Digestive System Anatomy

INTRODUCTION:
The anatomy of the digestive system can be divided into the gastrointestinal tract (GI tract) and accessory organs.  The GI tract is a long muscular tube that extends from the mouth to the anus.  The material within this tract is considered to be outside of the body.  Ingested materials must be first digested (broken down) and then absorbed across the epithelial lining of the GI tract before they can become available to body cells.  The accessory organs of the digestive system aid in the digestion process.


I.  Digestive System = Gastrointestinal tract + Accessory Organs
A. Major Regions of the Gastrointestinal tract, a.k.a. Alimentary Canal
1. MOUTH (ORAL CAVITY)
2. PHARYNX
3. ESOPHAGUS
4. STOMACH
5. SMALL INTESTINE
6. LARGE INTESTINE

B. Accessory Organs
1. SALIVARY GLANDS
2. TEETH
3. TONGUE
4. LIVER
 5. GALL BLADDER
6. PANCREAS

II.  Mouth / Oral Cavity / Buccal Cavity
A. Boundaries
1. Anterior – LABIA (lips)
2. Lateral – BUCCAE (cheeks)
3. Posterior – FAUCES
a. PALATOGLOSSAL ARCH – anterior arch
b. PALATINE TONSILS – located between the arches
c. PALATOPHARYNGEAL ARCH – posterior arch
d. The boundaries of the fauces are formed by a curving line connecting
the uvula and the palatoglossal arch
4. Superior – HARD PALATE AND SOFT PALATE      a. UVULA = tip of soft palate
5. Inferior – MYLOHYOID MUSCLE and TONGUE
B. Minor Regions
1. ORAL VESTIBULE – between lips/cheeks and teeth
2. ORAL CAVITY PROPER – space enclosed by teeth
C. Accessory Organs
1. TONGUE
a. Musculature
1. Intrinsic muscles of the tongue
a) muscles inside tongue
b) change shape of tongue
2. Extrinsic muscles of the tongue
a) moves whole tongue (gross movements)
b. Papillae (epithelial projections) of the tongue
1. FILLIFORM PAPILLAE
2. *FUNGIFORM PAPILLAE
3. *CIRCUMVALLATE PAPILLAE – forms V-shape that
separates tongue into anterior 2/3’s (BODY) with posterior
1/3 (ROOT)
a) * = house taste (gustatory) receptors
c. LINGUAL FRENULUM – connects body of tongue to floor of mouth
2. SALIVARY GLANDS – three pairs
a. PAROTID SALIVARY GLANDS
1. Parotid ducts (Stensen’s ducts) open into oral vestibule at
maxillary 2nd molars
b SUBMANDIBULAR SALIVARY GLANDS    1. Submandibular ducts (Wharton’s ducts) open on either side of
lingual frenulum
c. SUBLINGUAL SALIVARY GLANDS
1. Sublingual ducts (Rivinus’ducts) open on either side of lingual
frenulum

3. TEETH
a. INCISORS = cutting teeth
b. CANINES / CUSPIDS = tearing teeth
c. PREMOLARS / BICUSPIDS = small grinding teeth
d. MOLARS = large grinding teeth
e. DENTAL FORMULA for secondary or permanent teeth

3M 2PM 1C 2I   |   2I 1C 2PM 3M     Total = 32
3M 2PM 1C 2I   |   2I 1C 2PM 3M

*note – There are generally 20 primary or baby teeth
g. Structure of a Tooth
1. Regions
a) CROWN – exposed portion of tooth
b) NECK – between crown and root
c) ROOT – sits within bony socket or alveoli
d) PULP CAVITY – contains vessels and nerves
e) ROOT CANAL – tunnel from apical foramen to pulp
cavity; passageway for vessels and nerves
f) APICAL FORAMEN – opening to root canal
2. Composition
a) DENTIN – makes up bulk of tooth
b) ENAMEL – covers dentin of crown
c) CEMENTUM – covers dentin of root
3. PERIODONTAL LIGAMENT – collagen fibers supporting gomphosis
4. GINGIVAE – the gums

III.  PHARYNX AND ESOPHAGUS
A. PHARYNX
1. OROPHARYNX and LARYNGOPHARYNX
2. Muscles of pharynx, oral cavity, and esophagus coordinate to
push a bolus of food toward esophagus to initiate deglutition
B. ESOPHAGUS
1. Gross Anatomy
a. 1 foot in length and < 1 inch in diameter; posterior to trachea
b. carries ingested materials from laryngopharyx to stomach
c. pierces the diaphragm @ ESOPHAGEAL HIATUS
d. Upper esophageal sphincter
e. Lower esophageal sphincter (CARDIAC SPHINCTER)
f. Esophagus, unlike the trachea, is collapsed when not in use

IV. STOMACH
A. Gross Anatomy
1.a mobile, J-shaped sac; extends from cardiac spincter to pyloric sphincter
2. to left of midline mosty in epigastric region
3. lining exhibits RUGAE when empty
4. Regions of the Stomach
a. CARDIA – superior region at junction with esophagus
b. FUNDUS – superior bulge
c. BODY – bulk of stomach; between fundus and pylorus
d. PYLORUS
1) Two Regions
a) PYLORIC ANTRUM – proximal pylorus
b) PYLORIC CANAL – distal pylorus that empties into
small intestine
2) PYLORIC SPHINCTER –separates stomach and small intestine
5. Curvatures of the Stomach
a. GREATER CURVATURE
b. LESSER CURVATURE

V. SMALL INTESTINE
A. In death, length of approximately 20 feet; diameter range from 1-1.5 inches
B. Starts @ PYLORIC SPHINCTER
C. Ends @ ILEOCECAL VALVE
D. Regions of the Small Intestine
1. DUODENUM
a. “Mixing bowl” – receives chyme from stomach, enzymes and
bicarbonates from pancreas, and bile from liver (gallbladder)
b. Ducts from pancreas and liver empty at the DUODENAL AMPULLA
guarded by PANCREATICOHEPATIC SPHINCTER (Sphincter
of Oddi)
2. JEJUNUM
a. Majority of digestion and absorption
3. ILEUM
a. terminates at first portion of large intestine (cecum) at ileocecal valve

VI. LIVER
A. Gross Anatomy
1. Four  Lobes
a. RIGHT LOBE
b. LEFT LOBE
c. CAUDATE LOBE
d. QUADRATE LOBE
2. FALCIFORM LIGAMENT – divides left and right lobe
3. ROUND LIGAMENT (ligamentum teres) – remnant of fetal umbilical vein
4. HILUS (porta hepatis) – region where vessels and other structures enter liver

B. Blood to liver (vascular)
1.  HEPATIC ARTERY – fresh arterial blood from aorta
2.  HEPATIC PORTAL VEIN – nutrient rich blood from digestive system
C. Blood leaving liver
1. HEPATIC VEINS to INFERIOR VENA CAVA
D. Structures associated with movement of BILE
1. RIGHT AND LEFT HEPATIC DUCTS
2. COMMON HEPATIC DUCT
3. CYSTIC DUCT AND GALLBLADDER
4. COMMON BILE DUCT
5. DUODENAL AMPULLA

VII. PANCREAS
A. Gross Anatomy
1. Regions
a. HEAD
b. TAIL
2. Ducts
a. PANCREATIC DUCT (duct of Wirsung) fuses with COMMON BILE  DUCT and enters the DUODENAL AMPULLA which is guarded
by the PANCREATICOHEPATIC SPHINCTER
b. ACCESSORY PANCREATIC DUCT

VIII. LARGE INTESTINE
A. Gross Anatomy
1. 5 feet in length and 3 inches in diameter
2. Regions
a. CECUM
1)  ILEOCECAL VALVE – sphincter that controls movement of     material from ileum to cecum
2) (VERMIFORM) APPENDIX
b. COLON
1) ASCENDING COLON
a)Right Colic Flexure (Hepatic Flexure)
2) TRANSVERSE COLON
a)Left Colic Flexure (Splenic Flexure)
3) DESCENDING COLON
a)Sigmoid Flexure
4) SIGMOID COLON
5)RECTUM
a) ANORECTAL CANAL with RECTAL COLUMNS
b) ANUS – terminal opening of anorectal canal
1) Internal Anal Sphincter – smooth muscle
2) External Anal Sphincter – skeletal muscle

c. Other Structures
1) HAUSTRA – pouches
2) TAENIA COLI – ribbons of smooth muscle

IX.  PERITONEUM / PERITONEAL MEMBRANES
A. Serous Membranes of peritoneal cavity
1. Visceral peritoneum
a. Covers surface of most digestive organs in peritoneal cavity
b. Same as Serosa on any isolated piece of a digestive organ
2. Parietal peritoneum
a. Lines inner wall of abdominal cavity
b. MESENTERIES are folds of parietal peritoneum which connect
to visceral peritoneum
1) stabilize organs and provide routes for vessels and nerves