Chapter 14Digestive SystemAnatomy and Physiology IIMs. Harborth

PART I:Digestive SystemTakes in food (ingests)Breaks it down physically

(digests)Absorbs nutrientsRids body of indigestible

remains (defecates)

Anatomy of the Digestive System

Alimentary canal (GI tract)◦ Ingests,

digests, absorbs, defecates

Accessory digestive organs◦Teeth, tongue,

large digestive glands

Alimentary CanalContinuous, hollow muscular tubeSubmucosal and myenteric nerve

plexuses30 feet long in cadaver

◦Mouth◦Pharynx◦Esophagus◦Stomach◦Small intestine◦Large intestine◦Anus

MouthLabiaCheeksHard and soft

palateUvulaVestibuleOral cavity

properTongueLingual

frenulum

PharynxOropharynxLaryngopharyn

x2 skeletal

muscle layers◦Inner layer

longitudinal◦Outer layer

circularPeristalsis

Esophagus10 inches long4 tissue layers

◦Mucosa – innermost◦Submucosa◦Muscularis externa◦Serosa

Visceral peritoneum Parietal peritoneum

Mesentery

Stomach10 inches long,

can hold 1 gallonDiameter changesCardiac region

◦Cardioesphageal sphincter

FundusBodyPylorus

◦Pyloric sphincter

StomachRugaeGreater

curvatureLesser

curvatureLesser

omentumGreater

omentum

StomachGastric pits

◦Gastric glands◦Gastric juice

Ex: Intrinsic factorChief cells

◦pepsinogensParietal cellsMucous neck cellsChyme

Small Intestine 6-13 ft longIleocecal valveDuodenumJejunumIleumPancreatic ductsBile ductPeyer’s patches

Food AbsorptionMicrovilliVilli

◦Lacteal lymphatic capillary

Circular folds

Large Intestine5 ftCecumAppendixColon

◦Ascending colon◦Transverse colon◦Descending colon◦Sigmoid colon

RectumAnal canal

Accessory Digestive OrgansSalivary glands

◦Parotid glands◦Submandibular glands◦Sublingual glands

Saliva◦Bolus◦Salivary amylase◦Lysozyme and IgA antibodies

Accessory Digestive Organs

Teeth◦Masticate◦Deciduous teeth◦Permanent teeth◦Incisors◦Canines◦Premolars (bicuspids)◦Molars

Teeth ContinuedCrown and RootGingivaEnamelNeckCementumPeriodontal membrane (ligament)DentinPulp cavityPulpRoot canal

Accessory Digestive Organs

Pancreas◦Retroperitone

al◦Digestive

enzymes in alkaline fluid

◦Endocrine organ

Accessory Digestive Organs

Liver and Gallbladder◦Liver

4 lobes Bile Common hepatic duct

◦Gallbladder Cystic duct Stores and concentrates bile

Functions of Digestive System1. Ingestion2. Propulsion3. Food breakdown: mechanical

digestion4. Food breakdown: chemical

digestion5. Absorption6. Defecation

digestion animation

Digestion ReflexesMechano/Chemoreceptors

triggered by:◦Stretch of organ by food◦pH of contents◦Presence of certain breakdown

productsActivate or Inhibit:

◦Glands that secrete digestive juices or hormones

◦Smooth muscles that mix and propel food

Activities of Mouth, Pharynx, and Esophagus

Mouth – mechanical and chemical digestion

Deglutition (tongue, soft palate, pharynx, and esophagus)◦Buccal phase◦Pharyngeal-esophageal phase

FYI: Swallowing can occur while standing on your head!

Activities of StomachSight, smell, and taste of

food stimulates parasympathetic reflexes◦Gastric juices secreted◦Hormone gastrin released

Makes stomach glands produce pepsinogens, mucus, and HCl

FYI: You make 2-3 Liters of gastric juice a day!

Chemistry in the StomachHCl makes pepsinogen pepsinRennin: works on milk protein

(only in infants)Hardly any chemical digestion

occurs ◦Aspirin and alcohol are absorbed

through stomach wall

Food Propulsion from Stomach

Chyme is end productPylorus only allows liquid

and small particles to pass through sphincter

Each contraction squirts 3 ml of chyme

Rest is squeezed back into stomach◦ Causing enterogastric reflex

FYI: It usually takes 4 hours for your stomach to empty, or 6 hours if meal was high in fat

Activities of Small IntestineCarb and protein digestion had begun in

stomach, but no fat digestionMicrovilli make few enzymes

◦ Brush border enzymes◦ Hormones:

Secretin Cholecystokinin (CCK)

Pancreatic juices are enzyme and bicarbonate rich◦ Complete digestion of starch◦ Carry out ½ of protein digestion◦ Responsible for fat digestoin◦ Digest nucleic acids

Absorption in Small IntestineWater and end products absorbed

through intestinal cell plasma membranes via active transport◦Except lipids – absorbed through diffusion

Then to the hepatic portal veinBy the end of ileum, only water and

indigestible food materials and LOTS of bacteria

FYI: Takes about 3-6 hours for food to go through small intestine

Activities of Large Intestine

Bacteria metabolize and release gases (methane and hydrogen sulfide) and some vitamins

These gases make feces smell

Peristalsis and mass movements

Defecation reflex

PART II:Nutrition and MetabolismMajor nutrients

◦Carbohydrates◦Lipids◦Proteins

Vitamins and mineralsWater

MetabolismCatabolism and

anabolismCarbohydrate

metabolismFat metabolismProtein

metabolism

Carbohydrate MetabolismGlucose

ATPCellular

respiration◦Glycolysis,

Krebs cycle, electron transport chain

Fat MetabolismLiverFat is broken

down to acetic acid

Acetic acid is broken down in mitochondria to make ATP, CO2, and water

Protein MetabolismProteins are broken down

into amino acidsCellular uptake20 amino acids are

needed, 8 can’t be made by our cells (“essential amino acids”)

IF no other energy source is available, amine groups are removed as ammonia, and rest is used by mitochondria for ATP

Liver’s Role in MetabolismUsed in digestion, detoxifying

drugs & alcohol, degrades hormones, makes cholesterol, albumin, clotting proteins and lipoproteins, and METABOLISM

Blood circulates through, liver grabs nutrients and macrophages kill pathogens

LiverGlycogenesisGlycogenolysisGluconeogenesis

CholesterolHDL and LDL

Body Energy BalanceEnergy intake = heat + work +

energy sourceRising or falling blood levels of

nutrients, hormones, or body temperature affect eating behavior

Psychological factors influence as well

Metabolic RateBasal metabolic rate

◦Amount of heat produced when at rest◦ Influenced by:

Surface area Sex Age Emotions Amount of thyroxine

Total metabolic rate◦Amount of kilocalories body needs to fuel

all activities◦Stays elevated well after exercise

Body Temperature RegulationHypothalamus

◦Heat-promoting mechanisms Vasoconstriction Shivering

◦Heat loss mechanisms Radiation through skin