Digestive System

• Filter feeding


  Strain food from water as it passes through the body of the organism
• Deposit feeding


  Feeding on deposits of disintegrated organic material (detritus) that accumulates on and in the substratum

  
• Two groups of organs


  • The gastrointestinal (GI) tract, or alimentary canal
  • Accessory digestive organs

  
• Gastrointestinal (GI) tract, or alimentary canal

  • Continuous tube that extends from the mouth to the anus through the thoracic and abdominopelvic cavities
  • Organs include the mouth, pharynx, esophagus, stomach, small intestine, and large intestine
  • Length is about 5–7 meters (16.5–23 ft) in a living person

  
• Accessory digestive organs


  • Teeth
  • Tongue
  • Salivary glands
  • Liver
  • Gallbladder
  • Pancreas

  
• Teeth


  Aid in the physical breakdown of food
• Tongue


  Assists in chewing and swallowing
• Accessory digestive organs


  Produce or store secretions that flow into the GI tract through ducts for the breaking down of food
• Types of digestive processing


  • Mechanical (physical)
  • Chemical

  
• Human Mouth


  • Site of mechanical digestion

  
• Human Deciduous and Permanent Teeth (dentes)
• Dorsal Surface of the Tongue
• Digestive Activities in the Mouth (buccal cavity)


  • Mechanical breakdown of food

  
• Salivary Glands


  Glands that release a secretion called saliva into the oral cavity
• Salivary Glands


  • Parotid
  • Submandibular
  • Sublingual
• Parotid Salivary Gland


  Serous secretion containing water, enzymes, and ions
• Submandibular Salivary Gland

  Mucous or mixed secretion containing mucin, enzymes, and water
• Sublingual Salivary Gland


  Mucous or mixed secretion containing the most viscous mucin, enzymes, and water
• Saliva


  99.5% water and 0.5% solute including ions, dissolved gases, organic substances, mucus, enzymes, and immunoglobulin A

  
• Functions of Saliva


  • Provides a medium for dissolving foods so they can be tasted and digestive reactions can begin
  • Chloride ions activate salivary amylase
  • Mucus lubricates food for swallowing

  
• Pharynx (throat)


  Funnel-shaped, composed of skeletal muscle and lined by mucous membrane, divided into three parts: nasopharynx, oropharynx, and laryngopharynx

  
• Esophagus


  Collapsible muscular tube about 25 cm long that transports food from the pharynx to the stomach

  
• Esophagus Functions


  • Secrete mucous
  • Transport food

  
• Peristalsis and Segmentation


  Muscular contractions that move food through the esophagus and mix food in the stomach

  
• Stomach


  • Usually "J" shaped, located on the left side anterior to the spleen, has a mucous membrane lining
  • Gentle, rippling, peristaltic movements called mixing waves pass over the stomach every 15 to 25 seconds, macerating food and mixing it with secretions to form chyme
• Chyme


  Ingested food plus stomach secretions
• Mucus


  Secreted by surface and neck mucous cells in the stomach
• Functions of the Stomach

  • Mechanical breakdown of food
  • Mixing food with secretions to form chyme
• Small Intestines


  • Extends from the pyloric sphincter to the ileocecal valve, has regions including the duodenum, jejunum, and ileum
  • Contains villi, microvilli, and plicae circulares to increase surface area for absorption
• Plicae circulares/Kerckring folds/valves/bowel folds


  Structures in the small intestine that increase surface area
• Functions of the Small Intestine

  • Absorb nutrients from digested food

  
• Large Intestine

  • Extends from the ileocecal valve to the anus, has regions including the cecum, colon, rectum, and anus
• Functions of the Large Intestine


  • Absorb water and electrolytes from indigestible food matter
  • Store feces until elimination

  
• Mucus in the Large Intestine

  Provides protection for the epithelial lining
• Bacteria in the Large Intestine

  Produce acid, remove acid from epithelial cells, produce gases (flatus) from carbohydrates, and produce vitamin K
• Feces

  Consists of water, undigested food, microorganisms, and sloughed-off epithelial cells
• Liver


  • Located in the upper right part of the abdomen, anterior to the stomach
• Functions of the Liver

  • Bile production
  • Metabolism of carbohydrates, proteins, and lipids
  • Storage of vitamins and minerals
  • Detoxification of substances
  • Production of blood clotting factors

  
• Bile


  A yellow-green, alkaline solution containing bile salts, bile pigments, cholesterol, fats, fat-soluble hormones, and lecithin
• Bile Salts


  Cholesterol derivatives that emulsify fats and aid in their digestion and absorption