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BioSc 139
Digestive System Video Outline
Dr. Nancy Miller / 2006
Digestive System Video Outline
I. Functions of the digestive system
A. Breaking down foodstuff into nutrients
B. Absorption of nutrients into bloodstream and lymph fluid for distribution
II. Overview
A. Long tube open to environment on both ends
B. Mouth
1. Mastication (chewing) begins process of mechanical digestion
2. Secretions from salivary glands
a. Enzymes begin chemical digestion
b. Mucus binds food into compact bolus
3. Tongue moves food bolus to back of throat where it is swallowed
C. Esophagus
1. Peristaltic waves propel food to stomach
D. Stomach
1. Food stored temporarily
2. Mechanical digestion
3. Some chemical digestion
4. Limited absorption
E. Small intestine
1. Majority of digestion and absorption take place here
2. Secretions from liver, gall bladder and pancreas released into proximal small intestine
F. Large intestine (colon)
1. Water absorption from unabsorbed foodstuffs
2. Fecal matter (concentrated waste) eliminated from body through rectum
III. Mouth
A. Ingestion
B. Chewing (mastication) – mechanical breakdown of food
C. Initiation of starch digestion
D. Propulsion of food to pharynx (voluntary)
E. Lips and cheeks
1. Superior and inferior labial frenulum
2. Lingual frenulum
F. Vestibule
G. Teeth
1. Deciduous (20)
2. Permanent (32)
a. Incisors (central and lateral)
b. Cuspids (canines)
c. Bicuspids or premolars (2)
d. Molars (3)
H. Tongue
1. Skeletal muscle
2. Non keratinized stratified squamous epithelium
I. Bony hard palate and muscular soft palate
1. Maxillary and palatine bones
2. Uvula
3. Palatopharyngeal arch connects soft palate to pharynx
4. Palatoglossal arch (anterior) connects soft palate to tongue
5. Tonsils
a. Palatine tonsils reside in space between two arches
b. Lingual tonsils located near root of tongue
BioSc 139
Digestive System Video Outline
Dr. Nancy Miller / 2006
IV. Salivary glands
A. Saliva
1. Cleanses the mouth
2. Moistens food
3. Dissolves small food molecules for tasting
4. Amylase initiates chemical digestion of starch
B. Submandibular glands
1. Opening of duct near lingual frenulum
C. Sublingual glands (deeper, smaller)
1. Several ducts open on floor of mouth
D. Parotid glands
1. Largest salivary gland
2. Overlies masseter muscle anterior to ear
3. Duct passes through buccinator muscle
4. Opening of duct in vestibule near second upper molar tooth
V. Pharynx – see respiratory system video notes
VI. General histology of the GI tract
A. Mucosa
1. Function: protects, secretes, absorbs
2. Usually a simple columnar epithelium with goblet cells and mucus glands
3. Highly vascular lamina propria
a. Capillaries receive absorbed nutrients
b. Occasional lymphatic nodules
4. Muscularis mucosae
a. Thin layer of smooth muscle
B. Submucosa
1. Dense connective tissue
2. Blood vessels
3. Submucosal plexus (nerve plexus, part of enteric nervous system)
4. Lymphatic vessels and nodules
5. Elastic fibers
6. Submucosal glands
a. Products carried via ducts through mucosa and deposited into lumen of GI tract
C. Muscularis externa
1. Typically two layers of muscle
2. Inner circular layer of smooth muscle
3. Outer longitudinal layer of smooth muscle
4. Myenteric plexus between muscle layers (also part of the enteric nervous system)
5. Function: motility
D. Serosa (visceral peritoneum)
1. Outermost layer of intraperitoneal organs
2. Connective tissue and simple squamous epithelium (mesothelium)
3. Adventia: outermost layer of organs not covered by peritoneum
VII. Esophagus
A. Conducts food from the laryngeopharynx to the stomach
1. Posterior to trachea where they are concurrent
2. Travels behind heart
3. Passes through esophageal hiatus in diaphragm
B. Non keratinized stratifies squamous epithelium
C. Muscularis externa
1. Upper third skeletal muscle
2. Lower third smooth muscle
3. Middle third is mixed muscle types
D. Adventitia of fibrous connective tissue helps anchor esophagus to thoracic wall
BioSc 139
Digestive System Video Outline
Dr. Nancy Miller / 2006
VIII. Stomach
A. Functions
1. Primarily a storage organ
2. Protein digestion begins here
3. Some absorption of alcohol and drugs
B. Position in abdomen
1. Left of midline
2. Inferior to diaphragm
3. Partly covered by liver to the right
C. Regions of the stomach
1. Cardia – portion of the stomach where the esophagus joins
2. Fundus – left of cardia, most superior part of stomach
3. Body – large middle portion
4. Pylorus – narrowed region where stomach empties into duodenum
a. Pyloric sphincter
D. Lesser and greater curvature
E. Lesser omentum
1. Peritoneal reflection (fold) between (1) the liver and (2) the lesser curvature of stomach and
the duodenum
F. Greater omentum
1. Peritoneal reflection (fold) that hangs down like an apron from the greater curvature of
stomach
2. Covers small intestine mass
3. Contains collections of fat and lymph nodules with lymphocytes and macrophages
G. Rugae
1. Large longitudinal folds lining interior of empty stomach
2. Flatten out as stomach fills
H. Mucosal layer modifications (from typical GI tract histology)
1. Simple columnar epithelium with goblet cells secretes thick alkaline mucus
2. Gastric pits penetrate deep into lamina propria
3. Gastric glands deep to gastric pits
a. Mucus neck cells
i. Produce mucus
b. Parietal or oxyntic cells
i. Hydrochloric acid
ii. Intrinsic factor
c. Chief cells or zymogenic cells
i. Pepsinogen, the inactive form of a proteolytic (protein digesting) enzyme
ii. Converted to active pepsin in acidic environment
d. Enteroendocrine cells
i. Hormones influence digestive processes throughout digestive tract
I. Muscularis layer modifications
1. Three layers of muscle, not two
2. Innermost layer with fibers running obliquely
IX. Small intestine
A. Chemical digestion completed and most absorption takes place
B. Shorter in live individual than in cadaver (21 feet) due to muscle tone
C. Duodenum (1 foot long in cadaver)
1. Begins at pyloric sphincter
2. Secretions from pancreas and bile from liver and gall bladder enter lumen of GI tract here
3. Mostly retroperitoneal
a. Not covered by peritoneum but attached to dorsal abdominal wall by adventitia
D. Jejunum (8 feet long in cadaver)
1. Highly coiled tube between duodenum and ileum
E. Ileum (12 feet long in cadaver)
1. Terminates at ileocecal valve
BioSc 139
Digestive System Video Outline
Dr. Nancy Miller / 2006
F. Mesentery
1. Peritoneal reflection (fold)
2. Suspends ileum and jejunum from posterior body wall
3. Blood vessels, lymphatics and nerves
a. Superior mesenteric artery (SMA)
b. Arcades – arced vessels arising from adjacent branches of SMA
c. Vasa recta – straight vessels arising from arcades
d. Jejunum: fewer arcades, longer vasa recta
e. Ileum: more arcades, shorter vasa recta
G. Mucosal and submucosal layer modifications
1. Increase surface area 600x to facilitate absorption
2. Plicae circulares
a. Deep permanent circular folds in mucosal and submucosal layer
3. Villi
a. Fingerlike projections of the mucosa
b. Simple columnar epithelium
i. Absorptive cells
ii. Goblet cells
iii. Enteroendocrine cells
c. Core of lamina propria
i. Blood capillary network absorbs protein and carbohydrate breakdown products
ii. Lacteal (lymphatic capillary) absorbs fatty nutrients
d. Intestinal crypts
i. Between adjacent villi
ii. Lining cells secrete intestinal juices
4. Microvilli or brush border
a. Apical surface projections of absorptive cells
b. Brush border enzymes complete digestive process of disaccharides and small peptides
H. Muscularis layer is typical with two layers
I. Most of the small intestine covered with serosal layer (visceral peritoneum)
X. Liver, gallbladder and pancreas
A. Accessory organs
1. Not part of the GI tract per se
2. Produce substances that empty via a common duct into the duodenum to aid digestion
B. Liver
1. Largest gland of the body
2. Mostly lies to right of midline inferior to diaphragm, protected by ribcage
3. Lobes
a. Right lobe (largest)
b. Left lobe
c. Caudate lobe
i. Best seen from postro-inferior view
ii. Lies near inferior vena cava
d. Quadrate lobe
i. Best seen from postro-inferior view
ii. Lies near gall bladder
4. Falciform ligament
a. Separates right and left lobes of the liver
b. Attaches to the diaphragm and the anterior body wall
5. Round ligament or ligamentum teres
a. Inferior border of falciform ligament
b. Represents remnant of umbilical vein in the fetus
BioSc 139
Digestive System Video Outline
Dr. Nancy Miller / 2006
6. Liver lobules
a. Functional unit of the liver
b. Hexagonal in shape
c. Triads at corners of hexagon
i. Branch of hepatic artery
ii. Branch of hepatic portal vein
iii. Bile duct
d. Branch of hepatic vein at center of lobule
e. Liver cells or hepatocytes arranged in rays from central vein to periphery of lobule
i. Separated by sinusoids
ii. Arterial and portal venous blood flow from the triads toward the central vein
iii. Hepatocytes lining sinusoids process nutrients and toxins in the blood
iv. Hepatocytes also produce bile
f. Canaliculi
i. Small canals between hepatocytes that collect bile
ii. Bile flows from center to bile ducts in the triads
g. Hepatic macrophages (Kupffer cells) remove old blood cells and foreign material
C. Gall bladder
1. Lies inferior to liver
2. Bile stored and concentrated here
3. Cystic duct connects gall bladder to duct system exiting liver
D. Duct system
1. Bile flows from liver via the left and right hepatic duct
a. Unite to form common hepatic duct
2. Common bile duct
a. Formed by junction of common hepatic duct and cystic duct
3. Hepatopancreatic ampula
a. Formed by junction of common bile duct and main pancreatic duct
b. Opens into duodenum at major duodenal papilla
c. Hepatopancreatic sphincter controls movement of bile and pancreatic secretions into
duodenum
E. Pancreas
1. Duct system
a. Main pancreatic duct (see above)
b. Accessory pancreatic duct
i. Smaller
ii. Opens into duodenum proximal to major duodenal papilla
2. Secretions
a. Alkaline
b. Enzymes that digest fat, proteins and carbohydrates (starch)
3. Pancreas lies posterior to stomach
4. Parts of the pancreas
a. Head nearest to duodenum
b. Body
c. Tail nearest to spleen
BioSc 139
Digestive System Video Outline
Dr. Nancy Miller / 2006
XI. Large intestine
A. Functions to absorb water and eliminate indigestible foodstuffs
B. Cecum
1. Vermiform appendix (part of immune system)
C. Ascending colon
1. Retroperitoneal
2. From cecum to right colic flexure or hepatic flexure
D. Transverse colon
1. Anchored to posterior body wall by transverse mesocolon
2. From right colic flexure to left colic flexure or splenic flexure
E. Descending colon
1. Retroperitoneal
2. In abdominal cavity
F. Sigmoid colon
1. Anchored to posterior body wall by sigmoid mesocolon
2. In pelvic cavity
G. Rectum
1. Retroperitoneal
H. Anal canal
1. Epithelial lining is stratified squamous epithelium
I. Epiploic appendages or omental appendages
1. Fat filled tabs of visceral peritoneum that hang from the large intestine
J. Mucosa
1. Simple columnar cells with numerous goblet cells except in anal canal
K. Muscularis modifications
1. Longitudinal smooth muscle layer not complete except at terminal end
2. Teniae coli
a. Three longitudinal bands of longitudinal smooth muscle
b. Haustra – puckered sacs of large intestine due to muscle tone of the teniae coli