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A Trip Through The Digestive System

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by

Amir Salehnia

on 1 March 2011

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Transcript of A Trip Through The Digestive System

Destination: Human Digestive System Digestion takes place within a tube called the digestive tract, which begins with the mouth and ends with the anus. The Main functions of the Digestive system are Ingesting food, and to digest it to nutrients that can cross plasma membranes, absorb nutrients and eliminate the digestible remains. What is the Digestive system? Mechanical Digestion Starts: The Mouth (Oral Cavity) What is the Digestive system? The esophagus The teeth cut, tear, crush
and grind the food..
Incisors: Cutting and Biting
Canines: Tearing
Premolars: Grinding
Molars: Crushing Salivary glands have ducts that open on on the inner surface of the cheek at the location of the second molar. Another pair of salivary glands lies beneath the tongue, however there is still another pair of salivary glands that lie beneathe the floor of the oral cavity. By Amir Salehnia The Pancreas Why does Saliva Plays an Important role in the Digestive system? First of all, Salivary amylase(also called ptyalin) helps speed the chemical process of digesting starch(begins the break down of cooked starch molecules, and produces maltose).
Second, water moistens the food, which although seemingly useless, it aides in the movement through the esophagus when swallowing.
Third, a slippery Lubricant, known as "Mucin" also aides in the movement of food.
Last, but not least bicarbonate ions buffer the pH of the oral cavity to ensure it remains near neutral pH(7), even when acidic food is being consumed. The Tongue
Sensory receptors called taste buds occur primarily on the tongue, and when these are activated by the presence of food, nerve impulses travel by way of cranial nerves to the brain. The tongue itself is composed of skeletal muslce whose contraction changes the shape of the tongue. The tounge is very important as it pushes food to the pharynx via the form of a bolus.. The Pharynx is the region that receives food from the mouth and air from the nasal cavaties. The food passage and the air passage cross in the pharynx because the trachea(windpipe) is ventral to(in front of) the esophagus. "Swallowing", a process that occurs in the pharynx, is a reflex action that is performed without any conscious thought. The large Intestine which includes the cecum, the colon, the rectum and the anal canal, is larger in diameter than the small intestine (6.5 cm to 2.5 cm), but smaller in length. Its main sections form a rectangular shape, surrounding the small intestine. The large intestine absorbs water, salts, and some vitamins. It also stores indigestible materials until they are eliminated at the anus. Step By Step Guide: Chemical Digestion Starts: The three Pairs of Slivary Glands that send Saliva by way of ducts to the mouth.... When the Bolus is swallowed, the soft palate (Uvula) is forced upwards, sealing off the nasal passageway. During the procoss of "swallowing", food normally enters the esophagus because the air passages are blocked. This is because when nerves in the pharynx sense contact with the bolus, it stimulates glottis to close and and the movement of the bolus down the throat pushes the epiglottis over the glottis to protect it further from the entry of food or H20. The Pharynx Unfortunately, food can sometimes go "The wrong way". The wrong way may be either into the nasal cavities or into the trachea, usually coughing will most likely force the food up out of the trachea and into the pharynx again. The esophagus is a muscular tube that passes from the pharynx through the thoracic cavity and diaphgram into the abdominal cavity where it joins the stomach. Although normally collapsed, the esophagus opens and receives the bolus when swallowing occurs. Through a rhythmic contraction called peristalsis, food is pushed along the digestive tract. Sometimes peristalsis begins even when there is no food inside the esophagus, which results in the sensation of a lump in the throat.. The esophagus plays no role in the chemical digestion of food (Food is not changed in anyway by the esophagus), its sole purpose is to conduct the food bolus from the mouth. Sphincters are muscles that encircle tubes and act as valves; tubes close when sphincters contract and, and they open when sphincters relax. The Entrance of the esophagus to the stomach is marked by a constriction, often called a cardiac sphincter, and although the Cardiac sphincter is not as developed as in an actual sphincter, the relaxation/constriction of the cardiac sphincter allows for the bolus to enter the stomach and prevents the acidic contents of the stomach from backing up into the esophagus. The stomach is a thick-walled, J-shaped organ that lies on the left side of the body beneath the diaphragm. The stomach is continuous with the esophagus above and the duodenum of the small intestine below. The stomach stores food and aids in digestion. The wall of the stomach has deep folds, which disappear as the stomach fills to an approximate capacity of one liter. Its Muscular wall churns, mixing the food with gastric juice. The small intestine is the longest section of the digestive tract. Named for its small diameter(Compared to that of the long intestine), the small intestine averages about 7 meters (21 feet in length, compared to that of the large intestine which is 1.5 meters (4.5 feet in length). However after death, the small intestine becomes as long as 6 meters due to relaxation of muscles. Most of the chemical digestion of food and absorption of nutrients occur in the small intestine. With a mass of about 3-4 pounds, the Liver is the LARGEST organ in the human body. The liver lies just below the diaphragm. The Liver has two lobes: the right is SIX times bigger than the left and lies infront of the right kidney. It is composed of many small structures called lobules in which blood and bile flow through in opposite directions. DANGER!!
HCl could potentially penetrate the mucus, and the wall could begin to break down, resulting in what is known as an "Ulcer". First of all, the term "gastric" always refers to the stomach. The columnar epethelial lining of the stomach has millions of gastric pits, which lead into gastric glands. These gastric glands produce GASTRIC JUICE. Gastric juice contains an enzyme called pepsin, which digests protein, plus hydrochloric acid(HCL) and Mucus. Mucus whcich is made by Goblet cells, line the inner walls of the stomach. What is Gastric Juice ? Contrary to popular belief, Hydrochloric acid does not digest food, it breaks down the connective tissue of meat and activates pepsin. However HCl causes the stomach to have a high acidity with a pH of about 2, which is beneficial since it kills most bacteria present in food. When food leaves the stomach, its a thick, soupy liquid called "Chyme". Chyme leaves the stomach and enters the small intestine in squirts by way if of a sphincter that that repeatedly opens and closes... The Pancreas is a small grainy looking organ that sits behind the stomach. It is located deep in the abdominal cavity. It produces chemicals that are vital for not only proper digestion but blood sugar regulation. The pancreas is not limited to being part of either the endocrine or the exocrine system, it is used by both systems. The body's Endocrine systems regulates hormones and other substances throught its direct access to the bloodstream, organs, cells etc. Whereas, the exocrine system works via ducts to digest food in the intestnal tract. Through the "Islets of Langerhans" section of the pancreas, important regulatory hormones such as insulin and glucagons are secreted. However the pancreas plays a completely diffferent role in the exocrine system by producing digestive juices whom break down nutriets that the stomach's acids were effective at metabolizing. These enzymes such as lipase are capabale of digesting fat, trypsin, protein etc. Main Functions of the Stomach 1- Physical digestion of food: When food is present, the stomach churns, mixing food with acidic gastric juice.
2- Partial Chemical digestion of proteins.
3- Kill Bacteria in food(Stomach pH of 2(HCl))
4- Storage of Food. Digestion will be finished within the first 25 cm of the small intestine which is called the duodenum. Ducts from the liver and pancreas join to form usually one duct that enters the duodenum. The other two parts of the small intestine, (jejunum and ileum) function mainly in the absorption of nutrients and water The Small intestine receives bile from the liver and pancreatic juice from the pancreas via this duct.The small intestine has a slightly basic pH because pancreatic juice contains sodium bicarbonate (NaHCO3), which neutralizies chyme. The enzymes in pancreatic juice and enzymes produced by the intestinal wall complete the process of digestion. The Ggallbladder is a small pear-shaped sac that lies under a lobe of the liver. It stores bile and makes it more concentrated by absorbing water from it. It can store 1,000 ml of bile that is produced each day. The Bile exits the the gallbladder by a common bile duct(which opens into the duodenum) The Stomach The Small Intestine: Bile emulsifies fat: Emulsification is the process of breaking down large fat globules into small droplets.

The small intestine has a slightly basic pH because pancreatic juice contains sodium bicarbonate (NaHCO3), which neutralizies chyme.

The enzymes in pancreatic juice and enzymes produced by the intestinal wall complete the process of digestion. Experts believe that the surface area of the small intestine is equivalent to that of a Tennis Court's. The Reason as to why the small intestines surface area is so large is largely due to fingerlike projections called Villi which give the intestinal wall a soft, velvety appearance. each villus contains blood vessels and a small lymphatic vessel called a lacteal(lymphatic system;s vessels acarry a fluid called lymph to the cardiovascular veins.). The Main primary function of the villi, is to slow down movement through the digestive system, so that the small inestine can absorb a greater amount of nutrients. The Liver The liver's functions 1- Regulation of Blood Sugar levels: When the concentration of sugar in blood is high, the liver removes some glucose and stores it as Glycogen( Just in case, the concentration of sugar in the blood was ever to drop)

2- Fat Metabolism: The liver breaks down fatty acids, and builds up new substances from them everday. (I.E Bile, which is neccesary for digestion of fats in the small intestine.

3- Protein metabolism: Since Ammonia(TOXIC) is produced when amino acids are broken down, the liver converts the ammonia into urea, which is a harmless chemical that is excreted in urine.

4- Regulating Vitamins: The liver stores many fat-soluble vitamins, until they are needed.(Vitamin A of Carotene etc.)

5- Regulating Minerals: The liver removes hemoglobin from the broken down red cells, since hemoglobin is vital for transportation of oxygen, so the liver stores the hemoglobin until new red blood cells can be produced.

6- Regulating toxins : Harmful chemicals such as Alcohol, Drugs, and poisons, and surplus hormones are removed from the blood and broken down by enzymes in the liver.
The Gallbladder The Large Intestine: The Next section of the large intestine is the "Colon", which goes up the right side of the body to the level of the body. The colons wall has no Villi or folds, and no enzymes are produced. Absorptive cells remove water from the waste, ( as much as possible, over 90 % is taken back!!) Goblet cells produce mucus for lubrication, helping waste slide easily along the large intestine. Peristaltic waves continually push the liquid waste, additionally the colon generates between 3-12 of these waves each minute, forcing the contents into the rectum. Located below the junction with the small intestine, liquid waste passes through the first section, the cecum, through a sphincter-like structre called the "Ileocecal Valve". This is usually partly closed, allowing liquid through in a slow, steady trickle. The open end of the cecum leads next section, the colon. Attached to the cecum is as small narrow tube called the appendix, that does not play any role in the digestive system, but "MAY" play a role in the immune system. The Rectum opens at the anus, where defeciation ( the expolsion of feces ) occurs. When feces are forced into the rectum by peristalsis, a defeciation wave occurs. The strecthing of the rectal wall initiates nerve impulses to the spinal cord, and shortly thereafter contraction of the rectal muscles and relaxation of anal sphincters occur. The Feces are three quarter water, and one quarter solids. Bacteria, Fiber (indigestible remains) and other indigestible materials are in the solid portion. The Brown color of feces is due to bilirubin and the odor is due to the breakdown products as bacteria work on the nondigested remains.. The End Sources: Print:

Jakab, Cheryl. Our Body. Digestive System ed. North Mankato: Smart Apple Media, 2006. Print


Ballard, Caroll. Body Focus. The Digestive System ed. Chicago: Heinneman Library, 2003. Print.
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