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Introduction to the
gastrointestinal system
Learning objectives
Upon completion of this chapter, you should be able to:
1.
Label the parts of the gastrointestinal (GI) tract on a diagram, describing the secretions, absorption, digestion
and type of motility that occurs in each part.
2.
Discuss the nervous system control of the GI tract, including influences of the autonomic nervous system on
GI activity.
3.
List three of the local GI reflexes and describe the clinical application of each.
4.
Describe the steps involved in swallowing, including two factors that can influence this reflex.
5.
Discuss the vomiting reflex, addressing three factors that can stimulate the reflex.
Glossary of key terms
bile:
fluid stored in the gallbladder that contains cholesterol and bile salts; essential for the proper breakdown and absorption of fats
chyme:
contents of the stomach containing ingested food and secreted enzymes, water and mucus
gallstones:
hard crystals formed in the gallbladder when the bile is concentrated
gastrin:
substance secreted by the stomach in response to many stimuli; stimulates the release of hydrochloric acid from the parietal
cells and pepsin from the chief cells; causes histamine release at histamine-2 receptors to effect the release of acid
histamine-2 (H
2
) receptors:
sites near the parietal cells of the stomach that, when stimulated, cause the release of hydrochloric acid
into the lumen of the stomach; also found near cardiac cells
hydrochloric acid:
acid released by the parietal cells of the stomach in response to gastrin release or parasympathetic stimulation;
makes the stomach contents more acidic to aid digestion and breakdown of food products
local gastrointestinal reflex:
reflex response to various stimuli that allows the GI tract local control of its secretions and movements
based on the contents or activity of the whole GI system
nerve plexus:
network of nerve fibres running through the wall of the GI tract that allows local reflexes and control
pancreatic enzymes:
digestive enzymes secreted by the exocrine pancreas, including pancreatin and pancrelipase, which are needed
for the proper digestion of fats, proteins and carbohydrates
peristalsis:
type of GI movement that moves a food bolus forward; characterised by a progressive wave of muscle contraction
saliva:
fluid produced by the salivary glands in the mouth in response to tactile stimuli and cerebral stimulation; contains enzymes to
begin digestion, as well as water and mucus to make the food bolus slippery and easier to swallow
segmentation:
GI movement characterised by contraction of one segment of the small intestine while the next segment is relaxed;
the contracted segment then relaxes, and the relaxed segment contracts; exposes the chyme to a vast surface area to increase
absorption
swallowing:
complex reflex response to a bolus in the back of the throat; allows passage of the bolus into the oesophagus and
movement of ingested contents into the GI tract
vomiting:
complex reflex mediated through the medulla after stimulation of the chemoreceptor trigger zone; protective reflex to
remove possibly toxic substances from the stomach
Test your current knowledge of the gastrointestinal system with a PrepU Practice Quiz!
