What is Gastroileal Reflex?

Gastroileal reflex is a reflexstimulated by the opening of the ileocecal valve, pushing the digested material from the ileum present in the small intestine to the large intestineaccompanied by a desire to defecate. It is the third type of gastrointestinal reflex which is mediated by the vagus nerve and gastrin.

Gastrointestinal Reflexes

The movement of food in the digestive system is very complex and involves the regulation of secretion for proper digestion. The movement and secretion are regulated by both long reflexes (central nervous system) and short reflexes of the enteric nervous system alongwith the reflexes of the gastrointestinal system. Three more reflexes are involved in the movement, digestion, and defecation of food and food wastes. These reflexes are intragastric reflex, gastrocolic reflex, and gastroileal reflex.

What are Short and Long Reflexes?

The long reflex in the digestive system involves a sensory neuron sending information to the brain. This sensory information can be from the digestive system or from outside the body in the form of an emotional response, a reaction to food, or danger. Sometimes emotional reflexes also trigger gastrointestinal responses like the feeling of butterflies running in the stomach during nervousness. The digestive system is also regulated by the enteric nervous system which is considered the brain that controls motility, secretion, and growth. The enteric system acts as a rapid internal response to the digestive stimuli, a process called short reflex.

Types of Gastrointestinal Reflex

1. Enterogastric reflex: It gets stimulated when the pH level in the duodenum is between 3 and 4 or 1.5 in the stomach. When the enterogastric reflex is triggered, secretion of gastrin from the G (gastrin) cells present in the antrum of the stomach is inhibited. As a result, gastric motility and secretion of hydrochloric acid are decreased.
2. Gastrocolic reflex: This type of reflex regulates the motility or peristalsis of the gastrointestinal tract. It increases the motility of the colon when there is a stretch in the stomach followed by the presence of digestive by-products in the small intestine. The gastrocolic reflex urges to defecate after a meal. A similar kind of motility response is also observed in the small intestine. This reflex makes space for food in the stomach.
3. Gastroileal reflex: It is the third type of reflex that works with gastrocolic reflex to produce an urge to defecate. It is triggered by the opening of the ileocecal valve that moves the contents of the digestive material from the small intestine to the colon.

How does the Movement of food take Place in the Small Intestine?

• The peristaltic activity of the small intestine is increased while eating. It begins with the entry of chyme into the duodenum that stretches the duodenal wall.
• The gastrointestinal reflex is initiated when the stomach enlarges. It is conducted principally through the myenteric plexus from the stomach down along the wall of the small intestine.
• The secretion of insulin, serotonin, gastrin,cholecystokinin(CCK) enhancesintestinal motility. 
• The peristaltic wave in the small intestine not only pushes the chyme towards the ileocecal valve but also spreadsout the chyme along the intestinal mucosa.
• The food in the ileocecal valve is sometimes blocked for few hours until a person eats another meal.
• Later the gastroileal reflex intensifies peristalsis in the ileum and forces the remaining chyme through the ileocecal valve into the large intestine.

Role of the ileocecal Valve in the Gastroileal Reflex

• It prevents the backflow of contents from the colon into the small intestine.
• The valve protrudes into the lumen of the cecum and gets closed when excess pressure builds up in the cecum.
• The ileocecal sphincter remains constricted and gradually empties the ileal contents into the cecum after a meal. Peristalsis in the ileum occurs due to the gastroileal reflex.

Regulation of the Gastrointestinal Functions

The gastrointestinal function is controlled by two processes:

1. Neural reflexes: This process is initiated by distension, chemical substances, or irritation in the mucosa. The afferent fibers carry information from chemomechanoreceptors.
   • Local-integrated entirely within the enteric nervous system.
   • Long (parasympathetic) and local enteric nervous system: Peristalsis occurs at the caudal region of the stomach. It involves reflexes from the gut to the spinal cord or brain stem and then back to the gastrointestinal tract (gastroileal reflex, defecation reflex).
   • Sympathetic and local enteric nervous system: It involves the reflexes from the gut to the prevertebral (sympathetic) ganglia and back to the gastrointestinal tract.

2. Gastrointestinal peptides: The gastrointestinal hormones include:

• Gastrin: It is neural in origin and is secreted by G cells of the antrum of the stomach in response to stimuli produced after having a meal. The hormone is secreted as progastrin which gets activated to gastrin by hydrochloric acid.
• Cholecystokinin: It is secreted by I cells in the mucosa of the duodenum and jejunum in response to digestive products of fat, fatty acids, and monoglycerides in the intestine. It contracts the gall bladder to expel bile into the small intestine that helps in emulsifying fatty substances, allowing them to get digested and absorbed.
• Secretin: It is secreted by S cells in the mucosa of the duodenum in response to the emptying of gastric juice into the duodenum from the pylorus of the stomach. It promotes the pancreatic secretion of bicarbonate that helps to neutralize the acid in the stomach.
• Gastric inhibitory peptide (GIP): It is secreted by the mucosa of the upper small intestine in response to fatty acids, amino acids, and carbohydrates to a lesser extent. A high concentration of GIP decreases the motor activity of the stomach and slows the emptying of gastric contents into the duodenum when the upper small intestine is overloaded with food products.
• Motilin: It is produced by the upper duodenum in the fasting condition. The function of motilin is to increase gastrointestinal motility. It moves through the stomach and the small intestine every 90 minutes in a fasting person.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for;     

• Bachelor of Science in Anatomy and Physiology
• Bachelor of Science in Zoology
• Master of Science Anatomy and Physiology
• Master of Technology in Biomedical Engineering