Life science term 2

• Mechanical digestion


  1. Chewing with teeth

  2. Tongue movement

  3. Peristalsis in esophagus

  4. Churning in stomach
• Mechanical digestion


  Breaking down food physically into smaller particles
• Chemical digestion


  Using enzymes and acids to break down food into its simplest components (e.g. amino acids, glucose)
• Places chemical digestion occurs

  • Salivary glands
  • Stomach
  • Duodenum (first part of small intestine)
• No chemical digestion occurs after the duodenum, only absorption
• Enzymes in digestion


  Break down complex molecules (proteins, carbohydrates, fats) into simpler components that can be absorbed
• Enzyme action location


  1. Mouth: Carbohydrates digested by salivary amylase

  2. Stomach: Proteins digested by pepsin

  3. Small intestine: Carbohydrates digested by pancreatic amylase, proteins digested by trypsin, fats digested by lipase and bile salts
• All animals need to eat food to give them nutrients that they will use every day
• An animal's digestive system is designed to break down and absorb these nutrients
• Nutrients are used in the body to provide energy, repair damaged tissue and to regulate bodily processes
• Main types of teeth

  • Incisors
  • Canines
  • Premolars
  • Molars

  
• Mammalian animals


  • Have teeth that are adapted to eating certain types of food
  • Not all mammals have all types of teeth
• Types of diets


  • Herbivores
  • Carnivores
  • Omnivores
• Herbivores


  Animals that consume plant material
• Herbivores


  • Cow
  • Deer
  • Horse
  • Giraffe
  • Squirrel
  • Butterfly
• Carnivores


  Meat eating animals that have to hunt and kill their prey to eat
• Omnivores


  Adapted to eating both plant and animal tissue
• Omnivores


  • Bear
  • Raccoon
  • Crow
  • Human beings
• Activity 1 - Identify teeth types

  1. 1-2: Incisors

  2. 3: Canine

  3. 4-5: Premolars

  4. 6-8: Molars

  
• Molar teeth are represented by numbers 6-8 in the diagram

  
• Skull A belongs to a carnivore
• Skull B belongs to a herbivore
• Skull A has canines for biting and holding flesh of prey, and has carnassial teeth instead of flat molars

  
• Skull B has large flat molars for grinding plant material, and no canines
• Skull B does not have carnassial teeth
• Carnassial teeth are specialized molars and premolars that have triangular edges that can cut through meat

  
• Absorption


  Digested food is now in a soluble form and ready to be absorbed into the bloodstream
• Small intestine


  • Most absorption takes place here because most of the digestion has taken place by the time the food reaches the small intestine
  • Food particles are small enough to be absorbed

  
• Active absorption


  Requires energy for the nutrient to be absorbed against a concentration gradient (low to high)
• Passive absorption


  Does not require energy because it moves with the concentration gradient (high to low)
• Small intestine


  • Has a large surface area to absorb nutrients
  • Approximately 6 m long to ensure food remains for long periods, allowing enough time for maximum absorption

  
• Small intestine wall


  • Has transverse folds and millions of villi (finger-like projections) in the mucosa which increase the absorption surface considerably
• Villi


  • Soluble nutrients are mainly absorbed through them
  • Each villus contains microvilli to further increase the surface area
• Villi


  • Epithelium is only one-cell layer thick allowing nutrients to pass through quickly
  • Goblet cells secrete mucus to ensure the absorptive surface is moist and to allow nutrients to be dissolved and then absorbed
  • Epithelium contains many mitochondria to supply energy for active absorption of nutrients
  • Microvilli further increase the surface area
  • Contains a lymph vessel called a lacteal which absorbs and transports lipids
  • Richly supplied with blood capillaries to transport glucose and amino acids
• Absorption process


  1. Glycerol and fatty acids, the end products of lipid digestion, are absorbed by diffusion into the lacteals aided by bile salts

  2. Fat soluble vitamins (A, D, E and K) are passively absorbed or aided by carrier molecules

  3. Mineral salts are both actively and passively absorbed into the capillaries

  4. Water is absorbed into the capillaries by osmosis

  5. Glucose, the end product of carbohydrate digestion, is actively absorbed, against the concentration gradient, into the blood capillaries of the villi

  6. Amino acids, the end products of protein digestion, are also actively absorbed, against the concentration gradient, into the blood capillaries
• Transport of absorbed nutrients

  1. Remaining glucose and amino acids leave the liver via the hepatic veins and are transported in the inferior vena cava to the heart and to the rest of the body

  2. Fatty acids and glycerol are absorbed by the lacteals of the villi, which unite and form larger lymphatic vessels that eventually open into the thoracic duct

  3. Thoracic duct is the main channel for lymph, and fatty acids and glycerol in the thoracic duct enter the blood system at the left subclavian vein and are transported to the rest of the body via the heart