Some of the receptors and neurotransmitters involved in the regulation of this emetic pathway include dopamine type D2, serotonin types 2–4 (5HT2–4), histamine type 1(H1), and acetylcholine (muscarinic receptors type 1 to 5, M1–5). Some other receptors such as substance P, cannabinoid type 1 (CB1) and the endogenous opioids may also be involved.[10] Pathological conditions of the gastrointestinal tract: diseases and pathological conditions of the GIT may also lead to nausea and vomiting through direct or indirect stimulation of the above named pathways. Such conditions may include malignant bowel obstruction,[11] hypertrophic pyloric stenosis and gastritis.