Shaunquetta N. Johnson
The Mouth
The teeth tongue and saliva begins the process of digestion before food is swallowed. The teeth break food into smaller pieces. Saliva acts chemically on food to make it easier to swallow. The food is further broken down in the stomach and small intestine. The mouth is the only part of the digestive system that a person can control. The other parts work automatically
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The Teeth
Children have a set of 20 deciduous teeth known as baby or primary teeth. At the age of 6 or 7, these teeth come out and are replaced with adult teeth, or permanent teeth. Adults have a set of 32 teeth in which 16 each are fixed firmly along the upper and lower jaws by long roots. In the front of the mouth are 8 incisors and 4 canines. These sharp front teeth are used for tearing and biting bits off of food. Behind the incisors and canines are 8 premolars which mash up food. Moving toward the back are 12 molars which grind up food
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The Tongue
The tongue is a muscle that moves food around in the mouth. Clumps of food are moved toward the back so the teeth can chew and grind the clumps into smaller pieces. When the tongue pushes the chewed food to the back of the mouth, a lump of chewed food called a bolus is formed. The tongue has the ability to discern different tastes because it is covered with taste buds. The first defense of the digestive system is taste. If food tastes bad, the food is less likely to get swallowed
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Saliva
The salivary glands, located under the tongue and back of the mouth create watery liquid called saliva. When a person smells or tastes food, salivation occurs. Saliva is released through ducts inside the mouth. Saliva is a lubricant that softens food to ease chewing and swallowing. Additionally, saliva contains an enzyme called ptyalin that commences the chemical breakdown of starch in food. A person can produce approximately 2.5 pints (1.2 liters) of saliva a day
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Stomach
The stomach works automatically. It is a strong muscle shaped in the form of a bag or sack. It is controlled by nerves and hormones. The stomach releases chemicals and activates when food is smelled, tasted, and when nerves detect food in the mouth. Food passes into the stomach when it arrives at the bottom of the esophagus. The stomach expands so a meal of food can fit. The stomach's main function is to act as a storage place for food and begin digesting food with chemicals. After eating a meal, food can spend anywhere between 3 to 5 hours in the stomach. Food from the esophagus goes into the cardi which is the top region of the stomach. Then, food gradually moves into the pylorus which is the lower region of the stomach. Strong bands of stomach muscles move to grind food. The stomach walls expand to hold food until it is ready to steadily release into the intestines.
The stomach lining is full of tiny glands that make liquids which are released into the stomach and combine into a fluid called gastric juice. The gastric juice mixes with food when the stomach turns and squeezes. Gastric juice is a mixture of different chemicals. Some of these chemicals form hydrochloric acid, which aids in breaking up food and killing harmful microorganisms (bacteria) that food may contain.
Other chemicals begin to break down chemicals in food. Pepsinogen combines with stomach acid to form the chemical called pepsin. Pepsin breaks up chemicals in food called proteins in order for the body to use them. Gastric juice contains a chemical called intrinsic factor which allows the body to use a vitamin, B12, also found in food. The mixture of partly digested food and gastric juice is called chyme
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Small Intestine
The longest part of the digestive system is the small intestine. It is approximately 22 feet (7 meters) long and 1 inch (2.5 cm) in diameter. In comparison to the wider large intestine, the small intestine gets its name because it is narrower. The small intestine is coiled into the abdomen. Nutrients are absorbed into the blood in the small intestine. More digestion occurs in duodenum.
The duodenum is the first part of the small intestine. It is about 10 inches (25 cm) long. Chyme from the stomach is squirted into the duodenum through the pyloric sphincter valve. Other fluids are added in the duodenum to the chyme. Bile comes from the gall bladder, a small pouch-shaped organ. It breaks-up fat into droplets in order for chemicals to break up fat more easily. Pancreatic juice from the pancreas contains a mix of digestive chemicals that break up proteins, carbohydrates, and fats. Pancreatic juice contains alkalis, substances that neutralize or stop the effect of acid that comes from the stomach.
Nutrients, such as sugars, are made by digestion and absorbed into the blood stream and lymphatic system through the lining of the small intestine. Millions of villi, fingerlike tufts, cover the surface of the lining. This massive surface area aids in the body's ability to absorb large amounts of nutrients faster. The villi swim around stirring the contents of the intestines, which helps the nutrients to be absorbed. Within about 4 to 5 hours, food passes through the small intestine
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Pancreas
The pancreas is important in the digestive process because it produces pancreatic juice which flows into the duodenum and controls the amount of sugar in the blood. The pancreas is a gland that is comparable to the shape of a carrot and is about 6 to 8 inches (15 to 20 cm) long. The wide end of the pancreas is located next to the duodenum.
Pancreatic juice is made by a host of cells called acini. The juice follows through narrow tubes that connect to the pancreatic duct which connects to the alimentary canal in the duodenum. Pancreatic juice is a combination of various digestive chemicals. Trypsin and chymotrypsin break up protein; amylase breaks up starches; and lipase breaks up fat. In addition, pancreatic juice contains alkalis which neutralize stomach acid. The chemicals in the pancreatic juice are very potent. They begin to react when mixed with the alkalis; otherwise the chemicals would digest the pancreas itself
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Liver
Although the liver is not a part of the alimentary canal, it is another important part of the digestive system. The liver is a chemical-processing system. It takes chemicals that were absorbed in the small intestine and turns them into chemicals that the body uses and stores for future use. The liver makes bile and cleans the blood.
The liver is shaped almost like a triangle. It is about 8 inches long and weighs approximately 3 pounds. There are 4 parts to the liver called lobes. The liver contains thousands of lobules. Lobules are comprised of hundreds of liver cells located around a central blood vessel that carries blood to and from cells. Blood streams into the liver through two blood vessels, the portal vein and the hepatic artery. The portal vein brings nutrient-rich blood from the intestines. The hepatic artery brings oxygen-rich blood from the heart. These blood vessels divide into thousands of tiny blood vessels that pump blood into spaces in the liver called sinusoids. Food and oxygen are taken from the blood flowing through the sinusoids to fuel liver cells. The hepatic vein that carriers blood away from the liver is formed from blood vessels joining together from the lobules. Approximately 3 pints of blood is processed by the liver every minute.
Food molecules that came from the intestines are processed by liver cells. Liver cells break down molecules into simpler ones and create nutrients from them. Some of the nutrients are stored in the liver, while others are placed in the blood to be streamed to other parts of the body. The liver is responsible for turning glucose into glycogen and storing it. When the body is ready, glycogen can turn back into glucose and used for energy
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Large Intestine
The large intestine is the last part of the alimentary canal. The large intestine is shorter but wider than the small intestine. The large intestine absorbs water and small amounts of minerals from the watery material that enters from the small intestine. The water and minerals pass into the blood and leaves a firm material called feces that passes out of the body.
The large intestine is made up of the cecum, the colon, and the rectum. The short and wide cecum joins the small and large intestine together. The colon is comprised of four sections, the ascending colon, transverse colon, descending colon, and sigmoid colon. The large intestine receives a slushy mixture of water and undigested material through a valve that connects to the small intestine. The small intestine has had time to remove most nutrients from food and to keep some useful minerals. These minerals pass into the blood through the walls of the large intestine. Most of the water in the mixture is absorbed. Approximately 4 pints enters the large intestine daily and 3.6 pints of it are absorbed.
The material left over after the minerals and water have been removed is called feces. Two-thirds of fecal matter is made up of water. The other one-third is solid material, made of mostly undigested plant fiber, bacteria, bile, mucus, and old cells from the lining of the alimentary canal. Feces are stored in the rectum and released through the anus
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