Regulation of Digestion

Three Major Mechanisms Regulating Digestion

  • The three main mechanisms that regulate digestion are:

    • Local mechanisms

    • Neural mechanisms

    • Hormonal mechanisms

Local Mechanisms

  • These mechanisms occur locally where there is a presence of food and work to enhance or alter digestion.

  • Factors that assist with regulating digestion include:

    • Changes in pH

      • The pH and contents of the lumen, such as changes in acidity levels, affect digestion.

      • Hydrochloric acid in the stomach is released as chyme into the duodenum, resulting in changes in pH.

      • Buffers are secreted to alter the pH.

    • Physical stimulation

      • The presence of food or the bolus that has been ingested stretches and distorts the wall of the digestive tract.

      • This stimulates digestion, peristalsis, and movement through the digestive tract.

    • Chemical stimulation

      • Various chemical components of food and enzymes moving through the digestive tract stimulate digestion.

Neural Mechanisms

  • The digestive system is under autonomic control, which occurs without voluntary thought or control of the muscles of the digestive tract.

  • Sympathetic stimulation:

    • Inhibits or slows digestion.

    • Occurs during the fight or flight response or during exercise when blood flow is diverted away from the digestive tract to other organs.

    • Results in vasoconstriction and less blood flow, inhibiting and slowing down digestive processes.

    • This can be an issue in sports nutrition where people are exercising and have less blood flow going to their digestive tract, slowing their ability to digest and absorb nutrition.

  • Parasympathetic stimulation:

    • Promotes the stimulation of digestion, allowing us to digest foods.

  • Neuronal reflexes influence digestion:

    • Short reflexes

      • Various receptors, such as mechanoreceptors, chemoreceptors, and osmoreceptors, result in short reflexes.

      • These occur a short distance from where the receptors are.

    • Long reflexes

      • Stimulated by smell and taste, which can stimulate various parts of digestion to occur.

      • These happen a long way away from where the digestive process is taking place.

      • For example, the smell of food can make you start producing saliva before you have ingested any food.

  • Gastrocolic reflex:

    • When you ingest food, you may need to eliminate feces to make room for the incoming food.

    • This promotes a reflex further down the digestive tract, allowing you to make room to digest the food that is coming in.

Hormonal Mechanisms

  • Hormones are produced throughout the digestive tract and enter the bloodstream, where they reach their target organ or section to act on.

  • Examples of hormones and their functions:

    • Gastrin

      • Released in the stomach to assist with the secretion of hydrochloric acid and pepsinogen, which helps break down proteins.

      • HClHCl

      • Enhances stomach motility (contractions within the stomach).

    • Secretin

      • Stimulates bicarbonate secretion from the pancreas to neutralize the hydrochloric acid and the acidic nature of chyme in the intestine.

      • HCO3HCO_3 is a buffer.

    • Cholecystokinin (CCK)

      • Stimulates the pancreas to release lipase, which helps break down lipids, and the gallbladder to release stored bile.

    • Gastric Inhibitory Peptide (GIP)

      • Inhibits digestion by inhibiting gastric secretion and motility.

      • Hormones can both switch on and inhibit digestion.

These neural and hormonal mechanisms work simultaneously and in a coordinated manner to help us digest and absorb nutrients from the food we ingest.