Digestion

• What do animals need to live
    * Animals make energy using food and oxygen
    * Animals build bodies using food for raw materials and ATP energy for synthesis
• Different diets; different lives
    * All animals eat other organisms
    * Herbivores
      * Eat mainly plants
      * Ex: gorillas, cows, rabbits, snails
    * Carnivores
      * Eat other animals
      * Ex: sharks, hawks, spiders, snakes
    * Omnivores
      * Eat animals and plants
      * Ex: cockroaches, bears, raccoons, humans
        * Humans evolves as hunters, scavengers, and gatherers
• Getting and Using Food
    * Ingest
      * Taking in food
    * Digest
      * Mechanical digestion
        * Breaking up food into smaller pieces
      * Chemical digestion
        * Breaking down food into molecules small enough to be absorbed into cells
        * Enzymes
      * Absorb
        * Absorb nutrients across cell membranes
          * Diffusion
          * Active transport
      * Eliminate
        * Undigested material passes out of the body
• Mouth
    * Functions
      * Mechanical digestion
        * Teeth
          * Break up food
      * Chemical digestion
        * Saliva
        * Amylase enzyme
          * Digests starch
        * Mucus
          * Protects soft lining of digestive system
          * Lubricates foods for easier swallowing
        * Buffers
          * Neutralizes acid to prevent tooth decay
        * Antibacterial chemicals
          * Kill bacteria that enter mouth with food
• Swallowing
    * Epiglottis
      * Flap of cartilage
      * Closes trachea (windpipe) when swallowing
      * Food travels down the esophagus
    * Peristalsis
      * Involuntary muscle contractions to move food along
• Stomach
    * Functions
      * Disinfect food
        * Hydrochloric acid
          * pH 2
          * Kill bacteria
      * Food storage
        * Can stretch to fit about 2 liters of food
      * Digests protein
        * Pepsin enzyme
• Ulcers
    * Used to think that ulcers were caused by stress
      * Tried to control with antacids
    * Now know that ulcers are caused by a bacterial infection of the stomach
      * Now cure with antibiotics
• Small intestine
    * Functions
      * Digestion
        * Digests carbohydrates
          * Amylase from pancreas
        * Digests proteins
          * Trypsin and chymotrypsin from pancreas
        * Digest lipids
          * Bile from liver and lipase from pancreas
      * Absorption
        * Nutrients move into body cells by diffusion and active transport
        * Absorption through villi and microvilli
          * Finger-like projectors
          * Increases surface area for absorption
• Pancreas
    * Produces digestive enzymes
      * Digests proteins
        * Trypsin, chymotrypsin
      * Digests starch
        * Amylase
      * Digests lipids
        * Lipase
    * Buffers
      * Neutralize acid from stomach
• Liver and Gall Bladder
    * Produces bile
      * Breaks up fats
      * Gallbladder only stores bile
        * That’s why it can be removed
• Large intestines (colon)
    * Function
      * Reabsorbs water
        * Uses about 9 liters of water every day in digestive juices
          * If you don’t reabsorb water, would die of dehydration
        * \
          > 90% of water is reabsorbed
          * Not enough water reabsorbed

Diarrhea

Can be fatal

• Too much water reabsorbed

Constipation

• Reabsorb by diffusion
    * Company
      * Escherichia coli
        * E. coli
          * Digest cellulose

Digests fruits and vegetables

• Produce vitamins

Vitamin K and B vitamins

• Generate gases

By product of bacterial metabolism

Methane and hydrogen sulfide

• Rectum
    * Last section of large intestines
      * Eliminate feces
      * Left over
        * Undigested materials
          * Mainly cellulose from plants
          * Called roughage or fiber
          * Keeps everything moving and cleans out intestines
        * Masses of bacteria
• Different diets; different bodies
    * Adaptations of herbivores vs. carnivores
      * Teeth
      * Length of digestive system
      * Number and size of stomachs
• Teeth
    * Carnivore
      * Sharp ripping teeth
      * Canines
    * Herbivore
      * Wide grinding teeth
      * Molars
    * Omnivore
      * Both kinds of teeth
• Length of digestive system
    * Herbivores and omnivores
      * Long digestive systems
      * Harder to digest cellulose
        * Bacteria in intestines help
    * Carnivores
      * Short digestive systems
      * Protein easier to digest than cellulose
• Deficiency diseases
    * Scurvy - vitamin C
      * Collagen productions
    * Rickets - vitamin D
      * Calcium absorption
    * Blindness - vitamin A
      * Retinol production
    * Anemia - vitamin B12
      * Energy production
    * Kwashiorkor - protein
• Vegetarian diets
    * Need to make sure you get enough protein
      * 20 amino acids make protein
        * 12 amino acids humans can produce
        * 8 we have to eat
          * “Essential amino acids”
      * Grains like corn have 6 amino acids
      * Beans have 6 amino acids
        * Mix beans and grains for complete group of amino acids