Digestive System

• Digestive system


  The organ system responsible for the processing of food for the cells to acquire nutrients and energy
• Digestion


  Breaking down food through both mechanical and chemical means
• Mechanical digestion


  • Involves chewing, biting, and swallowing food in the mouth and stomach
  • Cuts food into smaller pieces to increase surface area for chemical digestion
• Chemical digestion


  • Involves different hydrolytic substances produced by various tissues of the digestive system
  • Enzymes target specific molecules of food to further break them down
• Absorption

  The process of taking nutrients from the digested food and transporting them to the blood stream for distribution to the cells of the body
• Capillaries


  • Tiny blood vessels that absorb water soluble nutrients, such as glucose and amino acids
• Lacteals


  • Lymphatic vessels that absorb fatty acids and glycerol
• Parts of the human digestive system

  • Mouth or oral cavity
  • Esophagus
  • Stomach
  • Small intestine
  • Large intestine
  • Anus
• Vertebrates, such as fish, birds, and mammals, have developed complex digestive systems that allow them to sustain their relatively more complex nutrient requirements
• Digestive System Dissection


  1. Form groups

  2. Open the body of the raw chicken

  3. Isolate the digestive tract

  4. Spread the digestive tract and identify the organs

  5. Take a photo and compare to human digestive system
• Digestive System

  The organ system in animals that is responsible for the processing of food materials for the cells to acquire nutrients and energy
• Digestion


  The biological process of breaking down food through both mechanical and chemical means
• Mechanical Digestion


  1. Chewing, biting, and swallowing food particles

  2. Happens in mouth and stomach

  3. Increases surface area for chemical digestion
• Chemical Digestion


  1. Hydrolytic substances produced by digestive system tissues

  2. Digestive enzymes break down food into absorbable molecules
• Absorption

  The process of taking nutrients from the digested food and transporting them to the bloodstream for distribution in the cells of the body
• Capillaries and Lacteals

  • Responsible for nutrient absorption in the intestines
  • Capillaries absorb water-soluble nutrients
  • Lacteals absorb fatty acids and glycerol
• Parts of Human Digestive System

  • Mouth Cavity
  • Pharynx
  • Epiglottis
  • Esophagus
  • Stomach
  • Small Intestine
  • Large Intestine
  • Rectum and Anus
  • Accessory Organs
• Mouth Cavity


  • Where mechanical and chemical digestion of food starts
  • Includes palate, tongue, and teeth
• Teeth


  • Incisors cut food
  • Canines tear food and hold prey
  • Premolars and molars crush and grind food
• Pharynx


  • Connects mouth to esophagus
  • Has nasopharynx, oropharynx, and laryngopharynx
• Epiglottis


  Prevents food from entering respiratory tract during swallowing
• Esophagus


  • Muscular tube that transports food from mouth to stomach
  • Uses peristalsis to move food
• Stomach


  • Hollow, curved, muscular organ for food storage and digestion
  • Has cardia, fundus, and pylorus sections
  • Produces acids, mucus, and enzymes for digestion
• Sections of Small Intestine

  • Duodenum
  • Jejunum
  • Ileum
• Small Intestine


  • 20 foot-long tube where most digestion and absorption occurs
  • Produces own digestive enzymes
• Large Intestine


  • 3-foot long tube with little digestive function
  • Primary site of vitamin, electrolyte, and water absorption
  • Converts chyme into feces
• Nucleosidases


  Enzymes for digesting nucleic acids
• After digestion, nutrient absorption occurs through the intestinal wall
• Large Intestine


  • Diameter twice that of the small intestine
  • Only around 3-feet long
  • Little to no digestive function
  • Primary site of vitamin, electrolyte, and water absorption
  • Major secretion is mucus
  • Bacterial cells inhabit and hydrolyze some indigestible components
  • Converts chyme into feces
  • Mass peristalsis moves undigested food material towards anus
• The inner wall structure of the small and large intestines form invaginations called crypts, which are different from the capillary-rich villi of the small intestine that function for absorption
• Rectum


  Last portion of the large intestine, connects the colon to the anus
• Anus


  • Last portion of the gastrointestinal tract, acts as the opening for feces
  • Has folds called anal columns and two sphincters to control excretion
• Accessory Organs


  • Aid in digestion even if not part of the gastrointestinal tract
  • Produce and secrete substances that assist in chemical digestion
• Accessory Organs


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


  • Secrete saliva into the oral cavity
  • Saliva mixes with food, cleans teeth, lubricates food, and contains enzymes like amylase that initiate carbohydrate digestion
  • Three pairs: parotid, submandibular, and sublingual
• Liver


  • Triangular-shaped organ below the diaphragm
  • Hepatocytes synthesize bile for storage in the gallbladder
• Gallbladder

  • Stores and holds bile until needed for lipid digestion in the duodenum
  • Helps break down large fat globules into smaller fatty acids
• Pancreas


  • Yellowish organ near the stomach
  • Secretes pancreatic juice essential for breaking down proteins, fats, and carbohydrates
  • Contains amylase, trypsin, lipase, and nucleases
• Ruminant Digestive System


  • Four-chambered stomach: rumen, reticulum, omasum, abomasum
  • Rumen allows initial mechanical digestion and exposure to bacterial enzymes to digest cellulose
  • Reticulum allows regurgitation for further chewing
  • Omasum for further mechanical digestion
  • Abomasum is the true stomach with digestive enzymes
  • Takes 1-3 days to completely digest plant diet
• Fish Digestive System


  • Curved or S-shaped
  • Mouth, jaw, teeth, and gill rakers adapted to diet
  • Gill rakers trap food in water
  • Esophagus lubricated with mucus
  • Stomach has pylorus to prevent backflow
  • Pyloric caeca with unknown role
  • Pancreas secretes digestive enzymes and hormones
  • Liver produces bile stored in gallbladder
  • Nutrients absorbed in intestine lined with villi