KD

Digestive System Vocabulary

Digestion Overview

  • Food is coated in saliva, forming a bolus.
  • Saliva contains salivary amylase, which begins chemical digestion by breaking down carbohydrates (polysaccharides into disaccharide maltose).
  • Teeth and tongue contribute to mechanical digestion, increasing surface area for amylase.
  • Swallowing moves food to the pharynx; the uvula and epiglottis prevent food from entering the nasal passages and trachea, respectively.

Esophagus

  • Transports food to the stomach via peristalsis (wave-like muscle contractions).
  • The cardiac sphincter prevents backflow from the stomach.

Stomach

  • Stores food temporarily and mixes it with enzymes and acids.
  • Mucosa contains glands that secrete mucus, HCl, and enzymes.
    • Parietal cells: secrete HCl.
    • Chief cells: secrete pepsinogen (converted to pepsin by HCl, breaks down proteins).
    • Mucus cells: secrete mucus (protects stomach lining) and bicarbonate (neutralizes acid).
    • G cells: secrete gastrin (hormone).
  • Rugae (ridges) flatten as the stomach fills.
  • Submucosa: connective tissue with blood/lymph vessels and nerves.
  • Muscularis externa: main muscle layer.
  • Serosa (visceral peritoneum): outer covering.
  • The stomach can absorb water, ions and drugs into the bloodstream.
  • Food mixes with gastric juices to form chyme, which passes through the pyloric valve to the small intestine.

Small Intestine

  • Breaks down food, absorbs nutrients, and propels food along the GI tract.
  • Semi-solid food is liquefied for nutrient absorption via villi in the mucosa.
  • Waste moves to the large intestine.

Duodenum

  • First part of the small intestine; receives chyme from the stomach.
  • Mixes digestive juices and enzymes from the gallbladder (bile) and pancreas (digestive enzymes).
  • Bile acids are extracted and reabsorbed into the bloodstream/liver, aiding fat digestion.

Nutrient Absorption & Liver

  • Small intestine absorbs nutrients; the circulatory system distributes them.
  • Blood carries simple sugars, amino acids, glycerol, vitamins, and salts to the liver.
  • The liver stores, processes, and delivers nutrients.
  • The liver produces bile from cholesterol, which is stored in the gallbladder and released when fats and proteins are detected in the small intestine.

Biliary Tract

  • Bile ducts connect the liver, gallbladder, and pancreas to the duodenum.
  • The common bile duct connects the liver to the gallbladder (via the cystic duct) and pancreas (via the pancreatic duct).
  • The ampulla of Vater is a reservoir for incoming bile and enzymes.

Jejunum

  • Mid-section of the small intestine (8 ft long).
  • Uses peristalsis to churn food with digestive juices towards the ileum.

Ileum

  • Last and largest section of the small intestine.
  • Absorbs nutrients (vitamins, minerals, carbohydrates, fats, and proteins).
  • Food spends the most time here before moving to the large intestine.

Large Intestine

  • Receives liquid waste from the small intestine; absorbs water and salts to form solid waste (feces).
  • Consists of the colon, rectum, and anus.

Colon

  • Cecum: receives waste from the small intestine; the appendix is attached.
  • Ascending colon: absorbs water and electrolytes.
  • Transverse colon: carries waste to the descending colon.
  • Descending colon: continues solid waste formation.
  • Sigmoid colon: finalizes solid waste formation.

Rectum & Anus

  • The rectum triggers the urge to defecate when filled with stool.
  • The anus controls stool release via muscle sphincters.