You have just eaten a bacon, lettuce and tomato sandwich with regular mayonnaise

Question

You have just eaten a bacon, lettuce and tomato sandwich with regular mayonnaise on whole wheat bread. Outline in the form of a flow chart or any other way that clearly shows what happens to the sandwich as it enters the digestive system and goes through the GI tract. Include all of the steps of digestion: ingestion, mechanical digestion, propulsion, chemical digestion, absorption and defecation. Also indicate the ultimate fate of the organic monomers (where do they go and by what means-blood or lymph).

Explanation / Answer

1) oral cavity --mechanical mastication: you chew the food and increase its surface area --chemical digestion: saliva (containing salivary amylase) begins to hydrolize starches into simple sugars. --tongue rolls food into bolus that's forced down the pharynx and swallowed. 2) Pharynx 3) Esophagus --Peristalis: involuntary muscular contractions that force bolus into stomach --esophageal sphincter opens to allow passage of food 4) Stomach --gastric glands: Parietal cells secrete hydrochloric acid which activates pepsinate (secreted by chief cells) into pepsin. Pepsin cuts up proteins into polypeptides. --pyloric glands: Secrete gastrin, a hormone which causes the release of more hydrochloric acid. This reduces bolus to an acidic mixture called chyme. --food leaves stomach through pyloric sphincter 5) Small Intestine/Duodenum-- Digestion --Chyme enters; this causes duodenum to release hormones: A. Secretin: Attaches to receptors on pancreas. Pancreas releases bicarbonate to neutralize acidic chyme. B. CCK: (1) signals gall bladder to release bile in order to emulsify chyme. (2) signals pancreas to release digestive enzymes: proteases, lipases, nucleases, amylases, peptidases C. The duodenum itself releases disaccharidases, peptidases, and enterokinases. 6) Small Intestine/ Jejunum & Ilium -- Absorption -- carbohydrates and amino acids are absorbed (actively) into epithelial cells of gut and into intestinal capillaries. There’s a lower concentration of them in the blood, so they diffuse into blood capillaries and absorbed by the liver. -- Large fats, like glycerol and cholesterol, are packaged into chylomicrons and enter lymphatic circulation directly through lacteals. 7) Large Intestine/ Cecum & Colon &Rectum --the colon absorbs water and salt in undigested material from small intestine. It also serves to reabsorb any nutrients missed by the small intestine. --rectum stores feces; the anus eliminates feces.

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