3 Digestion

• Living things require food to

  • provide them energy to do work
  • maintain a healthy body
  • grow new cells and tissues
  • repair worn-out tissues
• Three main types of nutrients - carbohydrates, fats and proteins
• Function of Carbohydrates

  provide primary source of energy for various activities such as growth and movement
• Function of Fats

  • Provide twice amount of energy compared to carbohydrates of the same mass
  • Stored under the skin to insulate body from excessive heat loss
• Function of Proteins

  • For growth of new cells and tissues
  • Repair of damaged tissues
  • Source of energy when carbohydrates and fats are not available
• Constituent elements of Carbohydrates

  • Carbon
  • Hydrogen
  • Oxygen
• Constituent elements of Fats

  • Carbon
  • Hydrogen
  • Oxygen
• Constituent elements of Proteins

  • Carbon
  • Hydrogen
  • Oxygen
  • Nitrogen
  • Sulfar
  • Phophrous
• Sources of nutrients of Carbohydrates

  • Starch in rice, bread, noodles, and potatoes
  • Different forms of sugars in fruits
• Sources of nutrients of Fats

  • Butter, margarine and cheese
• What's a balanced diet?

  right amount of all the nutrients the cells need to function properly.

  • carbohydrates
  • fats
  • proteins
  • vitamins
  • minerals
  • water
  • fibres
• The function of the digestive system

  to break down large and complex food substances in to small and simple food substances.
• Physical digestion

  • physical break down of large food pieces into smaller pieces
  • identities of food remain unchanged, no new products formed

  IMPORTANCE

  • to increase the surface area

  TAKE PLACE IN

  • Mouth - chewing action
  • Oesophagus - peristalsis
  • Stomach - churning action
• Chemical digestion

  • large and complex food substances are broken down into smaller and simple substances
  • identities of food substances changed, new products formed.

  IMPORTANCE

  • to allow food substances to enter bloodstream through the intestinal wall

  TAKE PLACE IN

  • mouth - starch
  • stomach - proteins
  • small intestine - carbohydrates, fats, proteins
• Vitamins help chemical reactions to take place in cells.
• Minerals provide strength and help cells to function properly.
• Fibre helps to pass through the digestive system quickly, so it prevents constipation.
• Enzymes are made of special type of proteins that speed up the rate of chemical digestion.
• The shape of the food substances must fit into the active site of enzymes like a 'lock and key' model.
• The food substance which an enzyme acts on is called substrate.
• Enzymes remain unchanged after the digestion of food has completed.
• Mouth


  a place where a food is received into the human body - ingestion
• Oesophagus


  • a muscular tube that moves food from mouth to the stomach through - alternate waves of relaxation and contraction of its muscular walls - peristalsis
  • the food present in the muscular tube is called bolus
• Stomach


  a J-shaped, sac-like muscular organ that lies in the upper part of the abdomen
• Gastric juice contains water, hydrochloric acid and proteases.
• The partly digested food is called chyme.
• The churning action helps food to mix with gastric juice.
• Bile is produced by the liver and stored in the gall bladder. Then released into the small intestine when the fats reach the region.
• Bile is a substance to break up fat molecules into fat globules. This process is called emulsification.
• In the large intestine, water and mineral salts are absorbed into the body.
• Solid waste, called faeces, is stored in the rectum temporarily. Then expelled through the anus by a process called egestion.
• Absorption of food take place in the small intestine.
• The surface of the small intestine has many finger-like structures called villi.
• The final products of digestion

  • Glucose
  • Amino acids
  • Fatty acids
  • Glycero
• The walls of the small intestine consist of lining of cells called epithelial cells and are only one cell thick wall.
• Food substances enter the bloodstream through diffusion or active transport.
• If the blood sugar level remains too high, it leads to a disease called diabetes.
• Diabetes is often linked with

  • obesity
  • heart attack
  • kidney problems
  • high blood pressure
  • blindness
  • stroke
• Starch is made of lots of glucose molecules joined together.
• Fats is used for building cells.