Nausea, vomiting and pain

Question 1

What coordinates the anti-poison defences?

Answer 1

Nucleus Tractus Solitarius (NTS)

Receives 4 different types of warning inputs which will trigger nausea and vomiting:

• visceral afferents
• area postrema
• vestibular system
• higher centres

Question 2

What are the Visceral Afferent nerves?

Answer 2

Axons run in the vagus nerve from oesophagus and stomach to the NTS and are associated with receptors that respond to toxins, irritants, inflammation and distension

Question 3

What is the Area Postrema (medulla)?

Answer 3

Chemoreceptor trigger zone in the medulla with chemoreceptors which detect toxins in the blood and induce vomiting (no blood brain barrier)

Question 4

What is the Vestibular System?

Answer 4

In the inner ear and helps with balance, but also is a potent trigger for emesis

receptors in vestibular system are sensitive to toxins and will produce aberrant activity in vestibular neural pathways, which will be interpreted by the brain as potential evidence as a poison, leading to nausea and emesis

*also triggers motion sickness (fairground rides)

Question 5

What are the Higher centres?

Answer 5

Higher centres include the limbic areas which feed down information about things that made you sick in the past or other people near you being sick

these centres develop aversions

Question 6

What is the Relationship between nausea and ADH?

Answer 6

When you’re feeling nauseas, one of the first things that happens is the NTS signals the hypothalamus to increase the release of ADH to conserve fluid because you might be about to lose a large amount of it via vomit.

Question 7

What is the Relationship between nausea and autonomic activity?

Answer 7

Sympathetic activity increases and that, in combination with reduced parasympathetic activity to upper GI tract, stops you from processing the food to prevent breaking down the food and passing it down the gut if It potentially contains poisons. The increased sympathetic activity will also make you go pale and increase sweating.

• Reduces mixing and peristalsis
• Relaxes proximal stomach
• Giant Retrograde Contractions

Question 8

How does NTS trigger vomiting?

Answer 8

Retching
-stimulation of phrenic and somatic nerves, producing fast contractions of diaphragm and abdominal muscles, compressing the stomach

Vomiting
-abdominal pressure triggers release of anti-reflux barriers and oesophageal sphincters and diaphragm relax, expelling stomach contents

Question 9

What are Visceral Pain Receptors?

Answer 9

Nociceptors associated with axons that run through sympathetic nerves

Question 10

What do nociceptors respond to?

Answer 10

DISTENSION
-more stretched gut wall causing more action potentials

INFLAMMATION
-inflammatory mediators produced which depolarise the nociceptors increasing action potentials at each level of distension, causing pain quicker. Also, depolarisation of nociceptors releases further inflammatory mediators, further increasing action potentials and pain (positive feedback loop)

MUSCLE SPASMS

Question 11

What is the Difference between visceral pain and somatic pain?

Answer 11

Visceral pain doesn’t necessarily produce pain in the area expected (referred pain)

Somatic pain is precisely located

Question 12

Describe the Somatic pain pathway.

Answer 12

Nociceptor axon enters spinal cord via dorsal root

first synapse is the dorsal horn

activates a second order neurones which has an axon running all the way up to the thalamus

activates a third order neurone which has an axon that runs up to the somatosensory cortex

Question 13

Why is the pain poorly localized?

Answer 13

Due to viscero-somatic convergence (convergence of viceral afferents with somatic pathways matching the embryonic region of each organ)