Mechanical Digestion in the Gastrointestinal Tract
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b. Open the Digestive System File.
c. Click Animations.
d. Click Mechanical Digestion in the Gastrointestinal Tract.
Define the gastrointestinal tract (GI). The GI tract is the stomach and intestine divided up into the upper and lower GI
Identify three mechanical digestion activities.
b. Mixing food and saliva with tongue
c. Churning food into the stomach
Name two feedback loops that regulate digestive system smooth muscle responsible for propulsive and mixing movements.
Alternating contractions of smooth muscle in the walls of the GI tract and motility
Neural Regulation of Mechanical Digestion
Identify three neural systems that control the mechanical movements in the GI tract.
Enteric Nervous System
Autonomic Nervous System
Central Nervous System
Describe the role of the CNS with regard to swallowing. What is the stimulus?
Nerve signals tell the brain what is the right thing to eat such as temperature and size and then causes saliva to be produced and moistens the food and forms the bolus which is then pushed down the throat after the CNS send the signal to contract smooth muscle
What are the components of the ANS (long) neural reflexes? Vagus nerve which supplies the parasympathetic fibers to most parts of the GI.
What is the stimulus for ANS regulation? Neurons and stretch receptors
What do ANS neurons regulate with regard to mechanical digestion? What are the possible responses?
They regulate smooth muscle and the glands within the GI tract.
Where are enteric nervous system plexuses located? In the submucosa
Define and describe the events of mastication. When food is manipulated by the tongue, ground up by the teeth and mixed with saliva to form bolus.
Define deglutition. The act of swallowing
Describes during each stage of deglutition.
Voluntary: The bolus is passed into the oropharynx
Involuntary pharyngeal: The bolus is passed from the pharynx to the esophagus
Involuntary esophageal: The bolus is passed through the esophagus into the stomach
Describe peristaltic movement. A progression of coordinated contractions and relaxations of the circular and longitudinal layers of the muscularis, which moves the bolus forward
Explain the role of stomach stretch receptors. These receptors are activated in the GI tract once it is distended by food
What is the function of stomach mixing waves? These waves passed over the stomach every 15 to 25 seconds and mix food with secretions of the gastric glands.
Describe the role of the parasympathetic nervous system relative to digestive movements. The system supplies the GI tract and form neural connections with the ENS
What are three functions of the enterogastric reflex?
a. Distention of the duodenum by the presence of partly digested food known as chyme
b. Gastric motility is inhibited, increasing the contraction of the pyloric sphincter
c. Decreases gastric emptying
Determine if these motor impulses are sympathetic or parasympathetic. Parasympathetic
Segmentation and Migrating Motility Complexes
Describe segmentation and its effect. Mixing contractions that occur in portions of the intestines that were distended by large amounts of partially digested food.
Describe migrating motility complexes. This contraction occurs in the small intestine and pushes the partially digested food forward
The ileocecal valve is normally closed. Explain the role of the gastroileal reflex.
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