human biology

• All cells require nutrients in order to provide energy to the cell's activities and materials for cell growth, cell reproduction, secretion and other metabolic processes
• Digestive system


  Extracts nutrients from the food we eat and absorbs them into the body for use by the cells
• 6 basic activities of the digestive system

  • Ingestion of food and water
  • Mechanical digestion of food
  • Chemical digestion of food
  • Movement of food along the alimentary canal
  • Absorption of digested food and water into the blood and lymph
  • Elimination of material that is not absorbed
• The structures of the digestive system work together to fulfill these functions
• Digestion


  The process in which carbohydrate, protein and fat molecules are broken down to products small enough to be absorbed into the blood and into the cells
• Types of digestion


  • Simple sugars, amino acids and fatty acids
  • Complex carbohydrates, proteins and fats
• Mechanical digestion


  1. The teeth cut, tear and grind the food

  2. Churning action in the stomach breaks the food down further

  3. The gall bladder releases bile into the small intestine, bile salts act as emulsifying agents, breaking fat down into smaller droplets
• Aim of mechanical digestion

  To break the food down into smaller pieces so that the total surface area increases, allowing more effective chemical digestion
• Chemical digestion


  1. Carbohydrates split into monosaccharides

  2. Proteins are split into peptides and amino acids

  3. Lipids are split into fatty acids and glycerol

  4. Nucleic acids are split into nucleotides
• Enzymes


  Biological catalysts - chemicals that are able to increase the rate of a reaction without being consumed
• Ingestion


  Intake of food at the mouth
• Mechanical and chemical digestion in the mouth

  1. Food is chewed

  2. Saliva containing salivary amylase is mixed with the food
• Types of teeth


  • Incisors
  • Canines
  • Premolars
  • Molars
• Oesophagus


  A tube that connects the pharynx to the stomach, has a double layer of muscle
• Peristalsis in the oesophagus


  Contraction of successive bands of circular muscle causes a constriction to move in a wave, pushing the food