Exercise 42 Digestive Physiology

Chemical digestion Digestive enzymes Proteins Catalysts Hydrolytic enzymes or hydrolases Highly specific in action

Figure 23.33a

Figure 23.33b

Physical digestion Deglutition Buccal phase Voluntary Compression of the bolus against the hard palate Retraction of the tongue Elevation of the soft palate to close the nasopharynx Propelling of the food to the oropharynx

Physical digestion Pharyngeal-esophageal phase Involuntary Begins with the swallowing reflex Pharyngeal contraction Closing of the glottis by the epiglottis Stopping of breathing Bolus reaches the esophagus Peristaltic movements take the bolus to the stomach

Physical digestion Peristalsis Waves of contraction alternated with waves of relaxation of the GI wall They propel the food through the digestive tract

Physical digestion Segmentation Rhythmic local constriction of the organ wall Mixes the chyme with digestive enzymes Increases the rate of food absorption 8