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.