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Chapter 6 Digestion and Human Health Welcome to Human Systems. First: Why do we need systems? In large, multicellular organisms (Like you!), a size problem begins to develop If your cells get too big, the surface area becomes too small to support the larger volume (Science 10)...

Chapter 6 Digestion and Human Health Welcome to Human Systems. First: Why do we need systems? In large, multicellular organisms (Like you!), a size problem begins to develop If your cells get too big, the surface area becomes too small to support the larger volume (Science 10) The solution: Divide cells! However, this creates a new problem: How do you get nutrients to these cells? Wastes out? (E.g. The muscle cells in your bicep don’t have direct access to either food nor waste removal) Welcome to Human Systems. First: Why do we need systems? The solution: organ systems Specialized sets of organs designed to complete a certain task In order for this to work systems have to be able to work together and communicate with each other, otherwise known as system integration For example, your digestive system needs to be able to hand nutrients to the circulatory system. These can be simple interactions, but they are often quite complex. The same thing occurs in any system. (You wouldn’t want your biology teacher to teach you how to write good.)  How do cells come together to make organs and organ systems? 1. Cells make tissues Cells within multicellular organisms are specialized to perform specific functions Their structures are adapted to their function, and cells work in a group to carry out functions at a sufficient level for the organism’s size A tissue may have more than one cell type to provide for different aspects of the tissue’s responsibilities e.g lung cells (will discuss later) Cells in a tissue stick to one another Plant cells use pectin (often used to thicken jam) Animal cells use proteins Cells can talk to each other! Bonne Maman Redcurrant Jam" by Texas Lane is licensed under CC BY 4.0 How do cells come together to make organs and organ systems? 2. Tissues make Organs! Organs are tissues that carry out a specific life function (e.g Kidney, heart) 3. Organs make organ systems Organs interact with each other to perform key life functions Often physically linked, but not always There are 11 systems in humans. How many can you identify? 4. Organs make organisms! Respiratory EndocrineMuscles Nervous Lymphatic Skeletal Digestion Circulatory Integumay Reproduction  y Negative Feedback Homeostasis  Chapter 6 Digestion and Human Health 1. The Molecules of Living Systems 2. The Human Digestive System 3. Health and the Digestive System Chapter 6 Digestion and Human Health In this chapter, you will learn: Macromolecules such as carbohydrates, lipids, proteins, and nucleic acids are made up of smaller subunits that are chemically separated through hydrolysis. Enzymes are biological catalysts. The digestive tract is a tube extending from the mouth to the anus through which food is broken down, nutrient molecules absorbed, and undigested material eliminated. Food is processed mechanically and chemically to reduce macromolecules to a form in which they may be absorbed into the bloodstream. An excess or deficiency of nutrients can lead to disorders that can be diagnosed and treated but not necessarily cured. 6.1 The Molecules of Living Systems In this section, you will: describe the chemical nature of carbohydrates, lipids, and proteins explain, in general terms, how carbohydrates, lipids, and proteins are synthesized and how they are broken down (hydrolyzed) perform standard tests to identify macromolecules  Metabolism refers to all the chemical reactions that occur in living things. Anabolism is the synthesis of complex molecules from simpler molecules. formation reactions A + B  AB  Metabolism refers to all the chemical reactions that occur in living things. Catabolism is the breakdown of complex molecules into simpler molecules. decomposition reactions AB  A + B Dehydration Synthesis Anabolet 20 Although each of the 4 macromolecules we will study are structurally different, they are all assembled the same way. To form a covalent bond between 2 subunit molecules a hydroxyl group (OH) is removed from one subunit and a hydrogen (H) is removed from another. This process is called dehydration synthesis because essentially you are removing one water molecule while forming the new covalent bond. Hydrolysis H2O Organic macromolecules are disassembled into their subunits by a process that is essentially the reverse of dehydration synthesis. During hydrolysis, a hydrogen atom from water is attached to one subunit and a hydroxyl is attached to another effectively breaking the covalent bond between the two subunits. Both hydrolysis and dehydration synthesis require enzymes.  Macromolecules Macromolecule Example(s) of Main functions Examples of subunits macromolecules carbohydrates sugars (such as energy storage sugars, starches, and glucose) and polymers glycogen of glucose lipids glycerol and three energy storage and cell fats, oils, and fatty acids or glycerol membranes phospholipids and two fatty acids proteins polymers of amino transport, blood clotting, hemoglobin, fibrin, acids support, immunity, collagen, antibodies, catalysis, and muscle enzymes, actin, and action myosin nucleic acids polymers of transfer and expression DNA and RNA nucleotides of genetic information Organic Compounds: Carbon atoms form the basis of the molecules of life because they can form four covalent bonds. Organic Compounds: Carbon atoms form the basis of the molecules of life because they can form four covalent bonds. Carbon can form single, double or triple bonds! These are called organic compounds. Organic means “relating to organisms”. They are made in living things. All organic compounds contain covalently bound carbon.  Carbohydrates make up about 1-2% of cell mass ATP are a major source of energy for most living things Simple Carbohydrates: SUGARS monosaccharides disaccharides 1 sugar 2 sugars I ring glucose glucose + glucose = maltose galactose glucose + galactose = lactose (milk sugar) fructose glucose + fructose = sucrose (table sugar) Malt sugar Milk sugar Table sugar used in beer Synthesis of a Disaccharide Complex Carbohydrates: POLYSACCAHARIDES many sugars a branched chain of sugars a straight chain of sugars Starch: a chain of glucosemolecules. Starch is found in plants Plants make starch to store glucose in stems, roots, seeds and leaves. Glucose is used for energy in living things. Animals can digest starch. Cellulose: a chain of glucose molecules. Cellulose is part of the structure of cell walls in plants Glycogen: a branched chain of glucose molecules. Glycogen is made by animals and is used to store glucose for energy. Glycogen is found in the liver and muscles.  Lipids (fats) Are fats good for you or bad for you?  Lipids (fats) Carbon compounds that are insoluble in water Can dissolve in non-polar solvents (acetone) Triglycerides are a highly concentrated source of energy (there is 2 times more energy in lipids than in an equal mass of carbohydrate) Triglycerides: made up of 1 glycerol molecule and 3 fatty acid molecules. Diversity fatty acids glycerol simplified drawing of a fatty acid Glycerol: a chain of 3 carbon atoms. Fatty Acid: a long chain of carbon with a carboxyl group at one end O C – (CH2)n – CH 3 n = 2 to over 20 HO butyric acid arachidic acid Some fatty acids are saturated. This means that the carbon atoms are bound to as many hydrogen atoms as possible. stearic acid n = 16 There are no double bonds between carbon atoms Solid Anil  Some fatty acids are unsaturated. oleic acid n = 16 Liquid Plants There is at least 1 double bond between carbon atoms. This makes the molecule bend. Dissoles Better  Unsaturated Fatty Acids: monounsaturated fatty acid polyunsaturated fatty acid (1 double bond) (>1 double bond)  Unsaturated cis and trans isomers: Isomer: trans: compounds hydrogen with the same atoms are on formula but a opposite different sides of the arrangement double bond. of atoms in the molecule; cis: hydrogen and different atoms are on properties. the same side of the double bond. How are these fatty acids different? Triglycerides made with Triglycerides made with saturated fatty acids: unsaturated fatty acids: - Very stable - Less stable - More difficult to digest - Easier to digest - Common in animals - Common in plants - Solid at room - Liquid at room temperature temperature Examples: cheese, butter, fat Examples: oils, peanut butter in meat Synthesis of Fat Functions of triglycerides 1. Long term storage of energy 2. Insulation for warmth and visceral fat as a “shock absorber” 3. Buoyancy An amino acid is the subunit of proteins. Synthesis of a Dipeptide  We need Amino Acids in our diets! There are 20 different amino acids, broken into two groups: Non-essential: AA’s that we can make from other intermediates Could be other AA’s, or other organic molecules Essential: Can’t make them on our own, need a dietary source In humans, 9 AA’s are essential A good balanced diet should supply adequate amounts of amino acids Not necessarily animal based: Plenty of plant-based foods have the amino acids we need, but those who choose a vegan/vegetarian diet may have to be careful to choose foods that meet this need  Amino Acids Generalized Amino Glycine Aspartic Acid acid structure R= H R= CH2-COOH OH OH OH H CH2 I COOH There are 20 different AMINO ACIDS in living organisms, each with a different “R” group. 20 different AMINO ACIDS with different properties Formation of Dipeptides: Draw and label a diagram showing 2 amino acids being joined by dehydration synthesis (condensation reaction). Label the peptide bond. (see page 250) Breakdown of Polypeptides: Polypeptides are broken down (peptide bonds are broken) by hydrolysis reactions. Primary Structure DNA 1330 is the order of amino acids in a polypeptide. Amino acids can be linked in any order creating a infinite variety of polypeptides. PRIMARY STRUCTURE Secondary Structure Parts of a polypeptide may twist into a _alpha helix shape, or fold into a beta pleated sheet. This is called the secondary structure of a protein. Secondary structure is held together by hydrogen bonds. SECONDARY STRUCTURE Tertiary Structure A polypeptide then folds on itself to create a 3- dimensional shape. This is called _tertiary structure of a protein. Tertiary structure is held together by interactions between R-groups. Important: The chemical Diversity of R groups Creates infinite possibilities for protein shape TERTIARY STRUCTURE Quaternary Structure Some proteins are made up of many polypeptides. Hemoglobin has 2 alpha polypeptides and 2 beta polypeptides called globins. QUATERNARY STRUCTURE The amino acid sequence determines the three- dimensional conformation of a protein. TERTIARY STRUCTURE Denaturation of a protein is when it loses its 3 dimensional structure. A denatured protein also lose its ability to function Some proteins will renature. They reform the same functional shape when the stimulus is removed. Control Some proteins will coagulate. They reform a different shape when the stimulus is removed. Nucleic Acids DNA 1330 Enzymes: The temperatures at which the reactions in the body would naturally take place are so high that they would permanently denature the body’s proteins. At normal body temperature these reactions would take a very long time to occur. A catalyst is a chemical that speeds up the rate of reaction but is not used up or changed during the reaction. Catalysts function by lowering the activation energy of the reaction. o Cells manufacture specialized proteins that act as catalysts called enzymes.  Each enzyme in the body has a unique 3-D shape that is specific to the kind of reactant molecule with which it can combine. The specific molecule that the enzyme combines with is called a substrate. Each enzyme has a specific shape and can combine with only its specific substrate. The part of the enzyme that binds to the substrate is called the active site.  When the substrate binds to the active site of the enzyme its bonds are weakened, making it more reactive. Enzymes are recovered unchanged after use, but do eventually wear out and require replacing. How are Enzymes and Substrates brought together so they can bind? In order for binding to occur, enzyme and substrate must collide. This relies on molecular motion Remember the Particle Model of Matter from Science 8? Just like PMoM, if there are more molecules or higher temperatures, collisions will happen more often. Enzyme and substrate must also collide in the correct configuration! There are some structures (charge attraction) that make this easier There are some special circumstances where this arrangement is different Large substrates Embedded enzymes 4 O I O Enzymes catalyze reactions by lowering the Activation energy 630 1 Spend I Releasing https://www.youtube.com/watch?annotation_id=annotation_414 5881127&feature=iv&src_vid=XUn64HY5bug&v=qgVFkRn8f10  Enzymes are specific Each enzyme catalyzes only one type of reaction! But, since the enzyme is not altered in the reaction, enzymes can be reused many times. Example: the active site in sucrase can bind to only sucrose. Sucrase can catalyze the breakdown of only sucrose. Some enzymes can bind more than 1 substrate Example: protease can bind many different proteins “Induced fit” model of enzyme action  “Induced fit” model of enzyme action The substrate and active site do not fit exactly. As the substrate begins to bind, the active site changes shape to fit the substrate. https://www.youtube.com/watch?v=d5pgvQ5wxx4  Enzyme action is affected by pH and temperature. Changes in pH and temperature change the 3-D shape of the enzyme. Each enzymes functions within an optimal range in pH and temperature. Substrate concentration affects the rate of enzyme action As substrate concentration increases, the reaction rate increases. When enzymes are all actively catalyzing reactions, the rate of reaction remains constant even when substrate concentration increases.  Enzymes are involved in biochemical pathways A metabolic pathway is a series of reactions in a living cell. Each reaction in the series is catalyzed by a different enzyme.  Biochemical pathways Biochemical pathways can be a can be a chain of reactions cycle of reactions Initial substrate Krebs Cycle Glycolysis ENZYME 1 ENZYME 1 Intermediate 1 ENZYME 2 ENZYME 2 ENZYME 6 Intermediate 2 ENZYME 3 ENZYME 3 ENZYME 5 Intermediate 3 ENZYME 4 ENZYME 4 End product https://www.youtube.com/watch?v=NRDTOdS-_4U https://www.youtube.com/watch?v=X9nQ6Qx16GM Inhibitors: Negative Feedback Inhibitors are molecules that attach to enzymes and reduce their ability to bind to the substrate. There are two classes of inhibitors: Competitive Inhibitors: Which attach to the active site of the enzyme, blocking the substrate from binding. Non-competitive inhibitors: Which attach elsewhere on the enzyme, changing its 3-D shape and making it unable to bind with the substrate.  Competitive Inhibition This slows the reaction, especially at low substrate concentrations. This prevents the reaction from reaching its maximum rate, especially at high substrate concentrations.  Organic C Coenzymes – vitamins that help enzyme fit perfectly with the substrate B vitamins Cofactors – minerals that help enzyme fit to substrate Inorganic Metals 6.2 The Human Digestive System In this section, you will: identify the main structures and functions of the digestive system describe the physical and chemical processing of food through the digestive system and into the bloodstream explain the action of enzymes in chemical digestion identify and describe, in general terms, how digested molecules enter the bloodstream How long is your digestive tract? The Digestive System Every cell in your body needs nourishment in the form of water, carbohydrates, fats, proteins, vitamins and minerals. The digestive system is specialized to ingest food and move it along an 8 m tract and break it down into smaller components. Digestive System Digestive Tract  Four Steps in Digestion 1. Ingestion 2. Digestion 3. Absorption 4. Egestion 1 Learn the process not just memorize organs terms 2 What type of digestion happen where a Chemical Digestion Enzymes Specific Substra b Physical Digestion Smaller pieces Surface Area 1. Ingestion: pharynx (throat) teeth epiglottis blocks trachea when swallowing tongue esophagus tube through which bolus travels to the stomach Digestion Begins: The Mouth and Esophagus The idea, smell, or taste of food triggers three pairs of salivary glands near the mouth to secrete saliva. Chemical digestion (hydrolysis) begins in the mouth as salivary amylase begins to break down starch into simpler sugars called disaccharides. Demo: experience this with a cracker Physical digestion also begins in the mouth as you chew your food. As you chew, your tongue rolls the food into a smooth lump-like mass called a bolus and pushes it to the back of your mouth for swallowing.  All 61 Demo: can you drink water upside down?  The bolus enters the esophagus, passing over the covered opening of the trachea. During swallowing the trachea is covered by a flap of tissue called the epiglottis to prevent food from entering the respiratory tract.  The esophagus is a muscular tube that directs food from the mouth to the stomach. Food moves through the esophagus aided by gravity, but mostly through rhythmic muscular contractions called peristalsis.  Peristalsis Peristaltic contractions are unconsciously controlled by the Enteric Nervous System (ENS) Allows for contractions to occur without nervous (brain) control Two parts of peristaltic contractions are under conscious control Swallowing (involving use of the tongue) Defecation (Thankfully) through potty training. The Stomach Entry into the stomach is controlled by a ring-like muscular structure called the esophagial sphincter. Relaxation of the sphincter allows food to pass from the esophagus to the stomach. Contraction of the sphincter prevents stomach acid from entering the esophagus and causing damage.  If acid is allowed to enter the esophagus from the stomach you feel a burning pain rising in your throat. This is commonly known as acid reflux or “heart burn” 1 Sphincter 2 Acids in food week Med  The stomach is a j-shaped muscular sac-like organ with 3 important functions: 1.Storage of food 2.Some digestion 3.Pushing food into small intestine When empty, the stomach is the size of a large sausage with a capacity of about 50 mL. The stomach can however expand to hold 2– 4L of food! After a large meal folds in the stomach unfurl like pleats in an accordion, increasing its capacity.  the folds in the stomach are called rugae Once in the stomach, waves of peristalsis churn the food, breaking it into smaller pieces (physical digestion) and mixing it with gastric juices to produce a thick liquid called chyme. Approx. 40 million cells lining the stomach secrete 2 – 3 L of gastric juice per day. This link shows a great capsule endoscopy of a woman eating pasta salad, complete with the sounds of digestion digesting pasta salad  Gastric juice is made of water, mucus, salts, hydrochloric acid (HCl), and enzymes. HCl has a pH of 1 – 3 and helps to soften the food and begin breaking down proteins. The low pH also kills most bacteria that may have been ingested. Some bacteria, however, can survive the low pH because they have an outer coating that protects them from the stomach acid. HCl is usually only secreted in the presence of food to prevent harming the stomach lining. Protein Digestion Begins in the Stomach: The enzyme pepsin is released in the stomach and used to digest proteins. When food is not present in the stomach, pepsin is stored as pepsinogen, an inactive form of the enzyme, in order to prevent digestion of the stomach lining. Pepsinogen is only activated into pepsin in the presence of HCl. Absorption in the Stomach: Few substances are absorbed in the stomach because they have not been sufficiently broken down at this point. The stomach does absorb some water and salts, as well as alcohol and some anti- inflammatory medicines like aspirin (ASA). The pyloric sphincter controls the exit of the stomach’s contents into the small intestine. stomach Endoscopy The small intestine: Digestion and Absorbing Nutrients The small intestine is so named because its diameter is smaller than that of the large intestine. The small intestine is actually the longest part of the digestive tract. The sound of your “stomach growling” actually the sound of gasses moving through fluid moving through your small intestine. (borborygmus) Some physical digestion occurs in the small intestine in a process called segmentation where the chyme sloshes back and forth between segments of the small intestine. Peristalsis pushes the food through the small intestine. The small intestine is divided into 3 regions: 1.The duodenum is the U-shaped first 25 cm of the small intestine. It is the shortest and widest section. The duodenum is an important site for chemical digestion. Ducts from the liver and pancreas join to form one duct that enters the duodenum. 2. The jejunum is the second segment of the small intestine. It is about 2.5 m long and contains more folds and secretory glands than the duodenum. It continues to break down the chyme. 3.The ileum is about 3 m long and contains fewer and smaller villi. It is the last segment of the small intestine. It’s job is to absorb nutrients and push the remaining undigested material to the large intestine. Parts of the Small Intestine  The innermost surface of the small intestine is corrugated with finger-like projections about 1.3 cm high called villi. The surface of the villi bristle with thousands of microscopic projections called microvilli. Because microvilli give a fuzzy, brush-like appearance in electron photomicrographs they are often referred to as the “brush boarder”. Villi in the Small Intestine Accessory Organs To digest macromolecules sill present in the chyme the small intestine has an arsenal of enzymes that are secreted from the microvilli. Digestive assistance is also provided by three organs located near the stomach and small intestine: 1. The pancreas 2. The liver 3. The gallbladder The Pancreas: Delivers about 1 L of pancreatic fluid to the duodenum each day. Pancreatic fluid contains a multitude of enzymes including: Trypsin and chymotrypsin which are proteases (digest proteins) Pancreatic amylase which is a carbohydrase (digests carbohydrates) Lipase which digests fats  Pancreatic enzymes are released into the duodenum in an inactive form. They are then activated by enzymes secreted by the brush border cells of the small intestine. Pancreatic enzymes digest: Proteins into smaller polypeptides Polysaccharides into shorter chains of simple sugars Fats into fatty acids and other products Pancreatic fluid also contain bicarbonate ions which neutralizes the HCl from the stomach giving the duodenum a slightly alkaline pH of about 8. Without bicarbonate, the stomach acid would burn a hole in the duodenum. 2. Digestion: small intestine Contents of pancreatic juice: Chemical Function Bicarbonate ions Buffers the pH to 8-9 Pancreatic lipase Digests lipids Pancreatic amylase Digests starch Protease Digests protein 113 Endopeptidase (protease) Digests protein IB The Liver: The liver is the largest internal organ in the human body. In an adult it is about the size of a football and weighs about 1.5 Kg. The main digestion related secretion is bile, a greenish-yellow fluid made up of bile pigments and bile salts.  Bile pigments are the waste products of the liver’s destruction of old red blood cells. They have no role in digestion and are eventually eliminated in the feces. Bile salts play a crucial role in the physical digestion of fats. Fats are insoluble in water and therefore enter the small intestine as large drops in the watery chyme. Bile salts act like detergents dispersing large fat droplets into a fine suspension so that they can be digested more quickly by lipases. This process is called emulsification. C C c c c 4 d c c c c I c c c c /asiatic-black-bear/use-in-traditional- medicine/  The Gall Bladder: After bile is produced in the liver it is sent to the gall bladder for storage between meals. The presence of fat in the chyme arriving in the duodenum triggers the gall bladder to contract, forcing bile through the bile duct and into the duodenum. gallbladder removal gallbladder dissection gallbladder disease Secretions of the Digestive Tract Secretion Site of production Function saliva mouth contributes to starch digestion via salivary amylase; lubricates the inside of the mouth to assist in swallowing mucus mouth, stomach, small protects the cells lining the innermost portion of intestine, and large intestine the digestive tract; lubricates food as it travels through the digestive tract enzymes mouth, stomach, small promote digestion of food masses into particles intestine, and pancreas small enough for absorption into the bloodstream acid stomach promotes digestion of protein bile liver (stored in gall bladder) suspends fat in water, using bile salts, cholesterol, and lecithin to aid digestion of fats in small intestine bicarbonate pancreas and small intestine neutralizes stomach acid when it reaches the small intestine hormones stomach, small intestine, stimulate production and/or release of acid, and pancreas enzymes, bile, and bicarbonate; help to regulate peristalsis Macromolecule Building Blocks Carbohydrates Monosaccharides Proteins Amino Acids Lipids Glycerol and Fatty Acids Nucleic Acids Nucleotides (made up of sugars, phosphate, and nitrogenous bases  Digestion of Macromolecules Mouth Stomach Small Intestine Carbohydrates Physical Physical Salivary amylase Physical Pancreatic Amylase Starch to disaccharides Starch to disaccharides (cont.) Carbohydrases (from pancreas) Disaccharides to monosaccharides Proteins Pepsin (activated by HCl) Proteins to smaller Trypsin (from pancreas) HOT Polypeptides to short polypeptides polypeptides Peptidases Short polypeptides to amino acids Only salivary glands in Bile from gall bladder emulsifies fat Lipids infants secrete lipases Lipases (from pancreas) Fats to fatty acids + glycerol Nucleases Nucleic Acids Nucleic acids to nucleotides Nucleosidases Nucleotides to nitrogen bases, sugars, and phosphates Carbohydrate Digestion Digestion of starch begins in the mouth with the action of salivary amylase. Salivary amylase is inactive in the stomach due to the low pH. Digestion of starch resumes in the small intestine where the pH is about 8. In the small intestine pancreatic amylase completes the digestion of starch into disaccharides. Other carbohydrases digest the disaccharides into monosaccharies like glucose, galactose, and fructose.  The monosaccharides are absorbed by active transport into the cells of the microvilli. From there, the monosaccharides enter the Diffusion bloodstream and are transported to the liver. Monosaccharides other than glucose are converted to glucose in the liver and circulated from the liver to all cells in the body. Excess glucose in the blood is converted to glycogen and temporarily stored in the liver and muscles. When blood glucose levels fall again glycogen is converted back to glucose to be used by the cells. Protein Digestion Protein digestion begins in the stomach where they are broken down into polypeptides by pepsin. In the small intestine two proteases secreted by the pancreas (trypsin and chymotrypsin) hydrolyse the polypeptides into short peptide chains of 2 to 10 amino acids. Different peptidase enzymes secreted from the small intestine and pancreas complete protein digestion by breaking the peptide chains down into individual amino acids.  The individual amino acids are absorbed by active transport into the villi of the small intestine. From there they diffuse into the blood and are carried to the liver. Once in the liver, amino acids undergo a variety of reactions. Some aa undergo deamination and are then converted to glucose, releasing energy. Other aa remain intact and are distributed by the blood to body cells to make new proteins and enzymes. NH Urea CHO COH Fat Digestion The salivary glands and stomach of infants produce lipases so fat digestion can begin quickly. In adults, however, very little fat digestion occurs until the duodenum. The arrival of fats in the duodenum triggers the release of bile by the gall bladder which emulsifies the fat droplets. Lipases secreted into the duodenum hydrolyse the fats into fatty acids and glycerol. The resulting fatty acids and glycerol is absorbed into the villi by simple diffusion.  Inside the cells of the villi fatty acids and glycerol are reassembled into triglycerides and coated with proteins to make them water soluble. They then enter the lymph vessels in the villi and are carried by lymph ducts to the chest region where they join the bloodstream. Once in the bloodstream the protein coating is removed by lipase in the lining of the blood vessels and the triglycerides are hydrolyzed back into fatty acids and glycerol and made available for the body Nucleic Acid Digestion In the small intestine nucleic acids are broken down by nucleases into nucleotides. Nuleosidases then hydrolyse the nucleotides to their constituent bases, sugars, and phosphates. These are then absorbed into the bloodstream by active transport. Summary of Absorption of Nutrients Chemical Digestion Selected Enzymes of the Digestive System Enzyme Where enzyme Substrate (food) Products of digestion Origin of enzymes acts/pH digested salivary mouth/7 starch, glycogen maltose (disaccharide) salivary glands amylase pancreatic small intestine/8 starch, glycogen maltose pancreas amylase carbohydrases small intestine/8 small intestine sucrase sucrose glucose + fructose maltase maltose glucose lactase lactose glucose + galactose pancreatic small intestine/8 lipids fatty acids and glycerol pancreas lipase proteases pepsin stomach/1–2 protein peptides stomach trypsin small intestine/8 peptides smaller peptides pancreas chymotrypsin small intestine/8 peptides smaller peptides pancreas peptidases small intestine/8 peptides smaller peptides and amino pancreas and small acids intestine nucleases small intestine/8 nucleic acids nucleotides and components pancreas nucleosidases small intestine/8 nucleotides bases, sugars, and small intestine phosphates Absorption of Nutrients Top: Glucose is actively transported into cells of the intestinal wall to move into the bloodstream. Middle: Amino acids are actively transported into the cells of the intestinal wall to move into the bloodstream. Bottom: Glycerol and fatty acid molecules diffuse into the cells of the intestinal wall where they are resynthesized into fats, coated with proteins, and moved into lymph vessels for eventual transport into the bloodstream. Hormone Regulation in the Small Intestine: The nervous system stimulates salivary and gastric secretions in response to smell, sight, and consumption of food. When proteins arrive at the stomach, a hormone called gastrin is secreted. Gastrin stimulates the release of HCl and pepsinogen into the stomach. The lower pH caused by the secreted HCl inhibits gastrin production. This negative feedback mechanism keeps acid and enzyme secretions in tight control. Status Akin up B  tost The passage of chyme into the duodenum causes the hormones secretin, cholecystokinin (CCK), and gastric inhibitory peptide (GIP) to be secreted. These three hormones inhibit contractions of the stomach so that no additional chyme enters the duodenum until the previous amount has been processed. Chyme with a high fat content triggers more CCK and GIP to be released so that fatty meals which take longer to digest stay in the small intestine longer.  CCK also stimulates the release of pancreatic secretion and gall bladder contractions. Chyme with a high acidity is the strongest stimulus for the release of secretin. Secretin also stimulates the pancreas to release more bicarbonate ions to neutralize acidic chyme. gastric hormone The Large Intestine Material remaining in the small intestine after nutrients are absorbed, enter the large intestine. The large intestine is only about 1.5 m long, but has a diameter of about 2.5 cm. Digestion does not occur in the large intestine. Its main function is to concentrate and eliminate waste material  The Large intestine consists of two main parts: The colon and rectum. Sketch the colon. The colon is composed of three sections: 1. The ascending colon appendix 2. The transverse colon 3. The descending colon  Each day your large intestine receives about 500 mL of indigestible material, reduces it to about 150 mL by removing water and salts, and eliminates the rest as feces. In the colon, water and salts are absorbed from the undigested food, while billions of anaerobic bacteria further break down the material, producing vitamins B-12, K and some amino acids in the process. The feces then passes from the colon to the rectum. The rectum is the final 20 cm of the large intestine. Its job is to store feces until they can be eliminated through the anus. Cool fact: The rectum has three folds that enable it to retain feces while flatuating!  The opening to the anus is controlled by two sphincters. One sphincter is under the control of the nervous system and opens automatically when the rectum is full. The other we have conscious control over (lucky for us). 4. Egestion: large intestine (colon) Composition of feces Cellulose Humans do not produce cellulase, so its not digested. It gives feces bulk to help it move through the colon to be egested (aka. fiber, roughage) Water Products of the breakdown of hemoglobin. Bile pigments Give feces their characteristic colour Bacteria enteric bacteria or pathogenic bacteria Epithelial cells Stomach lining is replaced every 5 days 6.3 Health and the Digestive System In this section, you will: recognize and appreciate the relationship between health and nutritional decisions identify conditions that adversely affect the health of the digestive system and the technologies that are available to treat them Digestive Disorders pill camera Ulcers An ulcer forms when the thick layer of mucus that protects the stomach lining is eroded and acid is allowed to eat away at the stomach wall. Most ulcers are caused by acid resistant Heliobacter pylori which attach to the stomach wall causing the cells to stop producing the protective mucus. Other contributing factors are: Smoking Caffeine and alcohol intake Stress Extreme Treatment includes: Medications that reduce acidity of the stomach or strengthen the mucus layer. Antibiotics Lifestyle adjustments Surgery Stomach Ulcer Duodenal Ulcer Inflammatory Bowel Diseases: Crohn’s Disease: Crohn’s Disease (ileitis, or enteritis) A serious inflammatory disease that usually affects the ileum of the small intestine, but can affect any part of the digestive tract. The inflammation extends deep into the affected tissues causing: 1. the intestines to empty frequently (diarrhea) 2.rectal bleeding. Crohn’s disease is very painful and often difficult to diagnose because its symptoms closely resemble other intestinal disorders.  some research indicates that Crohn’s may be an autoimmune disorder. Other research links Crohn’s to a bacteria originating in cows and not destroyed by pasteurization of milk Treatments focus on minimizing pain and suppressing inflammation and immune response in order to allow time for the tissues to heal. If medication can not control the symptoms surgery is sometimes performed to remove the affected portion of the digestive tract Colitis Colitis is the inflammation and ulceration of the colon. While Crohn’s affects the entire thickness of the colon, colitis is restricted to the innermost lining of the colon. Symptoms and treatment are similar to Crohn’s disease. A last resort for treatment is the complete removal of the bowel and rectum. An external opening is created for waste.  Disorders of Accessory Organs Hepatitis The inflammation of the liver There are 3 types of hepatitis Hep A is usually contracted by drinking contaminated drinking water Hep B is spread through sexual contact and is more contagious than HIV. Hep C is usually transmitted through contact with infected blood. There are vaccinations against Hep A and B, but not against Hep C. Cirrhosis of the Liver Cirrhosis of the liver is a chronic disease where scar tissue replaces normal liver tissue and prevents the liver from functioning properly. Chronic alcoholism and hepatitis C are the most common causes of cirrhosis. Gallstones Bile can sometime crystallize in the gallbladder forming small, hard, sharp gallstones. Factors that contribute to gallstone formation include: Obesity Alcohol intake Heredity Gallstones are treated with medications or with ultrasound shock waves to disintegrate the stones so that they can be passed out in the urine. If the gallstone problem is serious, the gallbladder may be surgically removed. Most gallbladder surgery is now done as laparoscopic surgery, which is much less invasive than traditional open surgical procedures.  Treatment of eating disorders is a long and difficult process. It begins by first stabilising the life-threatening complications of starvation and then a lengthy psychological rehabilitation process.  Chapter 6 Review Why are some amino acids classified as essential? Describe the relationship between the organs in the digestive tract. What are the benefits of having stomach stapling? What are the risks? Summarize chemical digestion of macromolecules. Explain how glucose levels are affected after meals. Include the effects of different foods. Concept Organizer Chapter 6 Summary The human body takes in matter from the environment in the form of food and water. The human digestive system processes the food and water in order to obtain the macromolecules it needs for survival. Chapter 6 Summary Food passes through the digestive tract—the mouth, pharynx, esophagus, stomach, small intestine, and large intestine—during physical digestion. The accessory organs—the salivary glands, liver, gall bladder, and pancreas—supply chemicals that also contribute to the digestion of food as it passes through the digestive tract. The stomach supplies chemicals to aid digestion as well as generating physical contractions to physically break down food. The food is eventually liquefied into soluble units that can pass through cell membranes for transport via the circulatory system to all the cells in the body. The waste materials from the digestive process leave the body via the large intestine. Chapter 6 Summary The nutrients that food supplies include carbohydrates, lipids (fats), protein, and nucleic acids. Carbohydrates and lipids are broken down to supply energy; lipids also supply material for the cell membranes. Proteins are more structurally and functionally diverse than carbohydrates and lipids. They assist in transport, immunity, and muscle action and are used to make up most cellular structures. Nucleic acids direct growth and development. Enzymes speed up chemical reactions, particularly for the production of energy. Vitamins and minerals are organic and inorganic substances that enable chemical reactions to occur and aid in tissue development and growth and immunity. These substances are needed for a healthy, functional human body. Chapter 6 Summary Disorders of the digestive system and its accessory organs include ulcers, inflammatory bowel disease, hepatitis, cirrhosis, and gallstones. All disorders that affect digestion, including eating disorders, can seriously damage overall health by depriving the body cells of the nutrients they need to survive.