Q. Define and Classify Gastrointestinal Reflexes
Generally, the term ‘reflex’ refers to any pathway that uses the nervous system, endocrine system, or both to receive input about a change, integrate the information, ad react appropriately. Gastrointestinal reflex refers to the use of this mechanism in the control of GI functions (motility, secretion, absorption, and digestion).
The digestive tract wall contains three types of sensory receptors that respond to local chemical or mechanical changes in the digestive tract:
- Chemoreceptors sensitive to chemical components within the lumen;
- Mechanoreceptors (pressure receptors) sensitive to stretch or tension within the wall; and
- Osmoreceptors sensitive to the osmolarity of the luminal contents
Stimulation of these receptors elicits neural reflexes or secretion of hormones, both of which alter the level of activity in the digestive system’s effector cells (the smooth muscle cells and the exocrine and endocrine gland cells.
Classes of Gastrointestinal Reflexes
Receptor activation may bring about two types of neural reflexes (short reflexes and long reflexes).
When the intrinsic nerve networks influence local motility or secretion in response to specific local stimulation, all elements of the reflex are located within the wall of the digestive tract itself; that is, a short reflex takes place.
Extrinsic autonomic nervous activity can be superimposed on the local controls to modify smooth muscle and glandular reponses, either to correlate activity between different regions of the digestive system or to modify digestive system activity in response to external influences. Because the autonomic nervous reflexes involve long pathways between the central nervous system and digestive system, they are known as long reflexes.
In addition to these neural reflexes, digestive system activity is also coordinated by the secretion of gastrointestinal hormones, which are triggered directly by local changes in the digestive tract or by short or long reflexes.