human nutrition

• Balanced diet


  Includes all essential nutrients, such as carbohydrates, fats and vitamins, in the correct amounts needed for growth and repair
• Balanced diets


  • Vary between people of different ages and genders
  • Amount of nutrients needed varies depending on the amount of physical activity undertaken by individual people each day
  • Pregnant and breastfeeding women need more nutrients as they must be able to feed their baby as well as themselves
• Nutrients


  • Carbohydrates
  • Fats
  • Protein
  • Vitamins (C and D)
  • Mineral salts (calcium and iron)
  • Fibre (roughage)
  • Water
• Carbohydrates


  Found in foods such as pasta, rice and potatoes; carbohydrates are used as a source of energy in respiration in cells
• Fats


  Found in fatty meats, cheese and butter; Fats have a variety of roles in organisms including insulation, energy, waterproofing, structure and protection around delicate organs
• Protein


  Found in meat, fish and eggs; Proteins are broken down into amino acids in digestion and absorbed into the blood; They are then used in cells to produce new proteins by protein synthesis, where they are used as enzymes in reactions and for structure; They can also be used for signalling as hormones, and carrying other molecules, for example haemoglobin which carries oxygen in the blood
• Vitamin C


  Found in citrus fruits and some other vegetables; Used in the synthesis of proteins which help make up the skin, ligaments and blood vessels; Also used in the repair of tissues
• Vitamin D


  Found in dairy products, eggs and fish oil; Helps the uptake of calcium during digestion and is also a factor in maintaining healthy bones; Vitamin D deficiency leads to rickets, a condition that causes weak and soft bones, as well as deformities; It can also cause stunted growth in children as the bones cannot develop correctly
• Calcium


  Needed for healthy bones and teeth; Found in dairy products and fish; Also has a role in blood clotting
• Iron


  Found in red meat and some green vegetables; Present in haemoglobin and plays an important role in transporting oxygen around the body in the blood for cells to use in respiration; A lack of iron leads to anaemia and can cause tiredness, as enough energy will not be produced
• Fibre (roughage)


  Found in vegetables, fruit and whole grains; Not digested and thus helps food to move through the stomach and intestines, it also adds bulk
• Water


  Comes from both drinks (80%) and food (20%); Moves into the blood via osmosis during digestion and then into cells; Acts as a solvent in which chemical reactions occur; Helps to maintain a constant temperature in the body due to its high specific heat capacity and is a metabolite
• Malnutrition conditions


  • Starvation
  • Constipation
  • Coronary heart disease
  • Obesity
  • Scurvy
  • Kwashiorkor
  • Marasmus
• Starvation


  Caused by eating too little food, leads to weight loss, organ damage, muscle atrophy and eventually death
• Constipation


  Caused by a lack of fibre, leads to pain, stomach ache and inability to defecate
• Coronary heart disease


  Caused by a build-up of cholesterol in the coronary artery which limits blood flow to the heart and can cause heart attacks; Cholesterol is a result of too much saturated fat in the diet, which comes from foods such as high fat dairy products and fatty meats
• Obesity


  Caused by eating too much food, leads to a range of health issues including diabetes, high blood pressure, strokes and heart disease
• Scurvy


  Caused by lack of vitamin C, leads to bleeding under the skin and around gums, premature stopping of bone growth in children leading to stunted growth, and very dry skin and hair
• Kwashiorkor


  Condition caused by protein-energy malnutrition, which is a result of having a protein or calorie deficiency over a long period; Occurs due to a severe protein deficiency and a carbohydrate-based diet and is often developed by older children
• Marasmus


  Condition caused by protein-energy malnutrition, which is a result of having a protein or calorie deficiency over a long period; More common with young children and babies
• Alimentary canal


  1. Ingestion

  2. Mechanical digestion

  3. Chemical digestion

  4. Absorption

  5. Assimilation

  6. Egestion
• Mechanical digestion


  Breaks down food into smaller molecules without chemical change; Occurs in the mouth due to chewing and in the stomach as food is churned
• Chemical digestion


  Breaking down of large, insoluble molecules into smaller, soluble molecules with the use of enzymes, so that the products can be absorbed
• Mouth and salivary glands

  • Food is mechanically digested in the mouth by the teeth; The salivary glands release saliva which contains carbohydrase enzymes that begin the chemical digestion of starch
• Oesophagus


  Allows food to pass from the mouth to the stomach by peristalsis
• Stomach


  • Protease enzymes break down protein in chemical digestion; The food is also churned to break it up more by mechanical digestion; Hydrochloric acid is present to maintain an optimum pH for enzyme action and kills bacteria by creating extremely acidic conditions, which denatures the enzymes within them
• Small intestine


  • In the duodenum, the acidity from the stomach is neutralised and protease, lipase and amylase enzymes are secreted to break down molecules; The ileum is the final part of the small intestine and is where the products of the digestion are absorbed into the blood
• Pancreas


  Secretes pancreatic juices into the small intestine, containing lipase, protease and amylase enzymes to break down food so that it can be absorbed
• Liver


  Makes bile, which is secreted into the small intestine; Bile neutralises the acidic conditions from the stomach (bile is alkaline) to provide a suitable pH for enzymes to work at; It also emulsifies fats, increasing their surface area so enzymes can digest them more quickly
• Gall bladder


  Bile made in the liver is stored here before being secreted into the small intestine
• Large intestine


  Indigestible food passes through the large intestine, which consists of the colon, rectum and anus; Remaining salts and water are absorbed here (most is absorbed in the small intestine)
• Cholera


  A disease caused by bacteria present in contaminated food and water; The bacteria stick to the intestinal walls and release toxic proteins that causes a secretion of chloride ions into the small intestine, lowering the water potential and leading to diarrhoea; Can be avoided using oral rehydration therapy where patients drink a mixture of water, glucose and salts to rehydrate themselves
• Mechanical digestion in the mouth

  • Incisors and canines at the front of the mouth are used to bite and tear food, before it is passed to the premolars and molars at the back of the mouth which are used for chewing and grinding food into smaller sections
• Tooth structure


  • Enamel - very hard, covers the tooth and protects the tissue inside
  • Dentine - found underneath the enamel, less hard than enamel and thus decays more easily if the enamel is worn away
  • Pulp - central part of the tooth, made of soft tissue which contains blood vessels and nerves
  • Cement - covers the root of the tooth and stabilises it
• Dental decay


  Occurs due to bacteria coating the teeth; When the bacteria respire using sugars from food, they produce acidic substances which dissolve the enamel on the outer layer of the teeth and then the dentine on the inside, leading to tooth decay; To avoid tooth decay, teeth should be regularly brushed to remove bacteria and sugary foods and drinks should be limited
• Amylase


  Breaks down starch into simpler sugars; Found in saliva and the small intestine
• Protease


  Breaks down protein into amino acids; Pepsin works in the stomach, whereas trypsin is present in the small intestine; These enzymes have different optimum pH, since in the stomach the conditions are very acidic (pH 1.5), whereas in the small intestine the pH is about 6-7; These enzymes will stop working in the wrong pH as they will become denatured
• Lipase


  Breaks down fats into glycerol and fatty acids; Secreted into the small intestine
• Absorption in the small intestine

  • Cells lining the small intestine are adapted for absorption by having hair-like projections called villi and microvilli, which increase the surface area; Each villus contains capillaries, which carry absorbed molecules away, maintaining a high concentration gradient which allows more molecules to diffuse into the capillaries; They also contain lacteals, which absorb fats
• Water is absorbed in the small intestine and in the colon, but most of the absorption occurs in the small intestine