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DIGESTIVE SYSTEM • The function of the system • The structure and function of each organ • Specialized cells/tissues in each organ YEAR 8 BODY SYSTEMS Let’s think about digestion! Umm…? Do you know which organs make up our digestive system? Do you know the pathway that food takes on its way through? Umm…? Do you know what the purpose of digestion is? Structures of the digestive system Gall bladder We’re needed too! Salivary glands Large intestine Stomach Mouth Digestive System Small intestine Pancreas Oesophagus Rectum Liver Pathway through the digestive system Salivary glands Mouth Don’t forget us! Stomach Oesophagus Liver Small intestine Pancreas Gall bladder Large intestine Rectum /Anus Purpose of the digestive system To break down large food molecules that we have consumed into smaller molecules The smaller molecules are needed so that: We can get them through the lining of the intestine and into our blood stream 2) We can use them to build our own larger molecules 1) Fun facts about the digestive system We eat about 500kg of food per year. We produce 1.7L of saliva each day. In the mouth, food is either cooled or warmed to a more suitable temperature. The oesophagus is approximately 25cm long. Muscles contract in waves to move the food down the oesophagus. This means that food would get to a person's stomach, even if they were standing on their head. Fun facts about the digestive system In an average person, it takes 8 seconds for food to travel down the food pipe, 3-5 hours in small intestine and 3-4 days in the large intestine. The human body takes 6hrs to digest a high fat meal and takes 2hrs for a carbohydrate meal. Every day 11.5L of digested food, liquids and digestive juices flow through the digestive system, but only 100mls is lost in faeces. The digestive system Anus Appendix Gall bladder Large intestine Liver Mouth Oesophagus Pancreas Rectum Salivary glands Small intestine Stomach Can you label this diagram? The digestive system Mouth Salivary glands Liver Oesophagus Stomach Gall bladder Small intestine Appendix Rectum Pancreas Large intestine Anus Let’s start at the very beginning… What do we need to begin digestion? o Mandible (jaw) o Teeth ─ These structures facilitate mechanical digestion. ─ The food is physically broken into smaller pieces by our teeth which are attached and moved by to our jaw. Saliva Tongue Taste buds Let’s start at the very beginning… Saliva begins the process of chemical digestion, as well as providing moisture that will help your food begin to break down. Chemical digestion involves enzymes. These are special chemicals that help chemical reactions occur at a faster rate. Saliva contains salivary amylase – an enzyme that helps the larger carbohydrate molecules (eg. starch) break down into smaller sugars (eg. maltose). Let’s start at the very beginning… Salivary amylase Starch Starch Starch Maltose Starch Maltose Does temperature affect enzymes? Investigation 4.10 Copy and complete the results table on p152 into your books. Complete the activity. Answer the discussion questions on p152 below the task. The oesophagus Food is now chewed and moisturized by saliva and is pushed back by the tongue. We swallow, and the food goes into the oesophageus. The muscles that surround this tube contract to push the food into the stomach. These contractions are called peristalsis and they are powerful enough to allow us to swallow even if lying down — or upside down. The stomach A temporary food storage area. It can expand to hold 2-4Ls of food. Muscle movements in the stomach wall mix the food with gastric juice. Gastric juice contains enzymes which help to break down proteins. The stomach also contains dilute hydrochloric acid, which kills germs and provides a suitable environment for protein digestion. o eg. the enzyme pepsin for protein breakdown works best in very acidic conditions The small intestine A tube about 6m long. Food moves through it by peristalsis. It makes more enzymes to complete digestion. Here, nutrients are absorbed into your bloodstream. The blood then carries the nutrients to all of the cells of your body, where they will be used to make our own large molecules. The pancreas, liver and gall bladder are all connected to the small intestine. The small intestine ...zoomed in! The small intestine is lined by tiny finger-like projections called villi. The outer layer of cells lining each villi (called epithelial cells) are covered in similar structures called microvilli The small intestine ...zoomed in! Why do you think thatthe thesurface small They increase needs area intestine across which the the villi andcan microvilli? small intestine absorb nutrients. It means that the organ can do its job faster and more efficiently. The pancreas Makes pancreatic juice, which is basic or alkaline so it neutralises the stomach acid. Gastric juice (HCl in stomach) Pancreatic juice The pancreas also makes enzymes that break down proteins, fats and carbohydrates. The liver The largest internal organ. It makes bile, which breaks down fats It also controls blood sugar It destroys poisons and toxins – like alcohol! It also stores vitamin A, vitamin D and iron. The liver The gall bladder Bile made in the liver is stored here. The bile is used to break up fats into droplets small enough to be transported to the rest of the body. This bile can sometimes form stones and cause severe pain. In this case, the individual would need to reduce their intake of fat, and possibly have to have their gall bladder removed. The large intestine The large intestine is also known as the colon. Undigested material passes into the large intestine and moves along by peristalsis. The large intestine absorbs water, salts, vitamins and any remaining sugars so that they can be reused by the body. The colon sits in an upside-down U-shape across your belly The appendix This organ is attached to the large intestine. It used to be involved in digesting woody stems and other plant materials back in the day... But now it plays no part in digestion in humans. However, it is believed to play a role in fighting some diseases. The rectum and anus Rectum: o The final part of the large intestine. o This is where the faeces are stored. Anus: o The faeces pass through here when you go to the toilet. What can go wrong? Heartburn Crohn’s disease Inflammatory bowel Diverticulosis disease Irritable bowel syndrome Appendicitis Constipation Gallstones Haemorrhoids Pancreatitis Peptic ulcer What do you do now? Watch the video on the next slide (also on eBook) and answer the worksheet Answer the following worksheet SQ8 p157 SQ8 p153 Q1, 5, 6, 8 Q1, 2, 4, 11 SQ8 Student workbook: Worksheet 4.6