Previous reading: Human Body Digestive System (Organs, Location and Function) Science, Class-7th, Rishi Valley School Next reading: Cardiovascular system Content Slide #s 1) Overview of human digestive system................................... 3-4 2) Organs of human digestive system....................................... 5-7 3) Mouth, Pharynx and Esophagus.......................................... 10-14 4) Movement of food ................................................................ 15-17 5) The Stomach.......................................................................... 19-21 6) The Small Intestine ............................................................... 22-23 7) The Large Intestine ............................................................... 24-25 8) The Gut Flora ........................................................................ 27 9) Summary of Digestive System............................................... 28 10) Common Digestive Disorders ............................................... 31-34 How to go about this module 1) Have your note book with you. You will be required to guess or answer many questions. Explain your guess with reasoning. You are required to show the work when you return to RV. 2) Move sequentially from 1st slide to last slide. Do it at your pace. 3) Many slides would ask you to sketch the figures. – Draw them neatly in a fresh, unruled page. – Put the title of the page as the slide title. – Read the entire slide and try to understand. – Copy the green shade portions in the note book. 4) Answer the questions (Q1,Q2 etc.) in the note book as you go over the slides. 5) Write the test (in a separate slide set). 6) Many new vocabularies needs to be memorized after you have understood them. This is a part of the course. They are summarized at regular intervals. Overview of Digestive System Your body cells can’t use the pizza you had for lunch in pizza form. As your body cells are much much smaller compared to the size of pizza, it needs to be broken down to small enough size to be absorbed by the blood stream and be useful to your body cells. As the pizza travels along the digestive tract, each organ along the way does it’s work to break it down gradually. The main functions of the digestive system are to ingest (take in) food, break down, and absorb the nutrients from our food. It also eliminates the wastes (anything not absorbed by the body) as faeces. Q1: Sketch figure-1 using pencil in a fresh page with title” Overview of digestive system”. Copy the following passage (shaded) below that. The digestive system is made up of digestive tract and other organs that help the body breakdown and absorb food. Nutrient from the food are used to build and nourish cells and provide energy to function. The organs that make up digestive tract are Oral cavity, Esophagus, Stomach, Small intestine, Large intestine, Rectum and Anus. The arrangement of these organs are shown in the figure. As food moves along the digestive tract, two different processes starts simultaneously to help digestion. Food is physically broken down into smaller pieces by teeth in mouth in a process called mechanical digestion. As the food is chewed, it gets mixed up with saliva which contains digestive enzymes that help breakdown some simple sugars in food. The saliva also moistens and softens the food to be swallowed easily for the next stages of digestion. Figure-1 Overview of Digestive System This mixing with various digestive enzymes happens through out the digestive tract and helps in breaking down the food chemically into simpler and simpler compounds that can be absorbed by the body. This process is called chemical digestion. When swallowed, the food moves into Esophagus which connects the mouth with the stomach. Swallowing is a reflex activity that prevents food from entering airways and into the lungs. The stomach stores the swallowed food and liquid. Stomach muscles expands and contracts helping to mix a different type of digestive juices with the food. Digestive juice in the stomach is highly acidic with PH nearly 2. This potent acid kills many bacteria and microbes which may be present in the food and thus protects the body from infections. Stomach slowly empties its content into the small intestine. Most of digestion and absorption occurs in the small intestine. Proteins are broken down into amino acids. Carbohydrates are broken down into simple sugars. Fats are broken down into fatty acids and cholesterol which the body can absorb. Two accessory digestive organs liver and pancreas, produce digestive juices that reach the small intestine through small tubes called ducts. The gall bladder stores bile produced by liver until it is needed. Bile mixes up and dissolves fat in the food. The fat is then digested by enzymes released from pancreas and lining of small intestine. Food then passes on to large intestine which is sometimes called as Colon. Here water and various minerals needed by the body are absorbed. Colon also stores the remaining undigested food until it leaves the body through the rectum and anus. Organs of Digestive System The main organs of the digestive system are arranged in the following order: 1) Mouth 2)Pharynx 3)Esophagus 4)Stomach 5)Small intestine 6)Large Intestine 7) Rectum 8)Anus They form what is called as digestive tract. It is also called by other names such as gastrointestinal tract (GI tract) or Alimentary canal. All of these words mean the same. The accessory organs are connected to the digestive tract and secrete additional digestive juices. Many accessory organs play roles beyond just digestive system. 1) The salivary glands produce saliva containing amylase, an enzyme that breaks down carbohydrates. They are located 2)The pancreas secretes digestive enzymes into the small intestine. It also neutralizes food coming out of stomach by secreting alkali compounds. Pancreas also works for another system called endocrine system. 3)The liver produces bile, which aids in fat digestion and absorption. It also has other roles beyond digestive system. It filters the blood coming from the digestive tract before it is released to rest of the body. 4)The gall bladder stores and concentrates bile in between meals and releases when required into the small intestine. Organs of Digestive System Q2: Figure-2 shows the human digestive system. Draw nicely this figure in a clean page. You may use colours if you wish to. Figure-2 Accessory Organs of Digestive System Gall bladder Pancreas Figure-4: In this figure, you can see the location of Gall bladder and Pancreas is shown but liver is not shown. Figure-3: Notice the location of 3 major salivary glands and how they are connected to the mouth cavity through ducts. Q3: Can you look at the previous figure and locate the position of liver in this figure-4? List of new vocabularies # Word Meaning 1 Mechanical Digestion Breaking down of food by physical force 2 Chemical Digestion Breaking down of food by chemical changes 3 Reflex Activity Activity that is automatic like heart beating 4 Esophagus Digestive tract from mouth to stomach 5 Small Intestine Digestive tract from end of stomach to Colon 6 Large Intestine, Colon Digestive tract from end of small intestine to rectum 7 Pharynx Throat 8 Rectum Digestive tract at the end of colon 9 Anus Part of digestive tract from which stool comes out 10 GI Tract, Alimentary Canal Entire digestive tract from mouth to anus Main Organs of Digestive System Mouth, Pharynx and Esophagus The first step in the digestive process happens before we even taste food. Just by smelling or seeing that pizza, your hormonal system (called Endocrine system) makes you salivate, your muscular and skeletal system rushing to grab the pizza--- and the digestive system preparing itself by secreting enzymes and hydrochloric acid in stomach in anticipation of of the first bite. This is a great example of how different systems of the body work together cohesively to successfully do a work. ( Next time you encounter your favourite food, watch out for this happening in you!!) As the teeth tear and chop the food, saliva moistens it for easy swallowing. After sometime, the food is finely chopped and mixed with saliva and is swallowed. This package of swallowed food is called Bolus. As you observe, your tongue can make different movements helping to move the chopped food around the mouth. The wonderful thing to notice is that even though the teeth can easily tear apart a piece of chilly chicken, the tongue does not come in-between two teeth (Well it does sometimes if the food is too tasty to hurry you up!!) . It is interesting that the body has this kind of perfection and coordination in controlling its organs. A digestive enzyme in saliva, called amylase, starts to break down some of the carbohydrates in the food even before it is swallowed. Activity-1 Take a bite of Roti or Chapati or Bread. Usually, they don’t taste sweet the moment you put in mouth. Just keep it in your mouth for 3 ~ 4 minutes and don’t chew. Let saliva soften it. Do you start getting the sweet taste taste of it? If yes, then it proves the point that the piece of bread contains glucose which tastes sweet. Q4: It also proves another point. Write your guess and justify in one-two sentences. (Hint: What is digesting it?) Mouth, Pharynx and Esophagus Swallowing, done by muscle movements in the tongue and mouth. The muscular system pushes the food into the throat, or pharynx. The pharynx is a passageway for both food and air. What if the bolus goes into the airway? Closely observe the following figure. A soft flap of tissue, called the Epiglottis, closes over (pushes down) the wind pipe when we swallow. This is to prevent the bolus entering lungs and choking. From the throat, food travels down to stomach in a muscular tube in the chest called the Esophagus.