THE EVENTS OF DIGESTION EVENTS IN THE MOUTH

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THE EVENTS OF DIGESTION

THE EVENTS OF DIGESTION

EVENTS IN THE MOUTH � Both chemical (via salivary amylase) and mechanical digestion (teeth)

EVENTS IN THE MOUTH � Both chemical (via salivary amylase) and mechanical digestion (teeth) take place in the mouth (chewing is mastication) � Salivary amylase breaks down starch via mixing with saliva � Chewed food is called a bolus once ready to swallow � Salivary reflexes are controlled by cranial nerves VII and IX and its parasympathetic control

EVENTS IN THE PHARYNX � Deglutition is the term for swallowing � Two phase

EVENTS IN THE PHARYNX � Deglutition is the term for swallowing � Two phase process � Phase one: Buccal Stage � Takes place in mouth, its when food is prepared for swallowing � Phase Two: Pharyngeal-Esophageal Phase: � Transport of food via peristalsis through the pharynx and esophagus

CONTROL OF SWALLOWING � Parasympathetic division of the nervous system controls this process �

CONTROL OF SWALLOWING � Parasympathetic division of the nervous system controls this process � Vagus nerve is the main nerve � Food can only move down to the stomach since all other openings are closed off and peristalsis only moves one way (to stomach)

EVENTS IN THE STOMACH � Food enters the stomach via the cardioesophageal sphincter �

EVENTS IN THE STOMACH � Food enters the stomach via the cardioesophageal sphincter � Gastric juices are released in response to the smell, taste, and sight of food � This prepares the stomach for the bolus which is coming down the esophagus � HCl is also released in response to rising GASTRIN levels (hormone released by stomach cells in response to food)

STOMACH � Gastrin stimulates the release of pepsinogens (protein digesters), mucus, and HCl. �

STOMACH � Gastrin stimulates the release of pepsinogens (protein digesters), mucus, and HCl. � Stomach releases mucus to protect itself from the HCl and enzymes that would digest it � HCl will activate the pepsinogen and convert it into pepsin which is the active protein digesting enzyme in the stomach

STOMACH � Rennin (second protein digesting enzyme) is released to work on dairy products

STOMACH � Rennin (second protein digesting enzyme) is released to work on dairy products (active in infants and children primarily) � Walls of the stomach churn to mechanically digest the food � The bolus is converted into a cream called chyme � 3 ml of chyme moves into the duodenum per contraction of the stomach � Takes 3 -6 hours to empty the stomach

SMALL INTESTINE � Fat digestion begins here, and all other digestion is completed �

SMALL INTESTINE � Fat digestion begins here, and all other digestion is completed � Brush-Boarder enzymes (associated with microvilli) complete carb digestion and protein digestion � Pancreatic juice is released into the intestine to assist and complete digestion

SMALL INTESTINE � Pancreatic juice consists of starch digesters (pancreatic amylases), protein digesters (trypsin,

SMALL INTESTINE � Pancreatic juice consists of starch digesters (pancreatic amylases), protein digesters (trypsin, chymotrypsin, carboxypeptidase), and all fat digesters (lipases), as well as nucleic acid digesters (nucleases) � Also contains bicarbonate ions to neutralize the chyme from the stomach � Secretin and cholecystokinin control the release of pancreatic juices and bile

SMALL INTESTINE � Bile is released from the gallbladder to emulsify fats � Nutrients

SMALL INTESTINE � Bile is released from the gallbladder to emulsify fats � Nutrients and water are absorbed as the chyme moves through � Wastes, ions, and water is all that should be left at the end of the small intestine (ilium)

EVENTS IN THE LARGE INTESTINE � Bacteria in the colon will metabolize any remaining

EVENTS IN THE LARGE INTESTINE � Bacteria in the colon will metabolize any remaining nutrients which produces gas � Vitamins B and K are produced and absorbed � Ions and water are absorbed � Feces is removed in mass movements as necessary � Materials can stay between 12 and 24 hours

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