Digestive System

• Digestive system


  • Mouth
  • Tongue
  • Pharynx
  • Esophagus
  • Stomach (or stomachs)
  • Small intestine
  • Large intestine
  • Anus
• Function of digestive system

  To break down and absorb nutrients, salts, and water, as well as to eliminate some wastes
• Stages of the digestive process

  1. Biting

  2. Chewing

  3. Swallowing and mixing of food

  4. Digestion and absorption of nutrients

  5. Excretion of waste
• Digestion


  The chemical breakdown of complex food into simple nutrients and ultimately into molecules that are small enough to pass across the wall of the intestines
• Absorption


  The passage of molecules across the intestinal wall into the blood or lymph system
• Types of animals based on digestive system

  • Herbivores
  • Carnivores
  • Omnivores
• Food must be broken down chemically into molecules before it can enter the blood stream of an animal and be used by its cells
• Different species of animals have digestive tracts adapted to the most efficient use of the feed they consume
• Components of food


  • Carbohydrates
  • Proteins
  • Lipids
  • Vitamins and minerals
• Carbohydrates


  Polysaccharides, which are made up of multiple monosaccharides
• Polysaccharides


  • Starch
  • Cellulose
  • Hemicellulose
  • Glycogen
• Starch


  Made up of multiple glucose molecules, therefore glucose is a monosaccharide
• Enzymes that hydrolyze polysaccharides

  Named after the specific polysaccharide that they break down (e.g. amylase breaks down starch, cellulase breaks down cellulose, sucrase breaks down sucrose)
• Proteins


  Broken down into amino acids by enzymes called proteases and peptidases
• Types of lipids


  • Triglycerides
  • Phospholipids
  • Waxes
• Triglycerides


  Made up of a glycerol molecule and three fatty acid molecules
• Lipase


  An enzyme that breaks down triglycerides
• Enzymes


  Protein molecules that work as catalysts to speed up a reaction, acting specifically on particular molecules
• Simple lipids


  • Fats: Esters of fatty acids with glycerol

  Oils: Fats in the liquid state

  Waxes: Esters of fatty acids with higher molecular weight monohydric alcohol
• Complex lipids


  • Phospholipids: Lipids containing fatty acids, alcohol, and phosphate group

  Glycolipids (glycosphingolipids): Lipids containing fatty acid, sphingosine, and carbohydrate

  Other complex lipids: Sulfolipids, amino lipids, lipoproteins
• Waxes


  Esters formed from long-alcohols and long-chain carboxylic acids, found as coatings on plants and animals
• Types of digestive system animals

  • Ruminants
  • Monogastrics
  • Hindgut
• Ruminants


  Animals with four stomachs: rumen, reticulum, abomasum, omasum
• Rumen


  • Largest chamber of ruminant stomach, contains microbes that digest food, produces methane gas
• Monogastrics


  Animals with a single glandular stomach, e.g. swine and poultry
• Hindgut


  Animals with a larger than normal cecum or hindgut, e.g. horses, donkeys, rabbits
• Components of digestive system

  • Mouth
  • Esophagus
  • Non-ruminant Stomach
  • Ruminant Stomach
  • Small intestine
  • Large intestine
  • Accessory digestive organs
• Mouth


  Tongue and lips select food, chewing physically breaks down food
• Saliva


  Provides lubrication and enzymes to begin chemical breakdown of nutrients
• Esophagus


  Tube-like tract that connects pharynx to stomach, food moves down by peristalsis
• Non-ruminant stomach


  Storage chamber that holds food particles, breakdown of food by enzymes continues
• Ruminant stomach


  Food particles enter rumen where microbes digest them, ruminants get protein from digesting microbes
• Ruminants expel methane and carbon dioxide gas by belching, which can cause bloat if allowed to accumulate
• Ruminant stomach function


  Ruminants chew food, swallow, regurgitate and rechew to further break down fibrous material
• Small intestine


  Main function is absorption, has villi to increase surface area
• Large intestine


  Removes water and prepares waste matter for feces and defecation
• Accessory digestive organs


  • Salivary glands
  • Pancreas
  • Liver
  • Gallbladder
• Salivary glands


  Produce saliva with pH balancing properties and enzymes for initial nutrient breakdown
• Pancreas


  Endocrine gland produces insulin, exocrine gland produces digestive enzymes
• Liver


  Converts molecules into compounds needed for growth, nerve formation, enzyme synthesis, and excretes bile