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Digestion – the complete process. fats proteins minerals vitaminscarbohydrates waterfibre The 7 food groups represent large chemicals. These chemicals.

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Presentation on theme: "Digestion – the complete process. fats proteins minerals vitaminscarbohydrates waterfibre The 7 food groups represent large chemicals. These chemicals."— Presentation transcript:

1 Digestion – the complete process

2 fats proteins minerals vitaminscarbohydrates waterfibre The 7 food groups represent large chemicals. These chemicals are often chains of smaller, more useful chemicals, joined together. Energy from food:

3 One example is carbohydrates. Carbohydrates are made of long chains of identical small sugar molecules. Energy molecules in food carbohydrate sugar molecule

4 The small sugar molecules are very useful. The body has to break these large food molecules up into single or small chain sugar molecules. These are used to make… ENERGY Small sugar molecules

5 This is because we can’t release sugars from carbohydrates by physically breaking them up. Problem One Physical means like slicing and cleaving food does not break down the long chain molecules and release the sugars. How can we release energy from food? - releasing smaller sugars

6 The chain of sugars is held together by… Chemical breakdown Chemical bonds require a chemical technique if they are to be broken. chemical bonds

7 - The food we start with is often large in size. Problem 2 Problem with food size Being large, the food tends to be unable to dissolve. We say it is large and insoluble.

8 Food solubility The food needs to be soluble so that it can dissolve in the blood and thus, be transported around the body. The smaller the food, the more likely they will dissolve. So the digestive system has to cope with both these problems. Blood vessel Digestion Soluble product

9 The digestive system, being an organ system, is made of a group of organs all working together. Each organ has a particular function and only by working together will they get the job done. The digestive system:

10 The sound of a rumbling stomach and the fact that food looks very different when it leaves, compared to when it enters mean that the body must be doing something to the food during its journey. The only visible parts of the digestive system are the entry and exit points. AnusMouth External digestive system What happens to the food in our bodies?

11 It is digested. This means it is broken down. This digestion happens in 2 ways. As we know all food has a physical shape and is made of chemicals. These chemicals are held together by chemical bonds. What happens to the food in our body?

12 Our digestive system uses both: chemical digestion physical digestion As we move through the digestive system, we will see one or both of these methods in action at any one time. The shape of the food must be physically changed so that it can fit through the small diameter of the digestive system. This allows useful chemicals to be released and dissolve in the blood. To be broken down chemically, the bonds must be broken. physicalchemical Chemical and physical digestion

13 Digestion is the chemical and physical breakdown of large insoluble molecules into small soluble molecules. Let’s take a close look at how this happens… In we go! Open wide

14 All food enters our digestive system through the mouth and waste material leaves through the anus. The digestive system is really one long tube with an opening at each end. Stretched out it is a 9m tube! anus mouth The digestive tract

15 In addition, the tube passes through organs on its route from the mouth to the anus. But how does a 9m tube fit into a space, which is less than a metre long? It is extremely folded! Our guts

16 Digestive system diagram

17 The mouth is where digestion begins. Here we find both chemical and physical methods of digestion. We will consider physical digestion first. If you look in the mirror and smile, you immediately notice your teeth. You will also realise that your teeth are different shapes. You have 4 basic types of teeth; each type is designed for a different role. Physical digestion

18 Each is designed to do a different job. premolarmolar canine 2 nd premolar latent incisor 1 st molar 3 rd molar 2 nd molar 1 st premolar central incisor Teeth: incisorcanine

19 Diagram of a tooth

20 The shape and size of each tooth is related to the function they have in digesting food. If we look at the teeth of other animals many of them too have these 4 types of teeth. However, the number of each type, their size and their shape differ between species. This is because other organisms have different diets. Tooth size and shape

21 Canine Sharp pointed teeth, which are used to bite and tear food. Incisors Small rectangular shaped teeth, which are found between the canines. They are used for cutting food. Molars Found behind the premolars and are used to grind hard food. Premolars Found behind the canines and are used to grind soft food. Mammalian tooth types

22 Together, these teeth can break up most foods that we put into our mouths. The mechanical act of chewing food is part of physical digestion. Once the teeth have digested the food, it may be small enough to be swallowed. However, some food can be sharp and it would be uncomfortable to swallow. The food also needs chemically breaking down. Therefore, the mouth produces a substance that solves both of these problems at the same time. Action in the mouth

23 These glands (a special type of tissue) produce saliva, a sticky liquid. As mentioned, the saliva has two jobs. Being a liquid, it softens the food and allows the digested food to be rolled into a ball just before it is swallowed. It also contains a chemical known as an enzyme. Saliva

24 Enzymes are chemicals, which act to speed up chemical reactions. They are produced from glandular tissue, which is found all over the body. In order to understand how an enzyme works, you have to think of it as having a particular shape. What is an enzyme? Enzyme properties: Somewhere on the surface of the enzyme is an important region known as the active site.

25 What’s so special about enzymes? We will use the shape below to represent on particular enzyme. enzyme In order for an enzyme to be able to speed up or catalyse a reaction, it must attach to the chemicals that are reacting. It does so using its active site. Active site

26 The red areas on these two reacting chemicals represents the areas where the active site of the enzyme will attach. The enzyme will attach to both at the same time. + Enzymes are very specific. Enzymes can only speed up certain reactions. If the shape of the reacting chemicals does not match the shape of the active site, the enzyme will not be able to work. Specificity of enzymes

27 Therefore, enzymes are specific to certain reactions. Enzymes are also very particular about the environment that they work in. To understand this, think of how you do homework. You probably have a certain place to work, or you work at a certain time, you may like listening to music whilst you work or else you can only work if it is completely silent. The environment matters

28 Enzymes and pH Different enzymes work best in different conditions. If the condition is wrong, their active site can change shape. Say one particular enzyme works best in acidic conditions (pH less than 7). If the pH rises and the conditions become alkaline, the enzyme changes shape and stops working. It can no longer fit with the reacting particles of the chemical reaction. pH 10pH< 7

29 Therefore, it is not surprising that the digestive system has enzyme- producing glands that relate to these three types of food. Remember that the shape of the chemicals within the different food groups will be different. Therefore the shape of the enzymes that digest these chemicals will also be different. The bulk of the food that enters the digestive system is from the three main food groups: proteins carbohydratesfats Food groups and enzymes

30 Carbohydrates are chains of identical sugar molecules. The enzyme that digests carbohydrates must be able to break the chemical bonds between the individual sugar molecules. The product of the chemical breakdown of carbohydrates is sugar. The sugar is known as glucose. Enzymes that digests carbohydrates are known as carbohydrases. Digestive enzymes: sugar sites of enzyme attack

31 The digestion of carbohydrates can be represented by the following equation. SugarsCarbohydrates carbohydrase Enzyme driven reaction carbohydrase

32 As with carbohydrates, proteins are made of chains of chemicals. However, instead of the chain containing identical molecules, in protein these molecules are different. Protein is made up of chains of amino acids. There are over 20 different kinds of amino acid. Proteins and amino acids Imagine a bead necklace made up of over 20 different kinds of bead. amino acids sites of enzyme attack

33 Enzymes for digesting proteins sites of enzyme attack The enzymes that digest proteins must be able to break the chemical bonds between the different amino acids. Enzymes that digest protein are known as proteases. amino acids The digestion of proteins can be represented by the following equation. protease ProteinAmino Acids

34 Fat in our food site of enzyme attack The enzymes that digest fats must be able to break the chemical bonds between the glycerol phosphates and the fatty acids. Fats are also known as lipids. Fats are made up of a molecule of glycerol phosphate attached to three fatty acid molecules. fatty acids glycerol phosphate

35 Fat digestion can be represented by the following equation: lipase Fat Fatty Acids + Glycerol Phosphate The enzymes that digest fats must be able to break the chemical bonds between the glycerol phosphates and the fatty acids. Fats are also known as lipids. Enzymes that digest fat (lipid) are known as lipases. Enzymes for digesting fat

36 Of these three enzymes, the only one that is released within the mouth is carbohydrase. This is partly because the conditions within the mouth are suitable for carbohydrase action. Carbohydrase in saliva It works best within an alkaline (pH > 7) environment. The carbohydrase in saliva in combination with other digestive carbohydrases added later from the pancreas and the small intestine complete carbohydrate digestion.

37 The food could now pass down either the trachea (windpipe) or the gullet/oesophagus. sugars chemically and physically digested physically digested physical digestion chemical digestion Carbohydrates Fats Proteins Digestive action of the mouth - summary

38 Contents Digestion – Part Two Lipid digestion Absorption The small intestine Mouth to gullet Gastric processes Summary

39 Digestive action of the mouth – reminder The food could now pass down either the trachea (windpipe) or the gullet/oesophagus. sugars chemically and physically digested physically digested physical digestion chemical digestion Carbohydrates Fats Proteins

40 The semi-digested food has been formed into a ball by the tongue and is now swallowed. The ball firstly moves to the pharynx, the region at the back of the mouth where there is a junction between two pipes. It needs to pass down through the gullet. To ensure that it does not fall into the trachea and thus block our breathing, a small flap moves to cover the tube. Mouth to the gullet:

41 Protecting the windpipe

42 How it gets down the gullet

43 The flap is known as the epiglottis. If ever food accidentally got into the trachea, we would choke and try to cough it back out. How do we swallow? Once the ball of food has passed through the top of the gullet, it is forced downwards by waves of muscular contraction. Epiglottis

44 The swallowing process finishes with a muscle known as a sphincter relaxing and the food passes into the stomach. It allows the stomach to shut off both entry and exit points and hold food inside it. The sphincter muscle found at the entry and exits points of the stomach acts rather like a drawstring on a bag. Keeping it down

45 The stomach is basically a muscular bag, filled with hydrochloric acid (HCl). cross section of stomach food enters from the gullet glandular tissue makes: hydrochloric acid, mucus and protease enzyme muscle tissue The basics on the stomach liquids mix with the fooddigested food leaves

46 …attacks any microbes (bacteria) that may have been swallowed accidentally when the food was eaten. The food is then subjected to a coordinated attack. Firstly the the hydrochloric acid When the food enters the stomach. The sphincter contracts behind it. Gastric processes: HCl Food bolus Microbes

47 These enzymes begin digesting the proteins in the swallowed food. These proteins are broken down to release the amino acids. protease protein Secondly, the hydrochloric acid provides the perfect conditions for protease enzyme. Protease enzymes work best under acidic conditions (pH < 7). Protein digestion amino acids

48 Thirdly, the muscular tissue of the stomach has the ability to contract and relax and in doing so, physically grinds the food inside it. Mucus is produced to protect the lining of the stomach from the acid. If the mucus were not present, the hydrochloric acid would actually digest the tissue that had made it! Mucus and muscles

49 presence of HCl The hydrochloric acid, mucus, food and enzyme solution is given the name - gastric juice. muscle and glandular tissue layer of mucus wall of stomach is protected Making gastric juice

50 muscular tissue of stomach protease enzyme and hydrochloric acid sugars amino acids carbohydrates proteins fats fat protein carbohydrate sugar physical digestion chemical digestion The stomach’s digestive action - summary

51 and after the stomach… It is also clear that the fat has yet to be chemically digested. This happens in the next section of the digestive system. By this stage many large insoluble molecules are slowly being digested to produce the small soluble molecules that can easily be absorbed into the blood system. Small soluble molecules Glucose Amino Acids Glycerol phosphate

52 Contents Digestion – Part Two Lipid digestion Absorption The small intestine Mouth to gullet Gastric processes Summary

53 When the gastric juices leave the stomach, they pass into the small intestine. The name of this organ is deceiving. Although it is called small, it can stretch up to 6 metres in length. In order to fit into the body, it is heavily folded. X-ray of the small intestine The small intestine:

54 Luckily two substances are produced to stop this happening. The first is mucus and we have seen how this works. The second is bile. A nasty problem! The gastric juices are very acidic. There could be a danger of the lining of the small intestine being digested. Bile is made in the liver. It is a yellow/green liquid that is naturally alkaline (pH > 7). Dealing with the acid

55 pH >7NeutralisationpH <7 + This is essential for lipase (the enzyme that digests fat) to function properly. This means that when bile and the gastric juices meet, the result is neutralisation of the acid. Why neutralise? The active site of the lipase enzymes is only effective in conditions above pH 7.

56 Parts of the small intestine

57 How is the fat digested? Let’s consider the process of fat digestion. This section of the digestive system exemplifies the true idea of an organ system as a group of organs working together for a common function. The influential organs in the digestion of fat are the: Each organ plays its part in turning fat into fatty acids and glycerol phosphates. liver gall bladder pancreas small intestine

58 The bile and the fat meet within the small intestine. The bile emulsifies the fat. This basically means the fat is physically broken into smaller pieces. emulsification by bile Notice that the fat has not been chemically digested, only physically. The result is a greater surface area over which the enzyme, lipase, can attack the fat. liver produces bile bile is released from the gall bladder and passes down through the bile duct A whole lot of bile fat within the gastric juice

59 The pancreas and the small intestine now release enzymes. Both organs produce all three enzyme types: Influx of enzymes small intestine pancreas carbohydrases proteases lipases

60 fat lipase fatty acids glycerol phosphate If we just consider fat, the lipase begins to break its chemical bonds: Lipid digestion:

61 bile emulsifies the fat muscular action of the small intestine lipase enzyme protease enzyme carbohydrase enzyme sugar amino acids fatty acids glycerol phosphate chemical digestionphysical digestion sugarfat carbohydrates amino acidsprotein Digestion in small intestine - summary

62 The three processes of chemical digestion can be summarized as follows. Large insoluble food Enzyme Small soluble food Carbohydrates carbohydrase sugars Proteins protease amino acids Fats lipase glycerol phosphates and fatty acids Digestive processes - summary

63 enzymes come into contact with food. There is a further advantage for the small intestine in being a narrow tube. With the enzymes being produced in the lining of the tube, it is essential that the food be forced to mix with them to ensure that there is efficient digestion before the food passes through the organ. If the tube is tight, the food is forced against the sides of the tube and thus, mixes directly with the enzymes. Design of the small intestine

64 Now that the large insoluble molecules have been digested down into the small soluble molecules, the body must separate them from the waste food that has not been digested. No food is 100% useful and so there will always be some waste that needs excreting. In order to understand how the body carries out this selection procedure, we need to take a closer look at the lining of the small intestine. What about the waste?

65 However, if we consider what it has to do, we will understand why this idea cannot be correct. At first glance, the small intestine appears to have a flat surface. Inside the small intestine

66 Contents Digestion – Part Two Lipid digestion Absorption The small intestine Mouth to gullet Gastric processes Summary

67 The small intestine is the site of absorption of useful molecules of digested food. These molecules must pass across the lining of the small intestine and enter the blood stream. Their destinations are the cells of the body. Our body cells constantly need these chemicals and therefore the absorption process must be very efficient to keep up with the high demand. Absorption:

68 If absorption were to occur across a flat lining, then not enough molecules would pass across the lining in the desired time. The only way to improve this situation would be to create a larger surface area over which absorption could occur. That is exactly what is present in the small intestine. Its lining is in fact a highly folded lining, which creates an enormous surface area in a small space. Surface area and absorption

69 The small intestine Have a look inside a human’s intestines

70 The result of this folding means that the surface area of the lining of the small intestine is enormous! Maximising the surface area This increases the number of places where small soluble food molecules can pass across and move into the blood. Direction of Food Epithelium of small intestine

71 The blood is found in minute small vessels known as capillaries. The capillaries are found protruding into the villi. The blood approaches the villus, picks up the absorbed food molecules and then leaves. Where is the blood?

72 Remember that the small intestine lining is made up of thousands of villi. Here is a summary of the process of absorption. sugars amino acids fatty acids and glycerol phosphates A S B R O T P N O I BLOODBLOOD Any indigestible food will leave the small intestine without having been absorbed. Digestive products in the blood

73 Let us now move on to the next organ in the system, the large intestine or colon. As the food enters this organ, all that is left is waste material and water. The body will want to leave the waste material within the digestive system but the water is valuable. The large intestine

74 This water will need to be retained by the body in order to prevent dehydration. Remember that all the liquids you drink provide the largest source of water for the body. The blood reabsorbs the excess water that is mixed with the waste food. Again, if something is going to be absorbed, it must have somewhere to go. Water regulation

75 The blood reabsorbs the excess water that is mixed with the waste food. Getting back excess water LARGE INTESTINE BLOODBLOOD

76 In order for the waste material to be removed, another sphincter muscle must relax. This opens the anus and the faeces can pass out of the system. Waste material then passes into a storage organ called the rectum. rectum This waste material mainly consists of indigestible food. It makes up the bulk of the faeces (solid excrement) that will be excreted. Expelling the waste

77 We have now finished our journey through the digestive system. We have seen the chemical and physical digestion of large & insoluble into small & soluble food. It is important to remember that the digestive system relies heavily on the presence of two important types of body tissue. Through constant contraction and relaxation, the food is kept moving through the system, from the mouth to the anus. 2. Muscular tissue This is responsible for the production of the digestive enzymes. 1. Glandular tissue Important body tissues in digestion

78 Chew it all over Chew it over


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