WWA #2 Ch. 3 The Alimentary Canal: Digestion and Absorption

Physiology of G.I Tract

alimentary canal: extending from the mouth to the anus, comprises all the body parts through which food passes

chemical action: hydrolysis reactions occur in the digestive tract for nutrients in food to be utilized


Protein + H20 --> amino acides


Fat +H20 ---> fatty acids + glycerol


Carbohydrates +H20 ---> monosaccharides

mechanical action: peristalsis: involuntary rhythmic waves of contraction traveling the length of the alimentary tract


valves or sphincter muscles: designed to a) retain food in each segment until completion of the mechanical actions and digestive juices b) allow measured amounts of food to pass into the next segment c) prevent food from "backing up"

Digestive functions of saliva

mucous - glycoprotein - lubricates food for easier passage and protects the lining of the G.I tract

ptyalin (salivary amylase) - enzyme - initiates hydrolysis of complex carbohydrates to simple sugars

lypozyme (antibody) - enzyme - breaks down cell walls of some ingested bacteria

salivary lipase - enzyme - initiates hydrolysis of lipids

saliva

remove debris and microorganisms

provide antibacterial action

lubricates oral tissues in the oral cavity and taste buds

neutralize, dilute, and buffer bacterial acids

promote ease of speech

remineralize (restoration or renewal of calcium, phosphates, and other minerals to areas damaged by incipient caries, abrasion, or erosion

facilitate taste

prevent plaque accumulation

digestive function organs

liver: regulates biochemical reactions; filters harmful substances, stores fat soluble vitamins and minerals; helps in metabolism of micronutrients; synthesizes proteins; produces bile

gallbladder: stores and secretes bile

stomach: mixes food with hydrochloric acid and enzymes to aid in digestion and kill harmful microorganisms; semi-liquid mixture is called chyme, limited absorption

pancreas: produces bicarbonates to neutralize stomach acid; secretes several digestive enzymes and insulin that regulates blood glucose

esophagus: transports food via peristalsis

small intestine: completes digestion by enzymes and bile; absorption of most nutrients

salivary glands: produces saliva to moisten food and produces digestive enzymes

large intestine: absorbs water and some ions; forms and store feces

pharynx: helps prevent food entering the lungs

rectum: stores and expels feces

mouth: breaks up food particles for swallowing and digestion

exit for fecal expulsion

key points

lower esophageal sphincter (LES) comprises a group of very strong circular muscle fibers just above the stomach

pancreatic enzymes enter the duodenum through the pancreatic duct and function best in neutralized chyme

digestion of food is facilitated by increasing its surface area

approximately 80-90% of fluid intake is absorbed in the small intestine by osmosis

larger pieces of food may obstruct airway (asphyxiation)

low pH of stomach contents

activates gastric enzymes

hydrolyzes some carbohydrates

denatures proteins and facilitates hydrolysis to amino acids

increases solubility and absorption of calcium and iron

kills or inhibits growth of most bacteria