The Events of Digestion

The Events of Digestion

Events in the MouthBoth chemical (via salivary amylase) and mechanical digestion (teeth) take place in the mouth (chewing is mastication)Salivary amylase breaks down starch via mixing with salivaChewed 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 PharynxDeglutition is the term for swallowingTwo phase processPhase one: Buccal StageTakes place in mouth, its when food is prepared for swallowingPhase Two: Pharyngeal-Esophageal Phase:Transport of food via peristalsis through the pharynx and esophagus

Control of SwallowingParasympathetic division of the nervous system controls this processVagus nerve is the main nerveFood 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 stomachFood enters the stomach via the cardioesophageal sphincterGastric juices are released in response to the smell, taste, and sight of foodThis prepares the stomach for the bolus which is coming down the esophagusHCl 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 releases mucus to protect itself from the HCl and enzymes that would digest itHCl will activate the pepsinogen and convert it into pepsin which is the active protein digesting enzyme in the stomachStomachRennin (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 foodThe bolus is converted into a cream called chyme3ml of chyme moves into the duodenum per contraction of the stomach Takes 3-6 hours to empty the stomach

Small IntestineFat digestion begins here, and all other digestion is completed Brush-Boarder enzymes (associated with microvilli) complete carb digestion and protein digestionPancreatic juice is released into the intestine to assist and complete digestion

Small intestinePancreatic 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 stomachSecretin and cholecystokinin control the release of pancreatic juices and bile

Small intestineBile is released from the gallbladder to emulsify fatsNutrients 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 intestineBacteria in the colon will metabolize any remaining nutrients which produces gasVitamins B and K are produced and absorbedIons and water are absorbedFeces is removed in mass movements as necessary Materials can stay between 12 and 24 hours

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