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.