vomiting and anti-emetics

Question 1

Steps to vomiting

Answer 1

Nausea
Salivation
Cold sweat
Increase in pulse and respiratory rate
Glottis closes
Diaphragm and abdominal contraction
Reterograde contraction of intestines

Question 2

The vomiting centre

Answer 2

Located in the lateral reticular formation of the medulla.
Control and integrate the visceral (GI smooth muscle) and somatic (skeletal muscle of diapharagm) functions involved in vomiting. Inputs from the NTS, CTZ and higher centers.

Question 3

Chemoreceptor trigger zone (CTZ)

Answer 3

Located in the area postrema on the floor of the 4th ventricle
No BBB
Activated by blood-bourne substances (drugs, toxins)
5HT3 and D2 receptors present
Other input from vestibular nucleas
Links to vomiting centre

Question 4

Insular cortex

Answer 4

Primative, vomiting in response to nasty smells, pain

Question 5

Receptors involved in the Control of vomiting

Answer 5

Histamine (H1)
Acetylcholine (M1)
Dopamine (D2)
5HT3
Possibly opiod

Question 6

Retching

Answer 6

A strong involuntary effort to vomit

Question 7

Dopamine antagonists

Answer 7

Metoclopramide - antidopaminergoc action, stimulates motility of upper gut, without stimulating gastic, bilary or pancreatic secretions.

Question 8

Antihistamines

Answer 8

Promethazine - long acting with sedative and anticholinergic actions that enhance anti emetic effect.

Question 9

5HT3 antagonists

Answer 9

Highly selective.
Mainly used to treat or prevent nausea following chemotherapy, radiotherapy or surgery.
Palonosetron, Granisetron, Ondansetron, Dolasetron, and Tropisetron.
As 5HT3 receptors are present on the vagal nerve terminals (peripherally) and the CTZ (centrally) antagonism here is a good method of preventing nausea and emesis.

Question 10

Anti cholinergics

Answer 10

Hyoscine - antispazmodic and anti-motilty effect on the gut but inhibiting ACh