UNIT 2

UNIT 2Digestion and Nutrition

1Human Digestive System FunctionThe main function of the digestive system is to break down large macromolecules (proteins, fats and starch) into smaller molecules (amino acids, fatty acids and glucose) that can be absorbed into the circulatory system for distribution around your body. This breakdown occurs because of a various mechanical and chemical processes. We need to digest food in order for us to get the energy (ATP) that is in it, into a useful form.

2Introduction to DigestionThe pathway that food takes as it moves through the body during digestion is known as the digestive tract or the alimentary canal.

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4Five Stages of the Digestive ProcessMotility movement of food through the digestive system.Secretion release of digestive juices in response to a specific stimulus.Digestion the physical and chemical breakdown of food into small particles.Absorption passage of the molecules into the bloodstream.Elimination removal of undigested food and waste.5Structures in the Human Digestive SystemFood enters the alimentary canal through the mouth opening; the chamber that it enters is called the oral cavity. 6The tongue helps to move the food around in the oral cavity, pushing the food between the teeth, which chew the food. The tearing and biting of food breaks it into smaller bits before it is swallowed. This is a very important step in human digestion, known as mechanical digestion.*Often referred to as mastication*7The food is also lubricated in the mouth by the saliva, which is produced by three sets of salivary glands. These glands send their secretion, saliva, through small ducts into the oral cavity. Not only does saliva lubricate the food, it also begins to chemically digest carbohydrates in the food you have eaten.

8There are 3 pairs of salivary glands that secrete their fluids into the mouth:The Parotid Gland is located just in front of and slightly below the level of the opening of the ear. This is the largest of the glands which secretes salts, an enzyme (salivary amylase) and a watery serous fluid into the mouth through the parotid duct.

The Submaxillary Gland is located below the parotid gland near the angle of the lower jaw. It produces some serous fluid and some mucous and delivers them to the mouth through the submaxillary duct.

9The Sublingual Gland is located under the tongue and secretes mostly thick stringy mucus, salts and salivary amylase. These substances are emptied into the mouth through the submaxillary duct.

Since the salivary glands deliver their secretions through ducts, they are called exocrine glands.

Saliva flows from the salivary glands at all times, keeping your mouth moist. However, the sight or smell of good food may cause your mouth to "water". Of the approximate 1L of saliva produced every day, 99% of that is water, with the remainder being mucus and enzymes. This water moistens and dissolves particles of food while mucous helps make chewed food smooth and easy to swallow.

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Submaxillary12The PharynxThe pharynx opens to two tubes that descend down into the neck.

Trachea, or windpipe, connects the pharynx to the lungs and is found in front of the esophagus.

Esophagus is the digestive tube that connects the pharynx to the stomach.

13Uvulaa small mass of tissue that hangs down in the back of the mouth, and moves up to close off the openings to the nasal cavity when food is swallowed into the esophagus.

14Soft Palatethe roof of the pharynx in the back of the mouththis soft tissue functions in closing off the openings to the nose and ears as food is swallowed.

15Epiglottisa thin, flaplike piece of cartilage that closes over the trachea opening, preventing food that is swallowed from entering the trachealies above the esophagus and diverts food into that tubepart of the larynx or voicebox

16The EsophagusFood that has been chewed and lubricated is ready to be swallowed. The bolus (ball of food) is swallowed and enters the esophagus or food tube, which lies behind the trachea and runs down the centre of your neck. The esophagus ends when it joins the stomach.

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18Food moves down your esophagus, pushed through by the rings of smooth muscle found in the walls of the esophagus. These muscles involuntarily contract and relax in waves as they push the food along. This rhythmic contraction is called peristalsis and it continues through the entire length of the digestive tract.

*involuntary - controlled subconsciously - will happen without you having to think about it.19

20Peristalsis VideosPeristalsis Throughout the Body

NOT FOR THE FAINT OF HEARTReview of Swallowing21The Stomach

Cardiacsphincter22Cardiac sphincter muscleClose off the opening to the stomach and serve to control the movement of swallowed material into the stomach.

Keeps partially digested food and stomach acid from working their way back up the esophagus, called reflux or better known as heartburn.23Three layers of muscle in the wall of the stomach contract and relax to mechanically break down the stomach's contents. The bolus is churned and mixed with stomach secretions.These secretions and the stomach's mechanical churning of the food act to further soften it and break it up into smaller pieces, taking on a soup-like consistency. What Happens in the Stomach?24Chymeterm used for food after the stomach has digested it. Rhymes with time (the h is silent)About 9L of chyme enters your small intestine every day.

25Hydrochloric AcidThis powerful acid protects us from harmful bacteria-what we may ingest with foods is fried by this strong acid. HCl also helps keep the three pounds of bacteria found in the colon from moving up into the small intestine. If this happens, "bad" bacteria and yeast can establish a foothold in the intestine, resulting in less than optimum absorption of nutrients and inflamed intestines.

26HCL is paramount in our digestive process. It begins the digestion of protein and stimulates the pancreas to produce digestive enzymes. When we dont digest foods well, there may be three results:

We don't get the nutrition we needOur food passes through our bodies and into our bloodstream too quickly and becomes seen as invaders (allergens) in our body.Food lingers and becomes a form of "bad" bacteria, which can make us very sick.Cheeseburger in HCl27PepsinIt is not an enzyme but a forerunner of the enzyme pepsin. Once the pH level of the stomach reaches a level of 2 or lower, pepsinogen is converted into pepsin, an active enzyme which begins the breakdown of proteins.

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MucousThe stomach is lined with mucous that coats the cells lining the stomach and protects them from the digestive action of the enzyme pepsin.

Unfortunately these protective measures do not always work, and the stomach starts to digest itself. The result is a peptic ulcer.

29The stomach is primarily an organ of digestion.The stomach is NOT an organ of absorption. 30The Small IntestineThe small intestine lies between the stomach and the large intestine. In adult humans, the small intestine is 5-6 metres in length, has a surface area of a 500-600m long tube and takes up a significant portion of the abdominal cavity. The main processes of digestion and absorption are accomplished by the small intestine.31

32Pyloric SphincterLocated between the stomach and the small intestineControls the movement of the chyme into the small intestine The stomach pushes chyme into it by peristalsis. 33Digestion in the Small IntestinesThe digestion that occurs is primarily chemical, most of which occurs in the duodenum. The enzymes that act chemically on food to digest it come from the small intestine and the pancreas. The pancreatic duct connects the pancreas with the small intestine and effectively carries pancreatic juice 34The small intestine also possesses intestine glands that produce its own secretions; intestinal juice.Peristalsis continues in the small intestine, churning and pushing the partially digested food through until it reaches the large intestine.

35The Importance of BileIn the small intestine, large lipid molecules (fats) are physically broken down or emulsified by bile (this is a mechanical process).

Droplets of lipids are formed that are more easily digested.

36Bile is a product of the liver and is stored temporarily in the gall bladder.

The bile duct carries bile into the duodenum of the small intestine where it acts to emulsify fats, breaking them up into tiny droplets.

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38VilliFacilitates the absorption that occurs in the small intestine

Tiny finger-like projections that line the walls of the small intestine.

39Capillaries uptake those food molecules and they are transported to other structures in the body via the blood.

The primary types of food molecules that are absorbed at this point are derived from the digestion of carbohydrates, proteins, and lipids.

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41The Large IntestineOnce the digestion of food in the small intestine is essentially finished, the remaining material passes into the large intestine or colon.

42It extends from the end of the small intestine to the anus and is 1.5 metres long. The large intestine is shorter than the small intestine but is larger in diameter.

There are three portions of the large intestine. These three sections create an upside-down U-shape and surround the small intestine. 43

Direction of food44What is left of the food after digestion is moved through the large intestine with the help of peristalsis. In the large intestine, water and essential minerals are reabsorbed into the bloodstream. Fibre, bacteria and other undigested products are then excreted as feces through the anus by peristalsis.

45AppendixA small pouch located at the point where the small intestine meets the large intestine. This organ apparently serves no function in humans unless it is infected. An infected appendix could rupture and release the infection into the body cavity which can be fatal.

46RectumLocated at the end of the large intestine. Primarily acts to store the feces before it is excreted by muscular contractions.The anus is the opening of the rectum to the outside of the body.The movement of feces to the exterior is controlled voluntarily by the external anal sphincter. Digestion47As we have seen, the organs in the digestive system secrete many different substances that play a role in the chemical digestion of food.Chemical Digestion48Aids in preparing food particles for absorption. Takes place through the action of enzymes. Large food molecules are chemically changed into smaller moleculesThe types of nutrients that are digested through mechanical and chemical action are carbohydrates, proteins, and lipids. Chemical Digestion49CarbohydratesMade up of carbon, hydrogen, and oxygen Quick sources of energy and include both simple molecules (sugars) and complex molecules (starches) Common food sources are breads, pasta, and fruit 50ProteinsLarge complex molecules that contain carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulphur. Serve as the structural framework of most living tissue and also serve as enzymes, but are not usually used as an energy source. Made up of smaller molecules called amino acids. Common food sources include meat, eggs, and nuts.51LipidsMake up fats, oils, and waxes. Contain carbon, hydrogen and oxygen. Capable of storing great amounts of energy in their chemical bonds. Common food sources include margarine, cooking oil, and animal fat found in meat.52EnzymesBiological catalyst that can speed up chemical reactions without being altered in the process.Allows for the reaction to occur at a faster rate.53Digestive EnzymesEnzymes are very specific; they only act on certain molecules called a substrate. Each type of enzyme is very specific in terms of which substrate it will act on. The names for enzymes start with the name of the substrate involved and end in "-ase". For example, an enzyme that acts on a protein molecule is a protease. An enzyme that acts on a carbohydrate molecule is a carbohydrase. And an enzyme that acts on a lipid molecule is a lipase.54An analogy that is often used to understand enzyme action is the lock and key" concept in which the substrate acts as the lock and the enzyme is the key. 55

KEYLOCKThe key is unchanged but the lock has been changed, opened.56Animation of an EnzymeEnzymes57Chemical Digestion in the Human Digestive TractLocationSecretionType of EnzymeActionMouthSalivaAmylaseBegins digestion of starch to simple sugars.StomachGastric JuiceProteaseBegins digestion of proteins.58LocationSecretionType of EnzymeActionSmall IntestinePancreatic JuiceAmylaseCompletes digestion of starch to simple sugars.ProteaseContinues digestion of proteins.LipaseCompletes digestion of lipids to fatty acids and glycerol with the help of bile.Intestinal JuiceProteaseCompletes digestion of proteins to amino acids.CarbohydraseCompletes digestion of carbohydrates to simple sugars.59In addition to carbohydrates, proteins, and lipids, nucleic acids are also nutrient molecules that are broken down in the digestive system. When nucleic acids are broken down chemically, the results are nucleotides, which contain nitrogen, phosphorus, and sugars.60Once nutrient molecules are broken down chemically and mechanically, they are absorbed into the circulatory system. Most absorption occurs in the small intestine except vitamins, minerals, and water are absorbed in the large intestine.

61Factors that Affect Enzyme ActionThe pH of a solution refers to how acidic or basic it is. An enzyme that is structurally changed as a result of pH is said to be denatured; which leads to a loss of enzymatic activity.

pH62The protease in the stomach, pepsin, is activated by this acidic environment and becomes deactivated when it enters the basic environment of the small intestine Less acidic environment of the small intestine allows the enzymes produced by the small intestine and pancreas to be more effective in digestion. 63Surface AreaWhen a food particle is mechanically broken down by chewing it into a number of smaller particles, the total surface area of exposed particles increases. An increased surface area allows more enzymes to act on the food particles. 64CoenzymesSmall organic molecules that are not proteins that help to facilitate the enzyme-substrate connection and are often produced from various vitaminsThey are located at the active site of the enzyme molecule and facilitate the "lock and key" action of the enzyme and substrate molecules.They are not themselves affected by the action of the enzyme on the substrate molecule.65InhibitorsCompete with substrate molecules for the active sites of the enzymes. Binds to the enzyme, rendering the enzyme ineffective on the substrate molecule that it was designed to act on. 66TemperatureMost reactions in the human body that involve enzyme activity occur within a fairly small temperature range usually from about 30C to 40C .Temperatures outside of this range can cause denaturation of the enzyme.

67Enzymes are very important in the human digestive system. Their production and accumulation in the body are carefully controlled so that homeostasis is maintained.68The LiverAlmost all the blood circulating from the intestines to the heart passes through the liver. Everything you eat that gets into the bloodstream passes through your liver. The liver then either stores nutrients or breaks them down even more. The liver transforms nutrients into proteins, fats, and cholesterol and stores vitamins (A, D, K, and B12), minerals, and carbohydrates.69The liver also plays the role of a filtering system. Toxic substances, including alcohol, are transformed into less harmful substances.70

71The Role of the Liver in HomeostasisRecall: Glucose is necessary for cells to produce ATP, the molecule that stores energy. The amount of ATP that the body needs at any one time changes; therefore, the body needs to be able to store glucose when it is not needed, but release glucose when it is needed.

72Two hormones responsible for controlling the concentration of glucose in the blood are insulin and glucagon, which are produced in the pancreas.

The liver also plays an important role in blood glucose control. It is here that excess glucose is stored in the form of glycogen.

73When you eat a meal, blood glucose levels start to rise. When they reach a certain concentration, receptors in the pancreas stimulate the production of insulin. This hormone reaches the liver, which then converts blood glucose into glycogen. Blood glucose levels drop and return to a normal level.

74If blood glucose levels drop below a certain level, receptors in the pancreas stimulate the production of glucagon. This hormone reaches the liver, which then converts glycogen into glucose. Glucose is released into the bloodstream and blood glucose levels rise until they return to a normal level.

75NutrientsThere are six basic types of nutrients used by the human body.carbohydrates, lipids, proteins, vitamins, minerals, and waterSome of the uses that your body makes of nutrients are functional and others are structural in nature.76CarbohydratesUsed by the cells of the body to produce energy. The human body cannot produce its own carbohydrates and must rely on eating other organisms to acquire them. Primary source of energy for humans, supplying 50 to 80% of the total energy required. Provide short-term energy to cells through the process of cellular respiration.

77MonosaccharidesSimple single sugarsMost common is glucose which provides energy for cellular respiration and the production of ATP and fructose which is found in fruit78Glucose

79DisaccharidesDouble sugarsMade by joining together simple sugars with chemical bonds. Most common is sucrose (white table sugar), lactose (dairy products)

80Sucrose

81PolysaccharidesComplex sugars made of many simple sugars joined by chemical bonds.Several hundred glucose molecules join together to form starches which are the primary form of storage carbohydrate used by plants. Cellulose, which is found in the cell wall of plants, is the fibre we need in our diets; which our digestive system requires to function correctly. 82Simple CarbohydratesUsually sweet-tasting like cookies, candy, pop, pastries, fruits, and juices. Good sources of carbohydrates, but do not always contain vitamins or minerals. Considered empty-carbs

83Complex CarbohydratesStarchy carbohydrates take longer to be digested than simple carbohydrates and therefore provide a more long-term source of energy for the body. Complex carbs, are found in breads, pasta, rice, and potatoes and most vegetables like corn, tomatoes, carrots, and lettuce

84Lipids (Fats)are only used for energy when the supply of carbohydrates in the bloodstream is lowdifficult to break downstored source of excess energy for the bodyabout twice as energetic as one gram of carbohydrate85important in helping the body absorb vitamins effectivelykey structural components of cell membranes, a form of insulation for the body and serve as protection for delicate vital organsthe raw material from which hormones are producedan important component in the transmission of nerve impulses in the nervous system86CholesterolFat molecule that occurs naturally in the bodyProduced by the liver and is transported by the blood to cells Found in all animal products Very important component of cell membranes. The body processes cholesterol in the diet in different ways, depending on what type of food contained the cholesterol that was ingested. 87LDL (bad cholesterol)Low-density lipoprotein Can accumulate on artery walls and restrict blood flow. Liver maintains a "normal" level of cholesterol by removing excess LDL from the blood 88HDL (good cholesterol)High-density lipoprotein Lowers blood cholesterol by carrying LDLs back to the liver which can break down the LDL moleculeThe level of HDL in the blood can be increased if you decrease the amount of saturated fat in your diet and if you increase your physical activity. HDL can reduce the risk of heart attack and stroke89Comparison between Unsaturated and Saturated FatsUnsaturated Fatsliquid at room temperatureusually come from plants oilsExample: olive oil sunflower oilcorn oil 90Saturated Fatssolid at room temperaturecome from animals linked to heart disease more difficult for the body to break down can accumulate on the inside of blood vessels, causing circulatory problems.Example: fat found in beef, pork, chicken, and dairy products made from milk, such as butter91It is recommended that no more than 30% of your total energy intake should be in the form of lipids, since lipid molecules store about twice as much chemical energy as carbohydrate molecules.

92ProteinsPrimary structural component of all cells

Broken down by your digestive system into amino acid molecules which are then rebuilt into other proteins.

Muscle, cartilage, ligaments, skin, and hair are all examples of protein molecules. 93Smaller protein molecules also play vital roles as hormones, antibodies, enzymes, and hemoglobin.

Vary in size and shape which allows for incredible diversity of functions performed by proteins 94Amino Acids20 amino acids 9 of them cannot be made by the human body and are referred to as the essential amino acids because they must be eaten. All 20 "building blocks" allow the synthesis of all of the many proteins that your body manufactures. 95Glycine

96Food Sources of ProteinsComplete Proteinscontain all of the essential amino acids beef, chicken, fish, eggs, milk, and many animal products97Incomplete Proteinsdo not have all of the essential amino acidsvegetables, fruits, grains, seeds, and nuts98It is recommended that you consume 0.8 - 1.5 grams of protein per kilogram of body weight. People who are on a vegetarian diet need to pay special attention to the foods they eat to make sure that they acquire adequate amounts of all amino acids.

99VitaminsOrganic substances (must contain a carbon chain) that are needed in very small amounts Part of the structure of many enzymesIf your diet is deficient in a certain vitamin, the result could be an enzyme deficiency that can in turn cause serious health problems100Are chemicals that are necessary for normal growth and metabolism. Some vitamins are required for the chemical reactions that result in the release of energy from carbohydrates, fats, and proteins.

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102 Fat-soluble vitamins (A, D, E, and K) are not as readily excreted from the bodystored in the liver

Water-soluble vitamins (C, and the B vitamins)can become depleted more quickly leading to a deficiencymust be included regularly in your diet103

104MineralsUnlike vitamins, minerals are inorganic that is, they are not based on a carbon chain. Most minerals are molecules of a single element. Minerals do not provide energy for the body, but they do play very important roles in many cellular reactions. For example, minerals are vital in maintaining nervous system functions, water balance, and skeletal health.10516 Essential MineralsSodium is found in table salt and helps maintain proper blood pressure. Potassium is found in bananas and keeps nerves and muscles working properly. Calcium is found in dairy products and is needed to build strong bones. Iron is found in red meats and wholegrain vegetables; it is very important in the production of red blood cells.106WaterWater is an essential component of cytoplasm the intracellular fluid that makes up all cells. Water is an important solvent because most chemical reactions in the body occur between molecules that are dissolved in it. Water is also an important lubricant and bathes body cells. 107Water is a primary component of blood and transports vital nutrients and unneeded wastes throughout the body.

Water also serves an important role in temperature regulation.

*without water, many life functions would not occur*108Water is acquired in many ways. Drinking water is the most obvious way that you obtain water. However, many foods have a high water content, such as fruit and vegetables. Also, many cellular processes involve the production of water. For these reasons, it is suggested that you drink about 8 cups of water or other non-caffeinated fluids per day to maintain adequate hydration.

109Dietary Decisions

110Guidelines for Healthy EatingEnjoy a variety of foods.

Emphasize whole grain cereals, breads, other whole grain products, vegetables, and fruit.

Choose lower-fat dairy products, leaner meats, and foods prepared with little or no fat.

Achieve and maintain a healthy body weight by enjoying regular physical activity and healthy eating.

Limit salt, alcohol, and caffeine.111