Digestive System: Macromolecules, Enzymes, and Absorption

SBI3U – ANIMAL SYSTEMS REVIEW Digestive System Macromolecules – larger, more complex assemblies of organic molecules, also known as nutrients. Consisting of carbs, lipids, proteins, and nucleic acids Energy released from these macromolecules and the nutrients supplied by them serve to maintain the body’s metabolism Metabolism – all chemical processes in an organism Essential nutrients – four major categories of macromolecules CARBOHYDRATES (carbs as the Kool kids call them) macromolecules that always contain: Carbon, Hydrogen, and Oxygen 2 atoms of hydrogen and one atom of oxygen for every atom of carbon They provide short term and long term energy storage for organisms two main types of carbohydrates: simple sugars and polysaccharides Monosaccharides simple sugars carbohydrate molecules with 3-7 carbon atoms examples: glucose (sugar found in blood) and fructose (sugar found in fruit) Disaccharides (double sugars) double sugars made up of 2 simple sugars common examples of disaccharides include: sucrose (table sugar), maltose (sugar found in grain) and lactose (sugar found in milk) Polysaccharides complex carbohydrates made up of many linked simple sugars examples: starch, cellulose and glycogen glycogen – a polysaccharide made up of glucose sub units starch performs the important function of storing energy in plants glycogen stores energy in animals LIPIDS (think liposuction — removal of *fat*) Group of macromolecules with one shared property: they are insoluble in water basic structure of lipids is a molecule of glycerol (an alcohol) consisting of three carbon atoms, attached to a fatty acid chain Lipids store 2.25 times more energy per gram than other biological molecules therefore, some lipids function as energy storage molecules Other lipids, known as phospholipids form the membrane that separates the cell from its external environment PROTEINS Assembled from small subunits known as amino acids Most protein molecules are made up of hundreds of amino acids joined together by peptide bonds into one or more chains. These chains are called POLYPEPTIDES Most enzymes are proteins and so are antibodies, which combat disease Proteins help build and repair muscles and cell membranes Nucleic Acids Nucleic Acids direct growth and development of all organisms through a chemical code The two types of nucleic acids are ribonucleic acid and deoxyribonucleic acid Breaking Down Macromolecules: Enzymes Before the body can use macromolecules, they must be chemically broken down into molecules small enough to be absorbed by the the cells lining the small intestine The process that carries out this chemical breakdown is known as hydrolysis When a water molecule is added to a macromolecule, the chemical bonds holding the smaller molecules that the macromolecule is made of together are broken. Enzymes, a distinct class of molecules, are involved in the dissolution of the chemical bonds in this process. Enzymes are secreted by cells in the digestive tract Enzymes act as biological catalysts, speeding up the breakdown of macromolecules Roles of Water in the Body Water makes up 2/3rds of the body’s mass and is needed for the proper functioning of all cells and organs Its many roles include: transporting dissolved nutrients into cells that line the small intestine flushing toxins from the cells lubricating tissues and joints forming essential body fluids such as blood and mucus regulating body temp (sweat) eliminating waste materials Water is vital for maintaining the body’s fluid balance, the condition in which the amount of fluid lost from the body equals the amount taken in Constant supply of water needed to maintain the fluid lost from daily normal bodily functions Average adult produces 1.5L of urine per day, and loses 1L through breath, perspiration, and bowel movements The Four Stages of Food Processing ingestion (the taking in of food) digestion (the chemical or mechanical breakdown of macromolecules so they are small enough so the cells of the body to absorb) absorption (the transport of the products of digestion from the digestive system to the circulatory system, which will distribute throughout the body) elimination (removal of unneeded solid waste from the body) Alimentary Canal – the long tube through which food is processed, beginning at the mouth and ending at the anus; also known as the digestive tract Mechanical digestion – the physical breakdown of food into smaller bits Chemical digestion – the chemical breakdown of food by enzymes The Human Digestive System Accessory organs (aid in digestion, but food does not pass through these organs): salivary glands, liver, gallbladder, pancreas Digestive tract (food passes through these organs): mouth, esophagus, stomach, small intestine, large intestine, rectum, anus function of mouth: used to physically break down food so that it can be safely transported to the stomach for further processing. It contains salivary glands that release saliva, which chemically breaks down the food. Saliva contains amylase, which breaks down starches. function of esophagus: transfer of food from the mouth to the stomach. Shape: long, hollow tube. Peristalsis is the series of wave like muscular contractions that move food through the esophagus ESOPHAGEAL SPHINCTER controls entry to the stomach Stomach: J shaped organ that temporarily holds food for later chemical and physical breakdown. Stomach is lined with millions of gastric glands that secrete gastric juice stomach contains three layers of muscle fibres that contract and relax to churn food and mix them with gastric juices. this churning results in chyme, which is what the food is called after it has been processed by the stomach at the end of the stomach there is a valve known as the pyloric sphincter. When this valve is closed, food stays within the stomach Stomach does not digest the proteins that make up its own cells as it has 3 methods of protection: stomach secretes little gastric juice until food is present in the stomach some stomach cells secrete mucus, which prevents gastric juice from harming the cells of the stomach lining stomach produces its protein digesting enzyme pepsin in a form that keeps it inactive until HCl (gastric juice) is present the stomach contains a network of nerves that regulate the system, these nerves initiate stomach contractions that released partially digested food into the small intestine. When the small intestine is full and digesting food, the stomach temporarily keeps the chyme until the small intestine is clear. The small intestine consists of three components: the duodenum, … the duodenum is a U shaped component of the small intestine where food first enters. The duodenum receives secretions from the pancreas and gall bladder that aid the function of digestion the small intestine contains folds that increase the surface area over which nutrients can be absorbed. Villi line the folds, which are further lined by microvilli. Through these projections, absorption of nutrients takes place jejunum: 2.5m, contains more folds than the duodenum, breaks down remaining carbohydrates and proteins so the end products can be absorbed into the bloodstream ileum: 3m long. Contains fewer and smaller villi than either the duodenum or jejunum. Its function is also to absorb nutrients and push undigested material to the large intestine Accessory Organs the pancreas and gall bladder are not part of the alimentary canal, but are closely connected to the canal by ducts because of this, they are considered accessory organs fluids produced by the accessory organs are essential to the process of digestion the pancreas secretes 1L of pancreatic fluid into the duodenum pancreatic fluid contains numerous enzymes that chemically digest carbs, lipids and proteins the fluid also contains bicarbonate, which is very important to the function of enzymes the bicarbonate alters the pH of the chyme from strongly acidic to slightly basic, allowing the enzymes found within the pancreatic fluid to work most effectively The liver is the largest internal organ of the body. It produces bile, a secretion that is made up of bile pigments and salts Bile pigments do not take part in the process of digestion. They are waste products produced when the liver destroys old red blood cells. Bile pigments are eventually eliminated from the body through feces After the bile is produced, it is sent to the gall bladder, which stores it Bile contains bile salts that are critical in the digestion of fats recall that fats cannot be dissolved in water, so the bile salts physically breaking up fat droplets in the chyme to allow for the enzymes to chemically break them down this allows for the intestinal cells to absorb the fats Factors that Affect Enzyme Action two factors: temperature and pH impact the rate at which enzymes function more energy is added at higher temperatures, so enzyme activity increases the chemical bonds become too weak to maintain the enzyme’s structure, and it breaks apart, or “denatures” (molecular shape and structure changes) Enzymes also function best within an optimal pH range Absorption in the Small Intestine Monosaccharides are absorbed into the bloodstream through the lining of the small intestine They are transported to the liver, where monosaccharides (other than glucose) are converted into glucose Glucose is carried from the liver to all other parts of the body via the circulatory system, and is used by cells as a source of energy The liver takes excess glucose and converts it into glycogen, which can be temp. stored in the liver and in much smaller amounts, in muscle When the body needs additional energy, the glycogen is converted back into glucose for the cells to use Like glucose, amino acids are transported to the liver from the small intestine in the liver, amino acids are processed by various reactions and are either converted to sugars or used in energy producing biochemical reactions Some of the amino acids produced by these reactions undergo a series of further transformations in the liver, and become a nitrogen rich waste known as “urea” Urea is filtered and expelled through urine Other amino acids are carried by the circulatory system to cells of the body where they are used to make enzymes and proteins Glycerol and fatty acid molecules are absorbed into the cells of the small intestine, where they are rearranged to form triglycerides the triglycerides are coated with proteins to make them water soluble Once in the blood, the protein coating is removed, and are again broken down into their component molecules to provide cells energy The Large Intestine After the nutrients found in food have been absorbed from the small intestine into the bloodstream, the remaining material moves into the large intestine, or colon the main function of the colon is to absorb water from the alimentary canal about 90% of water is absorbed back into the blood the volume of indigestible food matter is therefore reduced by two thirds Billions of anaerobic bacteria in the colon break down undigested matter further The leftover matter forms feces, which is forced through muscular contractions into the rectum The rectum stores the feces until it is expelled through the anus Digestive System Disorders Peptic Ulcers: symptoms include: abdominal pain, bloating, nausea, and loss of appetite sore in the lining of the stomach or duodenum, where HCl and pepsin are present ulcers form when the tissues become inflamed because the protective mucus that covers the lining has weakened Ulcers are very painful as exposed, unprotected tissue come into contact with acidic gastric juice Most ulcers are caused by acid immune bacteria, which attach themselves to the lining of the digestive tract and prevent the lining from secreting mucus because it is a bacterial infection, ulcers can be treated through antibiotics Inflammatory Bowel Disease: general name for a group of diseases that cause inflammation in the intestines IBD is a chronic disease, meaning it lasts for a prolonged period of time IBD can only be treated, not cured Crohn’s Disease is a form of IBD that can affect any part of the alimentary canal Children with it generally do not correctly develop during puberty: developing weak bones, with poor muscle development as well Ulcerative Colitis is a form that attacks the colon Symptoms of Ulcerative colitis include: loose and/or bloody stool, cramps and abdominal pain In severe cases of IBD, it may be necessary to remove a part of the colon and create a new external opening Constipation common disorder of the digestive system in which bowel movements are reduced to 3 per week or less stools are hard, dry and difficult to eliminate constipation can be caused by lack of proper water intake lack of good nerve and motor function in the bowels unhealthy diet and lack of physical activity may also cause constipation