The Digestive SystemThe Digestive System

Prepares food for use by all Prepares food for use by all body cells.body cells.

DigestionDigestionThe chemical breakdown of complex The chemical breakdown of complex biological molecules into their component biological molecules into their component parts.parts.– Lipids to fatty acids Lipids to fatty acids – Proteins to individual amino acidsProteins to individual amino acids– Carbohydrates into simple sugarsCarbohydrates into simple sugars

FunctionFunctionProduces various chemicals to Produces various chemicals to break down the food.break down the food.Filters out harmful substances.Filters out harmful substances.Gets rid of solid wastes.Gets rid of solid wastes.

DigestionDigestionMechanicalMechanical–Changes the physical form of foodChanges the physical form of food

Chew Chew TearTearGrindGrindMashMashMixMix

DigestionDigestionChemicalChemical– Changes the chemical composition of food Changes the chemical composition of food

with the aid of digestive enzymeswith the aid of digestive enzymesCarbohydrateCarbohydrateProteinProteinLipidLipid

– Digestive enzymes are special proteins that Digestive enzymes are special proteins that help break up large molecules of food into help break up large molecules of food into very tiny molecules that can be absorbed and very tiny molecules that can be absorbed and used by the cells in the form of nutrition.used by the cells in the form of nutrition.

Phases of DigestionPhases of Digestion

IngestionIngestionMovementMovementDigestionDigestionAbsorptionAbsorptionFurther digestionFurther digestion

The Digestive TractThe Digestive TractA long muscular A long muscular tube with many tube with many sections and sections and areas.areas.Begins with the Begins with the mouth and ends mouth and ends with the anus.with the anus.

The Digestive TractThe Digestive TractParts of the Digestive Parts of the Digestive TractTract– MouthMouth– PharynxPharynx– EsophagusEsophagus– Stomach Stomach – Small IntestineSmall Intestine– Large IntestineLarge Intestine

Accessory PartsAccessory PartsOrgans that are not in the digestive tract Organs that are not in the digestive tract but helps in the digestionbut helps in the digestion– TeethTeeth– Tongue Tongue – Salivary glandsSalivary glands– LiverLiver– Gall bladderGall bladder– PancreasPancreas

MouthMouthFunctions:Functions:– Food enters in the mouth or oral Food enters in the mouth or oral

cavitycavity– TastingTasting– Mechanical breakdown of foodMechanical breakdown of food– Secretion of salivary glands Secretion of salivary glands

(salivary amylase) (salivary amylase)

MouthMouthStructures in the mouth that aids digestion:Structures in the mouth that aids digestion:

Teeth – cut, tear, crush and grind food.Teeth – cut, tear, crush and grind food. Salivary glands – produce and secrete Salivary glands – produce and secrete saliva into the oral cavity. saliva into the oral cavity.

– Parotid (beneath the cheeks)Parotid (beneath the cheeks)– Submaxillary (below the jaw bone)Submaxillary (below the jaw bone)– Sublingual (below the tongue)Sublingual (below the tongue)

– – saliva moistens the food and contains saliva moistens the food and contains enzymes (enzymes (ptyalinptyalin or or salivarysalivary amylaseamylase) ) that begins digestion of starch into that begins digestion of starch into smaller polysaccharides.smaller polysaccharides.

MouthMouth TongueTongue– Mixes and rolls food into tiny Mixes and rolls food into tiny mashed up bitsmashed up bits ( (BolusBolus))

– Pushes the bolus toward the Pushes the bolus toward the pharynx and into the esophagus pharynx and into the esophagus when swallowing.when swallowing.

Anatomy of the Mouth and Anatomy of the Mouth and ThroatThroat

Human Deciduous and Human Deciduous and Permanent TeethPermanent Teeth

Mechanism of SwallowingMechanism of SwallowingSwallowing is a coordinated activity of the Swallowing is a coordinated activity of the tongue, soft palate, pharynx and esophagus.tongue, soft palate, pharynx and esophagus.PhasesPhases– Food is pushed into the Food is pushed into the pharynx pharynx by the by the

tongue. (voluntary) tongue. (voluntary) – Tongue blocks the mouthTongue blocks the mouth– Soft palate closes off the noseSoft palate closes off the nose– Larynx (Adam’s Apple) rises so the Larynx (Adam’s Apple) rises so the

Epiglottis Epiglottis (a flap of tissue) can close the (a flap of tissue) can close the opening of the trachea.opening of the trachea.

EsophagusEsophagusA straight muscular tube that is about 10 inches A straight muscular tube that is about 10 inches (25 cm) long which connects the mouth with the (25 cm) long which connects the mouth with the stomachstomachFood takes about 4 to 8 seconds as it passes Food takes about 4 to 8 seconds as it passes through to the stomach.through to the stomach.Its walls contain smooth muscles that contracts Its walls contain smooth muscles that contracts in wavy motion (in wavy motion (PeristalsisPeristalsis).).Peristalsis propels food and liquid slowly Peristalsis propels food and liquid slowly down the esophagus into the stomach.down the esophagus into the stomach.Cardiac Sphincter (ring-like valve) relaxes to Cardiac Sphincter (ring-like valve) relaxes to allow food into the stomach.allow food into the stomach.

PeristalsisPeristalsis

StomachStomachJ-shaped muscular sacJ-shaped muscular sacHas inner folds (Has inner folds (rugaerugae) that increases the ) that increases the surface area of the stomach.surface area of the stomach.Churns and grinds together the bolus into Churns and grinds together the bolus into smaller pieces.smaller pieces.Food is mixed with gastric juices Food is mixed with gastric juices (hydrochloric acid and enzymes) secreted (hydrochloric acid and enzymes) secreted by the stomach walls.by the stomach walls.HCL helps break down food and kills HCL helps break down food and kills bacteria that came along with the food.bacteria that came along with the food.

StomachStomach

StomachStomachPepsinPepsin – major enzyme; converts – major enzyme; converts proteins into peptides in the presence of proteins into peptides in the presence of HCL.HCL.MucusMucus – lubricates food and protects the – lubricates food and protects the gastric lining from strong digestive juices.gastric lining from strong digestive juices.Converts the bolus into a liquid Converts the bolus into a liquid ((chymechyme)) after 4 hrs of mechanical and after 4 hrs of mechanical and chemical digestionchemical digestionChyme passes through the Chyme passes through the pyloric pyloric sphinctersphincter into the small intestine. into the small intestine.

Movements in StomachMovements in Stomach

Small IntestineSmall IntestineLong (20 ft), coiled tube beneath the Long (20 ft), coiled tube beneath the stomach.stomach.Has three parts:Has three parts:

Duodenum – upper part; about 10 in; connected to Duodenum – upper part; about 10 in; connected to the stomach.the stomach.

– – where the digestive juices where the digestive juices from the pancreas and the liver combine with from the pancreas and the liver combine with chyme making it thin and watery. chyme making it thin and watery. Jejunum – about 8 ftJejunum – about 8 ftIleum – about 12 ftIleum – about 12 ft

Small IntestineSmall IntestineSite of greatest amount of digestion and absorptionSite of greatest amount of digestion and absorption

Small IntestineSmall IntestineTakes about 4 – 8 hrs to complete its journey.Takes about 4 – 8 hrs to complete its journey.Mucosa (inner wall) – secretes several enzymes Mucosa (inner wall) – secretes several enzymes that acts on the food.that acts on the food.Where the pancreatic enzymes are emptied into.Where the pancreatic enzymes are emptied into.Digested nutrients are absorbed through Digested nutrients are absorbed through intestinal walls.intestinal walls.Absorbed materials cross the mucosa into the Absorbed materials cross the mucosa into the blood then other parts of the body for storage or blood then other parts of the body for storage or further chemical change.further chemical change.

Small IntestineSmall IntestineHas folded inner walls covered with Has folded inner walls covered with fingerlike projections (fingerlike projections (villivilli; sing. – villus); sing. – villus)Each villus has tinier projections called Each villus has tinier projections called microvillimicrovilli that absorbs digested food. that absorbs digested food.Villi and microvilli increases the surface Villi and microvilli increases the surface area of the small intestine for greater area of the small intestine for greater absorption.absorption.Peristalsis moves the undigested food to Peristalsis moves the undigested food to the large intestine.the large intestine.

Movement in small intestine:Movement in small intestine:

Mixing: Segmental contraction that occurs in small intestineMixing: Segmental contraction that occurs in small intestineSecretion: Lubricate, liquefy, digestSecretion: Lubricate, liquefy, digestDigestion: Mechanical and chemicalDigestion: Mechanical and chemicalAbsorption: Movement from tract into circulation or lymphAbsorption: Movement from tract into circulation or lymphElimination: Waste products removed from bodyElimination: Waste products removed from body

Large IntestineLarge Intestinea.k.a. Colona.k.a. Colonlarger diameter, but shorter (5 ft)larger diameter, but shorter (5 ft)Water is absorbed from the Water is absorbed from the undigested food making the waste undigested food making the waste harder until it becomes solid.harder until it becomes solid.Waste stays for 10 – 12 hours.Waste stays for 10 – 12 hours.

Large IntestineLarge Intestine

Large IntestineLarge IntestineWaste is pushed into the expanded Waste is pushed into the expanded portion (rectum) of the large intestine.portion (rectum) of the large intestine.Solid waste stays in the rectum until it Solid waste stays in the rectum until it is excreted through the anus as is excreted through the anus as feces.feces.Appendix hangs on the right side of Appendix hangs on the right side of the large intestine.the large intestine.

Accessory OrgansAccessory OrgansProduce or store enzymes that helps in Produce or store enzymes that helps in digestion. digestion. Liver Liver – Largest gland of the bodyLargest gland of the body– Stores vitamins A,D,E,K Stores vitamins A,D,E,K – Stores sugar and glycogenStores sugar and glycogen– Produces Produces bilebile (watery, greenish (watery, greenish

substance) substance) – Secretes bile to the gall bladder via the Secretes bile to the gall bladder via the

hepatic duct and cystic duct.hepatic duct and cystic duct.

Accessory OrgansAccessory OrgansGall bladder Gall bladder – Stores bile in between mealsStores bile in between meals– Secretes bile to the duodenum through Secretes bile to the duodenum through

the bile duct during mealtime. the bile duct during mealtime. Bile contains bile salts, pigments, Bile contains bile salts, pigments, cholesterol and phospholipids.cholesterol and phospholipids.Bile is an emulsifier NOT an enzyme.Bile is an emulsifier NOT an enzyme.Emulsifier – dissolves fat into the Emulsifier – dissolves fat into the watery contents of the intestine.watery contents of the intestine.

Accessory OrgansAccessory OrgansPancreasPancreas– Produces a juice that contains Produces a juice that contains

enzymes (enzymes (amylase and insulinamylase and insulin) to ) to break down carbohydrates, fats break down carbohydrates, fats and protein.and protein.

– Secretes the juice into the Secretes the juice into the duodenum through the pancreatic duodenum through the pancreatic duct.duct.

Path of DigestionPath of Digestion

MouthMouthPharynxPharynxEsophagusEsophagusStomachStomachSmall IntestineSmall IntestineLarge IntestineLarge IntestineAnusAnus