Digestive System: Alimentary Canal

Anatomy of the Alimentary Canal

  • Definition: A musculomembranous tube from the mouth to the anus.
  • Components:
    • Mouth
    • Pharynx
    • Esophagus
    • Stomach
    • Small Intestine
    • Large Intestine (terminates at anus)

Esophagus

  • Structure: Long muscular tube.
  • Function: Conveys food and saliva from the laryngopharynx to the stomach.
  • Anatomical Position: Lies in the midsagittal plane (MSP).
  • Anatomy Details:
    • Origin: C6
    • Passes through diaphragm: T10
    • Joins stomach: T11 (esophagogastric junction)
    • Expanded terminal end is called the cardiac antrum.

Stomach

  • Description: Dilated, saclike portion of the digestive tract, extending between the esophagus and small intestine.
  • Four Distinct Parts:
    • Cardia: Surrounds the esophageal opening.
    • Fundus: Superior portion, fills the left hemidiaphragm.
    • Body: Located between the fundus and pyloric portion; contains numerous longitudinal folds called rugae.
    • Pyloric Portion: Consists of pyloric antrum and narrowed pyloric canal.
  • Curvatures:
    • Lesser curvature: right border.
    • Greater curvature: left border.
    • Cardiac notch: sharp angle at esophagogastric junction.
  • Sphincters:
    • Cardiac Sphincter: Controls the opening between the esophagus and stomach.
    • Pyloric Sphincter: Controls the opening between the stomach and small intestine.

Functions of the Stomach

  • Storage: Temporarily stores food during digestion.
  • Chemical Breakdown: Secretes acids, enzymes, and chemicals to chemically break down food.
  • Mechanical Breakdown: Churns food and moves it via peristalsis, converting it into chyme.

Body Habitus and Stomach Position

  • Body Habitus Types:
    • Hypersthenic (5% of population): Higher and more horizontal stomach position.
    • Sthenic (50%): Average body type.
    • Hyposthenic (35%): Similar to sthenic but slimmer.
    • Asthenic (10%): Lower and more midline stomach position.

Gastrointestinal Transit

  • Peristalsis: Contraction waves propelling contents toward the rectum.
    • 3-4 waves per minute in a filled stomach.
    • Average emptying time for the stomach: 2-3 hours.
    • Average transit time to ileocecal valve: 2-3 hours.

Contrast Media**

  • Barium Sulfate: Most common for radiographic demonstration of the alimentary canal.
  • Iodinated Contrast Media: Moves through the GI tract more quickly than barium (1-2 hours to clear the stomach).
  • Water-Soluble: Easily removed or absorbed, recommended in case of perforation.

Technical Considerations for Radiography**

  • Room Preparation: Ensure all equipment is ready before patient enters.
  • Exposure Time Challenges: Varies by region; fast for the stomach (0.2 seconds) and slower in distal parts of the GI tract.
  • Patient Positioning: Maintain correct body posture during exposure to capture precise anatomical structures.

Essential Projections for the Esophagus**

  • Types:
    • Anteroposterior (AP)
    • Posteroanterior (PA)
    • AP or PA Oblique
    • Lateral
  • Fluoroscopy: Initial examination with contrast for swallowing assessment, prior to overhead projections.

Small Intestine Overview**

  • Anatomy: Extends from pyloric sphincter to ileocecal valve; average length: 22 feet.
    • Three Portions:
    • Duodenum (8-10 inches long; C-shaped)
    • Jejunum
    • Ileum
  • Function: Key site for digestion and absorption of nutrients.

Large Intestine Structure**

  • Anatomy: Begins at the junction with small intestine and ends at the anus.
    • Four Main Parts:
    • Cecum
    • Colon (ascending, transverse, descending, sigmoid)
    • Rectum
    • Anal canal
  • Length: Approximately 5 feet; contains haustra (pouches) and taeniae coli (muscular bands).

Large Intestine Function**

  • Primary Roles:
    • Reabsorption of fluids
    • Elimination of waste products.

Examination and Preparation for Large Intestine Procedures**

  • Depending on the procedure: may need barium enema (single or double contrast).
  • Preparation typically includes a restricted diet and bowel cleansing.
  • Barium Administration Techniques:
    • Enema tips and apparatus alignment are critical for successful imaging.