GI System Notes

Gastrointestinal System Structure

  • Components of the GI Tract:
    • Major Organs:
    • Parotid gland
    • Tongue
    • Submandibular salivary gland
    • Pharynx
    • Larynx
    • Trachea
    • Esophagus
    • Diaphragm
    • Stomach
    • Spleen
    • Liver
    • Gallbladder
    • Transverse colon
    • Ascending colon
    • Small intestine
    • Cecum
    • Appendix
    • Rectum
    • Descending colon
    • Sigmoid colon
    • Anal canal

Layers of the GI Tract

  • Four Layers:
    • Mucosal lining: Innermost layer that secretes mucus and digestive enzymes.
    • Submucosa: Connective tissue that supports the mucosa and contains blood vessels and nerves.
    • Muscularis:
    • Three smooth muscle layers:
      • Oblique (inner)
      • Circular (middle)
      • Longitudinal (outer)
    • Serosa: Outermost layer that forms the protective outer covering.

Nervous System Innervation

  • Autonomic Nervous System:
    • Enteric Nervous System (ENS): Functions independently of the CNS.
    • Regulates motility and secretion throughout the GI tract.
    • Parasympathetic (Cholinergic): Excitatory effects on digestion.
    • Sympathetic (Adrenergic): Inhibitory effects on digestion.

GI Circulation

  • Major Arteries:
    • Celiac Artery: Supplies blood to the stomach and duodenum.
    • Superior Mesenteric Artery (SMA): Supplies distal small intestine to mid-large intestine.
    • Inferior Mesenteric Artery (IMA): Supplies distal large intestine through anus.

Functions of the GI System

  • Main Function: Supply nutrients to body cells through:
    • Ingestion: Intake of food.
    • Digestion: Breakdown of food into absorbable components.
    • Absorption: Movement of nutrients into circulation.
    • Elimination: Excretion of waste products.

Process of Digestion

  • Ingestion and Propulsion:

    • Controlled by the appetite center in hypothalamus.
    • Deglutition (Swallowing): Includes mouth, pharynx, and esophagus.

  • Physiology of Digestion:

    • Starts with saliva in mouth.
    • Proteins break down primarily in the stomach through pepsin.
    • Carbohydrates, fats, and proteins are further broken down in the small intestine.

  • Absorption:

    • Most occurs in the small intestine.
    • Involves transfer of absorbed substances across the intestinal wall into circulation.

Elimination of Waste

  • Large Intestine Functions:
    • Absorption of water and electrolytes.
    • Production of vitamins (e.g., vitamin K).
    • Formation and storage of fecal mass.
    • Secretion of mucus for lubrication.
    • Defecation: Involves the Valsalva maneuver to expel feces.

Liver, Biliary Tract, and Pancreas

  • Liver:

    • Largest internal organ.
    • Composed of left and right lobes.
    • Hepatocytes: Functional cells of the liver.
    • Kupffer Cells: Specialized macrophages in the liver that cleanse blood.

  • Biliary Tract:

    • Bile for fat emulsification.
    • Bilirubin Metabolism: Derived from hemoglobin breakdown, processed in the liver.

  • Pancreas:

    • Functions as both an endocrine (hormone production) and exocrine (digestive enzyme secretion) organ.

Aging and the GI System

  • Effects of Aging:
    • Decreased taste bud count and saliva production (Xerostomia).
    • Constipation due to decreased motility.
    • Liver size decreases, and gallbladder function may decline.
    • Risk of malnutrition due to the inability to obtain food.

Assessment of the GI System

  • Subjective Data:

    • Gather comprehensive health history including medications, surgeries, and treatment history.
    • Assess functional health patterns: nutritional, elimination, activity, sleep, and cognitive.

  • Objective Data:

    • Conduct physical examinations: inspection and palpation of the abdomen.
    • Assess for bowel sounds and potential abnormalities via percussion and auscultation.

Diagnostic Studies of the GI System

  • Radiologic Studies:

    • Upper and lower GI series, Virtual colonoscopy.
    • Endoscopy: Direct visualization with a focus on abnormalities.

  • Liver Function Tests (LFTs): Important for assessing liver health.

Audience Response Questions

  1. Question: What action should a nurse take if bowel sounds are absent?

    • Answer: Continue to listen for at least another 60 seconds.

  2. Concern for Liver Biopsy: Elevated prothrombin time suggests increased risk of bleeding.

    • Answer: Prothrombin time of 32 seconds is of most concern.