Digestive System & Related Disorders Summary

Digestive System Overview

  • Group of organs that digest food & absorb nutrients
  • Converts food into energy + building blocks; turns waste into stool
  • Optimal function essential for growth, health, disease prevention

Gastrointestinal (GI) Tract

  • Continuous tube: mouth → esophagus → stomach → small intestine → large intestine → anus
  • Total length if stretched: 30 ft (9 m)30\,\text{ft} \,(9\,\text{m}) (intestines coiled in abdomen)
Mouth
  • Digestion begins with sight/smell of food → saliva secretion to moisten & start breakdown
Esophagus
  • Transports bolus via peristalsis to stomach
Stomach
  • Releases acid & enzymes to form semi-solid chyme
Small Intestine (≈22 ft22\,\text{ft})
  • Converts chyme to fluid; primary site of nutrient absorption
  • Ends at ileocecal valve; remaining material enters large intestine
Large Intestine
  • Colon, rectum, anus
  • Reabsorbs water/electrolytes; houses bacteria; forms & stores feces

Biliary Tract & Accessory Organs

  • Liver, gallbladder, pancreas deliver bile & enzymes to duodenum for digestion
Pancreas
  • Exocrine: enzymes + alkaline fluid neutralize stomach acid in duodenum
  • Endocrine: secretes insulin & glucagon
Liver
  • Largest gland (under diaphragm, right side)
  • Produces bile (water, bile salts, pigments, cholesterol, phospholipids, electrolytes)
  • Bile salts emulsify fats → ↑ surface area for lipase action
Gallbladder
  • Stores & concentrates bile; releases it into duodenum on demand

Digestive Process (Key Steps)

  • Pre-ingestion: salivation triggered by sight/smell
  • Mastication in mouth → bolus formation
  • Esophageal peristalsis → stomach
  • Gastric acid & enzymes liquefy food
  • Chyme enters small intestine; mixed with bile & pancreatic juice
  • Nutrient absorption across intestinal wall
  • Residue → large intestine for water reabsorption & defecation

Propulsion & Mixing

  • Peristalsis: wave-like contractions move content forward ("toothpaste" squeeze)
  • Rhythmic segmentation: mixes chyme with digestive juices, aids absorption

Large Intestine Activities

  • Limited digestion; bacterial fermentation of debris
  • Absorbs water, electrolytes, some vitamins
  • Stores feces until defecation

Nutrient Absorption Highlights

  • Lipids absorbed passively by diffusion after emulsification

Common Digestive Conditions

  • Acid reflux / GERD
  • Constipation & diarrhea
  • Diverticulosis / diverticulitis
  • Gastroenteritis ("stomach flu")
  • Hemorrhoids
  • Cancers: colon, esophageal, liver, etc.

Celiac Disease Highlights

  • Autoimmune reaction to gluten → villous atrophy → malabsorption
  • Prevalence: ≈1%1\% in Europe & North America
  • Gene variants: HLA-DQ2HLA\text{-}DQ2 or HLA-DQ8HLA\text{-}DQ8 in 97%97\% of cases
  • Risk ↑ to 10%10\% with first-degree relative
  • More common in females (≥2:12:1) & in Down syndrome or other autoimmune disorders
  • Consequences: malnutrition, stunted growth (children), associated diseases

Quick Facts & Figures

  • GI tract length: 30 ft30\,\text{ft}; small intestine: 22 ft22\,\text{ft}
  • Liver has 4 lobes; suspended by falciform ligament
  • Bile contains no enzymes; acts mechanically on fats
  • Digestion begins before ingestion via cephalic phase (salivation)