The Digestive System and Body Metabolism -...

Essentials of Human Anatomy & Physiology

Seventh Edition

Elaine N. Marieb

Chapter 14

The Digestive System and

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Slides 14.1 – 14.14

The Digestive System and

Body Metabolism

Lecture Slides in PowerPoint by Jerry L. Cook

The Digestive System and BodyThe Digestive System and BodyMetabolismMetabolism

Digestion

Breakdown of ingested food

Absorption of nutrients into the blood

Slide 14.1Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Absorption of nutrients into the blood

Metabolism

Production of cellular energy (ATP)

Constructive and degradative cellularactivities

Organs of the Digestive SystemOrgans of the Digestive System

Two main groups

Alimentary canal – continuous coiled hollow

Slide 14.2aCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Alimentary canal – continuous coiled hollowtube

Accessory digestive organs

Organs of the Digestive SystemOrgans of the Digestive System

Slide 14.2bCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 14.1

Organs of the Alimentary CanalOrgans of the Alimentary Canal

Mouth

Pharynx

Esophagus


Stomach

Small intestine

Large intestine

Anus

Mouth (Oral Cavity) AnatomyMouth (Oral Cavity) Anatomy

Lips (labia) – protectthe anterior opening

Cheeks – form thelateral walls

Hard palate – forms


Hard palate – formsthe anterior roof

Soft palate – formsthe posterior roof

Uvula – fleshyprojection of thesoft palate

Figure 14.2a


Vestibule – spacebetween lipsexternally and teethand gums internally

Oral cavity – areacontained by the


Oral cavity – areacontained by theteeth

Tongue – attached athyoid and styloidprocesses of theskull, and by thelingual frenulum Figure 14.2a


Tonsils

Palatine tonsils


Palatine tonsils

Lingual tonsil

Figure 14.2a

Processes of the MouthProcesses of the Mouth

Mastication (chewing) of food

Mixing masticated food with saliva


Mixing masticated food with saliva

Initiation of swallowing by the tongue

Allowing for the sense of taste

Pharynx AnatomyPharynx Anatomy

Nasopharynx –not part of thedigestive system

Oropharynx –posterior to oral


posterior to oralcavity

Laryngopharynx –below the oropharynxand connected tothe esophagus

Figure 14.2a

Pharynx FunctionPharynx Function

Serves as a passageway for air andfood

Food is propelled to the esophagus bytwo muscle layers


two muscle layers

Longitudinal inner layer

Circular outer layer

Food movement is by alternatingcontractions of the muscle layers(peristalsis)

EsophagusEsophagus

Runs from pharynx to stomach throughthe diaphragm

Conducts food by peristalsis


Conducts food by peristalsis(slow rhythmic squeezing)

Passageway for food only (respiratorysystem branches off after the pharynx)

Layers of Alimentary Canal OrgansLayers of Alimentary Canal Organs

Mucosa

Innermost layer

Moist membrane


Moist membrane

Surface epithelium

Small amount of connective tissue(lamina propria)

Small smooth muscle layer


Submucosa

Just beneath the mucosa


Just beneath the mucosa

Soft connective tissue with blood vessels,nerve endings, and lymphatics


Muscularis externa – smooth muscle

Inner circular layer

Outer longitudinal layer


Outer longitudinal layer

Serosa

Outermost layer – visceral peritoneum

Layer of serous fluid-producing cells



Figure 14.3

Alimentary Canal Nerve PlexusesAlimentary Canal Nerve Plexuses

All are part of the autonomic nervoussystem

Three separate networks of nerve fibers


Three separate networks of nerve fibers

Submucosal nerve plexus

Myenteric nerve plexus

Subserous plexus

Stomach AnatomyStomach Anatomy

Located on the left side of theabdominal cavity


abdominal cavity

Food enters at the cardioesophagealsphincter


Regions of the stomach

Cardiac region – near the heart

Fundus


Body

Phylorus – funnel-shaped terminal end

Food empties into the small intestine atthe pyloric sphincter


Rugae – internal folds of the mucosa

External regions


External regions

Lesser curvature

Greater curvature


Layers of peritoneum attached to thestomach

Lesser omentum – attaches the liver to thelesser curvature


lesser curvature

Greater omentum – attaches the greatercurvature to the posterior body wall

Contains fat to insulate, cushion, andprotect abdominal organs



Figure 14.4a

Stomach FunctionsStomach Functions

Acts as a storage tank for food

Site of food breakdown


Chemical breakdown of protein begins

Delivers chyme (processed food) to thesmall intestine

Specialized Mucosa of the StomachSpecialized Mucosa of the Stomach

Simple columnar epithelium

Mucous neck cells – produce a stickyalkaline mucus

Gastric glands – secrete gastric juice


Gastric glands – secrete gastric juice

Chief cells – produce protein-digestingenzymes (pepsinogens)

Parietal cells – produce hydrochloric acid

Endocrine cells – produce gastrin

Structure of the Stomach MucosaStructure of the Stomach Mucosa

Gastric pits formed by folded mucosa


Glands and specialized cells are in thegastric gland region

Structure of the Stomach MucosaStructure of the Stomach Mucosa


Figure 14.4b, c

Small IntestineSmall Intestine

The body’s major digestive organ

Site of nutrient absorption into the blood


Muscular tube extending form thepyloric sphincter to the ileocecal valve

Suspended from the posteriorabdominal wall by the mesentery

Subdivisions of the Small IntestineSubdivisions of the Small Intestine

Duodenum

Attached to the stomach

Curves around the head of the pancreas


Jejunum

Attaches anteriorly to the duodenum

Ileum

Extends from jejunum to large intestine

Chemical Digestion in the SmallChemical Digestion in the SmallIntestineIntestine

Source of enzymes that are mixed withchyme


Intestinal cells

Pancreas

Bile enters from the gall bladder

Chemical Digestion in the SmallChemical Digestion in the SmallIntestineIntestine


Figure 14.6

Villi of the Small IntestineVilli of the Small Intestine

Fingerlikestructures formedby the mucosa


by the mucosa

Give the smallintestine moresurface area

Figure 14.7a

Microvilli of the Small IntestineMicrovilli of the Small Intestine

Small projections of theplasma membrane


plasma membrane

Found on absorptive cells

Figure 14.7c

Structures Involved in Absorption ofStructures Involved in Absorption ofNutrientsNutrients

Absorptive cells

Blood capillaries


Blood capillaries

Lacteals (specializedlymphatic capillaries)

Figure 14.7b

Folds of the Small IntestineFolds of the Small Intestine

Called circular folds or plicae circulares

Deep folds of the mucosa andsubmucosa


submucosa

Do not disappear when filled with food

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

Large IntestineLarge Intestine

Larger in diameter, but shorter than thesmall intestine


small intestine

Frames the internal abdomen

Large IntestineLarge Intestine


Figure 14.8

Functions of the Large IntestineFunctions of the Large Intestine

Absorption of water

Eliminates indigestible food from thebody as feces


body as feces

Does not participate in digestion of food

Goblet cells produce mucus to act as alubricant

Structures of the Large IntestineStructures of the Large Intestine

Cecum – saclike first part of the largeintestine

Appendix


Appendix

Accumulation of lymphatic tissue thatsometimes becomes inflamed(appendicitis)

Hangs from the cecum

Structures of the Large IntestineStructures of the Large Intestine

Colon

Ascending

Transverse


Descending

S-shaped sigmoidal

Rectum

Anus – external body opening

Modifications to the MuscularisModifications to the MuscularisExterna in the Large IntestineExterna in the Large Intestine

Smooth muscle is reduced to threebands (teniae coli)

Muscle bands have some degree of


Muscle bands have some degree oftone

Walls are formed into pocketlike sacscalled haustra

Accessory Digestive OrgansAccessory Digestive Organs

Salivary glands

Teeth

Pancreas


Pancreas

Liver

Gall bladder

Salivary GlandsSalivary Glands

Saliva-producing glands

Parotid glands – located anterior to ears


Parotid glands – located anterior to ears

Submandibular glands

Sublingual glands

SalivaSaliva

Mixture of mucus and serous fluids

Helps to form a food bolus

Contains salivary amylase to begin


Contains salivary amylase to beginstarch digestion

Dissolves chemicals so they can betasted

TeethTeeth

The role is to masticate (chew) food

Humans have two sets of teeth


Deciduous (baby or milk) teeth

20 teeth are fully formed by age two

TeethTeeth

Permanent teeth

Replace deciduous teeth beginningbetween the ages of 6 to 12


between the ages of 6 to 12

A full set is 32 teeth, but some people donot have wisdom teeth

Classification of TeethClassification of Teeth

Incisors

Canines


Canines

Premolars

Molars

Classification of TeethClassification of Teeth


Figure 14.9

Regions of a ToothRegions of a Tooth

Crown – exposedpart

Outer enamel

Dentin


Pulp cavity

Neck

Region in contactwith the gum

Connects crown toroot

Figure 14.10

Regions of a ToothRegions of a Tooth

Root

Periodontalmembrane


membraneattached to thebone

Root canal carryingblood vessels andnerves

Figure 14.10

PancreasPancreas

Produces a wide spectrum of digestiveenzymes that break down all categories of food

Enzymes are secreted into the duodenum

Alkaline fluid introduced with enzymes


Alkaline fluid introduced with enzymesneutralizes acidic chyme

Endocrine products of pancreas

Insulin

Glucagons

LiverLiver

Largest gland in the body

Located on the right side of the bodyunder the diaphragm

Consists of four lobes suspended from


Consists of four lobes suspended fromthe diaphragm and abdominal wall bythe falciform ligament

Connected to the gall bladder via thecommon hepatic duct

BileBile

Produced by cells in the liver

Composition

Bile salts


Bile pigment (mostly bilirubin from thebreakdown of hemoglobin)

Cholesterol

Phospholipids

Electrolytes

Gall BladderGall Bladder

Sac found in hollow fossa of liver

Stores bile from the liver by way of thecystic duct


cystic duct

Bile is introduced into the duodenum inthe presence of fatty food

Gallstones can cause blockages

Processes of the Digestive SystemProcesses of the Digestive System

Ingestion – getting food into the mouth

Propulsion – moving foods from one


Propulsion – moving foods from oneregion of the digestive system toanother


Peristalsis – alternatingwaves of contraction


Segmentation – movingmaterials back and forthto aid in mixing

Figure 14.12


Mechanical digestion

Mixing of food in the mouth by the tongue


Mixing of food in the mouth by the tongue

Churning of food in the stomach

Segmentation in the small intestine


Chemical Digestion

Enzymes break down food molecules intotheir building blocks

Each major food group uses different


Each major food group uses differentenzymes

Carbohydrates are broken to simple sugars

Proteins are broken to amino acids

Fats are broken to fatty acids and alcohols


Absorption

End products of digestion are absorbed inthe blood or lymph

Food must enter mucosal cells and then


Food must enter mucosal cells and theninto blood or lymph capillaries

Defecation

Elimination of indigestible substances asfeces



Figure 14.11

Control of Digestive ActivityControl of Digestive Activity

Mostly controlled by reflexes via theparasympathetic division


Chemical and mechanical receptors arelocated in organ walls that triggerreflexes

Control of Digestive ActivityControl of Digestive Activity

Stimuli include:

Stretch of the organ

pH of the contents


Presence of breakdown products

Reflexes include:

Activation or inhibition of glandularsecretions

Smooth muscle activity

Digestive Activities of the MouthDigestive Activities of the Mouth

Mechanical breakdown

Food is physically broken down by chewing


Chemical digestion

Food is mixed with saliva

Breaking of starch into maltose by salivaryamylase

Activities of the Pharynx andActivities of the Pharynx andEsophagusEsophagus

These organs have no digestive function


Serve as passageways to the stomach

Deglutition (Swallowing)Deglutition (Swallowing)

Buccal phase

Voluntary

Occurs in the mouth


Occurs in the mouth

Food is formed into a bolus

The bolus is forced into the pharynx by thetongue


Pharyngeal-esophageal phase

Involuntary transport of the bolus

All passageways except to the stomach areblocked


blocked

Tongue blocks off the mouth

Soft palate (uvula) blocks thenasopharynx

Epiglottis blocks the larynx


Pharyngeal-esophogeal phase(continued)

Peristalsis moves the bolus toward the


Peristalsis moves the bolus toward thestomach

The cardioesophageal sphincter is openedwhen food presses against it



Figure 14.13

Food Breakdown in the StomachFood Breakdown in the Stomach

Gastric juice is regulated by neural andhormonal factors

Presence of food or falling pH causesthe release of gastrin


the release of gastrin

Gastrin causes stomach glands toproduce protein-digesting enzymes

Hydrocholoric acid makes the stomachcontents very acidic

Necessity of an Extremely AcidNecessity of an Extremely AcidEnvironment in the StomachEnvironment in the Stomach

Activates pepsinogen to pepsin forprotein digestion


protein digestion

Provides a hostile environment formicroorganisms

Digestion and Absorption in theDigestion and Absorption in theStomachStomach

Protein digestion enzymes

Pepsin – an active protein digesting


Pepsin – an active protein digestingenzyme

Rennin – works on digesting milk protein

The only absorption that occurs in thestomach is of alcohol and aspirin

Propulsion in the StomachPropulsion in the Stomach

Food must first be well mixed

Rippling peristalsis occurs in the lowerstomach


Figure 14.14

Propulsion in the StomachPropulsion in the Stomach

The pylorus meters out chyme into thesmall intestine (30 ml at a time)

The stomach empties in four to sixhours


hours

Figure 14.14

Digestion in the Small IntestineDigestion in the Small Intestine

Enzymes from the brush border

Break double sugars into simple sugars

Complete some protein digestion

Pancreatic enzymes play the major


Pancreatic enzymes play the majordigestive function

Help complete digestion of starch(pancreatic amylase)

Carry out about half of all protein digestion(trypsin, etc.)

Digestion in the Small IntestineDigestion in the Small Intestine

Pancreatic enzymes play the majordigestive function (continued)


Responsible for fat digestion (lipase)

Digest nucleic acids (nucleases)

Alkaline content neutralizes acidic chyme

Stimulation of the Release of PancreaticStimulation of the Release of PancreaticJuiceJuice

Vagus nerve

Local hormones


Local hormones

Secretin

Cholecystokinin

Figure 14.15

Absorption in the Small IntestineAbsorption in the Small Intestine

Water is absorbed along the length ofthe small intestine

End products of digestion

Most substances are absorbed by active


Most substances are absorbed by activetransport through cell membranes

Lipids are absorbed by diffusion

Substances are transported to the liverby the hepatic portal vein or lymph

Propulsion in the Small IntestinePropulsion in the Small Intestine

Peristalsis is the major means ofmoving food


Segmental movements

Mix chyme with digestive juices

Aid in propelling food

Food Breakdown and Absorption inFood Breakdown and Absorption inthe Large Intestinethe Large Intestine

No digestive enzymes are produced

Resident bacteria digest remainingnutrients


Produce some vitamin K and B

Release gases

Water and vitamins K and B are absorbed

Remaining materials are eliminated viafeces

Propulsion in the Large IntestinePropulsion in the Large Intestine

Sluggish peristalsis

Mass movements

Slow, powerful movements

Occur three to four times per day


Occur three to four times per day

Presence of feces in the rectum causesa defecation reflex

Internal anal sphincter is relaxed

Defecation occurs with relaxation of thevoluntary (external) anal sphincter

NutritionNutrition

Nutrient – substance used by the bodyfor growth, maintenance, and repair

Categories of nutrients

Carbohydrates


Lipids

Proteins

Vitamins

Mineral

Water

Dietary Sources of Major NutrientsDietary Sources of Major Nutrients

Carbohydrates

Most are derived from plants

Exceptions: lactose from milk and smallamounts of glycogens from meats

Lipids


Lipids

Saturated fats from animal products

Unsaturated fats from nuts, seeds, andvegetable oils

Cholesterol from egg yolk, meats, and milkproducts


Proteins

Complete proteins – contain all essentialamino acids

Most are from animal products


Legumes and beans also have proteins,but are incomplete

Vitamins

Most vitamins are used as cofactors andact with enzymes

Found in all major food groups


Minerals

Play many roles in the body


Play many roles in the body

Most mineral-rich foods are vegetables,legumes, milk, and some meats

MetabolismMetabolism

Chemical reactions necessary tomaintain life

Catabolism – substances are broken down


Catabolism – substances are broken downto simpler substances

Anabolism – larger molecules are built fromsmaller ones

Energy is released during catabolism

Carbohydrate MetabolismCarbohydrate Metabolism

The body’s preferred source to producecellular energy (ATP)

Glucose (blood sugar) is the majorbreakdown product and fuel to make


breakdown product and fuel to makeATP

Figure 14.16

Cellular RespirationCellular Respiration

Oxygen-using events take place within thecell to create ATP from ADP

Carbon leaves cells as carbon dioxide (CO2)

Hydrogen atoms are combined with oxygen


Hydrogen atoms are combined with oxygento form water

Energy produced by these reactions adds aphosphorus to ADP to produce ATP

ATP can be broken down to release energyfor cellular use

Metabolic Pathways Involved inMetabolic Pathways Involved inCellular RespirationCellular Respiration

Glycolysis – energizes a glucose


Glycolysis – energizes a glucosemolecule so that it can be split into twopyruvic acid molecules and yield ATP



Figure 14.17


Krebs cycle

Produces virtually all the carbon dioxide


Produces virtually all the carbon dioxideand water resulting from cell respiration

Yields a small amount of ATP


Electron transport chain

Hydrogen atomsremoved during


removed duringglycolysis andthe Krebs cycleare delivered toprotein carriers

Figure 14.18


Electron transport chain (continued)

Hydrogen issplit into


split intohydrogen ionsand electronsin themitochondria

Figure 14.18


Electron transport chain (continued)

Electrons giveoff energy in a

Slide 14.72cCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

off energy in aseries of stepsto enable theproduction ofATP

Figure 14.18

Fat MetabolismFat Metabolism

Handled mostly by the liver

Use some fats to make ATP

Synthesize lipoproteins, thromboplastin,


Synthesize lipoproteins, thromboplastin,and cholesterol

Release breakdown products to the blood

Body cells remove fat and cholesterol tobuild membranes and steroid hormones

Use of Fats for ATP SynthesisUse of Fats for ATP Synthesis

Fats must first be broken down to aceticacid


Within mitochondira, acetic acid iscompletely oxidized to produce water,carbon dioxide, and ATP

Protein MetabolismProtein Metabolism

Proteins are conserved by body cellsbecause they are used for most cellularstructures


structures

Ingested proteins are broken down toamino acids

Protein MetabolismProtein Metabolism

Cells remove amino acids to buildproteins

Synthesized proteins are actively


Synthesized proteins are activelytransported across cell membranes

Amino acids are used to make ATP onlywhen proteins are overabundant orthere is a shortage of other sources

Production of ATP from ProteinProduction of ATP from Protein

Amine groups are removed fromproteins as ammonia

The rest of the protein molecule enters


The rest of the protein molecule entersthe Krebs cycle in mitochondria

The liver converts harmful ammonia tourea which can be eliminated in urine

Role of the Liver in MetabolismRole of the Liver in Metabolism

Several roles in digestion

Detoxifies drugs and alcohol

Degrades hormones


Degrades hormones

Produce cholesterol, blood proteins(albumin and clotting proteins)

Plays a central role in metabolism

Metabolic Functions of the LiverMetabolic Functions of the Liver

Glycogenesis

Glucose molecules are converted toglycogen

Glycogen molecules are stored in the liver


Glycogenolysis

Glucose is released from the liver afterconversion from glycogen

Gluconeogenesis

Glucose is produced from fats and proteins



Figure 14.20


Fats and fatty acids are picked up bythe liver


Some are oxidized to provide energy forliver cells

The rest are broken down into simplercompounds and released into the blood

Cholesterol MetabolismCholesterol Metabolism

Functions of cholesterol

Serves as a structural basis of steroidhormones and vitamin D


Is a major building block of plasmamembranes

Most cholesterol is produced in the liverand is not from diet

Cholesterol TransportCholesterol Transport

Cholesterol and fatty acids cannot freelycirculate in the bloodstream

They are transported by lipoproteins(lipid-protein complexes)


(lipid-protein complexes)

Low-density lipoproteins (LDLs) transport tobody cells

High-density lilpoproteins (HDLs) transportfrom body cells to the liver

Body Energy BalanceBody Energy Balance

Energy intake = total energy output(heat + work + energy storage)

Energy intake is liberated during foodoxidation


oxidation

Energy output

Heat is usually about 60%

Storage energy is in the form of fat orglycogen

Regulation of Food IntakeRegulation of Food Intake

Body weight is usually relatively stable

Energy intake and output remain aboutequal

Mechanisms that may regulate foodintake


intake

Levels of nutrients in the blood

Hormones

Body temperature

Psychological factors

Metabolic Rate and Body HeatMetabolic Rate and Body HeatProductionProduction

Basic metabolic rate (BMR) – amount ofheat produced by the body per unit oftime at rest


time at rest

Factors that influence BMR

Surface area – small body usually hashigher BMR

Gender – males tend to have higher BMR

Metabolic Rate and Body HeatMetabolic Rate and Body HeatProductionProduction

Factors that influence BMR (continued)

Age – children and adolescents have ahigher BMR


higher BMR

The amount of thyroxine produced is themost important control factor

More thyroxine means higher metabolicrate

Total Metabolic Rate (TMR)Total Metabolic Rate (TMR)

Total amount of kilocalories the bodymust consume to fuel ongoing activities

TMR increases with an increase in body


TMR increases with an increase in bodyactivity

TMR must equal calories consumed tomaintain homeostasis and maintain aconstant weight

Body Temperature RegulationBody Temperature Regulation

Most energy is released as foods areoxidized


oxidized

Most energy escapes as heat

Body Temperature RegulationBody Temperature Regulation

The body has a narrow range ofhomeostatic temperature

Must remain between 35.6° to 37.8°C


Must remain between 35.6° to 37.8°C(96° to 100° F)

The body’s thermostat is in thehypothalamus

Initiates heat-loss or heat-promotingmechanisms

Heat Promoting MechanismsHeat Promoting Mechanisms

Vasoconstriction of blood vessels

Blood is rerouted to deeper, more vital bodyorgans


organs

Shivering – contraction of musclesproduces heat

Heat Loss MechanismsHeat Loss Mechanisms

Heat loss from the skin via radiation andevaporation


Skin blood vessels and capillaries areflushed with warm blood

Evaporation of perspiration cools the skin

BodyBodyTemperatureTemperatureRegulationRegulation


Figure 14.21

Developmental Aspects of theDevelopmental Aspects of theDigestive SystemDigestive System

The alimentary canal is a continuous tubeby the fifth week of development

Digestive glands bud from the mucosa ofthe alimentary tube


the alimentary tube

The developing fetus receives allnutrients through the placenta

In newborns, feeding must be frequent,peristalsis is inefficient, and vomiting iscommon


Teething begins around age six months

Metabolism decreases with old age


Middle age digestive problems

Ulcers

Gall bladder problems


Activity of digestive tract in old age

Fewer digestive juices


Fewer digestive juices

Peristalsis slows

Diverticulosis and cancer are morecommon

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