Human Nutrition

• A balanced diet includes the appropriate proportions of carbohydrates, proteins, lipids, vitamins, minerals, water and dietary fibres.
• Sources of different food groups:

  • Carbohydrates: Bread, rice and pasta
  • Lipids: Cheese, eggs
  • Proteins: Meat, fish, cheese
  • Vitamin A: Oils, butter, carrots
  • Vitamin C: Citrus fruits, peppers, potatoes
  • Vitamin D: Fatty fish, fish liver oils
  • Minerals: Red meat, dairy products, vegetables
  • Water: "...."
  • Dietary fibres: Whole-grain cereal, fruits, vegetables
• Importance of different food groups:

  • Carbohydrates: source of energy
  • Proteins: growth and repair of cells
  • Lipids: Insulation and energy storage
  • Dietary fibers: provides roughage for intestine to push food through
  • Vitamin A: makes pigment in retina for vision
  • Vitamin C: prevent scurvy
  • Vitamin D: strong bones and teeth
  • Calcium: strong bones and teeth
  • Iron: makes haemoglobin
  • Water: required for chemical reactions to take place in cells
  • Dietary fibres: constipation
• Factors affecting energy requirements include

  • Activity levels
  • Age
  • Pregnancy
• Digestion Pathway:

  1. Mouth
  2. Oesophagus
  3. Stomach
  4. Small intestine
  5. Large intestine
  6. Rectum
  7. Anus
• Role of mouth in alimentary canal:

  Food enters the mouth were mechanical digestion takes place

  The teeth break down the large food molecules into small food molecules.

  Amylase enzymes in saliva, digest starch into maltose

  The food is shaped into a bolus by the tongue and lubricated by the saliva
• Role of Oesophagus in alimentary canal:

  Oesphagus connects mouth and stomach and the food molecules will travel to the stomach via the oesphagus through peristalsis
• Role of stomach in alimentary canal:

  Food is churned and mechanical digestion takes place

  Protease enzymes digest proteins

  Hydrochloric acid in stomach kills of bacteria in food and provides optimum pH for protease enzymes to work
• Role of small intestine in alimentary canal:

  Duodenum- where food coming out from stomach finishes digesting by enzymes produced here and enzymes secreted by pancreas

  pH of small intestine is around 8-9 (slightly alkaline)

  Ileum- absorption of digested food molecules takes place

  Ileum has villi which increase SA for absorption to take place
• Role of large intestine in alimentary canal:

  Water is absorbed from remaining material in the colon to produce faeces

  The faeces is stored in the rectum and leaves through the anus
• Role of pancreas in alimentary canal:

  Produces amylase, protease and lipase

  Secretes enzymes into the small intestine
• Role of liver in alimentary canal:

  Produces bile to emulsify fats

  Unused amino acids are used to make urea
• Role of gall bladder in alimentary canal:

  Stores bile to release into small intestine
• Peristalsis:

  • Wave of muscle contractions to move food along alimentary canal
  • Circular and longitudinal muscles contract
  • Mucus lubricates food
  • Fibre provides roughage for muscles to push against
• Role of digestive enzymes:

  Carbohydrases: break down carbohydrates to simple sugars such as glucose

  • Amylase breaks down starch into maltose
  • Maltase breaks down maltose into glucose

  Proteases: break down proteins into amino acids

  • Pepsin breaks down proteins into polypeptide chains
  • Proteases break down peptides into amino acids

  Lipases: break down lipids into a glycerol molecule and 3 fatty acids
• Bile is produced in the liver and stored in the gall bladder before it is released into the small intestine
• Bile function:

  • Neutralise HCL in stomach to give alkaline conditions for enzymes in small intestine to work faster
  • Emulsify fats to give them a large SA for lipase enzymes to work which increases the speed of digestion
• Adaptations of the small intestine:

  • Has many villi which increase the SA, allowing absorption to take place faster
  • Micro villi on the surface of the villus increase the SA further
  • Short diffusion distance of villi as it is only one cell thick
  • Steep concentration gradient as villi are well supplied with blood capillaries
• Investigating energy content of a food sample:

  • Use the measuring cylinder to measure out 25 cm3 of water and pour it into the boiling tube
  • Record the starting temperature of the water using the thermometer
  • Record the mass of the food sample
  • Set fire to the sample of food using the bunsen burner and hold the sample 2 cm from the boiling tube until it has completely burned
  • Record the final temperature of the water