Human Diet & Digestion PDF

Unit 7 - Human Diet & Digestion 7.1 Diet & Deficiencies Balanced Diet A balanced diet consists of all of the food groups in the correct proportions The necessary food groups are: Carbohydrates Proteins Lipids Vitamins Minerals Dietary Fibre Water Food groups Vitamin a...

Unit 7 - Human Diet & Digestion 7.1 Diet & Deficiencies Balanced Diet A balanced diet consists of all of the food groups in the correct proportions The necessary food groups are: Carbohydrates Proteins Lipids Vitamins Minerals Dietary Fibre Water Food groups Vitamin and Mineral Requirements le arying Dietary Needs of Individua Varying Dietary Needs of Individual Scurvy & Rickets Scurvy Scurvy is the name for a severe vitamin C deficiency It is caused by a lack of vitamin C in the diet for over 3 months Its symptoms include: Anemia Exhaustion Spontaneous bleeding Pain in the limbs Swelling Gum ulcerations Tooth loss It is a condition that was commonly seen in sailors between the 15th to 18th centuries Long sea voyages made it very hard to access a ready supply of fresh produce Scurvy can be treated with oral or intravenous vitamin C supplements Rickets Rickets is a condition in children characterised by poor bone development Symptoms include: Bone pain Lack of bone growth Soft, weak bones (sometimes causing deformities) Rickets is caused by a severe lack of vitamin D Vitamin D is required for the absorption of calcium into the body Calcium is a key component of bones and teeth  Vitamin D mostly comes from exposure to sunlight but it can also be found in some foods (fish, eggs and butter) The treatment for rickets is to increase consumption of foods containing calcium and vitamin D Alternatively vitamin D supplements can be prescribed 7.2 Digestive System Digestive system: organs The digestive system is an example of an organ system Some of the digestive system organs make up the alimentary canal; food passes directly through these organs as it moves through the body: Mouth Oesphagus Stomach small intestine, including the duodenum and the ileum large intestine, including the colon, rectum and anus Some of the organs of the digestive system do not form part of the route travelled by food, but are still involved with digestion; these are the associated organs, or accessory organs, and include the: salivary glands Pancreas Liver Gallbladder Digestive system organs Digestive system: function The function of the digestive system is to digest food and absorb nutrients The digestive system carries out its function in several stages: ingestion: food and drink are taken into the body through the mouth mechanical digestion: food is broken down into smaller pieces without chemical change to the food molecules chemical digestion: large, insoluble molecules are broken down into small, soluble molecules absorption: small food molecules and ions move through the wall of the intestine into the blood egestion: food that has not been digested or absorbed passes out of the body as faeces Once nutrients have been absorbed into the blood by the digestive system they can be assimilated into the body; this occurs when they are taken up by the cells of the body Digestive system functions 7.3 Physical Digestion Physical Digestion Physical digestion (sometimes referred to as mechanical digestion) is the breakdown of food into smaller pieces without chemical change to the food molecules The processes that take place during physical digestion help to increase the surface area of food for the action of enzymes during chemical digestion It is mainly carried out by the chewing action of the teeth, the churning action of the stomach and the emulsification of fats by bile in the duodenum 7.4 Teeth & Digestion Types of Human Teeth Mechanical digestion is the breakdown of food into smaller pieces without chemical change to the food molecules It is mainly carried out by the chewing action of the teeth, the churning action of the stomach and the emulsification of fats by bile in the duodenum Teeth are held firmly in the bone of the jaw They are used for chewing to increase the surface area of the food so that it can be exposed to saliva and other digestive juices and broken down more quickly The differing shapes and sizes of teeth enable them to perform slightly different functions: Incisors - chisel-shaped for biting and cutting Canines - pointed for tearing, holding and biting Premolars and molars - larger, flat surfaces with ridges at the edges for chewing and grinding up food Structure of a Tooth 7.5 The Stomach The Stomach The stomach is one of a number of organs that make up the digestive system The role of the digestive system is to break down large insoluble molecules into smaller, soluble food molecules to provide the body with nutrients The stomach lining contains muscles which contract to physically squeeze and mix the food with the strong digestive juices that are present Also known as "stomach churning" Food is digested within the stomach for several hours 7.6 Emulsification of Fats & Oils Emulsification of Fats & Oils (Extended) Cells in the liver produce bile which is then stored in the gallbladder Bile has two main roles: It is alkaline to neutralise the hydrochloric acid which comes from the stomach The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach It breaks down large drops of fat into smaller ones. This is known as emulsification. The larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids faster 7.7 Chemical Digestion Chemical Digestion Stages of food breakdown Food taken into the body goes through 5 different stages during its passage through the alimentary canal (the gut):  Ingestion- the taking of substances, e.g. food and drink, into the body through the mouth Mechanical digestion- the breakdown of food into smaller pieces without chemical change to the food molecules Chemical digestion- the breakdown of large, insoluble molecules into small, soluble molecules Absorption- the movement of small food molecules and ions through the wall of the intestine into the blood Assimilation- the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells Egestion- the passing out of food that has not been digested or absorbed, as faeces, through the anus The role of chemical digestion is to produce small soluble molecules that can be absorbed 7.8 Enzymes in Digestion Enzymes in Digestion Amylases Amylases are produced in the mouth and the pancreas (secreted into the duodenum) Amylases digest starch into smaller sugars Proteases Proteases are a group of enzymes that break down proteins into amino acids in the stomach and small intestine (with the enzymes in the small intestine having been produced in the pancreas) Lipases Lipase enzymes are produced in the pancreas and secreted into the duodenum They digest lipids into fatty acids and glycerol Starch (Extended) Amylases are produced in the mouth and the pancreas (secreted into the duodenum) Amylases digest starch into smaller sugars Amylase is secreted into the alimentary canal in the mouth and the duodenum (from the pancreas) and digests starch to maltose (a disaccharide) Maltose is digested by the enzyme maltase into glucose on the membranes of the epithelium lining of the small intestine Protein (Extended) Proteases are a group of enzymes that break down proteins into amino acids in the stomach and small intestine (with the enzymes in the small intestine having been produced in the pancreas) The digestion of proteins Protein digestion takes place in the stomach and duodenum with two main enzymes produced: Pepsin is produced in the stomach and breaks down protein in acidic conditions Trypsin is produced in the pancreas and secreted into the duodenum where is breaks down protein in alkaline conditions 7.9 Hydrochloric Acid Hydrochloric Acid The stomach produces several fluids which together are known as gastric juice One of the fluids produced is hydrochloric acid This kills bacteria in food and gives an acid pH for enzymes to work in the stomach How is a low pH helpful in the stomach? The low pH kills bacteria in food that we have ingested as it denatures the enzymes in their cells,meaning they cannot carry out any cell reactions to maintain life Pepsin, produced in the stomach, is an example of an enzyme which has a very low optimum pH -around pH 2 The hydrochloric acid produced in the stomach ensures that conditions in the stomach remain within the optimum range for pepsin to work at its fastest rate 7.10 Bile Bile (Extended) Cells in the liver produce bile which is then stored in the gallbladder Bile production and secretion Bile has two main roles: It is alkaline to neutralise the hydrochloric acid which comes from the stomach The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach It breaks down large drops of fat into smaller ones. This is known as emulsification. The larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids faster 7.11 Absorption Absorbing Nutrients Absorption is the movement of digested food molecules from the digestive system into the blood (glucose and amino acids) and lymph (fatty acids and glycerol) Nutrients are absorbed in the small intestine Absorbing Water Water is absorbed in both the small intestine and the colon, but most absorption of water (around 80%) happens in the small intestine 7.12 Adaptations of the Small Intestine Adaptations of the Small Intestine (Extended) The ileum is adapted for absorption as it is very long and has a highly folded surface with millions of villi (tiny, finger like projections) These adaptations massively increase the surface area of the ileum, allowing absorption to take place faster and more efficiently Microvilli on the surface of the villus further increase surface area for faster absorption of nutrients Wall of the villus is one cell thick meaning that there is only a short distance for absorption to happen by diffusion and active transport Well supplied with a network of blood capillaries that transport glucose and amino acids away from the small intestine in the blood Lacteal runs through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph