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.

Various accessory organs empty secretions into them.

What is the function of the digestive system?

The digestive tube is called the alimentary canal or gastrointestinal tract (GI)

• 1st food is broken down physically- mastication

• then chemically by digestion (enzymatic degradation)

• then nutrients are absorbed

Digestive process:

1) Ingestion  2)Propulsion3)Mechanical digestion4)Chemical digestion5)Absorption6)Defecation

GI Tract- 4 basic tunics:

1.Mucosa2.Submucosa3.Muscularis externa4.Serosa (adventia)

Mucosa: wet epithelial membrane; consists of mostly simple columnar epithelium, lamina propria (areolar connective tissue), muscularis mucosa (sm layer of smooth muscle fibers)--enables local movement of mucosa

Function: • secretion (enzymes, mucous,

hormones…) • absorption of digestive food stuff• protection against bacterial invasion• reduces friction • protects cells from being digested

Submucosa- moderately dense connective tissue containing:blood, lymphatic vessels, scattered, lymph nodules and nerve fibersassociated nerve- submucosal plexusFunction: nutrition and protection

Muscularis externa- bilayer of smooth muscle and superficial longitudinal muscleassociated nerve- myenteric plexusFunction: regulated GI motility (churning)

Serosa- equivalent to visceral peritoneum (serous membrane) consists of mesothelium in a thin layer of areolar connective tissue

In areas outside abdominopelvic cavity- serosa replaced by an adventia (course fibrous connective tissue)

Function- reduces friction, anchors and protects 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

Teeth

Teeth

Salivary GlandsSalivary Glands

Extrinsic salivary glands Extrinsic salivary glands

ParotidParotid

SubmandibularSubmandibular

SublingualSublingual

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

Salivary GlandsSalivary Glands

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

muscle 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 Glands

Composition of SalivaComposition of Saliva

Secreted by serous and mucous cells Secreted by serous and mucous cells 97–99.5% water, slightly acidic solution 97–99.5% water, slightly acidic solution

containingcontaining• Electrolytes—NaElectrolytes—Na++, K, K++, Cl, Cl––, PO, PO4 4

2–2–, HCO, HCO33––

• Salivary amylase and lingual lipaseSalivary amylase and lingual lipase• MucinMucin• Metabolic wastes—urea and uric acidMetabolic wastes—urea and uric acid• Lysozyme, IgA, defensins, and a cyanide Lysozyme, IgA, defensins, and a cyanide

compound protect against microorganismscompound protect against microorganisms

TongueTongue

Functions 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 positionLingual frenulum: attachment to the floor of Lingual frenulum: attachment to the floor of

the mouththe mouth

TongueTongue Surface bears papillaeSurface bears papillae

1.1. Filiform—whitish, give the tongue roughness Filiform—whitish, give the tongue roughness and provide friction and provide friction

2.2. Fungiform—reddish, scattered over the Fungiform—reddish, scattered over the tongue tongue

3.3. 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

4.4. 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 Secretions

Gastric Pit:Gastric Pit:hydrochloric acidhydrochloric acid

pepsinogenpepsinogenmucusmucus

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--- new research90% of recurrent ulcers due to bacterial infection (Helicobacter pylori), which destroys mucous protective barrier; use antibiotic therapy to kill bacteria

Bacteria

Mucosalayer ofstomach

(a) A gastric ulcer lesion (b) H. pylori bacteria

BileBileBile saltsBile salts

Bile pigmentsBile pigmentsCholesterolCholesterolNeutral fatsNeutral fats

PhospholipidsPhospholipidsOther electrolytesOther electrolytes

Bile secretion

Small Intestine, Gallbladder, & Pancreas

PancreasPancreas

Endocrine 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 Amylase, lipases, nucleases are

secreted in active form but require ions secreted in active form but require ions or bile for optimal activityor bile for optimal activity

• Proteases secreted in inactive formProteases secreted in inactive form

Pancreatic JuicePancreatic Juice

Protease activation in duodenumProtease activation in duodenum• Trypsinogen is activated to trypsin by Trypsinogen is activated to trypsin by

brush border enzyme brush border enzyme enteropeptidaseenteropeptidase

• Procarboxypeptidase and Procarboxypeptidase and chymotrypsinogen are activated by chymotrypsinogen are activated by trypsintrypsin

Pancreatic Enzymes

trypsintrypsinchemotrypsinchemotrypsin

carboxypeptidasecarboxypeptidaseamylaseamylase

phospholipasephospholipaselipaselipase

nucleasesnucleases

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 Intestinal Membrane EnzymesEnzymes

disaccharidasesdisaccharidasesaminopeptidaseaminopeptidase

dipeptidasesdipeptidasesnucleotidasesnucleotidasesNucleosidasesNucleosidases

LactaseLactaseMaltaseMaltase

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

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 AbsorptionVitamin Absorption

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

carried by micelles and then diffuse into carried by micelles and then diffuse into absorptive cellsabsorptive cells

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

• Vitamin BVitamin B1212 binds with intrinsic factor, and binds with intrinsic factor, and is absorbed by endocytosis is absorbed by endocytosis

Vitamin AbsorptionVitamin Absorption

In large intestineIn large intestine Vitamin K and B vitamins from bacterial Vitamin K and B vitamins from bacterial

metabolism are absorbedmetabolism are absorbed

Electrolyte AbsorptionElectrolyte Absorption

Mostly along the length of small intestineMostly along the length of small intestine Iron and calcium are absorbed in duodenum Iron and calcium are absorbed in 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 AbsorptionWater Absorption

95% is absorbed in the small intestine 95% is absorbed in the small intestine by osmosisby osmosis

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

Water uptake is coupled with solute Water uptake is coupled with solute uptakeuptake

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.