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Digestive System Anatomy
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Digestive System Anatomy

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

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