The The Digestive Digestive SystemSystem

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:

1.Mucosa2.Submucosa3.Muscularis externa4.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

incisors

cuspid

premolars

molars

Teeth

Teeth

nerve

enamel

dentin

pulp cavityroot canalbone

blood vessels

crown

neck

root

Salivary Glands

SalivaSaliva• Water (99.5%)Water (99.5%)• mucinmucin• AmylaseAmylase• ElectrolytesElectrolytes• GlycoproteinsGlycoproteins• antibacterial compounds such as antibacterial compounds such as

secretory IgA and lysozymesecretory IgA and lysozyme

The TongueThe Tongue

Taste Taste BudsBuds

PeristalsisPeristalsis

The StomachThe Stomachesophagus

gastroesophageal sphincter

pyloric sphincter

duodenumlongitudinal muscle

circular muscle

oblique musclerugae

Gastric Pit:Gastric Pit:

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

lumenmuscle layers

foldsvilli

Intestinal StructureIntestinal Structure

epithelial cells

capillaries

lacteal

Intestinal VillusIntestinal Villus

Intestinal Intestinal Epithelial Epithelial CellCell

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

duodenum

pancreas

pancreatic duct

common

bile duct

gallbladder

liver

BileBile• bile salts (potassium & sodium)bile salts (potassium & sodium)• bile pigments (bilirubin)bile pigments (bilirubin)• cholesterolcholesterol

Pancreatic EnzymesPancreatic Enzymes

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

Intestinal Membrane Intestinal Membrane EnzymesEnzymes

• disaccharidasesdisaccharidases• aminopeptidaseaminopeptidase• dipeptidasesdipeptidases• nucleotidasesnucleotidases• nucleosidasesnucleosidases

cecum appendix

ascending colon

transverse colon

descending

colon

sigmoidal colon

rectum

internal anal

sphincter

external anal

sphincter

anal canal

INQUIRYINQUIRY

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

2.2. What type of nervous stimulation increase digestive What type of nervous stimulation increase digestive activities?activities?

3.3. What type of tooth is likely to be involved in grinding food?What type of tooth is likely to be involved in grinding food?4.4. What portion of the tooth is below the gum line?What portion of the tooth is below the gum line?5.5. Which gastric cells secrete intrinsic factor?Which gastric cells secrete intrinsic factor?6.6. Which enzyme secreted from the pancreas breaks down Which enzyme secreted from the pancreas breaks down

fats?fats?7.7. The surface area of the stomach is enhanced by the The surface area of the stomach is enhanced by the

presence of folds called ____.presence of folds called ____.8.8. Name the valve between the stomach and duodenum.Name the valve between the stomach and duodenum.