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Understanding the Digestive System Essay.

Understanding the Digestive System Essay.

 

Module 2 Written Assignment 1. What are enzymes? What specifically is the role of an enzyme in digestion? Enzymes are working proteins that facilitate chemical reactions without being changed in the process. Organs of the digestive system excrete digestive juices, which contain enzymes that break the bonds of nutrients that can be absorbed. 2. Trace the path of a cheeseburger and fries through the digestive tract. Indicate each place where mechanical digestion, chemical digestion, and absorption occurs FOR EACH NUTRIENT (carbohydrates, lipids, proteins).Understanding the Digestive System Essay. Be sure to fully explain the role of EACH organ involved (including the pancreas, liver, and gallbladder). In the mouth – food is crushed and chewed by teeth (mechanical…show more content…

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The small intestine also contributes enzymes to complete the digestion process before nutrients are small enough for the cells to absorb (chemical). In the large intestine – The digestion and absorption of proteins, fats and carbohydrates are essentially complete by the time the intestinal contents enter the colon.Understanding the Digestive System Essay. Only water, fiber and some minerals remain. Only certain fibers can be broken down by bacteria (chemical digestion).The colon’s task is mostly to reabsorb water and minerals, leaving a paste of fiber and feces for excretion (mechanical) via rectum and anus. 3. How is the lining of the small intestine protected from acidic chyme entering from the stomach? The pyloric valve of the lower stomach regulates the amount of chyme that exits into the small intestine, allowing only a little at a time to exit. Also, once chyme enters the small intestine, hormonal messengers signal the pancreas to release alkaline pancreatic juice, bicarbonate, to neutralize the stomach acid that has reached the small intestine.Understanding the Digestive System Essay.

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Digestive System The human body uses various kinds of food for energy and growth. To be used, however, food must be changed into a form that can be carried through the bloodstream. The body’s process of extracting useful nutrients from food is called digestion. The digestive system of humans and other higher animals is the group of organs that changes food–carbohydrates, fats, and proteins–into soluble products that can be used by the body. Both mechanical action and chemical action are necessary to change food into products that are usable by the body. Human digestion, or the change that food undergoes in the digestive system, takes place in a long tubelike canal called the alimentary canal, or the digestive tract.Understanding the Digestive System Essay. There is good reason why the passageway used by food to travel through the body is called the alimentary canal. Just as canals are constructed to guide ships through waterways to their destinations, the alimentary canal guides food as it travels through the human body. The whole canal is lined with a mucous membrane. Digestion begins in the mouth. Here the food is cut and chopped by the teeth. The tongue helps mix the food particles with a digestive juice called saliva, which is secreted in the mouth. Saliva moistens the food so it can be swallowed easily. It also changes some starches into simple sugars. It is important to chew food thoroughly to mix it well with saliva. Thorough chewing cuts food into small pieces that are more easily attacked by digestive juices. Food should not be washed down with quantities of liquid to avoid chewing. From the mouth the food is swallowed into a transport tube, named the esophagus, or gullet.Understanding the Digestive System Essay. A flap called the epiglottis closes the windpipe while food is being swallowed. Peristalsis, a wavelike muscular movement of the esophagus walls, forces food down the tube to the stomach. Peristalsis takes place throughout the digestive tract. It is an automatic, or involuntary, action, carried out in response to nerve impulses set up by the contents of the tube. When digestion is working normally, a person is unaware of the movements of the gullet, stomach, and most of the intestine. Swallowing is a voluntary muscular action. At the end of the esophagus there is a muscular valve, or sphincter, through which food enters the stomach. This sphincter muscle keeps food in the stomach from being forced back into the esophagus.Understanding the Digestive System Essay. Peristalsis in the stomach churns the food and mixes it with mucus and with gastric juices, which contain enzymes and hydrochloric acid. These gastric juices are secreted from millions of small glands in the lining of the upper stomach walls. These glands pour about three quarts of fluid into the stomach daily. Similar glands in the small intestine also secrete enzymes and fluid. Hydrochloric acid secreted by the stomach sets up the sour or acid condition necessary for digestion. Certain remedies for indigestion are advertised as correcting this acid condition. If these remedies actually do get rid of the stomach acids it is not wise to take them. Acid is required for digestion to be properly undertaken in the stomach. The stomach churns the food into a thick liquid, called chyme, before it is passed on by peristalsis into the small intestine. Another strong sphincter muscle further mashes the chyme and has some control over the rate at which it is passed out of the stomach into the duodenum, or upper small intestine.Understanding the Digestive System Essay. The sphincter also prevents the chyme from passing back into the stomach. Little by little, as the digestive process in the stomach is completed, all the chyme is passed through the sphincter into the duodenum. This peristalsis is regulated by the autonomic nervous system. This process does not take place all at once. It continues over a period of time. From the time a meal is eaten, it takes from 30 to 40 hours for food to travel the length of the alimentary canal. Different kinds of food, depending on their components, are held in the stomach for varying lengths of time. Starch and sugar are held in the stomach for a short time only, usually no more than one to two hours.Understanding the Digestive System Essay. Protein foods are there from three to five hours. Fat foods may remain in the stomach even longer than proteins. This is why eating a heavy dinner of meat, potatoes, and gravy satisfies our hunger longer than one made up entirely of sweets or greens. Furthermore, food made up of easily digested carbohydrates passes quickly from the stomach and into the small intestine. The stomach, though important, is not considered by physicians to be essential to life. People who have had their stomachs completely or partially removed are frequently able to live by taking special foods in small quantities many times a day.Understanding the Digestive System Essay. The small intestine is then able to perform all necessary digestion. The small intestine, which is from 22 to 25 feet (6.7 to 7.6 meters) long, is the longest part of the digestive tract of humans. The main parts of the small intestine are the duodenum, jejunum, and ileum. Food remains in the small intestine for several hours. Two large glands, the liver and the pancreas, connect with the small intestine by ducts, or tubes. Through these ducts the liver and pancreas pour secretions which further aid digestion. Fluid from the pancreas is called pancreatic juice. Fluid from the liver is called bile. The pancreas is one of the most important glands in the body. It secretes up to a pint of pancreatic juice a day. This digestive fluid contains enzymes which help digest carbohydrates, proteins, and fats. One of these enzymes is trypsin, which helps digest protein foods. Other enzymes are amylase and maltase, which help digest carbohydrates. The pancreatic enzyme lipase, along with bile from the liver, helps digest fat. Bile, however, does not contain important enzymes. Bile is stored in the gall bladder, a small hollow organ located just under the liver. We could not live without the liver but the gall bladder can be removed by surgery without serious effect. The liver stores glycogen for later use by the body and furnishes clotting material for the blood. When fully digested, proteins are changed into amino acids; fat foods are changed into fatty acids; and carbohydrates are changed into sugars. These soluble food products are dissolved and then absorbed into the bloodstream through the walls of the small intestine. While food is in the small intestine it is further diluted by fluid secreted by the intestinal glands. In an adult the small intestine is about 21 feet long. By the time the diluted food products have traveled its length, most of their nutrients have been absorbed into the bloodstream.Understanding the Digestive System Essay.

The nutrition in human beings (or man) takes place through human digestive system. The human digestive system consists of the alimentary canal and its associated glands. The various organs of the human digestive system in sequence are: Mouth, Oesophagus (or Food pipe), Stomach, Small intestine and Large intestine.Understanding the Digestive System Essay.

The glands which are associated with the human digestive system and form a part of the human digestive system are: Salivary glands, Liver and Pancreas. The human alimentary canal which runs from mouth to anus is about 9 meters long tube. The ducts of various glands open into the alimentary canal and pour the secretions of the digestive juices into the alimentary canal. We will now describe the various steps of nutrition in human beings (or man).Understanding the Digestive System Essay.

1. Ingestion :

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The human beings have a special organ for the ingestion of food. It is called mouth. So, in human beings, food is ingested through the mouth. The food is put into the mouth with the help of hands.Understanding the Digestive System Essay.

2. Digestion :

In human beings, the digestion of food begins in the mouth itself. In fact, the digestion of food starts as soon as we put food in our mouth. This happens as follows: The mouth cavity (or buccal cavity) contains teeth, tongue, and salivary glands. The teeth cut the food into small pieces, chew and grind it. So, the teeth help in physical digestion. The salivary glands in our mouth produce saliva.Understanding the Digestive System Essay.

Our tongue helps in mixing this saliva with food. Saliva is a watery liquid so it wets the food in our mouth. The wetted food can be swallowed more easily. Many times we have observed that when we see or eat a food which we really like, our mouth ‘waters’. This watering of mouth is due to the production of saliva by the salivary glands in the mouth.

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The salivary glands help in chemical digestion by secreting enzymes. The human saliva contains an enzyme called salivary amylase which digests the starch present in food into sugar. Thus, the digestion of starch (carbohydrate) begins in the mouth itself. Since the food remains in the mouth only for a short time, so the digestion of food remains incomplete in mouth.Understanding the Digestive System Essay.

The slightly digested food in the mouth is swallowed by the tongue and goes down the food pipe called oesophagus. The oesophagus carries food to the stomach. This happens as follows: The walls of food pipe have muscles which can contract and expand alternately. When the slightly digested food enters the food pipe, the walls of food pipe start contraction and expansion movements.Understanding the Digestive System Essay.

The contraction and expansion movement of the walls of food pipe is called peristaltic movement. This peristaltic movement of food pipe (or oesophagus) pushes the slightly digested food into the stomach (In fact, the peristaltic movement moves the food in all the digestive organs throughout the alimentary canal).Understanding the Digestive System Essay.

The stomach is a J-shaped organ present on the left side of the abdomen. The food is further digested in the stomach.

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The food is churned in the stomach for about three hours. During this time, the food breaks down into still smaller pieces and forms a semi-solid paste. The stomach wall contains three tubular glands in its walls. The glands present in the walls of the stomach secrete gastric juice.

The gastric juice contains three substances: hydrochloric acid, the enzyme pepsin and mucus. Due to the presence of hydrochloric acid, the gastric juice is acidic in nature. In the acidic medium, the enzyme pepsin begins the digestion of proteins present in food to form smaller molecules.Understanding the Digestive System Essay.

Thus, the protein digestion begins in the stomach. Please note that the protein digesting enzyme pepsin is active only in the presence of an acid. So, the function of hydrochloric acid in the stomach is to make the medium of gastric juice acidic so that the enzyme pepsin can digest the proteins properly.Understanding the Digestive System Essay.

Another function of hydrochloric acid is that it kills any bacteria which may enter the stomach with food. The mucus helps to protect the stomach wall from its own secretions of hydrochloric acid.

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If mucus is not secreted, hydrochloric acid will cause the erosion of inner lining of stomach leading to the formation of ulcers in the stomach. The partially digested food then goes from the stomach into the small intestine. The exit of food from stomach is regulated by a ‘sphincter muscle’ which releases it in small amounts into the small intestine.Understanding the Digestive System Essay.

From the stomach, the partially digested food enters the small intestine. The small intestine is the largest part of the alimentary canal. It is about 6.5 metres long in an adult man. Though the small intestine is very long, it is called small intestine because it is very narrow.Understanding the Digestive System Essay.

The small intestine is arranged in the form of a coil in our belly. Please note that the length of the small intestine differs in various animals depending on the type of food they eat. For example, cellulose is a carbohydrate food which is digested with difficulty. So, the herbivorous animals like cow which eat grass need a longer ‘small intestine’ to allow the cellulose present in grass to be digested completely. On the other hand, meat is a food which is easier to digest. So, the carnivorous animals like tigers which eat meat have a shorter ‘small intestine’.Understanding the Digestive System Essay.

The small intestine in human beings is the site of complete digestion of food (like carbohydrates, proteins and fats). This happens as follows:

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(a) The small intestine receives the secretions of two glands: liver and pancreas. Liver secretes bile. Bile is a greenish yellow liquid made in the liver which is normally stored in the gall bladder. Bile is alkaline, and contains salts which help to emulsify or break the fats (or lipids) present in the food. Thus, bile performs two functions:Understanding the Digestive System Essay.

(i) makes the acidic food coming from the stomach alkaline so that pancreatic enzymes can act on it, and (ii) bile salts break the fats present in the food into small globules making it easy for the enzymes to act and digest them.Understanding the Digestive System Essay.

Pancreas is a large gland which lies parallel to and beneath the stomach. Pancreas secretes pancreatic juice which contains digestive enzymes like pancreatic amylase, trypsin and lipase. The enzyme amylase breaks down the starch, the enzyme trypsin digests the proteins and the enzyme lipase breaks down the emulsified fats.

(b) The walls of small intestine contain glands which secrete intestinal juice. The intestinal juice contains a number of enzymes which complete the digestion of complex carbohydrates into glucose, proteins into amino acids and fats into fatty acids and glycerol. Glucose, amino acids, fatty acids and glycerol are small, water soluble molecules. In this way, the process of digestion converts the large and insoluble food molecules into small, water soluble molecules. The chemical digestion of food is brought about by biological catalysts called enzymes.Understanding the Digestive System Essay.

3. Absorption :

After digestion, the molecules of food become so small that they can pass through the walls of the small intestine (which contain blood capillaries) and go into our blood. This is called absorption. The small intestine is the main region for the absorption of digested food. In fact, the small intestine is especially adapted for absorbing the digested food.Understanding the Digestive System Essay.

The inner surface of small intestine has millions of tiny, finger­like projections called villi. The presence of villi gives the inner walls of the small intestine a very large surface area. And the large surface area of small intestine helps in the rapid absorption of digested food. The digested food which is absorbed through the walls of the small intestine goes into our blood.Understanding the Digestive System Essay.

4. Assimilation:

The blood carries digested and dissolved food to all the parts of the body where it becomes assimilated as part of the cells. This assimilated food is used by the body cells for obtaining energy as well as for growth and repair of the body.Understanding the Digestive System Essay.

The energy is released by the oxidation of assimilated food in the cells during respiration. The digested food which is not used by our body immediately is stored in the liver in the form of a carbohydrate called ‘glycogen’. This stored glycogen can be used as a source of energy by the body as and when required.Understanding the Digestive System Essay.

5. Egestion:

A part of the food which we eat cannot be digested by our body. This undigested food cannot be absorbed in the small intestine. So, the undigested food passes from the small intestine into a wider tube called large intestine. (It is called large intestine because it is a quite wide tube).Understanding the Digestive System Essay.

The walls of large intestine absorb most of the water from the undigested food (with the help of villi). Due to this, the undigested part of food becomes almost solid. The last part of the large intestine called ‘rectum’ stores this undigested food for some time. And when we go to the toilet, then this undigested food is passed out (or egested) from our body through anus as faeces or ‘stool’. The act of expelling the faeces is called egestion or defecation. The exit of faeces is controlled by the anal sphincter.Understanding the Digestive System Essay.

Let us solve one problem now.

Sample Problem:

1 ml of very dilute starch solution (1% starch solution) is taken in a test-tube and 1 ml of saliva is added to it. After keeping this mixture for half an hour, a few drops of dilute iodine solution are added to the test-tube. There is no change in colour on adding iodine solution. What does this tell you about the action of saliva on starch?Understanding the Digestive System Essay.

Answer:

When a mixture of dilute starch solution and saliva is kept in a test-tube for half an hour, it does not produce a blue-black colour with iodine solution showing that no starch is left in the test-tube. This tells us that the action of saliva has broken down starch into some other substance which does not give any colour with iodine solution. Actually, saliva contains an enzyme ‘amylase’ which converts starch into a sugar.Understanding the Digestive System Essay.

Dental Caries :

The hard, outer covering of a tooth is called enamel. Tooth enamel is the hardest material in our body. It is harder than even bones. The part of tooth below enamel is called dentine. Dentine is similar to bone. Inside the dentine is pulp cavity. The pulp cavity contains nerves and blood vessels. The formation of small cavities (or holes) in the teeth due to the action of acid-forming bacteria and improper dental care is called dental caries. This happens as follows.Understanding the Digestive System Essay.

When we eat sugary food, the bacteria in our mouth act on sugar to produce acids. These acids first dissolve the calcium salts from the tooth enamel and then from dentine forming small cavities (or holes) in the tooth over a period of time. The formation of cavities reduces the distance between the outside of the tooth and the pulp cavity which contains nerves and blood vessels.Understanding the Digestive System Essay.

The acids produced by bacteria irritate the nerve endings inside the tooth and cause toothache. If the cavities caused by dental decay are not cleaned and filled by a dentist, the bacteria will get into the pulp cavity of tooth causing inflammation and infection leading to severe pain.Understanding the Digestive System Essay.

If the teeth are not cleaned regularly, they become covered with a sticky, yellowish layer of food particles and bacteria cells called ‘dental plaque’. Since plaque covers the teeth forming a layer over them, the alkaline saliva cannot reach the tooth surface to neutralise the acid formed by bacteria and hence tooth decay sets in. Brushing the teeth regularly, after eating food, removes the plaque before bacteria produces acids. This will prevent dental caries or tooth decay. Before we go further and discuss respiration.Understanding the Digestive System Essay.

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