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The Digestive System Primary Science Teaching Resources Monash Science Centre © 2006 Eat your Jelly Bean •Put your jelly bean on your tongue •Suck it for a while •Chew •Swallow Think about what is ACTUALLY happening! Primary Science Teaching Resources Monash Science Centre © 2006 What happened? •What did you need to taste the jelly bean? •What happened when it left your mouth? •What happens once its in your stomach? Primary Science Teaching Resources Monash Science Centre © 2006 Our own food breakdown factory! Primary Science Teaching Resources Monash Science Centre © 2006 Interesting Facts about the Digestive System… •We eat about 500kg of food per year. •We produce 1.7 litres 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 esophageus. This means that food would get to a person's stomach, even if they were standing on their head. •An adults stomach can hold approximately 1.5 litres of material and produces about 2.5 litres of gastric juice everyday. •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 6 hours to digest a high fat meal and takes 2 hours for a carbohydrate meal. •Every day 11.5 litres of digested food, liquids and digestive juices flow through the digestive system, but only 100mls is lost in faeces. •Most of us pass somewhere between 200 and 2,000 ml of gas per day. These emissions are composed of five gasses: nitrogen (N2), oxygen (O2), carbon dioxide (CO2), hydrogen (H2), and methane (CH4). Primary Science Teaching Resources Monash Science Centre © 2006 Overview of the Digestive System Mouth - the first part of the digestive system, where food enters the body. Chewing and salivary enzymes in the mouth are the beginning of the digestive process (breaking down the food). Salivary glands - glands located in the mouth that produce saliva. Saliva contains enzymes that break down carbohydrates (starch) into smaller molecules. Esophageus - the long tube between the mouth and the stomach. It uses rhythmic muscle movements (called peristalsis) to force food from the throat into the stomach. Peristalsis - rhythmic muscle movements that force food in the esophagus from the throat into the stomach. Peristalsis is involuntary - you cannot control it. It is also what allows you to eat and drink while upside-down. Liver - a large organ located above and in front of the stomach. It filters toxins from the blood, and makes bile (which breaks down fats) and some blood proteins. Stomach - a sack-like, muscular organ that is attached to the esophagus. Both chemical and mechanical digestion takes place in the stomach. When food enters the stomach, it is churned in a bath of acids and enzymes. Primary Science Teaching Resources Monash Science Centre © 2006 Overview of the Digestive System Chyme - food in the stomach that is partly digested and mixed with stomach acids. Chyme goes on to the small intestine for further digestion. Gall bladder - a small, sac-like organ located by the duodenum. It stores and releases bile (a digestive chemical which is produced in the liver) into the small intestine. Bile - a digestive chemical that is produced in the liver, stored in the gall bladder, and secreted into the small intestine. Pancreas - an enzyme-producing gland located below the stomach and above the intestines. Enzymes from the pancreas help in the digestion of carbohydrates, fats and proteins in the small intestine. Duodenum - the first part of the small intestine; it is C-shaped and runs from the stomach to the jejunum. Jejunum - the long, coiled mid-section of the small intestine; it is between the duodenum and the ileum. Primary Science Teaching Resources Monash Science Centre © 2006 Overview of the Digestive System Ileum - the last part of the small intestine before the large intestine begins. Cecum - the first part of the large intestine; the appendix is connected to the cecum. Appendix - a small sac located on the cecum. Ascending colon - the part of the large intestine that run upwards; it is located after the cecum. Transverse colon - the part of the large intestine that runs horizontally across the abdomen. Descending colon - the part of the large intestine that run downwards after the transverse colon and before the sigmoid colon. Sigmoid colon - the part of the large intestine between the descending colon and the rectum. Rectum - the lower part of the large intestine, where faeces are stored before they are excreted. Anus - the opening at the end of the digestive system from which faeces (waste) exits the body Primary Science Teaching Resources Monash Science Centre © 2006 The Digestive System Primary Science Teaching Resources Monash Science Centre © 2006 Answers Primary Science Teaching Resources Monash Science Centre © 2006 Starting at the Beginning • What is needed before our digestive system can be put into action? Food •Where is the first place that digestion starts? Mouth Primary Science Teaching Resources Monash Science Centre © 2006 What is needed for the initial stages of digestion to occur? •Mandible (jaw) •Teeth Facilitates mechanical digestion. The food is physically broken into smaller pieces by our teeth which are attached and moved by to our jaw. This process is called mastication •Saliva •Tongue •Taste buds Primary Science Teaching Resources Monash Science Centre © 2006 Lets Test our Taste Buds •In groups, decide who will taste each liquid (A,B,C,D,E). •One person should come up and get the containers. •Use a new straw to taste each substance. (Why?) •Write down on a list what you think each one is. Primary Science Teaching Resources Monash Science Centre © 2006 What did you taste? A – Pineapple juice B – Coffee C – Salty water D – chicken stock E – lemon juice Primary Science Teaching Resources Monash Science Centre © 2006 How do we know what things taste like? •Tongue •Taste buds Each taste bud can detect all tastes, but prefers some more than others. Saliva Cells on the tongue secrete either: Watery or mucous fluid -water -electrolytes -enzymes Turns food into “bolus” Primary Science Teaching Resources Monash Science Centre © 2006 Esophageus •Once the food is chewed and moisturized by the saliva, it is pushed back by the tongue into the throat. •When we swallow the food it goes into a tube called the esophageus. •This food pipe is a muscular tube that is connected to the stomach. The muscles that surround the esophagus help to squeeze and push the food into the stomach, through a process called peristalsis. •These contractions, which push the food down into the stomach, are powerful enough to allow us to swallow even if lying down — or upside down. •Between the esophagus and the stomach a sphincter ensures that the passage normally opens only one way — from the esophagus into the stomach. Primary Science Teaching Resources Monash Science Centre © 2006 Peristalsis The esophagus pushes the food downward by an action that we call peristalsis, which is basically an orderly sequence of contractions like the wave motion moving across stadium bleachers. Volunteers to mimic the muscular action called peristalsis. •It enables food to move down the esophageus as well as the small and large intestine. •It causes mixing of the gastric juices and food stuff in the stomach. Primary Science Teaching Resources Monash Science Centre © 2006 Stomach Four main roles of the Stomach: 1. Short term storage 2. Enzymes start to digest proteins 3. Churning of the stomach turning food into “chyme”. 4. Liquefying the food to pass slowly into intestine. The lower part works harder than the upper part Food must be ground to 1-2mm to pass through the gate-keeper called “pylorus”. Primary Science Teaching Resources Monash Science Centre © 2006 A Real Stomach Primary Science Teaching Resources Monash Science Centre © 2006 Small Intestine •Absorbs ALL nutrients into the bloodstream. •With the help of the liver and pancreas it breaks down large particles so they can be absorbed. •Liver secretes bile to break down fat. •Pancreas secretes enzymes to breakdown everything and neutralize acid to protect small intestine lining. Primary Science Teaching Resources Monash Science Centre © 2006 How Long are the Intestines? •How long is the small intestine? - 6.0 meters •How long is the large intestine? -1.5 meters Primary Science Teaching Resources Monash Science Centre © 2006 Large Intestine •Absorbs water •Has good bacteria that help to digest food that can’t be digested by our own body. •Stores faeces Primary Science Teaching Resources Monash Science Centre © 2006 What goes in must come out! Primary Science Teaching Resources Monash Science Centre © 2006