They reside alongside the epithelium lining the lumen of the digestive tract and play a crucial role in gastrointestinal regulation, particularly intestinal motility and secretion.

As enteric afferent and efferent nerves do not protrude into the intestinal lumen, EC cells act as a form of sensory transduction.

ECs known as neuropod cells rapidly relay signals from gut to brain via a direct communication with vagal and primary sensory neurons.

[7] EC cells typically extend down to the basal lamina with cytoplasmic extensions known to pass through the connective tissue and neighbouring glands.

Tissue beneath EC cells typically contains abundant fenestrated capillaries, lymph vessels and small unmyelinated nerve fibres.

Release of serotonin from EC cells can be triggered by a multitude of stimuli, particularly luminal distension, parasympathetic innervation or changes in osmotic concentrations in intestinal contents.

[1] Release of the vesicles occurs after chemical, neurological or mechanical stimulation of the EC cells and is predominantly calcium dependent, suggesting excretion via exocytosis.

[14] The vesicles pass from the basal margin into the surrounding lamina propria for interaction with nearby nerve synapses, lymph and blood vessels.

The serotonin synthesised by EC cells is predominately exocytosed from the basal border, but is also known to be apically secreted into the lumen of the gut and can be present in faecal samples.

In patients suffering post-infectious IBS, rectal biopsies have shown a dramatic increase in populations of EC cells associated with diarrhoeal symptoms.

[16] Likewise, reduced populations of EC cells in patients suffering chronic constipation have been observed, indicating a lack of 5-HT, and therefore decreased GI motility and secretion.

[17] Carcinoid syndrome is a rare condition characterized by an abnormal increase in circulating biologically active hormones, largely serotonin, with early symptoms involving diarrhea, abdominal cramping and episodic flushing.