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