1. The Digestive System and pH

2. Digestive System The digestive system is responsible for processing food, breaking it down into usable proteins, carbohydrates, minerals, fats, and other substances, and sending these into the bloodstream so that they can be used by the body. The digestive tract begins at the mouth, where the teeth and tongue begin the breakdown of food, helped by saliva. The chewed food, with saliva, is swallowed, carrying it down to the stomach. In the stomach, the food combines with hydrochloric acid and enzymes that only work in acidic conditions, which further breaks it down. When the food is completely digested, it is sent to the small and large intestines. The nutrients go into the bloodstream, leaving what can’t be used. outline the role of the stomach and the small intestine in breaking down food

3. Digestive System N identify the parts of the digestive system

4. Digestive System

5. Stages of Digestion Ingestion, digestion, absorption, and elimination are the four main stages of food processing in the body. Ingestion is the first stage and is the act of eating Digestion is the second stage and is the process of breaking down food into small molecules the body can absorb. Includes both mechanical and chemical (enzymatic) digestion Absorption is the third stage of the process and involves the uptake of the small molecules resulting from digestion Elimination is the fourth, and last, stage where undigested material passes out of the digestive compartment. outline the role of the stomach and the small intestine in breaking down food

6. The Stomach The pH of stomach is low, around 2. The low pH acts as a microbiological barrier. The discovery that most stomach ulcers are caused by a bacterium ( Helicobacter pylori ) was made by an Australian scientist. Bacterial number in the stomach contents is low, but walls can be heavily colonised –Primarily Lactobacillus and Streptococcus* (don’t memorise!) discuss the difference in pH of the stomach and the small intestine

8. Normal flora of the GI tract help to digest the food we eat The upper portions of the small intestine are acidic (pH <7), similar to, but not as acidic as the stomach. The lower portions are alkaline (pH > 7), and have increasing numbers of bacteria the further one moves along the intestine, from 10 5 to 10 7 per gram of contents. The large intestine has enormous numbers of bacteria, 10 10 to 10 11 cells/gram! Is essentially a fermentation vessel. outline the role of the stomach and the small intestine in breaking down food

9. the small intestine lining has a heavily folded structure villi project outwards from the folds each villus has lymph vessels and blood capillaries the epithelial cells have microscopic projections, microvilli, through the walls of which the nutrients are absorbed The Small Intestine N outline the role of the stomach and the small intestine in breaking down food

10. The Small Intestine Intestinal villi

11. The Role of the Stomach Syll:Outline the role of the stomach and the small intestine in breaking down food The stomach is a muscular organ that moves the food around, mixing it with the stomach secretions The stomach produces hydrochloric acid which aids digestion by lowering the pH to enable the enzymes that break down food, particularly carbohydrates and proteins to work effectively and optimally. NOTE The hydrochloric acid itself does not break down the food. N Outline the role of the stomach and the small intestine in breaking down food

12. The Role of the Small Intestine Syll:Outline the role of the stomach and the small intestine in breaking down food The small intestine is a muscular organ that moves the food along its passage, mixing it with the secretions from the intestinal wall and the gall bladder The small intestine has an alkaline pH to enable the specific enzymes that act there to work effectively and optimally. Enzymes that are active in the small intestine are secreted by the pancreas as well as the wall of the small intestine. Fats, carbohydrate and proteins are all digested in the small intestine. The digestion of fats is of particular significance. Outline the role of the stomach and the small intestine in breaking down food

13. Stomach and Small Intestine pH Differences Syll:Discuss the differences in pH of the stomach and small intestine The stomach contents are acidic with a pH range 1-3 The small intestine contents are alkaline with a pH range 7-9 The effectiveness of enzymes is very dependent on the pH in which the enzyme works. Different enzymes act in the stomach and the small intestine. Secretions from and into these organs produce a pH facilitating optimal digestion. The low pH of the stomach kills many bacteria, acting as a barrier to harmful pathogens passing further along the GIT Discuss the differences in pH of the stomach and small intestine

14. Solubility of Materials and Drug Design Syll:Explain why a knowledge of the solubility of materials can be used to design drugs for specific tasks The ease with which drugs cross membranes in the body is dependent on whether they are fat or water soluble Drugs cross the blood-brain barrier more readily if they are fat soluble HENCE, drugs designed to act on the brain need to be fat soluble The blood-brain barrier is a membrane made of tightly packed cells that prevent pathogens from entering the brain. The barrier makes the delivery of some drugs to the brain very difficult. explain why a knowledge of the solubility of materials can be used to design drugs for specific tasks