Anatomy of Digestive System

Digestive System

• Consists of oral cavity, pharynx, esophagus, stomach, small and large intestine, liver, and gallbladder, and pancreas.

Oral Cavity

• Located inferior to nasal cavities
• Has roof, floor, and lateral walls
• Opens onto face through the oral fissure
• Continuous with pharynx at the oropharyngeal isthmus

Tongue

• Muscular structure forming part of floor of oral cavity and anterior wall of oropharynx

Pharynx

• Musculo-fascial tube extending from base of skull to esophagus
• Pharyngeal cavity is a common pathway for air and food
• Attached above to base of skull and continuous below with esophagus at approximately vertebra CVI
• Subdivided into nasopharynx, oropharynx, and laryngopharynx

Esophagus

• Muscular tube passing between pharynx in neck and stomach in abdomen
• 20-25 cm long and above level of umbilicus
• Lumen is the widest of small intestine

Small Intestine

• Consists of duodenum, jejunum, and ileum

Duodenum

• Divided into four parts
• First part: extends from pyloric orifice of stomach to neck of gallbladder
• Second part: extends from neck of gallbladder to lower border of vertebra LIII
• Third part: crosses inferior vena cava, aorta, and vertebral column
• Fourth part: passes upward and terminates at duodenojejunal flexure

Jejunum

• Proximal two-fifths of small intestine
• Larger in diameter and thicker-walled than ileum
• Inner mucosal lining characterized by numerous prominent folds (plicae circulares)
• Arterial supply includes jejunal arteries from superior mesenteric artery

Ileum

• Distal three-fifths of small intestine
• Thinner-walled and fewer mucosal folds than jejunum
• Opens into large intestine where cecum and ascending colon join
• Arterial supply from superior mesenteric artery

Large Intestine

• Begins at ileocecal junction and ends at anal orifice

Caecum

• Large blind pouch lying in right iliac fossa
• Continuous superiorly with ascending colon
• Ileocecal valve formed of two segments: upper and lower

Vermiform Appendix

• Narrow tube arising from posteromedial caecal wall
• May occupy one of several positions: retrocaecal, retrocolic, pelvic, descending, subcaecal, preilial, or postileal

Ascending Colon

• 15 cm long and narrower than caecum
• Ascends to inferior surface of right lobe of liver
• Turns sharply forward and to left at hepatic flexure

Transverse Colon

• 50 cm long
• Extends from hepatic flexure to left hypochondriac region
• Curves posteroinferiorly below spleen as splenic flexure

Descending Colon

• 25 cm long
• Descends through left lumbar and hypochondriac regions
• Curves inferomedially to become sigmoid colon at inlet of lesser pelvis

Sigmoid Colon

• Begins at pelvic inlet and ends at rectum
• Sigmoid loop ends just to left of midline at level of third sacral body

Rectum

• Most distal segment of large intestine
• Continuous proximally with sigmoid colon and terminates into anal canal
• Begins at level of S3

Liver

• Largest visceral organ in body
• Primarily in right hypochondrium and epigastric region, extending into left hypochondrium
• Surfaces include diaphragmatic and visceral surfaces

Gallbladder

• Pear-shaped sac lying on visceral surface of right lobe of liver in a fossa between right and quadrate lobes

Pancreas

• Lies mostly posterior to stomach
• Extends across posterior abdominal wall from duodenum on the right to spleen on the left
• Consists of head, uncinate process, neck, body, and tail
• Head of pancreas lies within C-shaped concavity of duodenum