The Digestive SystemThe Digestive System

Objectives:Objectives:• List and describe the major functions of List and describe the major functions of

the digestive system.the digestive system.• Describe why digestion of food is Describe why digestion of food is

necessary and compare mechanical and necessary and compare mechanical and chemical digestionchemical digestion

• Identify the major digestive organs, the Identify the major digestive organs, the digestive accessory glands, and their digestive accessory glands, and their functionsfunctions

• Describe the absorption of food in the Describe the absorption of food in the small intestine and the absorption of small intestine and the absorption of water in the large intestinewater in the large intestine

• List and describe disorders and diseases List and describe disorders and diseases of the digestive systemof the digestive system..

FunctionFunction

• DigestionDigestion– Breakdown of ingested foodBreakdown of ingested food– Absorption of nutrients into the bloodAbsorption of nutrients into the blood

• Once the nutrients are absorbed by the Once the nutrients are absorbed by the digestive system they are transported by digestive system they are transported by the blood to the tissues for metabolism.the blood to the tissues for metabolism.– Production of cellular energy (ATP)Production of cellular energy (ATP)– Constructive and degradative cellular Constructive and degradative cellular

activitiesactivities

Types of DigestionTypes of Digestion• Digestion is a catabolic process in which large Digestion is a catabolic process in which large

complex molecules (carbohydrates, lipids, complex molecules (carbohydrates, lipids, proteins, nucleic acids) are broken down into proteins, nucleic acids) are broken down into simpler monomers (monosaccharides, glycerol simpler monomers (monosaccharides, glycerol and fatty acids, amino acids, and nucleotides) and fatty acids, amino acids, and nucleotides) which can be absorbed by the body.which can be absorbed by the body.

• There are two forms of digestion:There are two forms of digestion:a. a. mechanical:mechanical: In mechanical there In mechanical there

is no chemical change in the food. The food is is no chemical change in the food. The food is simply broken down into smaller pieces and simply broken down into smaller pieces and mixed with digestive juices secreted in the mixed with digestive juices secreted in the body. Ex. Mastication (chewing)body. Ex. Mastication (chewing)

b. b. chemicalchemical: In chemical digestion : In chemical digestion the is a chemical change in the food. The the is a chemical change in the food. The polymers are broken down into monomers polymers are broken down into monomers commonly by hydrolysis reactions carried out commonly by hydrolysis reactions carried out by enzymes contained within the digestive by enzymes contained within the digestive juices.juices.

Six Processes of Six Processes of DigestionDigestion

• Ingestion – getting food into the mouthIngestion – getting food into the mouth• Propulsion – moving foods from one region of the Propulsion – moving foods from one region of the

digestive system to anotherdigestive system to another• Mechanical digestionMechanical digestion

– Mixing of food in the mouth by the tongueMixing of food in the mouth by the tongue– Churning of food in the stomachChurning of food in the stomach– Segmentation in the small intestineSegmentation in the small intestine

• Chemical DigestionChemical Digestion– Enzymes break down food molecules into their building Enzymes break down food molecules into their building

blocksblocks– Each major food group uses different enzymesEach major food group uses different enzymes

• Carbohydrates are broken to simple sugarsCarbohydrates are broken to simple sugars• Proteins are broken to amino acidsProteins are broken to amino acids• Fats are broken to fatty acids and alcoholsFats are broken to fatty acids and alcohols

• AbsorptionAbsorption– End products of digestion are absorbed in the blood or End products of digestion are absorbed in the blood or

lymphlymph– Food must enter mucosal cells and then into blood or Food must enter mucosal cells and then into blood or

lymph capillarieslymph capillaries• DefecationDefecation

– Elimination of indigestible substances as fecesElimination of indigestible substances as feces

Digestive ProcessesDigestive Processes

Divisions of Digestive Divisions of Digestive System OrgansSystem Organs

• Two main groupsTwo main groups– Alimentary canal – continuous Alimentary canal – continuous

coiled hollow tube that runs from coiled hollow tube that runs from the mouth to the anusthe mouth to the anus

– Accessory digestive organs- secrete Accessory digestive organs- secrete digestive juices by ducts (exocrine digestive juices by ducts (exocrine glands) into the alimentary canal.glands) into the alimentary canal.

Organs of the Alimentary Organs of the Alimentary CanalCanal

• MouthMouth• PharynxPharynx• EsophagusEsophagus• StomachStomach• Small intestineSmall intestine• Large intestineLarge intestine• AnusAnus

Accessory Digestive Accessory Digestive OrgansOrgans

• Salivary glandsSalivary glands• TeethTeeth• PancreasPancreas• LiverLiver• Gall BladderGall Bladder

Digestive OrgansDigestive Organs

Mouth Oral Cavity Mouth Oral Cavity (Alimentary Canal)(Alimentary Canal)

• Mastication Mastication (chewing) of food(chewing) of food

• Mixing Mixing masticated food masticated food with salivawith saliva

• Initiation of Initiation of swallowing by swallowing by the tonguethe tongue

• Allowing for the Allowing for the sense of tastesense of taste

Salivary Glands (Accessory Salivary Glands (Accessory Organs)Organs)

Salivary Glands:Salivary Glands:• Saliva-producing glandsSaliva-producing glands

– Parotid glands – located anterior to earsParotid glands – located anterior to ears– Submandibular glandsSubmandibular glands– Sublingual glandsSublingual glands

Saliva:Saliva:• Mixture of mucus and serous fluidsMixture of mucus and serous fluids• Helps to form a food bolusHelps to form a food bolus• Contains salivary amylase to begin Contains salivary amylase to begin

starch digestionstarch digestion• Dissolves chemicals so they can be Dissolves chemicals so they can be

tastedtasted

Teeth (Accessory Teeth (Accessory Organs)Organs)

• The role is to masticate The role is to masticate (chew) food(chew) food

• Humans have two sets of Humans have two sets of teethteeth– Deciduous (baby or milk) Deciduous (baby or milk)

teethteeth– 20 teeth are fully formed 20 teeth are fully formed

by age twoby age two• Permanent teethPermanent teeth

– Replace deciduous teeth Replace deciduous teeth beginning between the beginning between the ages of 6 to 12ages of 6 to 12

– A full set is 32 teeth, but A full set is 32 teeth, but some people do not have some people do not have wisdom teethwisdom teeth

• Types of teeth:Types of teeth:Incisors - cuttingIncisors - cuttingCanines - tearingCanines - tearingPremolars – Premolars –

shearing, shearing, shreddingshreddingMolars - grindingMolars - grinding

Tooth StructureTooth Structure• Crown – exposed partCrown – exposed part

– Outer enamelOuter enamel– DentinDentin– Pulp cavityPulp cavity

• NeckNeck– Region in contact with Region in contact with

the gumthe gum– Connects crown to rootConnects crown to root

• RootRoot– Periodontal membrane Periodontal membrane

attached to the boneattached to the bone– Root canal carrying Root canal carrying

blood vessels and blood vessels and nervesnerves

Pharynx (Alimentary Pharynx (Alimentary Canal)Canal)

• Serves as a passageway Serves as a passageway for air and foodfor air and food

• Food is propelled to Food is propelled to the esophagus by two the esophagus by two muscle layersmuscle layers– Longitudinal inner layerLongitudinal inner layer– Circular outer layerCircular outer layer

• Food movement is by Food movement is by alternating alternating contractions of the contractions of the muscle layers muscle layers (peristalsis)(peristalsis)

Esophagus (Alimentary Esophagus (Alimentary Canal)Canal)

• Runs from pharynx to stomach Runs from pharynx to stomach through the diaphragmthrough the diaphragm

• Conducts food by peristalsis Conducts food by peristalsis (slow rhythmic squeezing)(slow rhythmic squeezing)

• Passageway for food only Passageway for food only (respiratory system branches off (respiratory system branches off after the pharynx)after the pharynx)

Alimentary Canal Organ Alimentary Canal Organ Structure and Tissue Structure and Tissue

ArrangementArrangement• MucosaMucosa– Innermost layerInnermost layer– Moist membraneMoist membrane

• Surface epitheliumSurface epithelium• Small amount of connective Small amount of connective

tissue tissue (lamina propria)(lamina propria)

• Small smooth muscle layerSmall smooth muscle layer• SubmucosaSubmucosa

– Just beneath the mucosaJust beneath the mucosa– Soft connective tissue with Soft connective tissue with

blood vessels, nerve endings, blood vessels, nerve endings, and lymphaticsand lymphatics

• Muscularis externa – smooth Muscularis externa – smooth musclemuscle– Inner circular layerInner circular layer– Outer longitudinal layerOuter longitudinal layer

• SerosaSerosa– Outermost layer – visceral Outermost layer – visceral

peritoneumperitoneum– Layer of serous fluid-Layer of serous fluid-

producing cellsproducing cells

Stomach (Alimentary Stomach (Alimentary Canal)Canal)

• Located on the left side of the abdominal Located on the left side of the abdominal cavitycavity

• Food enters at the cardioesophageal sphincterFood enters at the cardioesophageal sphincter• Regions of the stomachRegions of the stomach

– Cardiac region – near the heartCardiac region – near the heart– FundusFundus– BodyBody– Pylorus – funnel-shaped terminal endPylorus – funnel-shaped terminal end

• Food empties into the small intestine at the Food empties into the small intestine at the pyloric sphincterpyloric sphincter

• Rugae – internal folds of the mucosaRugae – internal folds of the mucosa• External regionsExternal regions

– Lesser curvatureLesser curvature– Greater curvatureGreater curvature

Stomach (Alimentary Stomach (Alimentary Canal)Canal)

• Acts as a storage Acts as a storage tank for foodtank for food

• Site of food Site of food breakdownbreakdown

• Chemical Chemical breakdown of breakdown of protein beginsprotein begins

• Delivers chyme Delivers chyme (processed food) to (processed food) to the small intestinethe small intestine

Stomach: Mucosal LayerStomach: Mucosal Layer• Simple columnar Simple columnar

epitheliumepithelium– Mucous neck cells Mucous neck cells

(goblet cells) – produce a (goblet cells) – produce a sticky alkaline mucussticky alkaline mucus

– Gastric glands – secrete Gastric glands – secrete gastric juicegastric juice

– Chief cells – produce Chief cells – produce protein-digesting protein-digesting enzymes (pepsinogens)enzymes (pepsinogens)

– Parietal cells – produce Parietal cells – produce hydrochloric acidhydrochloric acid

– Endocrine cells – Endocrine cells – produce gastrinproduce gastrin

• Gastric pits formed by Gastric pits formed by folded mucosafolded mucosa

• Glands and specialized Glands and specialized cells are in the gastric cells are in the gastric gland regiongland region

Small Intestine (Alimentary Small Intestine (Alimentary Canal)Canal)

• The body’s major digestive organ all digestion of food The body’s major digestive organ all digestion of food is completed in this organis completed in this organ

• Site of nutrient absorption into the bloodSite of nutrient absorption into the blood• Muscular tube extending form the pyloric sphincter Muscular tube extending form the pyloric sphincter

to the ileocecal valveto the ileocecal valve• Suspended from the posterior abdominal wall by the Suspended from the posterior abdominal wall by the

mesenterymesentery• Duodenum (25cm = 10 inches) “12 finger widths Duodenum (25cm = 10 inches) “12 finger widths

long”long”– Attached to the stomachAttached to the stomach– Curves around the head of the pancreasCurves around the head of the pancreas– Where bile and pancreatic juices enter the alimentary Where bile and pancreatic juices enter the alimentary

canalcanal• Jejunum (2.5m = 8 feet) “empty”Jejunum (2.5m = 8 feet) “empty”

– Attaches anteriorly to the duodenumAttaches anteriorly to the duodenum• Ileum (3.6m = 12 feet) “twisted”Ileum (3.6m = 12 feet) “twisted”

– Extends from jejunum to large intestineExtends from jejunum to large intestine

Duodenum and Accessory Duodenum and Accessory Glands ConnectedGlands Connected

Small Intestine Internal Small Intestine Internal StructureStructure

• Villi are small fingerlike Villi are small fingerlike structures formed by the structures formed by the mucosamucosa

• Give the small intestine Give the small intestine more surface area for more surface area for absorptionabsorption

• Fold in the intestine are Fold in the intestine are called circular folds or called circular folds or plicae circularesplicae circulares

• Deep folds of the Deep folds of the mucosa and submucosamucosa and submucosa

• Do not disappear when Do not disappear when filled with foodfilled with food

• The submucosa has The submucosa has Peyer’s patches Peyer’s patches (collections of lymphatic (collections of lymphatic tissue)tissue)

Villi Internal Structure and Villi Internal Structure and FunctionFunction

• Absorptive cellsAbsorptive cells are found are found on the surface epithelium on the surface epithelium which are simple columnar which are simple columnar microvilliated epitheliummicrovilliated epithelium

• Blood capillariesBlood capillaries are below are below the surface epithelium and the surface epithelium and this is where this is where monosaccharides, amino monosaccharides, amino acids, and nucleic acids acids, and nucleic acids enter into the blood stream enter into the blood stream and are taken to the liver and are taken to the liver for processingfor processing

• LactealsLacteals (specialized (specialized lymphatic capillaries) where lymphatic capillaries) where lipids are absorbed and lipids are absorbed and eventually re-enter the eventually re-enter the blood stream to be taken to blood stream to be taken to the liver for processing.the liver for processing.

Pancreas (Accessory Pancreas (Accessory Organ)Organ)

• Produces a wide spectrum of Produces a wide spectrum of digestive enzymes that break down digestive enzymes that break down all categories of foodall categories of food

• Enzymes are secreted into the Enzymes are secreted into the duodenumduodenum

• Alkaline fluid introduced with Alkaline fluid introduced with enzymes neutralizes acidic chymeenzymes neutralizes acidic chyme

• Endocrine products of pancreasEndocrine products of pancreas– InsulinInsulin– GlucagonGlucagon

Liver and Gall Bladder Liver and Gall Bladder (Accessory Organs)(Accessory Organs)

• Largest gland in the bodyLargest gland in the body• Located on the right side of the Located on the right side of the

body under the diaphragmbody under the diaphragm• Consists of four lobes suspended Consists of four lobes suspended

from the diaphragm and from the diaphragm and abdominal wall by the falciform abdominal wall by the falciform ligamentligament

• Connected to the gall bladder via Connected to the gall bladder via the common hepatic ductthe common hepatic duct

• Produced by cells in the liverProduced by cells in the liver• CompositionComposition

– Bile saltsBile salts– Bile pigment (mostly bilirubin Bile pigment (mostly bilirubin

from the breakdown of from the breakdown of hemoglobin)hemoglobin)

– CholesterolCholesterol– PhospholipidsPhospholipids– ElectrolytesElectrolytes

• Sac found in hollow fossa of liverSac found in hollow fossa of liver• Stores bile from the liver by way of Stores bile from the liver by way of

the cystic ductthe cystic duct• Bile is introduced into the Bile is introduced into the

duodenum in the presence of fatty duodenum in the presence of fatty foodfood

• Gallstones can cause blockagesGallstones can cause blockages

Large Intestine (Alimentary Large Intestine (Alimentary Canal)Canal)

• Larger in diameter, but Larger in diameter, but shorter than the small shorter than the small intestineintestine

• Frames the internal Frames the internal abdomenabdomen

• Cecum – saclike first part of Cecum – saclike first part of the large intestinethe large intestine

• AppendixAppendix– Accumulation of lymphatic Accumulation of lymphatic

tissue that sometimes tissue that sometimes becomes inflamed becomes inflamed (appendicitis)(appendicitis)

– Hangs from the cecumHangs from the cecum• ColonColon

– AscendingAscending– TransverseTransverse– DescendingDescending– S-shaped sigmoidalS-shaped sigmoidal

• RectumRectum• Anus – external body Anus – external body

openingopening

Functions of Large Functions of Large IntestineIntestine

• Absorption of waterAbsorption of water• Eliminates indigestible food from the Eliminates indigestible food from the

body as fecesbody as feces• Does not participate in digestion or Does not participate in digestion or

absorption of digested foodabsorption of digested food• Goblet cells produce mucus to act as a Goblet cells produce mucus to act as a

lubricantlubricant• Site of production of Vitamin K by Site of production of Vitamin K by

symbiotic bacteria which live off the symbiotic bacteria which live off the remains of food that have not been remains of food that have not been digested or absorbed in the small digested or absorbed in the small intestine. These bacteria produce over intestine. These bacteria produce over 50% of fecal matter.50% of fecal matter.

NutritionNutrition• Nutrient – substance used by the body for Nutrient – substance used by the body for

growth, maintenance, and repair. growth, maintenance, and repair. Macronutrients are those which are required in Macronutrients are those which are required in large amounts. Micronutrients required in large amounts. Micronutrients required in smaller amounts.smaller amounts.

• Categories of nutrientsCategories of nutrients– Carbohydrates ( macro)Carbohydrates ( macro)– Lipids (macro)Lipids (macro)– Proteins (macro)Proteins (macro)– Vitamins (micro)Vitamins (micro)– Mineral (micro)Mineral (micro)– WaterWater

• A lack of the proper nutrients or an imbalance A lack of the proper nutrients or an imbalance in the correct amounts of each is called in the correct amounts of each is called malnutrition. Even though a person is obese malnutrition. Even though a person is obese they often suffer from malnutrition!they often suffer from malnutrition!

Source of NutrientsSource of Nutrients• CarbohydratesCarbohydrates

– Most are derived from plantsMost are derived from plants– Exceptions: lactose from milk and small amounts of Exceptions: lactose from milk and small amounts of

glycogens from meatsglycogens from meats• LipidsLipids

– Saturated fats from animal productsSaturated fats from animal products– Unsaturated fats from nuts, seeds, and vegetable oilsUnsaturated fats from nuts, seeds, and vegetable oils– Cholesterol from egg yolk, meats, and milk productsCholesterol from egg yolk, meats, and milk products

• ProteinsProteins– Complete proteins – contain all essential amino acidsComplete proteins – contain all essential amino acids

• Most are from animal productsMost are from animal products– Legumes and beans also have proteins, but are Legumes and beans also have proteins, but are

incompleteincomplete• VitaminsVitamins

– Most vitamins are used as cofactors and act with enzymes Most vitamins are used as cofactors and act with enzymes many are produced by plantsmany are produced by plants

– Found in all major food groupsFound in all major food groups• MineralsMinerals

– Play many roles in the bodyPlay many roles in the body– Most mineral-rich foods are vegetables, legumes, milk, Most mineral-rich foods are vegetables, legumes, milk,

and some meatsand some meats

Diseases and Disorders of Diseases and Disorders of the Digestive Systemthe Digestive System

• Heartburn (Acid Heartburn (Acid RefluxReflux))

This is due to acid from This is due to acid from the stomach entering the stomach entering into the esophagus into the esophagus which results in a which results in a burning sensation. In burning sensation. In chronic severe cases chronic severe cases this can lead to this can lead to damage, ulceration, damage, ulceration, scarring, and possibly scarring, and possibly cancer of the cancer of the esophagus if not esophagus if not treatedtreated..

Diseases and Disorders of Diseases and Disorders of the Digestive Systemthe Digestive System

• UlcersUlcers: Ulcers occur : Ulcers occur when the lining of the when the lining of the stomach or the stomach or the duodenum becomes duodenum becomes weakened and exposed to weakened and exposed to the effects of digestive the effects of digestive enzymes and stomach enzymes and stomach acid. It eventually will acid. It eventually will digest a hole through the digest a hole through the mucosa and may cause mucosa and may cause severe bleeding if a blood severe bleeding if a blood vessel of the stomach is vessel of the stomach is involved. It is now known involved. It is now known that ulcers are closely that ulcers are closely associated with infection associated with infection by a bacteria called by a bacteria called Helicobacter pyloriHelicobacter pylori..

Diseases and Disorders of Diseases and Disorders of the Digestive Systemthe Digestive System

• Crohn’s Disease: Crohn's Crohn’s Disease: Crohn's Disease is an inflammatory Disease is an inflammatory disease of the bowel. It can disease of the bowel. It can cause fever, pain, diarrhoea cause fever, pain, diarrhoea and significant loss of and significant loss of weight. Crohn's Disease can weight. Crohn's Disease can affect any part of the bowel, affect any part of the bowel, but most typically affects but most typically affects the lower end of the small the lower end of the small intestine, where it joins the intestine, where it joins the large intestine. The large intestine. The intestinal wall becomes intestinal wall becomes thick and inflamed, thick and inflamed, producing ulcers and producing ulcers and fissures, and can in addition fissures, and can in addition cause abnormal cause abnormal passageways to form passageways to form between adjacent portions between adjacent portions of the intestine. The of the intestine. The intestinal space becomes so intestinal space becomes so narrow that the passage of narrow that the passage of food can become obstructed.food can become obstructed.

Diseases and Disorders of Diseases and Disorders of the Digestive Systemthe Digestive System

• Colon CancerColon Cancer: Cancer starts in the : Cancer starts in the inner layer and can grow through inner layer and can grow through some or all of the other layers. some or all of the other layers. Knowing a little about these layers Knowing a little about these layers is helpful because the stage (extent is helpful because the stage (extent of spread) of a cancer depends to a of spread) of a cancer depends to a great degree on which of these great degree on which of these layers it affects.layers it affects.

• Cancer that starts in the different Cancer that starts in the different areas may cause different areas may cause different symptoms. Colon and rectum symptoms. Colon and rectum cancers probably develop slowly cancers probably develop slowly over a period of several years. We over a period of several years. We now know that most of these now know that most of these cancers begin as a polyp--a growth cancers begin as a polyp--a growth of tissue into the center of the colon of tissue into the center of the colon or rectum. Polyps are also known as or rectum. Polyps are also known as adenomas. Removing the polyp early adenomas. Removing the polyp early may prevent it from becoming may prevent it from becoming cancer.cancer.

• Over 95% of colon and rectal Over 95% of colon and rectal cancers are adenocarcinomas. These cancers are adenocarcinomas. These are cancers of the cells that line the are cancers of the cells that line the inside of the colon and rectum. inside of the colon and rectum. There are some other, more rare, There are some other, more rare, types of tumors of the colon and types of tumors of the colon and rectum, but the facts given here rectum, but the facts given here refer only to adenocarcinomas. refer only to adenocarcinomas.

• Colon and rectal cancer have many Colon and rectal cancer have many featuresfeatures in in common and are often common and are often referred to together as colorectal referred to together as colorectal cancer.cancer.