Digestive System

• Organs of the digestive system

  • Alimentary canal
  • Accessory digestive organs
• Organs of the alimentary canal

  • Mouth
  • Pharynx
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
• Alimentary canal


  • Continuous, coiled, hollow muscular tube that winds through the ventral body cavity from mouth to anus
• Organs of the mouth

  • Lips
  • Cheeks
  • Hard palate
  • Soft palate
  • Uvula
  • Vestibule
  • Oral cavity proper
  • Tongue
  • Lingual frenulum
  • Palatine tonsils
  • Lingual tonsils
• Food processing in the mouth

  1. Mixed with saliva

  2. Masticated (chewed)
• Subdivisions of the pharynx

  • Nasopharynx
  • Oropharynx
  • Laryngopharynx
• Walls of the pharynx

  • Contain two skeletal muscle layers
  • Outer layer runs longitudinally
  • Inner layer runs circularly
• Peristalsis


  Propelling mechanism that moves food through the pharynx into the esophagus
• Esophagus


  Passageway that conducts food to the stomach
• Regions of the stomach

  • Cardia
  • Fundus
  • Body
  • Greater curvature
  • Lesser curvature
  • Pyloric antrum
  • Pylorus
• Stomach


  • C-shaped, on the left side of the abdominal cavity
  • Varies from 15-25cm in length
  • Can hold up to 4 liters when full
  • Collapses inward when empty, with rugae
• Greater omentum


  Extension of the peritoneum that drapes over the abdominal organs
• Functions of the stomach

  • Temporary storage tank for food
  • Moves, churns, and mixes food
  • Begins chemical breakdown of proteins
• Gastric pits


  Deep pits in the stomach mucosa that lead to gastric glands
• Gastric juice


  Secreted by the gastric glands, contains pepsinogen, hydrochloric acid, and other components
• Chyme


  The thick, creamy mixture of food and digestive juices that leaves the stomach
• Subdivisions of the small intestine

  • Duodenum
  • Jejunum
  • Ileum
• Small intestine


  • Major digestive organ
  • Processes food in small amounts at a time
  • Pyloric sphincter controls movement of chyme into small intestine
• Enzymes in the small intestine

  Produced by the intestinal walls, pancreas, and liver
• Absorptive structures in the small intestine

  • Villi
  • Microvilli
  • Circular folds
• Subdivisions of the large intestine

  • Cecum
  • Appendix
  • Colon
  • Rectum
  • Anal canal
• Functions of the large intestine

  • Absorb water from indigestible food residue
  • Eliminate waste as feces
• Haustra


  Pocketlike sacs formed by the tenia coli in the large intestine
• Accessory digestive organs


  • Teeth
  • Salivary glands
  • Pancreas
  • Liver
  • Gallbladder
• Mastication


  The process of chewing food using the teeth, tongue, and cheek muscles
• Saliva


  Mixture of mucus and serous fluids secreted by the salivary glands
• Functions of the pancreas

  • Produces enzymes that break down all categories of digestible foods
  • Produces the hormones insulin and glucagon
• Bile


  Secreted by the liver, contains bile salts, bile pigments, cholesterol, phospholipids, and electrolytes
• Gallstones


  Crystalized cholesterol that can form in the gallbladder
• Jaundice


  Yellowing of the tissues due to the buildup of bile pigments in the blood
• Major functions of the digestive system

  • Digestion
  • Absorption
• Essential activities of the digestive system

  • Ingestion
  • Propulsion
  • Mechanical breakdown
  • Chemical breakdown (digestion)
  • Absorption
  • Defecation
• The energy value of food is measured in kilocalories
• Breakdown


  1. Physically fragments food into smaller particles, increasing surface area

  2. Preparing food in the mouth by teeth and tongue

  3. Churning food in the stomach

  4. Segmentation in the small intestines moves food back and forth across the internal wall of the organ, mixing it with digestive juices
• Digestion


  The sequence of steps in which large food molecules are chemically broken down to their building blocks of enzymes
• Absorption


  1. Transport of digestive and products from the lumen of the GI tract to the blood or lymph

  2. Digested foods must first enter the mucosal cells by active or passive transport process

  3. The small intestine is the major absorptive site
• Defecation


  Elimination of indigestible residues from the GI tract via the anus in the form of feces
• The common saying "you are what you eat" is true in that part of the food we eat is converted to our living flesh
• Nutrient


  A substance of food that the body uses to promote normal growth, maintenance, and repair
• Major nutrients


  • Carbohydrates
  • Lipids
  • Proteins