The Digestive System Student Objectives:
Terms for review:
 Recall the definitions of the following terms
pH
Acidic pH
Basic pH
Neutral pH
Enzyme
Catalyze
Starch
Carbohydrate
Protein
Lipid
Triglyceride
Fatty acid
Protein denaturation
Peptide bond
Buffer
Exocrine gland
Endocrine gland
Vasoconstriction
Vasodilation
Terms:
 Define the following terms
Peristalsis
Bolus
Segmentation
Protease (proteinase)
Peptidase
Chyme
Feces
Excretion
Emulsification
Defecation
Proenzyme
Ingestion
Digestion (chemical digestion)
Mechanical processing (mechanical digestion)
Absorption
Secretion
Mastication
Mucins
GI tract or alimentary canal
Accessory digestive organs
Overview:
 Explain the primary functions of the digestive system
 Define and discuss the digestive processes
 Identify the structures on a diagram
 Identify the structures on the available models
 Trace the path of bile salts from hepatocytes to digestive tract lumen
 Trace flow of blood from hepatic portal vein through liver to inferior vena cava
 Describe the histology of the structures
 Identify the organs and tissue structures on a diagram or prepared slide
 Discuss the functions for the specific layers of the GI tract
 Describe the processes involved in the movement of digestive materials through the GI tract.
 Explain the physiology of digestion through the GI tract.
 List and describe the mechanisms that regulate the activities of the digestive system.
 Discuss the regulation and coordination of gastric and intestinal movements and emptying.
 Explain where nutrients are absorbed in the GI tract.
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Layers of the GI Tract
I. Mucosa
A. Epithelium
1. Stratified squamous or simple columnar
2. Goblet cells
3. Enteroendocrine cells
B. Lamina propria - areolar tissue
C. Muscularis mucosae - smooth muscle
1. circular
2. longitudinal
II. Submucosa
A. Dense irregular connective tissue
B. Submucosal plexus - plexus of Meissner
III. Muscularis externa
A. Skeletal and smooth muscle
1. Oblique smooth muscle fibers
2. Circular smooth muscle fibers
3. Longitudinal smooth muscle fibers
B. Myenteric plexus
IV. Serosa or adventitia
A. Serosa (visceral peritoneum) - connective tissue covered with simple squamous
epithelium
B. Adventitia – dense network of collagen fibers
Anatomy of The Gastrointestinal Tract (GI tract) – alimentary canal
Peritoneum
Parietal peritoneum
Visceral peritoneum (serosa)
Peritoneal fluid (serous fluid)
Peritoneal cavity
Retroperitoneal organs
Mesenteries
Mesocolon
Falciform ligament
Greater omentum
Lesser omentum
Mesentery proper
Oral or buccal cavity (mouth)
Lips or labia
cheeks
Vestibule
Labial frenulum
Hard palate
Soft palate
Uvula
Pharyngeal arches
Palatine tonsils
Lingual tonsil
Fauces
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Tongue
Lingual lipase
Body
Root
Lingual frenulum
Intrinsic and extrinsic tongue muscles
papillae
Salivary Glands
Parotid glands and ducts
Submandibular glands and ducts
Sublingual glands and lesser sublingual ducts
Saliva
Salivary amylase
Teeth
Crown
Neck
Root
Pulp cavity
Root canal
Apical foramen
Gingiva
Enamel
Dentin
Cementum
Periodontal ligament
Incisors
Cuspids or canines
Bicuspids or premolars
Molars
Deciduous teeth (children’s teeth, primary teeth)
Secondary dentition (permanent teeth)
Pharynx
Nasopharynx
Oropharynx
laryngopharynx
Esophagus
Upper and lower esophageal sphincters
Hiatus
Histology
 Mucosa
 Stratified squamous epithelium
 Lamina propria
 Muscularis mucosa
 Submucosa
 Muscularis
 Circular muscle fibers
 Longitudinal muscle fibers
 Adventitia
Stomach
Cardia
Fundus
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Body
Pylorus
Pyloric antrum
Pyloric canal
Pyloric sphincter
Rugae
Histology
 Mucosa
 Simple columnar epithelium
o Goblet cells
 Gastric pits
 Gastric glands
o Chief cells
o Parietal cells
 Lamina propria
 Muscularis mucosa
 Submucosa
 Muscularis
 Oblique, circular, and longitudinal smooth muscle
 Serosa
Small Intestine
Duodenum
Jejunum
Ileum
Ileocecal valve (sphincter)
Plica circularis (circular folds)
Villi
Lacteals
Microvilli – brush border
Peyers patch
Histology - duodenum
 Villi
 Mucosa
o Simple columnar epithelium
 Microvilli – brush border
 Goblet cells
o Lamina propria
 Arteriole
 Venule
 Blood capillary
 Lacteal
o Intestinal glands (crypt’s of Leiberkuhn)
 Base of villi – entrances
 Extend deep into underlying lamina propria
o Muscularis mucosae
 Submucosa
 Duodenal glands (Brunner’s glands)
 Muscularis
 Circular and longitudinal smooth muscle
Pancreas
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Pancreatic duct (duct of Wirsung)
Accessory pancreatic duct (accessory duct, duct of Santorini)
Histology
 Acini
 Pancreatic islet (islet of Langerhans)
Liver and gallbladder
Falciform ligament
Right and left lobe
Caudate lobe
Quadrate lobe
Hilus
Right and left hepatic ducts
Common hepatic duct
Cystic duct
Common bile duct
Histology – liver
 Lobules
 Central vein
 hepatocytes
 Sinusoids
 Hepatic macrophages (kupffer cells)
 Portal triad
 Hepatic portal vein – edge of lobule
 Hepatic artery – edge of lobule
 Bile canaliculus – edge of lobule or in lobule
Large Intestine
Cecum
Appendix (vermiform appendix)
Colon
Ascending, transverse, descending, and sigmoid colon
Right colic flexure (hepatic flexure), left colic flexure (splenic flexure), and sigmoid
flexure
Rectum
Anal canal
Anal columns
Anus (anal orifice)
Internal anal sphincter
External anal sphincter
Teniae coli
Haustra
Physiology of The Gastrointestinal Tract (GI tract) – alimentary canal
I. Oral or buccal cavity
A. Functions of oral cavity
1. oral cavity
a. Analysis of material
b. Mechanical processing
c. Lubrication
d. Limited Digestion
i Carbohydrates
ii Lipids
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2. Tongue
a. Functions
i Mechanical processing
ii Assist in chewing and swallowing
iii Sensory analysis
iv Secretion
 Lingual lipase
 mucins - glycoproteins for lubrication
3. Salivary Glands
a. Composition and functions of saliva
i Wet food
 Mucins
ii Dissolves food
iii Bicarbonate ions buffer acidic food
iv Chemical digestion
 Salivary amylase
v Protects mouth from infections
 Lysozyme
 Rinsing action
b. mumps
c. regulation of salivation
i increase salivation - parasympathetic
ii stop salivation – sympathetic
4. Teeth (dentition)
a. Functions of teeth
i Incisors
ii Cuspids or canines
iii Bicuspids or premolars
iv Molars
b. Dental succession
i Deciduous teeth
ii Secondary dentition
iii Eruption (emerge)
 Impacted teeth
B. Digestion in oral cavity
1. Mechanical digestion – mastication or chewing
a. Bolus
2. Chemical digestion
a. Amylase – starch
b. Lingual lipase – lipids
II. Pharynx and esophagus
A. Functions
1. pharynx
a. Function: common passageway for solid food, liquid, and air
2. Esophagus
a. Function: carry solid foods and liquid to somach
b. Histology
i Muscosa and submucosa have large folds for expansion
B. Deglutition
1. buccal phase
2. pharyngeal phase
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3. esophageal phase
III. Stomach
A. Functions
1. Bulk storage of ingested food
a. Pylorospasm
b. Phyloric stenosis
2. Mechanical digestion
3. Chemical digestion
4. Production of intrinsic factor
B. Histology of the Stomach
1. Mucosa
a. Simple columnar epithelium
b. Gastric pits
i Mucous cells – alkaline mucous
ii Gastric glands (body and fundus of stomach)
(a) Parietal cells
 Intrinsic factor for vitamin B12 absorption
 Hydrochloric acid
 Carbonic anhydrase
 Alkaline tide
(b) Chief cells
 Pepsinogen
 Gastric lipase
iii Pyloric glands (pylorus of stomach)
(a) Enteroendocrine glands
 G cells: gastrin
 Stimulates secretion of parietal and chief cells
 Stimulates contraction of gastric wall
 D cells: somatostatin
 Inhibits gastrin
2. Submucosa
3. Muscularis – longitudinal, circular, oblique
4. serosa
C. Digestion in the stomach
1. Mechanical digestion - peristalsis
2. Chemical digestion
a. Proteins
i HCl - denaturation of protein molecules
ii Pepsin – breaks peptide bonds
b. Milk fats
i Gastric lipase
ii Primarily in infant stomachs
D. Absorption of nutrients in the stomach
1. some electrolytes
2. Drugs: aspirin, alcohol
a. Alcohol dehydrogenase
E. Regulation of gastric activity
1. Cephalic phase
2. Gastric phase
3. Intestinal phase
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V. Pancreas
A. Functions
1. Hormone production
2. Digestive enzyme production
3. Buffer production
B. Histology of the pancreas
1. Pancreatic acini (acinar) – pancreatic juice
2. Pancreatic islets (islets of Langerhans) – insulin
C. Regulation of pancreas
1. nervous system control – parasympathetic NS
2. endocrine control
a. CCK
b. GIP
c. Secretin
VI. Liver
A. Functions
1. Metabolic regulation
2. Hematological regulation
3. Bile production
B. Histology
1. Hepatocytes
2. Lobules
a. Interlobular septum
b. Sinusoids
c. Central vein
d. Kupffer cells (stellate reticuloendothelial cells)
i Phagocytes for pathogens, cell debris, damaged blood cells
ii Storage
(a) Iron
(b) Some lipids
(c) Heavy metals
3. Portal area/hepatic triad
a. Hepatic portal vein
b. Hepatic artery proper
c. Small branch of bile duct
C. Flow of bile through liver
1. Bile canaliculi
2. Bile ductules
3. Bile ducts
4. Right and left hepatic ducts
5. Common hepatic duct
6. Cystic duct
7. Common bile duct (bile duct)
VII. Gallbladder
A. Functions
1. Bile storage
2. Bile modification
B. Gallstones
VIII. Small Intestine
A. Functions
1. Chemical digestion is completed
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B.
C.
D.
E.
F.
2. Nutrient absorption
Histology of Small Intestine
1. Structures that increase surface area
a. Plica circularis (circular folds)
b. Villi
i Intestinal glands, intestinal crypts or crypts of Lieberkuhn
ii Goblet cells
iii lacteals
c. Microvilli – brush border
2. Submucosa
a. Duodenal glands (Brunner’s glands)
Hormones of small intestine
1. Cholecystokinin (CCK)
2. Enterocrinin
3. Gastrin
4. Glucose-dependent insulinotropic peptide (Gastric inhibitory peptide)
5. Secretin
6. Vasoactive intestinal peptide (VIP)
Digestion in the small intestine
1. Mechanical digestion
a. Peristalsis
b. Segmentation
2. Chemical digestion
a. Enzymes from small intestine: Brush Border Enzymes
i Carbohydrases
ii Dipeptidases and peptidases
iii Enterokinase
b. Enzymes from pancreas
i Pancreatic amylase
ii Pancreatic lipase
iii Pancreatic nucleases
iv Protein digestion
(a) Proteases: break apart large protein complexes
(b) Peptidases: break small peptide chains into individual amino acids
(c) Released as proenzymes that are activated in small intestine
(d) Enzymes
 Trypsinogen
 Chymotrypsinogen
 procarboxypeptidase
v Trypsin inhibitor
c. Bile from liver
Absorption in small intestine
1. Lipids
2. Amino acids
3. Water
4. Ions
5. Vitamins
Regulation
1. Small intestine
a. Parasympathetic and sympathetic NS
b. Myenteric reflexes
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c. Gastroileal reflex
IX. Large Intestine
A. Functions
1. Reabsorption of water and compaction of intestinal contents into feces
2. Absorption of vitamins produced by bacteria
3. Storage of fecal material
B. Histology
1. Mucosa
a. Intestinal glands
i Simple columnar cells
ii Goblet cells
2. Submucosa
3. Muscular layer
a. Internal circular layer of smooth muscle is normal
b. Outer longitudinal muscle
i Taeniae coli
ii Haustra
4. Serosa filled with fat
C. Hemorrhoids
I. Large intestine
A. Digestion
1. Mechanical digestion
a. Peristaltic waves
b. Haustral churning
2. Chemical digestion
a. No enzymes secreted
b. Bacterial actions
i Fermentation
ii Vitamin production
B. Absorption in large intestine
1. Some electrolytes
2. Water
3. Bile salts
4. Vitamins
5. Organic wastes
C. Regulation of large intestine
1. Gastroilial reflex
2. Gastrocolic (gastroenteric reflex) and duodenocolic reflexes
a. responds to stretch receptors in stomach and duodenum
3. Stimulates motility and secretion in colon
4. Spinal reflex
5. Limited voluntary control




Explain where the hormones are released.
Explain what stimulates release of the hormones.
List the target(s) for each of the hormones.
Explain the action(s) of the hormone.
1. Intrinsic factor
2. Gastrin
3. Somoatostatin
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4.
5.
6.
7.
8.
Cholecystokinin
Enterocrinin
Gastric Inhibitory peptide
Secretin
Vasoactive intestinal peptide (VIP)
Clinical applications:
Peptic ulcer
Gallstones – cholecystitis
Pancreatitis
Acites
Chrohn disease
Diverticulitis
Dysphagia
Hiatal hernia
Ulcerative colitis
Mumps
Diarrhea
Constipation
Gastroesophageal reflux disease
Pylorospasm
Pyloric stenosis
Lactose intolerance
Dental caries
Gingivitis
Heartburn
Hemorrhoids
Impacted molars
Periodontal disease
Bulimia
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