Provide the body w/nutrients, water and electrolytes.

The organs of this system are responsible for:

• Food ingestion

• Digestion

• Absorption

• Elimination

The digestive system consists of a hollow tube extending from the mouth to the anus (GI tract or alimentary canal).

Various accessory organs empty secretions into them.

What is the function of the digestive system?

Digestive ProcessDigestive Process

1.1. IngestionIngestion2.2. PropulsionPropulsion3.3. Mechanical DigestionMechanical Digestion

• MasticationMastication• Churning food in stomachChurning food in stomach

4.4. Chemical digestionChemical digestion5.5. AbsorptionAbsorption6.6. DefecationDefecation

GI Tract- 4 basic tunics:

• Mucosa• Submucosa• Muscularis externa• Serosa (adventia)

GI Tract (alimentary canal)GI Tract (alimentary canal)1. Mucosa- wet epithelial membrane

Major function:• secretion• absorption• protection• reduce friction• protect cells from being digested

2. Submucosa- moderately dense connective tissueContains:• blood• lymphatic vessels• scattered lymph nodules and nerve fibersMajor function:• nutrition• protection

3. Muscularis externa- bilayer of smooth muscle and superficial longitudinal muscleMajor function:

• regulate GI motility (churning)

4. Serosa- serous membraneMajor function:

• reduce friction• anchor and protect the surrounding

GI tract organ

Parasympathetic Nerve Innervation of the GI Tract

Enteric Nervous System (Autonomic & Somatic Connections)

Myenteric Plexus

Myenteric Plexus

Submucosal Plexus

Submucosal Plexus

MuscularisMuscularis MucosalMucosal

To ANS & CNS neurons

To ANS & CNS neurons

Enteric Nervous System

motor motor sensory

Figure 23.10a

IncisorsCentral (6–8 mo)

IncisorsCentral (7 yr)

Canine (eyetooth)(16–20 mo)

Canine (eyetooth)(11 yr)Premolars(bicuspids)

First premolar(11 yr)

MolarsFirst molar(10–15 mo)

MolarsFirst molar (6–7 yr)

Lateral (8–10 mo) Lateral (8 yr)

Second molar(about 2 yr)

Second molar(12–13 yr)Third molar(wisdom tooth)(17–25 yr)(a)

Permanentteeth

Deciduous(milk) teeth Second premolar

(12–13 yr)

Teeth

Teeth

Figure 23.10b

Deciduous teeth Permanent teeth(b)

Teeth

Teeth

incisors

cuspid

premolars

molars

TeethTeeth

Salivary GlandsSalivary Glands

Extrinsic salivary glands Extrinsic salivary glands

ParotidParotid

SubmandibularSubmandibular

SublingualSublingual

Salivary GlandsSalivary Glands

Parotid glandParotid gland• Anterior to the ear external to the Anterior to the ear external to the

masseter muscle masseter muscle • Parotid duct opens into the vestibule next Parotid duct opens into the vestibule next

to second upper molarto second upper molar

Submandibular gland Submandibular gland • Medial to the body of the mandibleMedial to the body of the mandible• Duct opens at the base of the lingual Duct opens at the base of the lingual

frenulumfrenulum

Salivary GlandsSalivary Glands

Sublingual glandSublingual gland• Anterior to the submandibular gland Anterior to the submandibular gland

under the tongueunder the tongue

• Opens via 10–12 ducts into the floor Opens via 10–12 ducts into the floor of the mouthof the mouth

Salivary GlandsSalivary Glands

Secretion (saliva) Secretion (saliva) • Cleanses the mouthCleanses the mouth

• Moistens and dissolves food Moistens and dissolves food chemicals chemicals

• Aids in bolus formationAids in bolus formation

• Contains enzymes that begin the Contains enzymes that begin the breakdown of starchbreakdown of starch

SalivaSaliva• Water (99.5%)Water (99.5%)• mucinmucin• Amylase and lingual lipaseAmylase and lingual lipase• ElectrolytesElectrolytes- - NaNa++, K, K++, Cl, Cl––, PO, PO4 4

2–2–, HCO, HCO33

• GlycoproteinsGlycoproteins• antibacterial compounds such as antibacterial compounds such as

secretory IgA and lysozymesecretory IgA and lysozyme

Salivary Glands

TongueTongueFunctions includeFunctions include

• Repositioning and mixing food during chewing Repositioning and mixing food during chewing • Formation of the bolusFormation of the bolus• Initiation of swallowing, speech, and tasteInitiation of swallowing, speech, and taste

Intrinsic muscles change the shape of the Intrinsic muscles change the shape of the tonguetongue

Extrinsic muscles alter the tongue’s positionExtrinsic muscles alter the tongue’s position Lingual frenulum: attachment to the floor of Lingual frenulum: attachment to the floor of

the mouththe mouth

TongueTongueSurface bears papillaeSurface bears papillae• Filiform—whitish, give the tongue roughness Filiform—whitish, give the tongue roughness

and provide friction and provide friction • Fungiform—reddish, scattered over the Fungiform—reddish, scattered over the

tongue tongue • Circumvallate (vallate)—V-shaped row in Circumvallate (vallate)—V-shaped row in

back of tongueback of tongue– These three house taste budsThese three house taste buds

• Foliate—on the lateral aspects of the Foliate—on the lateral aspects of the posterior tongueposterior tongue

Figure 23.8

Epiglottis

Palatine tonsil

Lingual tonsil

Foliate papillae

Circumvallatepapilla

Filiform papilla

Fungiform papilla

Peristalsis

Peristalsis

Deglutition (swallowing)

Peristalsis Waves

(b) Enlarged view of gastric pits and gastric glands

Mucous neck cells

Parietal cell

Surface epithelium(mucous cells)

Gastric pits

Chief cell

Enteroendocrine cell

Gastric pit

Gastric gland

Stomach Lining

Stomach SecretionsStomach Secretions

Gastric Pit:Gastric Pit:• hydrochloric acidhydrochloric acid• pepsinogenpepsinogen• MucusMucus• Hormones that regulate GI Hormones that regulate GI

motilitymotility

Mucous neck cells- found in upper region of gastric glands produce

• mucous Parietal cells- in gastric gland of mucosa

produce• HCl – kills most bacteria• Intrinsic factor (required for absorption of vit. B12 in

sm intestine, which is needed for producing mature erythrocytes)

 Zymogenic (chief) cells-

produce• pepsinogen (inactive form of pepsin, which becomes active in presence

of HCl) • rennin (milk digestion in children) protein digestion

  

Enteroendocrine cells in stomach mucosaproduces:

• Gastrin- regulates stomach secretions and mobility

• Histamine- activates parietal cells to release HCl• Endorphins- natural opiates• Serotonin- causes contraction of stomach

muscle• Cholecystokinin (CCK)- (in duodenal mucosa)

many functions and affects many organs• Somatostatin- (stomach and duodenal mucosa)

- inhibits gastrin, pancreatic secretions, inhibits GI blood flow in sm intestine…

  

Gastric ulcers• erosion of stomach wall; pain occurs 1-3 hrs after

eating• 90% of recurrent ulcers due to bacterial infection,

which destroys mucous protective barrier; • Treatment- use antibiotic therapy to kill bacteria

Helicobacter pyloriHelicobacter pylori Barry Marshal

BileBile• Bile saltsBile salts• Bile pigmentsBile pigments• CholesterolCholesterol• Neutral fatsNeutral fats• PhospholipidsPhospholipids• Other electrolytesOther electrolytes

Bile secretion

Small Intestine, Gallbladder, & Pancreas

PancreasPancreasEndocrine functionEndocrine function

• Pancreatic islets secrete insulin and Pancreatic islets secrete insulin and glucagonglucagon

Exocrine functionExocrine function• Acini (clusters of secretory cells) Acini (clusters of secretory cells)

secrete pancreatic juice secrete pancreatic juice • Zymogen granules of secretory cells Zymogen granules of secretory cells

contain digestive enzymescontain digestive enzymes

Figure 23.26a

Smallduct

Acinar cells

Basementmembrane

Zymogengranules

Roughendoplasmicreticulum

(a)

Pancreatic JuicePancreatic Juice Watery alkaline solution (pH 8) Watery alkaline solution (pH 8)

neutralizes chymeneutralizes chyme Electrolytes (primarily HCOElectrolytes (primarily HCO33

––) ) EnzymesEnzymes

• Amylase, lipases, nucleases are secreted Amylase, lipases, nucleases are secreted in active form but require ions or bile for in active form but require ions or bile for optimal activityoptimal activity

• Proteases secreted in inactive formProteases secreted in inactive form

Pancreatic JuicePancreatic Juice

Protease activation in duodenum• Trypsinogen is activated to trypsin

by brush border enzyme enteropeptidase

• Procarboxypeptidase and chymotrypsinogen are activated by trypsin

Pancreatic EnzymesPancreatic Enzymes

• trypsin• chemotrypsin• carboxypeptidase• amylase• phospholipase• lipase• nucleases

Small Intestine: Gross Small Intestine: Gross AnatomyAnatomy

Major organ of digestion and absorption 2–4 m long; from pyloric sphincter to

ileocecal valve Subdivisions

1. Duodenum (retroperitoneal)

2. Jejunum (attached posteriorly by mesentery)

3. Ileum (attached posteriorly by mesentery)

lumenmuscle layers

foldsvilli

Intestinal StructureIntestinal Structure

Small Intestine

epithelial cells

capillaries

lacteal

Intestinal Villus

Intestinal Villus

Intestinal Intestinal Epithelial CellEpithelial Cell

Intestinal Membrane EnzymesIntestinal Membrane Enzymes

• disaccharidasesdisaccharidases• aminopeptidaseaminopeptidase• dipeptidasesdipeptidases• nucleotidasesnucleotidases• NucleosidasesNucleosidases• LactaseLactase• MaltaseMaltase• EnterokinaseEnterokinase

Figure 23.21

Jejunum

Mucosawith folds

Cystic duct

DuodenumHepatopancreaticampulla and sphincter

Gallbladder

Right and lefthepatic ducts of liver

Bile duct and sphincter

Main pancreatic ductand sphincter

PancreasTail of pancreas

Head of pancreas

Common hepatic duct

Major duodenalpapilla

Accessory pancreatic duct

Liver

Liver

Removes debris such as bacteria

Liver

• Detoxify poisonous substances• Make bile (500-1000 ml/day)• Store glycogen (100 g)• Stores vitamin A, D, B12 and iron• Stores fat• Regulates plasma cholesterol• Forms urea

Large IntestineLarge Intestine

Regions• Cecum (pouch with attached

vermiform appendix)

• Colon

• Rectum

• Anal canal

Major function: • absorption of water• produce some electrolytes and

vitamins made by enteric bacteria• propulsion of feces• defecation

Large IntestineLarge Intestine

Large Intestine

Bacterial Flora

Enter from the small intestine or anus • Colonize the colon

• Ferment indigestible carbohydrates

• Release irritating acids and gases

• Synthesize B complex vitamins and vitamin K

Defecation

Mass movements force feces into rectum Distension initiates spinal defecation reflex Parasympathetic signals

• Stimulate contraction of the sigmoid colon and rectum

• Relax the internal anal sphincter Conscious control allows relaxation of

external anal sphincter

Vitamin Absorption

In small intestine• Fat-soluble vitamins (A, D, E, and K) are

carried by micelles and then diffuse into absorptive cells

• Water-soluble vitamins (vitamin C and B vitamins) are absorbed by diffusion or by passive or active transporters.

• Vitamin B12 binds with intrinsic factor, and is absorbed by endocytosis

Vitamin Absorption

In large intestineVitamin K and B vitamins from

bacterial metabolism are absorbed

Electrolyte AbsorptionElectrolyte Absorption Mostly along the length of small intestineMostly along the length of small intestine Iron and calcium are absorbed in Iron and calcium are absorbed in

duodenum duodenum • NaNa++ is coupled with absorption of glucose and is coupled with absorption of glucose and

amino acidsamino acids• Ionic iron is stored in mucosal cells with ferritinIonic iron is stored in mucosal cells with ferritin• KK++ diffuses in response to osmotic gradients diffuses in response to osmotic gradients• CaCa2+2+ absorption is regulated by vitamin D and absorption is regulated by vitamin D and

parathyroid hormone (PTH)parathyroid hormone (PTH)

Water Absorption

95% is absorbed in the small intestine by osmosis

Net osmosis occurs whenever a concentration gradient is established by active transport of solutes

Water uptake is coupled with solute uptake

INQUIRYINQUIRY

1. Which layer of the alimentary canal contains loose connective tissue, glands, blood, lymphatic vessels, and nerves?

2. What type of nervous stimulation increase digestive activities?

3. What type of tooth is likely to be involved in grinding food?4. What portion of the tooth is below the gum line?5. Which gastric cells secrete intrinsic factor?6. Which enzyme secreted from the pancreas breaks down

fats?7. The surface area of the stomach is enhanced by the

presence of folds called ____.8. Name the valve between the stomach and duodenum.