Digestive System

• Basic Divisions

– Digestive tract

– Accessory organs: various exocrine glands

• Digestive Processes

– Ingestion

– Mechanical Processing

– Motility

• Peristalsis

• Segmentation movements

– Chemical digestion

– Secretion

– Absorption

– Excretion and defecation

• Non-Digestive Functions of Digestive Tract

– Immunity

– Storage of iron

• Layers of the digestive tract

– Mucosa

• Epithelium

• Lamina propria (areolar CT)

• Muscularis mucosae

– Submucosa

• includes the submucosal plexus

– Muscularis externa: responsible for peristalsis and segmentation movements

• longitudinal layer

• circular layer

• myenteric plexus

– Serosa (example of the visceral peritoneum)

• Simple squamous epithelium

• Areolar CT

–Within peritoneal cavity only

– Adventitia

• Dense irregular CT

– Oral cavity, pharynx, esophagus, rectum

• The Peritoneum

– Parietal p.

– Visceral p.

• The mesenteries

– Mesentery proper

– Mesocolon

– Greater omentum

– Lesser omentum

• Oral (buccal) cavity

– Salivary Glands

• buccal glands

• lingual glands

• major salivary glands

– parotid

– sublingual

– submandibular

– Structure of salivary glands

• glandular epithelium

• merocrine cells

– Structure of salivary glands

• glandular epithelium

• merocrine cells

– Functions of saliva

• lubrication for swallowing, speaking

• re-mineralizes tooth enamel

• buffer

• antibodies (IgA)

• dissolves food molecules

• some chemical digestion

• Pharynx

– 3 divisions

• Nasopharynx

• Oropharynx

• Laryngopharynx

– Structural features

• Lined with a stratified squamous epithelium

• Skeletal muscle in wall

• eustachian tube opening

• uvula

• tonsils

– Functions

• food and air pathways

• resonating chamber for voice

• swallowing http://www.innerbody.com/anim/mouth.html

• Esophagus

– Structural features

• muscular tube about 25 cm long

• posterior to larynx, trachea

• pierces diaphragm through esophageal hiatus

• 2 sphincters:

– upper esophageal sphincter

– lower esophageal sphincter

– Histology highlights

• mucosa: strat. sqaumous

• submucosa: lots of mucous glands

• muscularis: from skeletal to smooth

• adventitia (no serosa)

• Stomach

– Location: from epigastric and umbilical to left hypochondriac regions

– Gross Structural Features

• cardiac region

• fundus

• body

• pylorus

• pyloric sphincter

– Stomach Histology

• mucosa: location of gastric glands

• muscularis: three layers

– Stomach Functions

• food reservoir

• formation of chyme

• some chemical digestion

• regulation of chyme entry into S.I.

• intrinsic factor production

• some absorption

• Pancreas

– Location

• Umbilical region

• Retroperitoneal

– Pancreas Gross Structure

• Head

• Body

• Tail

• Ducts

– pancreatic

– accessory

– Pancreas Histology

• mostly glandular epithelium

• exocrine pancreas

• endocrine pancreas

– Exocrine Pancreas

• structure: compound tubuloacinar gland

• functions

–digestive enzymes

–sodium bicarbonate

– Endocrine Pancreas

• structure: thousands of islets of Langerhans

• function

– glucagon

– insulin

– somatostatin

• Liver

– Gross structure: 2 major lobes separated by falciform ligament

– Liver Blood Supply

• Hepatic portal vein

• Hepatic arteries

– Liver Histology

• Functional unit: liver lobule

• Liver cells

– hepatocytes

– Kupffer cells

– Each lobule supplied by branches of:

• hepatic arteries

• hepatic portal veins

– Blood drains out lobule in central veins

– Bile drained from lobule by bile canaliculi

– Liver Functions

• Maintains blood glucose levels

• Cholesterol synthesis

• HDL and LDL synthesis

• Plasma protein synthesis

• Hormone and drug removal

• Phagocytosis

• Bilirubin excretion

• Bile salt secretion

• Gall Bladder

– Location

• Right lumbar region

– Gross Structural Features

• Muscular sac

• Mucosa folded into rugae

• Bile enters and leaves through cystic duct

– Gall Bladder Function

• Stores and concentrates bile

• Contracts during meals to force bile into SI

– Biliary Pathway: “plumbing” which drains bile to duodenum from liver and gall bladder

• Small Intestine

– 1 inch diameter

– 10-20 ft. in length

• duodenum (10 in)

• jejunum (3-6 ft.)

• ileum (6-12 ft)

– Features of SI mucosa

• Plica circularis

• Villi

• Microvilli

• Epithelial cell types:

–Absorptive cells

–Goblet cells

–Endocrine cells

–Paneth cells

–MALT in lamina propria

–Intestinal glands (“crypts”)

– Features of SI submucosa

• Submucosal glands in duodenum

– Motility of SI

• Segmentation movements

• Peristalsis

– Functions of small intestine

• Completion of chemical digestion

– “brush-border” enzymes required

• Absorption

• Endocrine control of some digestive processes

• Large Intestine (large bowel)

– 2.5 inches in diameter

– 5-6 feet long

• Cecum

• Colon

– Ascending

– Transverse

– Descending

– Sigmoid

• Rectum

• Anal canal

– Features of LI mucosa

• no villi

• numerous intestinal glands

• goblet and absorptive cells in epithelium

• MALT in lamina propria

– Structural Features of cecum and colon

• Taeniae coli

• Haustra

• Epiploic appendages

– Other Structural Features

• Vermiform appendix

• Ileocecal valve

• Stretch receptors in rectum

– initiate defecation reflex

• Anal sphincters of anal canal

– Motility of Large Intestine

• From cecum to transverse colon: peristalisis

• From transverse colon to rectum: mass movements

– Functions of Large Intestine

• Water and electrolyte absorption

• Feces formation

• Defecation

– Large Intestinal Bacteria

• Coat surface of mucosa

• Examples: E. coli

• Keep out pathogenic bacteria