Bio

• Ingestion


  Food is taken in through the mouth
• Solid food


  • Chewed
  • Cut into small pieces by teeth
  • Mastication
  • Chewing
• Types of teeth in humans

  • Embedded in upper jaw
  • Embedded in lower jaw
  • Connected by jaw bones
  • Four types in total
  • Differ in shapes, sizes and function
• Incisor


  • At the front of the jaw
  • Features chisel shaped, flat sharp edges
  • One root
  • For biting and cutting food
• Canine


  • Next to incisors
  • Features pointed
  • One root
  • For tearing food, especially flesh
• Premolar


  • At the side of each jaw, behind canine
  • Features broad, flattened top with 2 cusps
  • 1 or 2 roots
  • For crushing and grinding food
• Molar


  • At the back of each jaw, behind premolars
  • Larger than premolars
  • Broad top with 4 cusps
  • 2 or 3 roots
  • For crushing and grinding food
• Structure of a tooth

  • Enamel
  • Dentine
  • Pulp cavity

  
• Enamel


  • Forms majority of the crown
  • Fixes tooth into jaw bones
  • Hardest substance in human body
  • Thin layer
  • Made up of calcium salts
  • Non-living
  • Acts as shock absorber during biting and chewing
  • Protects tooth from wear during biting and chewing
  • Gives sensation

  
• Dentine


  • Living layer
  • Contains living cells, blood vessels and nerves
  • Numerous small canals to represent and produce dentine
  • Supply nutrients to living tissues of tooth
• Dental formula


  • Arrangement of different types of teeth
  • Can be expressed as a dental formula
  • Shows type and number of teeth on one side of the upper and lower jaw

  
• Dental formula for human adult

  • Upper jaw: 2123
  • Lower jaw: 2123
  • Total number of teeth: 32
• Milk teeth


  • 20 teeth
  • Replaced by permanent teeth between ages 6 and 12
• Permanent teeth


  • 32 teeth
  • Function for most of our lifetime
• Digestion in the mouth cavity

  1. Food ingested is usually solid and contains large, complex molecules

  2. Large food molecules must be broken down into smaller and simple soluble molecules

  3. Digestion begins in the mouth cavity

  4. Food ingested stimulates salivary glands to secrete saliva

  5. Chewing action of teeth breaks food into smaller pieces

  6. Mixes food with saliva

  
• Physical digestion


  • Breaking up of food into smaller pieces by physical means, e.g. chewing action of teeth
  • Breaks food into smaller pieces
  • Increases surface area of food for the action of digestive enzymes
  • Chemical structure of food unchanged

  
• Chemical digestion


  • Breakdown of large, complex food molecules into small, simple molecules through chemical reactions
  • Catalysed by digestive enzymes
• Components of saliva


  • Water (99.5%)
  • Mineral salts
  • Mucus
• Salivary amylase


  • Enzyme that catalyses the breakdown of starch into maltose
  • Optimum pH is 7.5
• How food is swallowed

  1. Food is ground by teeth

  2. Mixed with saliva

  3. Rolled into a mass by tongue (bolus)

  4. Passes over entrance of trachea

  5. Enters oesophagus

  
• How food is moved along the alimentary canal by peristalsis

  1. Swallowing forces bolus into oesophagus

  2. Wall of alimentary canal consists of two layers of smooth muscle: longitudinal and circular

  3. Muscles behind bolus contract, muscles in front of bolus relax to push bolus forward

  4. Peristalsis benefits: pushes food forward, mixes food with digestive juices, speeds up digestion

  
• Digestion in the stomach

  1. Bolus enters stomach

  2. Stomach churns and mixes food with gastric juice

  3. Gastric juice contains enzyme pepsin and hydrochloric acid

  4. Pepsin catalyses breakdown of proteins

  5. Hydrochloric acid provides acidic pH, kills bacteria, denatures proteins

  
• Digestion and absorption in the small intestines

  1. Chyme passes into small intestine

  2. Digestion of carbohydrates and proteins continues

  3. Digestion of lipids begins

  4. Products of digestion are absorbed into the blood through the epithelium of the small intestine

  
• Digestive juices in the small intestine

  • Bile produced in the liver and stored in the gall bladder
  • Pancreatic juice produced in the pancreas
  • Intestinal juice secreted by glands in the wall of the small intestine

  
• Bile


  • Green, alkaline fluid
  • Contains digestive enzymes and bile salts
  • Emulsifies lipids to break them up into small oil droplets, increasing surface area for lipase enzyme

  
• Pancreatic juice


  • Contains pancreatic amylase to break down starch
  • Contains lipase to break down lipids
  • Contains proteases to break down proteins
  • Contains sodium hydrogen carbonate to neutralize acidic chyme from stomach
• Intestinal juice


  Contains water, mucus, and sodium hydrogen carbonate to provide optimal pH for enzymes
• Enzymes in the small intestine

  • Carbohydrases (e.g. maltase, lactase, sucrase)
  • Proteases
  • Lipases
• Pancreatic juice


  Produced in the pancreas, which also produces insulin, released into the duodenum through the pancreatic duct, contains 3 types of digestive enzymes
• Pancreatic amylase


  Catalyses breakdown of starch in chyme into maltose
• Lipase


  Catalyses breakdown of lipids into fatty acids and glycerol
• Proteases


  Catalyse breakdown of proteins into peptides and amino acids
• Sodium hydrogencarbonate


  Neutralizes acidic chyme from stomach, maintains optimum pH for enzymes
• Intestinal juice


  Secreted by glands in wall of small intestines, especially duodenum, contains water, mucus (as lubricant), and sodium hydrogencarbonate (to provide optimum pH)

  
• Enzymes in small intestine

  • Found within cell membrane of epithelial cells, contain carbohydrases (e.g. maltase, lactase, sucrase) that catalyse breakdown of disaccharides to monosaccharides, and proteases that catalyse breakdown of peptides into amino acids
• Peristalsis of small intestine

  Mixes food with digestive juices, increases chance of contact of enzymes on epithelial cells with food molecules

  
• Carbohydrates, lipids, and proteins are completely digested in the small intestine</b>

  
• Chyle


  A watery emulsion containing monosaccharides, amino acids, fatty acids, and glycerol, readily absorbed
• Small intestine for absorption

  • Very long to allow sufficient time for food absorption, highly folded with circular folds and numerous tiny projections (villi) to increase surface area, epithelium of villi is very thin (one cell thick) to shorten distance for transport, epithelial cells contain many mitochondria to provide energy for active transport, each villus has a lymph vessel (lacteal) surrounded by blood capillaries to carry away lipids, sugars, and amino acids, constant motion of villi due to peristalsis brings digested food molecules into close contact with villi for rapid absorption

  
• Absorption of digested food

  Water-soluble molecules (monosaccharides, amino acids, minerals, certain vitamins) absorbed into blood by diffusion and active transport, fatty acids and glycerol absorbed into lymph (lacteal) and then into bloodstream