Chapter 14: Functions of the Digestive System What activities occur within the GI Tract?
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Transcript of Chapter 14: Functions of the Digestive System What activities occur within the GI Tract?
Chapter 14: Functions of the Digestive System
What activities occur within the GI Tract?
Essential Activities of the GI Tract
• Ingestion• Propulsion• Mechanical Digestion• Chemical Digestion• Absorption• Defacation
IngestionIngestionFood enters the mouth• leads to Mechanical and Chemical Digestion• Teeth and tongue help to Physically Break it down
Saliva:starts to break down starch (into maltose)is continuously produced, but in excess with food
ingestionother stimuli can cause production of Saliva
(smells, thoughts, nervous response)
Propulsion
Food need to be moved from one digestive organ to another
Peristalsis rhythmic contractions of smooth muscle to propel food forward
Segmentation single segments of the small intestine alternately contract/relax
Propulsion and Swallowing
Swallowing (Deglutition) has 2 phases and involvesmany structures:
Tongue, soft palate, pharynx, esophagus
Phase 1 Buccal Phase (this is voluntary action in the mouth)Phase 2 Pharyngeal-Esophageal Phase –transport through
the pharynx and esophagus
Involuntary action controlled by the Autonomic Nervous System
Propulsion
At the end of the esophagus swallowed food presses against the Cardioesophageal sphincter
Chyme approaches the pyloric region of the stomach
Pyloric Sphincter—allows passage into the small intestine
Mechanical Digestion
Mechanical Digestion prepares food for further breakdown by enzymes
Grinding action of the teeth Mixing of the food by the tongue churning of food in the stomach
Mechanical DigestionFood Breakdown regulated by hormones and
neural factors
Sight and smell of foods can initiate the secretion of gastric juices
Gastrin hormone that causes the stomach to produce more:
1.) Pepsinogens (enzymes)2.) Mucus3.) Hydrochloric Acid
Chemical Digestion
Chemical Digestion the sequence of steps that occur in which large food molecules are broken down to their building blocks by enzymes
Break down:Carbs, Lipids, Proteins
Chemical DigestionCarbohydrates sucrose, lactose, maltose and starch
ex.) Polysaccharides broken down into Monosaccharides
Cellulose containing foodstuffs cannot be digested by the human stomach (FIBER)
*These provide bulk and help move foodstuffs along
Proteins broken down into their building blocks: Amino Acids
Lipids yield two types of building blocks when digested: Fatty Acids and Glycerols
AbsorptionAbsorption transport of digested end products
(from Carbs / Proteins / Fats) to the blood
DefacationElimination of solid wastesMass Movements Movement of the colon that
will propel solid wastes alongGoblet Cells produces mucus that will lubricate
the colonDisruptions to homeostasis:Constipation slow movement of wastesDiarrhea rapid waste movement with fluid loss
Nervous Control
Autonomic Nervous System controls function
Sensory receptors respond to:1.) Stretch of an organ caused by food2.) pH of the foodstuffs3.) presence of certain breakdown products
Receptors then:1.) activate / inhibit glands that secrete essential digestive juices2.) activate / inhibit the smooth muscles that mix and propel
food along
Stomach ActionAs food enters the stomach:1.) Walls are stretched2.) Gastric Juices are produced3.) Stomach smooth muscle layers (3) begin to churn and
break apart food4.) Chyme is produced (which will move along to the small
intestine)
Stomach Enzymes:1.) Pepsin (acts to break down proteins)2.) Rennin (acts to break down milk proteins)
Digestive Enzymes Brush Border Enzymes break double sugars into
simple sugars for digestion
Pancreatic Juice: 1.) completes the digestion of starch2.) carries of about half of the protein digestion3.) responsible for fat digestion4.) digest nucleic acids
Insulin and Glucagon Controls blood sugar
Digestive HormonesHormones Secretin and Cholecystokinin
influence the release of pancreatic juice and bile
Secretin causes the liver to increase the output of bileCholecystokinin causes the gallbladder to contract and
release stored bile