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Introduction Whether it is the single celled amoeba or a complex organism like humans, each is provided with a body structure that helps it perform all the activities necessary for it’s survival. The single celled amoeba is the simplest organism in which the cell performs all the metabolic activiti...

Introduction Whether it is the single celled amoeba or a complex organism like humans, each is provided with a body structure that helps it perform all the activities necessary for it’s survival. The single celled amoeba is the simplest organism in which the cell performs all the metabolic activities such as feeding, digestion, assimilation, excretion and reproduction. However, as the body size increases, a single cell is not e cient to carry out all the functions. Therefore the body becomes complex with more cells coming together to perform the same function. A group of cells performing the same function is called a tissue. A collection of tissues performing the same general function is called a tissue system. Tissue systems make up an organ. Organs make up an organ system. Organ systems make up an organism. The organ systems in the body work together in groups to perform varied functions. TEN WELL DEVELOPED ORGAN SYSTEMS OF THE HUMAN BODY 1. The digestive system 2. The respiratory system 3. The circulatory system 4. The excretory system 5. The reproductive system 6. The skeletal system 7. The muscular system 8. The nervous system 9. The integumentary system (skin) 10. The endocrine system ENERGY, TRANSPORT AND REPRODUCTION GROUP 1. Digestive 2. Respiratory 3. Circulatory 4. Excretory 5. Reproductive MOVEMENT GROUP 1. Skeletal 2. Muscular CONTROL AND COORDINATION GROUP 1. Nervous 2. Integumentary 3. Endocrine The Digestive System Digestion i s the process which breaks down complex food into simple, soluble substances so that they can be easily absorbed by the blood. For complete digestion of food, the food has to travel through a 9 metre long canal from the mouth to the rectum. This canal is called the alimentary canal. Along this journey, chemical substances called enzymes are added to the food for it’s quick break ffi down. Enzymes are produced from organs called glands. PARTS OF THE DIGESTIVE SYSTEM 1. Mouth: Tongue, teeth, salivary glands 2. Oesophagus (food pipe) 3. Stomach 4. Liver and gall bladder 5. Small intestine 6. Pancreas 7. Large intestine PARTS OF THE ALIMENTARY CANAL 1. Mouth 2. Oesophagus 3. Stomach 4. Small intestine 5. Large intestine ASSOCIATED GLANDS 1. Salivary glands 2. Liver 3. Pancreas ROLE OF ENZYMES IN DIGESTION The physical handling of food involves the mechanical breaking down and mixing of the food. The chemical aspect of digestion includes the processing of food by enzymes contained in digestive gland secretions. Enzymes are biocatalysts, that is, chemical substances present in the body which greatly speed up (almost a million times) the rate of the physiochemical reactions. At the end of the reaction, the enzyme remains unchanged and separates from the product of the reaction. Without enzymes, reactions would occur very slowly or not at all, making life almost impossible. All living cells make enzymes, but enzymes themselves are non-living. CHARACTERISTIC OF ENZYMES All enzymes are proteins and are destroyed by heating. They act best within a temperature range of 35°C to 40°C. Enzymes are speci c in their action: A particular enzyme acts only on one substance (substrate) and always forms the same-end products. Enzymes can be reused. Enzymes only speed up the rate of reaction. Parts of the Alimentary Canal Mouth: Digestion begins in the mouth. The teeth helps break down the food into small pieces. The salivary glands secrete saliva. Saliva contains enzymes which help digestion and also moisten the food so that it can be easily swallowed. The tongue helps roll and push food into the pharynx. Taste is also a function of the tongue. Oesophagus: It is a narrow tube that connects the mouth to the stomach. It thus helps carry food from the mouth to the stomach. fi  Stomach: It is a muscular pouch like structure in which the food remains for almost four hours. The walls of the stomach secrete gastric juice (contains hydrochloric acid) which partially digests proteins. Small intestines: From the stomach, the food passes into the small intestines. The small intestine is a long, narrow, highly coiled structure in which the food remains for 4 to 5 hours and gets completely digested. The small intestine receives enzymes and secretions from the pancreas (pancreatic juice) and the liver. The liver produces bile which is temporarily stored in the gallbladder. Large intestine: The small intestine continues into the large intestine. It absorbs water. The undigested, solid food wastes pass along the tube and is temporarily stored in the rectum. It is then removed as feces through the anus. Food remains here for nearly twelve hours. Organs that help in the Digestion of food Carbohydrate: Digestion occurs in the mouth, the stomach, the upper part of the small intestines (duodenum) and the small intestine (ileum). Protein: Digested in the stomach, and the small intestine. Enzyme secreted by the stomach, the pancreas, and the small intestines help to digest proteins. Fats: Digested in the duodenum with the help of bile (bile is secreted by the liver.) Absorption absorption is a process by which various substances pass across a layer of cells into the internal environment of the body. Due to absorption, the body is supplied with all the nutrients that requires for activities. Absorption occurs in all parts of the digestive track, but the main side of absorption is in the ileum. Water, mineral salts and vitamins are absorbed into the blood throughout the length of the small intestine. Water and mineral salts are also absorbed in the stomach and in the large intestines. Simple sugars like glucose, fructose, and galactose, and amino acids, which are the end products of protein digestion, are absorbed in the ileum. Assimilation The food that has been digested and absorbed into the bloodstream, is converted into body substances and becomes part of the organism. The nutrients are carried to the liver. In the liver, the following metabolic conversion take place: - Glucose: Glucose from the intestines is converted into insoluble, glycogen and stored and deliver itself. When required by the body has an energy source, delivery converts the glycogen into glucose and returns it to the blood. Excess glucose is converted and transported to adipose cells around the body, to be stored as fat. - Fats: Some of the fatty products of digestion that arrive in the liver are used to manufacture. Fatty substance is like cholesterol. - Amino acids: Amino acids are used to make new proteins. The liver produces a certain amount of surplus nitrogen, which is rapidly converted to urea urea is a chief product formed. Some of the excess amino acids may also be converted into glucose.