Regulation of Digestion

Flashcards covering the regulation of digestion, including neural and hormonal control, reflexes, and the roles of various organs and hormones.

Digestion Control Purpose

To create conditions in GI tract to maximise digestion & absorption & To slow down gut movements & secretions during post- absorptive phase (conserve energy)

Activities Controlled in Digestion

Salivary secretion, Gastric juice secretion & motility of stomach, Secretion of bile & pancreatic juice into small intestine & motility, Movements of large intestine

How is the GIT Controlled?

Digestive Reflexes (Automatic responses to stimuli) are mediated via the Nervous System and the Endocrine System.

Enteric Nervous System

The 'built-in' nervous system of the GIT that controls most gut movements & secretions. Consists of the Submucosal plexus (controls secretions) and the Myenteric plexus (controls motility).

Vagus Nerve (Parasympathetic)

Innervates stomach, liver & small intestine and Increases activity of the GIT

Sympathetic Nerves

Decreases activity of the GIT

Ivan Pavlov

First physiologist to win the Nobel Prize in 1904 for Understanding/research on neural control of salivary, gastric and pancreatic secretion and Pavlov theory of “Classical Conditioning” (learning by association)

Salivary Secretion Control

Entirely nervous -no hormones involved and Salivary center in medulla oblongata

Conditioned Reflex

Sight, smell, or even thought of food can increase saliva secretion, as demonstrated by Pavlov's dogs conditioned to salivate at the sound of a bell

Main Hormones Involved in Endocrine Control

Gastrin, Cholecystokinin (CCK), and Secretin

Gastric Activity Phases

Cephalic phase (before food arrives), Gastric phase (when food reaches stomach), and Intestinal phase (when chyme enters duodenum)

Cephalic Phase

Occurs before food arrives in stomach and prepares the stomach for digestion by Increasing gastric juice production via neural control.

Gastric Phase

Starts when food reaches the stomach. Neural & hormonal control. Need to ↑ gastric secretion & motility. Lasts 3-4h

Intestinal Phase

Chyme gradually leaves stomach & enters duodenum. Need to :↓ gastric secretion & motility and: ↑ bile secretion, ↑ pancreatic juice, 2 main hormones involved: CCK & Secretin

Cholecystokinin (CCK)

Released in response to Fats & peptides in chyme. Results = Contraction of gall bladder, ↑ pancreatic enzymes, ↑BILE, ↑ fat & protein digestion (also↓ gastric activity; relaxes hepatopancreatic sphincter)

Secretin

Released due to Acidic chyme in duodenum. Results= ↑ bicarbonate-rich pancreatic juice which Neutralises acidic chyme (Also ↓ gastric secretion & motility)

Enterogastric Reflex

Distention in duodenum initiates this reflex to Decrease gastric juice & motility, Increase segmentation in SI, and cause Contraction of pyloric sphincter.

Gastroileal Reflex

Stomach fills, Stretch receptors activated, Peristalsis in SI & relaxation of ileocaecal sphincter, pushes remnants into LI (caecum)

Gastrocolic Reflex

Distention of stomach while eating causes Powerful peristaltic contractions from middle of colon (3-4 times/d) (Mass peristalsis) that Forces faeces into rectum and Defaecation reflex