Digestive Hormones – Chemicals that Control Digestion

What are Digestion Hormones?

Digestive hormones (gut hormones) are chemical ‘messengers’ which signal the gastrointestinal tract and accessory organs to perform different actions in order to coordinate the digestive process. It may act on an entire organ, part of the organ or specific tissues and cells to :

  • Secrete enzymes for digestion – chemical digestion.
  • Stimulate muscle contraction/relaxation – open/close sphincters and move food through the gut.
  • Increase blood flow to the gut – absorption of nutrients.
  • Regulate the flow of water and electrolytes – between the gut and bloodstream.

The digestive hormones should not be confused with digestive enzymes. The hormones coordinate the digestive process by acting as a chemical messenger. The enzymes are a part of chemical digestion by acting as a catalyst to breakdown food within the gut.

Since most digestion hormones play multiple roles, any deficiency or excess can have a profound impact on the digestive process as described in Digestive Problems. Simply replacing the digestive enzymes will not compensate for digestive hormone disorders.

Gut Hormones – Trigger, Sources, Function

The digestive hormones are secreted in response to specific stimuli (triggers). This ensures that the entire process of digestion is coordinated in response to the changes within the gut and in the bloodstream. The actions or functions of these hormones as discussed below are in relation to its effect on digestion and/or absorption.

Digestive hormones may play additional roles in the body that is indirectly related to digestion, absorption and metabolism of nutrients. For example : ghrelin may stimulate the secretion of growth hormone.

Gastrin

  • Source
    • G cells in the stomach.
  • Trigger
    • Protein and amino acids stimulate gastrin secretion but somatostatin and acid suppresses gastrin secretion.
  • Action
    • Increases gastric acid secretion.

Somastatin

  • Source
    • D cells which are located throughout the gastrointestinal tract (gut).
  • Trigger
    • Eating fatty foods.
  • Actions
    • Reduces gastrin and stomach acid secretion.
    • Inhibits insulin and pancreatic enzyme secretion.
    • Decreases nutrient absorption from the gut.

Grehlin

  • Source
    • Stomach
  • Trigger
    • Secretion stimulated by fasting or starvation and suppressed by eating food.
  • Action
    • Stimulates appetite.

Cholecystokinin (CCK)

  • Source
    • First two parts of the small intestine (duodenum, jejunum) – I cells.
    • Nerve endings in the last part of the small intestine (ileum) and colon.
  • Triggers
    • Protein and amino acids.
    • Fatty foods.
    • Trypsin which is a pancreatic enzyme that assists with the digestion of proteins suppresses the secretion of CCK.
  • Actions
    • Feeling of satiety which reduces appetite.
    • Reduces gastric acid secretion and gastric emptying (passing of food from the stomach into the duodenum)
    • Stimulates pancreatic enzyme secretion.
    • Stimulates gallbladder contraction and bile flow.
    • Opens the sphincter of Oddi which allows the pancreatic enzymes and bile to enter the small intestine.

Secretin

  • Source
    • First two parts of the small intestine (duodenum, jejunum) – S cells.
  • Triggers
    • Acid in the duodenum (small intestine) – increase in pH.
    • Fatty acids.
  • Actions
    • Stimulates pancreatic fluid and bicarbonate secretion for the dilution and neutralization of stomach acid in the small intestine.
    • Decreases gastric acid secretion.
    • Reduces gastric emptying (passing of food from the stomach into the duodenum).

Motilin

  • Source
    • Small intestine
    • Colon
  • Triggers
    • Fasting, starvation.
    • Fatty foods.
  • Actions
    • Controls peristalsis by stimulating smooth muscle contraction and relaxation to coordinate the movement of food through the gut.
    • Regulates movement of residual undigested material¬† through the gut (migrating motor complexes or MMC) between meals.

Gastric Inihibitory Polypeptide (GIP)

  • Source
    • Duodenum and jejunum – K cells.
  • Triggers
    • Glucose.
    • Fatty foods.
  • Actions
    • Reduces gastric acid secretion.
    • Decreases gastric emptying.
    • Stimulates the release of insulin.

Vasoactive Intestinal Peptide (VIP)

  • Source
    • Nerve fibers supplying all parts of the gastrointestinal tract.
  • Triggers
    • Unknown at this point.
  • Actions
    • May have various effects on many parts of the body, not only the gastrointestinal tract.
    • Vasodilator – increases blood flow to the gut.
    • Empties water and electrolytes into pancreatic enzymes and bile.
    • May affect water and electrolyte transport between the bloodstream and gut lumen.
    • Relaxes smooth muscle, particularly that of the sphincters.
    • May play a role in blood glucose regulation.

Guanylin

  • Source
    • Small intestine.
    • Colon
  • Trigger
    • Unknown at this point.
    • Causes diarrhea which may be in response to certain stimuli (not as yet ascertained).
  • Actions
    • Secretion of chloride.
    • Decreases absorption of water from the gut.