Overview of Gastrointestinal Anatomy

Overview of Gastrointestinal Anatomy

Sections

Overview
Anatomy & Physiology
Supplemental Materials

Overview of Digestive Organ Anatomy

Overview

6 key functions of the digestive system:

• Ingestion of foods and liquids
• Digestion (chemical and mechanical) of foods and liquids
• Propulsion of materials through the body
• Secretion of digestive enzymes and hormones
• Absorption of nutrients and water from foods and liquids
• Elimination of wastes (aka feces)

Anatomical & Functional Divisions

• Gastrointestinal tract (aka, GI tract, alimentary canal, gut)
• Accessory organs

Anatomy & Physiology

GI tract:

Oral cavity (aka, mouth)

• Initiates digestion of foods and liquids
• Is bound anteriorly by the lips, opens posteriorly to the oropharynx.

Pharynx

• Open to the nasal cavity, the oral cavity, and the larynx because the pharynx is a common passageway for both the digestive and respiratory systems.

Esophagus

• Muscular tube that transports foods and liquids to the stomach.

Stomach

See: Stomach

• J-shaped pouch
• Where foods and liquids are stored and also converted to a thick, soup-like substance called chyme
• See: Physiology of Swallowing & Gastric Filling

Small Intestine

See: Small intestine

• Long tube that coils upon itself
• it's the primary site of nutrient absorption
• Its length increases contact with absorptive tissues, which optimizes nutrient absorption.
• Small intestine subdivisions:
  — Duodenum, which is relatively short, and receives chyme from the stomach.
  — Jejunum, which is the longer middle segment.
  — Ileum, which is the terminal segment of the small intestine.

Large Intestine

See: Large intestine

• Primary site of water absorption.
• Large intestine subdivisions:
  — Ascending colon, which ascends the right side of the abdomen.
  — Transverse colon, which passes along the transverse plane of the body.
  — Descending colon, which descends the left side of the abdomen.
  — The sigmoid colon, which is the S-shaped (aka, sigmoid) portion of the colon within the pelvis.
  — Cecum, which is a small, pouch-like structure.
  — Vermiform appendix extends from the cecum; this wormlike (aka, "vermiform") structure houses lymphoid tissue.
  — Rectum is the distal-most portion of the large intestine and receives the sigmoid colon.

Anus

• Terminal end of the GI tract – where wastes exit.

Sphincters

• Muscular rings that regulate the movement of materials through the GI tract.

Accessory organs

• Teeth, which mash the food
• Tongue, which shapes food into a "bolus"
• Salivary glands, which produce saliva
  — Parotid, the largest, lies in the cheek
  — Sublingual lies under the tongue ("lingual" refers to the tongue)
  — Submandibular lies below the mandible
• Liver produces the bile
• Gallbladder stores and secretes bile
• Pancreas produces enzyme-rich pancreatic juice.
• Ducts connect the liver, gallbladder, and pancreas to the duodenum, which receives bile and pancreatic juices to the duodenum.

CT Scans

For more, see our Abdominal CT Scan Atlas on the Course Page

Supplemental Materials

Drawing Highlight

• Digestive Organs
• Digestive Organs Video

Clinical Correlations

• Gastric reflux occurs when stomach acids move "backwards" through the inferior esophageal sphincter, which manifests symptomatically as "heart burn" (aka, pyrosis).
• The vermiform appendix is susceptible to infection, known as appendicitis, which can spread if it ruptures, an extremely worrisome complication.
• Endoscopy, we examine the upper GI tract (the mouth to the proximal small intestine) – the tube is inserted into the mouth
• Colonoscopy, we examine the lower GI tract (the distal small intestine to the rectum) – the tube is inserted into the anus.