The Human Digestive System

Intro To The Human Digestive System http://www.online-health-source.info/Digestive-System/Intro-To-Th e-Human-Digestive-System/ All animals, fungi and humans are heterotrophs. A heterotroph is an organism that obtains their nutrition by breaking down organic molecules in foods. The digestive system varies depending on the type of organisms; Fungi have the simplest system and humans having the most elaborate. Like the digestive systems in all organisms, the digestive system of the human is vital for survival. Most of the organs in the human body play a roll in the digestion of nutrients. A nutrient basically is any element or compound essential to maintain life and health. Nutrients can be split up into 2 parts; Essential nutrients and Non-essential nutrients. Essential nutrients include vitamins, minerals, amino acids, fatty acids and some carbohydrates as a source of energy. Non-essential nutrients are nutrients which the body has the ability to synthesis from other compounds, as well as, from food sources. Macro nutrients are nutrients that the body needs to acquire daily in large amounts to sustain good health, and micro nutrients are nutrients the body needs very little of and are often stored in the body; both are vital. These nutrients are found in the food we eat, this is where the body must break down and digest the food and "extract" the nutrients from it. Believe it or not, gravity helps the body digest food. Think of the digestive system as an organic assembly line that starts at the mouths and ends at the anus and urethra. There is anywhere from 10 main parts to 100's of parts of the digestive system, depending on how detailed it needs to be explained. The digestive system is truly a marvelous attribute we have and should not be taken for granted, or be neglected. This is why a good general knowledge of the digestive system is important, not only for self/health awareness, healthy living and BIO class but because it is indeed, truly fascinating. The Human Digestive System Part 1 http://www.online-health-source.info/Digestive-System/The-Human-D igestive-System-Part-1/ It all starts in the brain. The brain sends signals to the organs involved in digesting, to the muscles, mouth, glands and every thing that is living in the body. It produces hormones that make us hungry and do an assortment of other tasks that aid the digestive system. The hypothalamus (part of the brain) has two centers that control hunger. One is the appetite center, the other the satiety center. The body produces 3 main hormones that control digestion. The hormones that control digestion are gastrin, secretin, and cholecystokinin (CCK). Gastrin causes increased stomach acid secretion and mobility of the digestive tract to move food. It is also necessary for the normal growth of the lining of the stomach, small intestine, and colon. Secretin causes the pancreas to send out a digestive juice that is rich in bicarbonate. It stimulates the stomach to produce pepsin, an enzyme that digests protein, and it also stimulates the liver to produce bile. CCK causes the pancreas to grow and to produce the enzymes of pancreatic juice, and it causes the gallbladder to empty. Two others that control appetite are; Ghrelin which is produced in the stomach and upper intestine in the absence of food in the digestive system and stimulates appetite and Peptide YY which is produced in the GI tract in response to a meal in the system and inhibits appetite. They both help the brain regulate the intake of food for energy. The Mouth: The moment you take a bite of that apple or pull that tasty piece of chicken off of your fork with your teeth, into your mouth, the digestive system kicks in. As the mouth chews the body starts signaling the rest of the digestive system, preparing it for the work ahead. The salivary glands secrete Salivary Amylase and Ptyalin enzymes begin the chemical breakdown of starch into glucose. IgA antibodies are also found in saliva, also found present is lysozyme; an anti bacterial enzyme. Bicarbonate ions in saliva neutralize the acids in foods. Mucus moistens the food and lubricates the esophagus and then we swallow. Esophagus: Not much happens in the Esophagus. Its major role in digestion is directing the food into our stomachs and not our lungs, and keeping stomach content from spilling upwards into it ("heart burn" -> "esophagus burn"). The Esophagus has a sphincter that closes the stomach off from itself. Without it standing on our heads would be a messy and painful maneuver. It also has a small flap that directs water and food down into our stomach and air into our lungs. Carbohydrate digestion, begun by salivary amylase in the mouth, continues in the bolus (word for chewed up food) as it passes thru the esophagus into the stomach. The food reaches the stomach and that's where the body really starts to work. The Human Digestive System Part 2 http://www.online-health-source.info/Digestive-System/The-Human-D igestive-System-Part-2/ First, the stomach must store the swallowed food and liquid. This requires the muscle of the upper part of the stomach to relax and accept large volumes of swallowed material. The stomach has a capacity of 1 liter, from an empty capacity of 50-100 milliliters, but the stomach can distend to hold 2 liters or more. With most people, the stomach mucosa (lining) is able to resist the juices in the stomach, although food and other tissues of the body cannot. The stomach starts to churn the food by muscular layers to form chyme. Epithelial cells line inner surface of the stomach, and secrete about 2 liters of gastric juices per day. Gastric juice contains hydrochloric acid, pepsinogen, and mucus. Hydrochloric acid (HCl) lowers pH of the stomach so that pepsin can is activated and also gives the stomach the right acidity to inhibit further carbohydrate breakdown. The enzyme pepsin splits off fragments of peptides from protein molecules, and begin the break down of protein. Chyme, the mix of acid and food in the stomach, then leaves the stomach and enters the small intestine. Liver: Duodenum: Gallbladder: Pancreas: These 4 organs do various tasks involved with digestion, the main one being the production and secretion of enzymes needed to break down Chyme. Bile, a watery greenish fluid that is produced by the liver and secreted via the hepatic duct and cystic duct to the gall bladder for storage. At mealtime, it is squeezed out of the gallbladder into the Duodenum via the bile duct. The Duodenum(upper third of small intestine) releases Bile, controlled by pyloric sphincter, into the small intestine as food enters it. Bile contains cholesterol, phospholipids, bilirubin, bile pigments, and a mix of salts. Bile lowers pH of the chyme, Bile salts and phospholipids emulsify fats, facilitating their breakdown into progressively smaller fat globules until they can be acted upon by lipases (enzyme secreted by the small intestine). After the fat is dissolved, it is digested by enzymes from the pancreas and the lining of the intestine. The pancreas secretes digestive enzymes and stomach acid-neutralizing bicarbonate. Proteases (enzymes secreted from the pancreas) continue the breakdown of protein into small peptide fragments and some amino acids. Small Intestines: As the food is digested in the small intestine and dissolved into the juices from the pancreas, liver, and intestine, the contents of the intestine are mixed and pushed forward. Digestion of carbohydrates, proteins, and fats continues in the small intestine. Starch and glycogen are broken down into maltose. Maltose, sucrose, and lactose are the main carbohydrates present in the small intestine; they are absorbed by the microvilli. Jejunum(8 feet)(second third of the small intestine) Final digestion of proteins and carbohydrates must occur, and fats have not yet been digested. Starch is broken down into two-glucose units(maltose). Ileum(13 feet)(lower third) - Fats are completely digested, digested fats are not very soluble. Bile salts surround fats to form micelles that can pass into the epithelial cells. The bile salts return to the lumen to repeat the process. Fat digestion is usually completed by the time the food reaches the ileum of the small intestine. Bile salts are in turn absorbed in the ileum and are recycled by the liver and gall bladder. Fats pass from the epithelial cells to the small lymph vessel that also runs through the villus. The small intestine drains fat and other nutrient rich lymph into it via the hepatic portal system. Villi (intestinal folds) have cells that produce intestinal enzymes which complete the digestion of peptides and sugars and push the remaining contents into the Caecum. The Human Digestive System Part 3 http://www.online-health-source.info/Digestive-System/The-Human-D igestive-System-Part-3/ Large intestines: Caecum Ascending Colon Transverse Colon Descending Colon Sighnoid Colon The first part of the large intestine is the caecum. It is a repository for bacteria and other organisms able to digest cellulose. Enzyme lactase produced by the intestinal walls helps to break down lactose. Secretions in the large intestine are an alkaline mucus that protects epithelial tissues and neutralizes acids produced by bacterial metabolism. Water, salts, and vitamins are absorbed, the remaining contents in the lumen form feces (mostly cellulose, bacteria, bilirubin). Bacteria in the large intestine, such as E. coli, produce vitamins (including vitamin K) that are absorbed. where they remain, usually for a day or two, until the feces are expelled by a bowel movement. Anus has voluntary and involuntary sphincter and ability to distinguish whether contents are gas or solid. Urinary system: The urinary system is a whole other system in itself, but is a part of the digestion process. Liquids are absorbed in the intestines and sent thru the blood stream and empty off into the beginning of the urinary system. But that's a whole other journey. Conclusion: In conclusion, even though this is only a brief explanation of the basics of the digestive system, you can see how incredibly complex it is. The true miracle is how every part works in perfect harmony with one each other, "a well oiled machine" if you will. The total time it takes for a meal to take the entire journey depends on what was eaten. The time it takes to fully digest a meal is anywhere from 2 hours to over 24 hours. High fat diets make this time longer. It's important to take care of your digestive system. Neglect can lead to digestive system diseases, mal-nutrition and poor a quality of life.