain is very imprecisely localised, and is referred to the body wall.
• Where the visceral afferent nociceptor enters the spinal cord, converges with the somatic nociceptor, and goes along the same pathway to the brain.