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ANATOMY

DIGESTIVE SYSTEM
• The system involved in the breaking down of food
• Gastroenterology: deals with the structure, function, diagnosis and treatment of
diseases of the stomach and intestine
• Proctology: deals with diagnosis and treatment of disorders of the rectum and
anus
FUNCTIONS OF DIGESTIVE SYSTEM
• Breaking down of food
• Absorption of water, vitamins and minerals
• Elimination of waste products
SIX BASIC PROCESSES
• Ingestion – taking of foods and liquids into the mouth (eating)
• Secretion – release of water, acid, buffers and enzymes into the lumen of the GI
tract
o Total: 7 L
• Mixing and propulsion – churning and propulsion of food through GI tract
o Motility: capability of the GI tract to mix and move material along its length
• Digestion – mechanical and chemical processes break down of ingested food
o Mechanical: teeth cut and grind food
o Chemical: digestive enzymes produced by accessory glands
• Absorption – passage of digested products from the GI tract into blood and lymph
• Defecation – the elimination of feces in the GI tract
o Feces: the eliminated material

TWO PARTS OF DIGESTIVE SYSTEM
1
...
5-23 ft)
• Cadaver: 7-9 m (23-29
...
) ACCESSORY GLANDS
• Teeth – aid in physical breakdown of foods
• Tongue – assists in chewing and swallowing
• Salivary glands – produce saliva
• Liver – produces bile
• Gall bladder – stores bile
• Pancreas – produces pancreatic juices
• General: they secrete digestive enzymes into the alimentary canal
MOUTH
• Oral or buccal cavity
• Formed by: cheeks, hard and soft palate and tongue
• Lips/labia: fleshy folds
• Labial frenulum: folds of mucous membrane; b/n inner surface of lip and gums
• Oral vestibule: space bounded by
o Cheeks and lips (externally)
o Gums and teeth (internally)
• Oral cavity proper: space from gums and teeth to fauces
• Fauces: opening b/n oral cavity and oropharynx (throat)
• Palate: wall/septum
o Separates oral cavity from nasal cavity
• Hard palate: anterior portion of roof of the mouth
• Soft palate: posterior portion of roof of the mouth
• Uvula (little grape): conical muscular process
o Function: helps prevent foods and liquids from entering the nasal cavity
during swallowing
• Two muscular folds:
o Palatoglossal arch
▪ Anteriorly
▪ Side of the base of the tongue
o Palatopharyngeal arch
▪ Posteriorly
▪ Side of the pharynx
• Tongue: forms the floor of oral cavity
o Lingual frenulum:
▪ Folds of mucous membrane
▪ Attached to floor of the mouth

o
o
o
o

▪ Aids in limiting the movement of tongue posteriorly
Ankyloglossia: abnormally short or rigid lingual frenulum
Papillae: nipple-shaped projections
▪ Contains taste buds
Taste buds: the receptor for gustation (taste)
Lingual glands: secrete mucus and water serous fluid
▪ Enzyme: lingual lipase

TEETH/DENTES
• Accessory digestive organs
• Gingivae: gums
• Three major external regions:
o Crown – visible portion above the gums
o Root – embedded in the socket
o Neck – constricted junction of crown and root
• Dentin: forms majority of the tooth (internally)
o Gives tooth its shape and rigidity
o Harder than bone
▪ Rationale: contains 70% of calcium salts
• Enamel: covered the dentin of the crown
o Hardest substance in the body
▪ Rationale: contains 90% of calcium salts
o Protects the tooth from wear and tear
o Protects tooth from acid
• Cementum: covered the dentin of the root
• Pulp cavity: space within the crown
o Contains pulp
• Root canals: narrow extension of pulp cavity
• Apical foramen: opening at the base of root canal
• Endodontics: prevention, diagnosis, and treatment of disease affecting pulp, root,
periodontal ligament and alveolar bone
• Orthodontics: prevention and correction of abnormally aligned teeth
• Periodontics: treatment of abnormal conditions of tissues surrounding the teeth
• Two dentition/sets of teeth:
o Deciduous teeth
▪ Decidu = “falling out”
▪ Primary, milk, or baby teeth
▪ 20 teeth
▪ Appear: 6 months old
▪ Lost: 6-12 y/o

o Permanent teeth
▪ Secondary teeth
▪ 32 teeth
▪ Appear: 6 y/o or adulthood
▪ First premolar (bicuspids):
• For crushing and grinding
• Appear: 9-10 y/o
▪ Second premolar (bicuspid):
• For crushing and grinding
• Appear: 10-12 y/o
▪ Permanent molars:
• 1st molar – 6-7 y/o
• 2nd molar – 12-13 y/o
• 3rd molar – 17-21 y/o or not at all
ESOPHAGUS
• Long muscular tube
• Carries food and saliva (laryngopharynx to the stomach)
• Physiology:
o Secretes mucus
o Transports food into stomach
o Does not produce digestive enzymes
o Does not carry on absorption
• Length: 10 in
...
(1
...
) MUCOSA
• Contains mucous glands

•
•

Layers: epithelium, lamina propia, muscularis mucosae
Epithelium layer:
o Stratified squamous epithelium: serves a protective function against
wear-and-tear from food particles
• Lamina propria:
• Muscularis mucosae: smooth muscle fibers
2
...
) MUSCULARIS
• Superior third: skeletal muscle
• Intermediate third: skeletal and smooth muscles
• Two sphincters:
o Upper esophageal sphincter (UES): skeletal muscle (voluntary)
▪ Regulates movement of food from pharynx into esophagus
o Lower esophageal sphincter (LES): smooth muscle (involuntary)
▪ Regulates movement of food from esophagus into stomach
4
...
) MUCOSA
• Inner lining of the GI tract

•
•
•

Cell renewal rate: rapid (5-7 days)
Layers: epithelium, lamina propia, muscularis mucosae
Epithelium layer:
o Stratified squamous epithelium: serves a protective function
o Simple columnar epithelium: for secretion and absorption
o Gastic glands: columns of secretory cells
o Mucous neck cells: secretes mucus
o Parietal cells: produce intrinsic factor (needed for absorption of Vitamin
B12) & HCl
o Chief cells: secrete pepsinogen and gastric lipase
o G-cell (in pyloric antrum): secretes gastrin
o Gastric juices: 2000-3000 mL/day (2-3 qt/day)
o Gastric pits: narrow channel at the bottom of gastric glands
• Lamina propria:
o Connective tissue layer
o Contains many blood and lymphatic vessels
o Contains MALT (mucosa-associated lymphatic tissue)
▪ Protection against disease
• Muscularis mucosae: smooth muscle fibers
2
...
) MUSCULARIS
• Three smooth muscle layers
o Longitudinal layer
o Middle layer
o Inner oblique layer
• Contains myenteric plexus (plexus of Auerbach)
• Skeletal muscle (voluntary):
o muscularis of mouth, pharynx, superior and middle parts of esophagus –
produces voluntary swallowing
o external anal sphincter – voluntary control of defecation
• Smooth muscle (involuntary):
o Inner sheets – circular fibers
o Outer sheets – longitudinal fibers
o Functions: break down, mix and propel foods
4
...
)
• Thickness: 2
...
)
• Location: posterior to greater curvature of stomach
• Consists of:
o Head – expanded portion
o Body – central portion
o Tail – tapered end
• Exocrine cells: secretes pancreatic juices
• Pancreatic duct: duct of Wirsung
• Accessory pancreatic duct: duct of Santorini
• Hepatopancreatic ampulla: ampulla of Vater
o Opens on major duodenal papilla
• Sphincter of Oddi: sphincter of hepatopancreatic ampula
• Acini: clusters of glandular epithelial cells
o Secretes fluid and digestive enzymes
o Pancreatic juice – 99%
▪ 1200-1500 mL/day (1
...
5 qt/day)
o Pancreatic islets (islets of Langerhans) – 1%
▪ Secretes glucagon, insulin, somatostatin & pancreatic polypeptide
• Enzymes in pancreatic juice:
o Pancreatic amylase – starch-digesting enzymes
o Trypsin, chymotrypsin, carboxypeptidase, elastase – protein-digesting
enzymes
o Pancreatic lipase – principal tryglycerides-digesting enzymes in adults
o Ribonuclease & deoxyribonuclease – nucleic acid-digesting enzymes
DUCT CARRYING BILE FROM LIVER AND GALLBLADDER AND PANCREATIC
JUICE FROM PANCREAS TO THE DUODENUM

LIVER
• Heaviest gland
• Largest internal organ
• Second largest organ
• Skin: largest organ in the body
• Weight: 1
...
6-8
...
)
• Parts:
o Fundus – broad portion; projects inferiorly
o Body – central portion; projects superiorly
o Neck – tapered end; projects superiorly
SMALL INTESTINE
• Functions:
o Mechanical and chemical digestion of food
o Completes the digestion of carbohydrates, proteins, and lipids
o Begins and completes the digestion of nucleic acids
...
(2
...
(25 cm)
Four regions:
• Superior/duodenal bulb
• Descending/duodenal loop
o Fixed part
• Horizontal/inferior
• Ascending
o Joins the jejunum (duodenojejunal flexure)
▪ Hepatopancreatic ampulla
• Union of pancreatic and common bile ducts
• Open on duodenal papilla
▪ Ligament of Treitz
• Suspensory muscle of the duodenum
• Supports duodenojejunal flexure
o Jejunum
▪ It means “empty”
• Rationale: found empty at death
▪ Upper two fifths of small intestine
▪ Length: 1 m (3 ft)
o Ileum
▪ Largest portion
▪ Lower two fifths
▪ Length: 2 m (6 ft)
o Gyri: freely movable loops (jejunum and ileum)
o Mesentery: attached jejunum and ileum to the posterior wall of the
abdomen
Intestinal juice: clear yellow fluid
o 1-2 L/day (1-2 qt/day)
Total fluid ingested and secreted:
o 9
...
3 L
▪ GI secretions – 7 L
• Saliva (1 L)
• Gastric juice (2 L)
• Bile (1 L)
• Pancreatic juice (2 L)

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•
•

• Intestinal juice (1 L)
0
...
5 L/day: excreted in urine
Total fluid absorbed:
o 8
...
9 L: absorbed by LI

FOUR LAYERS OF SMALL INTESTINE
o From deep to superficial
1
...
) SUBMUCOSA
• Contains duodenal glands (Bruner’s glands)
o Secrete alkaline mucus
o Helps neutralize gastric acid in chime
3
...
) SEROSA
• Visceral peritoneum
• Completely surrounds the small intestine
SPECIAL STRUCTURES IN SMALL INTESTINE
1
...
) VILLI
• “tufts of hair”
• Fingerlike projection of the mucosa
• For digestion and absorption
• Length: 0
...
0 mm
• Surface area: 20-40/mm2
• Lacteal (milky): a lymphatic capillary
3
...
5 m)
Diameter: 6
...
5 in)
Mesocolon: double layer of peritoneum
o Attached LI to posterior abdominal wall
Ileocecal sphincter/valve: opening b/n ileum and LI
o Allows material from SI to pass LI
Four major region: cecum, colon, rectum and anal canal
o Cecum
▪ A small pouch (6 cm long)
▪ Inferior to ileocecal valve
▪ Length: 2
...
(6 cm)
▪ Diameter: 3 in
...
6 cm)
▪ Appendix/Vermiform appendix:
• Attached to cecum
• Vermiform = “worm-shaped”
▪ Mesoappendix: mesentery of appendix
• Attaches appendix to inferior part of mesentery of ileum
o Colon
▪ Colon = “food passage”
▪ Ascending portion
• Retroperitoneal
• Right colic/hepatic flexure
o Junction of ascending and transverse
▪ Transverse portion
• Longest and most movable
• Left colic/spleenic flexure
o Junction of transverse and descending
▪ Descending portion
• Retroperitoneal
▪ Sigmoid portion
• S-shaped loop
• Ends at rectum (S3)
o Rectum
▪ Anterior to sacrum and coccyx
▪ Level: sigmoid colon to the anal canal
▪ Length: 8 in
...
5 cm)
▪ Rectal ampulla: dilation above the anal canal
o Anal canal
▪ Terminal of the rectum

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▪
▪
▪

•
•
•

•
•
•

Terminates at the anus
Length: 2-3 cm (1 in)
Anus: opening of the anal canal to the exterior
Internal anal sphincter:
• Smooth muscle
• Involuntary
▪ External anal
sphincter:
• Skeletal muscle
• Voluntary
o Two AP curves of rectum and anal canal: must be remembered during
enema tip insertion
▪ Passes inferiorly and posteriorly to level of pelvic floor
▪ Bends anteriorly and inferiorly into anal canal
Bacterial action: last stage of chemical digestion in LI
Gastrin: relaxes the sphincter
Occult blood: refers to blood that is hidden
o Occult blood testing: to screen for colorectal cancer
▪ Examined: feces and urine
Chyme: remain in the LI in 3-10 hours
Diarrhea: increased in frequency, volume and fluid content of the feces
o Increased motility and decreased absorption of intestine
Constipation: infrequent or difficult defecation
o Decreased motility of intestine

FOUR LAYERS OF LARGE INTESTINE
• From deep to superficial
1
...
) SUBMUCOSA

• Contains areolar connective tissue
3
...
) SEROSA
• Visceral peritoneum
• Omental (fatty) appendices: small pouches filled with fat
o Attached to teniae coli



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