Digestion 4 28 14 11 55 AM pdf version of lecture Objective List and explain the basic process of digestion Digestion This section was probably covered in biology and probably in high school There are a just a few key points that must be covered to make an understanding of other sections more complete Digestion is really about getting nutrients from the food and into the body where they can be used for energy or other purposes In most cases for something to be absorbed into the blood stream it must exist in the simplest chemical form If it is two sugars hooked together they can only be absorbed if they are separated into two individual sugars The body seems to go on the principle that if it cannot convert it into the simplest form it may either be toxic or of no use This is especially true for substances that are water soluble For those that are fat soluble a mechanism exists for absorption of slightly larger molecules The processing of food takes place in four stages Ingestion Digestion Absorption Elimination Ingestion The act of eating This is only the rst of four main stages of food processing Very little true digestion occurs at this stage Some digestion of starch by enzymes in saliva amylases Main purpose is for mechanical break down of food down chewing to speed subsequent steps Digestion Absorption Process that breaks down food into molecules small enough to absorb Breaks polymers into monomers that are easier to absorb and that can be used to synthesize new polymers required by the organism Cells that line tract take up nutrients https carmen osu edu content 1144 FDSCTE 2200 fdscte 2200 su2 ssionVal 8KMB32UCTXaqzANqxsQZoSNda ou 11349922 d2l body type 3 Page 1 of 12 Digestion 4 28 14 11 55 AM Nutrients move to cells where they are Incorporated into the cells Converted to energy which may be used immediately or stored until needed In the last stage of food processing elimination undigested waste pass out of the digestive tract Components of the Human Digestive System Elimination Mouth Oral cavity Tongue Pharynx Salivary Glands Esophagus Stomach Liver Gall Bladder Pancreas Small Intestine Large Intestine Rectum Anus Oral Cavity Food enters the mouth and is reduced in size by teeth and tongue Salivary glands secrete saliva which Lubricates Lubricates Buffers Contains antimicrobial substances Contains amylase to digest starch The main purpose of the action in the mouth is to decrease the size of the food to make it easier to digest in subsequent stages Saliva contains an enzyme called lysozyme that has some bactericidal action Saliva also lubricates the food to make it easier to swallow There is a little of the enzyme amylase produced in the mouth This will start digesting starch and converting into sugar You can detect the action of this enzyme by placing a thin slice of cooked potato or bread on your tongue and https carmen osu edu content 1144 FDSCTE 2200 fdscte 2200 su2 ssionVal 8KMB32UCTXaqzANqxsQZoSNda ou 11349922 d2l body type 3 Page 2 of 12 Digestion 4 28 14 11 55 AM holding it there for a couple of minutes In time you will start to detect sweetness This results from starch being converted to smaller molecules and eventually into glucose Swallowing Food passes to the pharynx that contains both the trachea and the esophagus Epiglottis prevents food from entering the trachea Food passes through the esophagus into the stomach Food moves through the digestive system by a process known as peristalsis This is a wavelike muscular squeezing that moves food through the esophagus and intestines Stomach https www youtube com watch v 3MerYzqqZP0 Stores and digests food Contains pits leading to Gastric glands with three types of cells Mucous cells produce mucous that lubricates and protects lining Parietal cells secrete hydrochloric acid Chief cells secrete pepsinogen The stomach is a very muscular organ that serves a number of purposes It stores food until it is ready to move into the small intestine Some cells secrete hydrochloric acid This is a strong acid and one of its purposes is to kill bacteria It doesn t kill all of them but bacterial numbers are greatly reduced by the acid This acid also causes proteins to start to unfold This unfolding makes them easier for https carmen osu edu content 1144 FDSCTE 2200 fdscte 2200 su2 ssionVal 8KMB32UCTXaqzANqxsQZoSNda ou 11349922 d2l body type 3 Page 3 of 12 Digestion 4 28 14 11 55 AM digestives enzymes to break them down One such enzyme pepsin is produced from pepsinogen in the presence of acid It is the only digestive enzyme that can work in the high acid environment found in the stomach It works on proteins and makes them easier for subsequent enzymes to digest The muscular action of the stomach also serves to mix food with its secretions and to greatly reduce its size The smaller the food is the easier it will be for subsequent processing to occur Some cells in the stomach secrete mucous This helps to lubricate the food and also protects the lining of the stomach from harm caused by the hydrochloric acid When acid repeatedly penetrates this barrier the damage to the stomach is called a peptic ulcer Small Intestine Receives food from the stomach Receives bile from liver via the Gall bladder Receives enzymes from pancreas Is the site of most digestion of food Is the site of most absorption of food http www youtube com watch v xu5jDCX2cHM The small intestine is where most the chemical changes occur during digestion It is also where most nutrients are absorbed into the blood stream The chemical processing occurs in the rst portion of the small intestine and absorption in the last portion The small intestine in adults is over 20 feet in length and gets the term small because it has a much smaller diameter than the large intestine https carmen osu edu content 1144 FDSCTE 2200 fdscte 2200 su2 ssionVal 8KMB32UCTXaqzANqxsQZoSNda ou 11349922 d2l body type 3 Page 4 of 12 Digestion 4 28 14 11 55 AM The small intestine receives food from the stomach and digestive juices from the gall bladder and pancreas The pancreatic juices contain bicarbonate to neutralize the acid produced in the stomach It also contains a number of enzymes that break the food down into smaller units The cells in the small intestine produce some enzymes that help with the nal breakdown of protein Most of the chemical processing occurs in the rst section known as the duodenum Duodenum First 25 cm of small intestine Receives enzymes from pancreas Neutralizes acid from