The Digestive SystemThe Digestive System

By: Aubrey By: Aubrey

BibliographyBibliography

http://celiacdisease.about.comhttp://celiacdisease.about.comhttp://www.biology-online.orghttp://www.nlm.nih.govhttp://www.britannica.com

http://en.wikipedia.org

http://www.buzzle.com

http://mechanicaldigestion.org

http://www.livestrong.com

http://www.enchantedlearning.com

http://www.webmd.com/

MucusMucus

Mucus is something everyone has, Mucus is something everyone has, and some people wish they had a lot and some people wish they had a lot less of the stringy, gooey stuff.  Sure, less of the stringy, gooey stuff.  Sure, it can be gross to blow globs of snot it can be gross to blow globs of snot into tissue after tissue when you into tissue after tissue when you have a cold or have a cold or sinus infectionsinus infection, but , but mucus actually serves a very mucus actually serves a very important purpose.important purpose.

Chemical DigestionChemical Digestion

Chemical digestion doesn't begin in your Chemical digestion doesn't begin in your stomach, but in your mouth. The moment you stomach, but in your mouth. The moment you see, smell or even think about food, your mouth see, smell or even think about food, your mouth begins to produce extra saliva. Saliva contains an begins to produce extra saliva. Saliva contains an amylase enzyme called ptyalin, which breaks amylase enzyme called ptyalin, which breaks starches down into dextrose and maltose by starches down into dextrose and maltose by adding a water molecule into the starch adding a water molecule into the starch compound. Once food is swallowed, powerful compound. Once food is swallowed, powerful muscles in the esophagus push it downward into muscles in the esophagus push it downward into the stomach in a continuous wave motion.the stomach in a continuous wave motion.

MouthMouth

The digestive process begins in the The digestive process begins in the mouth. Food is partly broken down mouth. Food is partly broken down by the process of chewing and by the by the process of chewing and by the chemical action of salivary enzymes chemical action of salivary enzymes (these enzymes are produced by the (these enzymes are produced by the salivary glands and break down salivary glands and break down starches into smaller molecules). starches into smaller molecules).

EnzymesEnzymes

Enzymes have extremely interesting properties that make Enzymes have extremely interesting properties that make them little chemical-reaction machines. The purpose of an them little chemical-reaction machines. The purpose of an enzyme in a cell is to allow the cell to carry out chemical enzyme in a cell is to allow the cell to carry out chemical reactions very quickly. These reactions allow the cell to reactions very quickly. These reactions allow the cell to build things or take things apart as needed. This is how a build things or take things apart as needed. This is how a cell grows and reproduces. At the most basic level, a cell is cell grows and reproduces. At the most basic level, a cell is really a little bag full of chemical reactions that are made really a little bag full of chemical reactions that are made possible by enzymes!possible by enzymes!

Enzymes are made from Enzymes are made from amino acids, and they are , and they are proteins. When an enzyme is formed, it is made by stringing proteins. When an enzyme is formed, it is made by stringing together between 100 and 1,000 amino acids in a very together between 100 and 1,000 amino acids in a very specific and unique order. The chain of amino acids then specific and unique order. The chain of amino acids then folds into a unique shape. That shape allows the enzyme to folds into a unique shape. That shape allows the enzyme to carry out specific chemical reactions -- an enzyme acts as a carry out specific chemical reactions -- an enzyme acts as a very efficient catalyst for a specific chemical reaction. The very efficient catalyst for a specific chemical reaction. The enzyme speeds that reaction up tremendously.enzyme speeds that reaction up tremendously.

Mechanical DigestionMechanical Digestion

Mechanical digestion happens in the Mechanical digestion happens in the mouth with the help of the saliva, teeth mouth with the help of the saliva, teeth and tongue. It is the actual break down of and tongue. It is the actual break down of food into smaller bits. This makes food food into smaller bits. This makes food easier to digest. The chemical content of easier to digest. The chemical content of the food is extracted during the process.  the food is extracted during the process.  This is largely carried out by by digestive This is largely carried out by by digestive enzymes which are enzymes that break enzymes which are enzymes that break down polymeric macromolecules into their down polymeric macromolecules into their smaller parts, so that they can be smaller parts, so that they can be absorbed by the body.absorbed by the body.

  

Salivary AmylaseSalivary Amylase

Amylase is an enzyme found in human saliva which is Amylase is an enzyme found in human saliva which is

responsible for the breaking down of starch into sugar. The responsible for the breaking down of starch into sugar. The process of digestion begins with the chewing of food, in the process of digestion begins with the chewing of food, in the presence of salivary amylase in the mouth, to convert the presence of salivary amylase in the mouth, to convert the starch in food to sugar. Foods that are high in starch, like starch in food to sugar. Foods that are high in starch, like potatoes or bread, will taste slightly sweet when chewed - potatoes or bread, will taste slightly sweet when chewed - this is because of the action of amylase. The enzyme this is because of the action of amylase. The enzyme amylase is also secreted by the pancreas, where it is called amylase is also secreted by the pancreas, where it is called pancreatic amylase; its presence in the gastrointestinal pancreatic amylase; its presence in the gastrointestinal tract aids in the breakdown of food molecules into energy tract aids in the breakdown of food molecules into energy for the body to store and use. The diagram of the digestive for the body to store and use. The diagram of the digestive system will clarify the sequence of digestion and also help system will clarify the sequence of digestion and also help in the identification of the organs of the digestive system.in the identification of the organs of the digestive system.

The EsophagusThe Esophagus

The esophagus is a muscular tube The esophagus is a muscular tube connecting the throat (pharynx) with the connecting the throat (pharynx) with the stomach. The esophagus is about 8 inches stomach. The esophagus is about 8 inches long, and is lined by moist pink tissue called long, and is lined by moist pink tissue called mucosa. The esophagus runs behind the mucosa. The esophagus runs behind the windpipe (trachea) and heart, and in front of windpipe (trachea) and heart, and in front of the spine. Just before entering the stomach, the spine. Just before entering the stomach, the esophagus passes through the the esophagus passes through the diaphragm.diaphragm.

The Stomach The Stomach

The stomach is a muscular organ located on the left The stomach is a muscular organ located on the left side of the upper abdomen. The stomach receives side of the upper abdomen. The stomach receives food from the esophagus. As food reaches the end food from the esophagus. As food reaches the end of the esophagus, it enters the stomach through a of the esophagus, it enters the stomach through a muscular valve called the lower esophageal muscular valve called the lower esophageal sphincter.sphincter.

The stomach secretes acid and enzymes that digest The stomach secretes acid and enzymes that digest food. Ridges of muscle tissue called rugae line the food. Ridges of muscle tissue called rugae line the stomach. The stomach muscles contract stomach. The stomach muscles contract periodically, churning food to enhance digestion. periodically, churning food to enhance digestion. The pyloric sphincter is a muscular valve that opens The pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small to allow food to pass from the stomach to the small intestine.intestine.

Gastric JuicesGastric Juices

The gastric juice is made up of The gastric juice is made up of hydrochloric acidhydrochloric acid, , pepsinogenpepsinogen and other and other digestive enzymesdigestive enzymes, , intrinsic factorintrinsic factor, , gastringastrin, , mucusmucus, and , and bicarbonatesbicarbonates. It has a pH . It has a pH ranging from 1 to 2. Its low pH is essential ranging from 1 to 2. Its low pH is essential in activating many in activating many digestive enzymesdigestive enzymes and and in destroying various in destroying various pathogenspathogens. The gastric . The gastric juice also contains juice also contains bicarbonatesbicarbonates to to neutralize the neutralize the acidacid and thereby regulate the and thereby regulate the pHpH level in the level in the stomachstomach. .

ChymeChyme

chyme, a thick semifluid mass of partially digested , a thick semifluid mass of partially digested food and digestive secretions that is formed in the food and digestive secretions that is formed in the stomachstomach and and intestineintestine during digestion. In the during digestion. In the stomach, digestive juices are formed by the gastric stomach, digestive juices are formed by the gastric glands; these secretions include the enzyme pepsin, glands; these secretions include the enzyme pepsin, which breaks down proteins, and hydrochloric acid. which breaks down proteins, and hydrochloric acid. Once food is in the small intestine, it stimulates the Once food is in the small intestine, it stimulates the pancreaspancreas to release fluid containing a high to release fluid containing a high concentration of bicarbonate. This fluid neutralizes concentration of bicarbonate. This fluid neutralizes the highly acidic gastric juice, which would otherwise the highly acidic gastric juice, which would otherwise damage the membrane lining of the intestine, damage the membrane lining of the intestine, resulting in a duodenal resulting in a duodenal ulcerulcer. Other secretions from . Other secretions from the pancreas, gallbladder, the pancreas, gallbladder, liverliver, and glands in the , and glands in the intestinal wall add to the total volume of chyme.intestinal wall add to the total volume of chyme.

VilliVilli

Microscopic finger-like projections Microscopic finger-like projections that line the inner wall of the small that line the inner wall of the small intestine. (Singular: villus.) After food intestine. (Singular: villus.) After food passes from the stomach into the passes from the stomach into the small intestine, nutrients in the food small intestine, nutrients in the food are absorbed into the body through are absorbed into the body through the villi. Every person has millions of the villi. Every person has millions of villi in his intestines. villi in his intestines.

Small IntestineSmall Intestine

The small intestine consists of three The small intestine consists of three sections. The first portion, called the sections. The first portion, called the duodenum, connects to the stomach. duodenum, connects to the stomach. The middle portion is the jejunum. The middle portion is the jejunum. The final section, called the ileum, The final section, called the ileum, attaches to the first portion of the attaches to the first portion of the large intestine large intestine

AppendixAppendix

The appendix sits at the junction of the small The appendix sits at the junction of the small intestine and large intestine. It’s a thin tube about intestine and large intestine. It’s a thin tube about four inches long. Normally, the appendix sits in four inches long. Normally, the appendix sits in the lower right abdomen.the lower right abdomen.

The function of the appendix is unknown. One The function of the appendix is unknown. One theory is that the appendix acts as a storehouse theory is that the appendix acts as a storehouse for good bacteria, “rebooting” the digestive for good bacteria, “rebooting” the digestive system after diarrheal illnesses. Other experts system after diarrheal illnesses. Other experts believe the appendix is just a useless remnant believe the appendix is just a useless remnant from our evolutionary past. Surgical removal of from our evolutionary past. Surgical removal of the appendix causes no observable health the appendix causes no observable health problems.problems.

DuodenumDuodenum

The duodenum is the first part of the small The duodenum is the first part of the small intestine. It is located between the intestine. It is located between the stomach and the middle part of the small stomach and the middle part of the small intestine, or jejunum.intestine, or jejunum.

After foods mix with After foods mix with stomach acidstomach acid, they , they move into the duodenum, where they mix move into the duodenum, where they mix with with bilebile from the gallbladder and from the gallbladder and digestive juices from the pancreas.digestive juices from the pancreas.

Absorption of vitamins, minerals, and Absorption of vitamins, minerals, and other nutrients begins in the duodenum.other nutrients begins in the duodenum.

PancreasPancreas

The pancreas is about 6 inches long and sits The pancreas is about 6 inches long and sits across the back of the abdomen, behind the across the back of the abdomen, behind the stomach. The head of the pancreas is on the stomach. The head of the pancreas is on the right side of the abdomen and is connected right side of the abdomen and is connected to the duodenum (the first section of the to the duodenum (the first section of the small intestine) through a small tube called small intestine) through a small tube called the pancreatic duct. The narrow end of the the pancreatic duct. The narrow end of the pancreas, called the tail, extends to the left pancreas, called the tail, extends to the left side of the body side of the body

LiverLiver

The liver is a large, meaty organ that sits on the right side The liver is a large, meaty organ that sits on the right side of the belly. Weighing about 3 pounds, the liver is reddish-of the belly. Weighing about 3 pounds, the liver is reddish-brown in color and feels rubbery to the touch. Normally you brown in color and feels rubbery to the touch. Normally you can't feel the liver, because it's protected by the rib cage.can't feel the liver, because it's protected by the rib cage.

The liver has two large sections, called the right and the left The liver has two large sections, called the right and the left lobes. The gallbladder sits under the liver, along with parts lobes. The gallbladder sits under the liver, along with parts of the pancreas and intestines. The liver and these organs of the pancreas and intestines. The liver and these organs work together to digest, absorb, and process food.work together to digest, absorb, and process food.

The liver's main job is to filter the blood coming from the The liver's main job is to filter the blood coming from the digestive tract, before passing it to the rest of the body. digestive tract, before passing it to the rest of the body. The liver also detoxifies chemicals and metabolizes drugs. The liver also detoxifies chemicals and metabolizes drugs. As it does so, the liver secretes bile that ends up back in As it does so, the liver secretes bile that ends up back in the intestines. The liver also makes proteins important for the intestines. The liver also makes proteins important for blood clotting and other functions.blood clotting and other functions.

Bile/Bile DuctBile/Bile Duct

A A bile ductbile duct is any of a number of long tube- is any of a number of long tube-like structures that carry like structures that carry bilebile..

Bile, required for the Bile, required for the digestiondigestion of food, is of food, is secreted by the liver into passages that carry secreted by the liver into passages that carry bile toward the hepatic duct, which joins with bile toward the hepatic duct, which joins with the cystic duct (carrying bile to and from the the cystic duct (carrying bile to and from the gallbladder) to form the common bile duct, gallbladder) to form the common bile duct, which opens into the intestine.which opens into the intestine.

The The biliary treebiliary tree is the whole network of is the whole network of various sized ducts branching through the various sized ducts branching through the liver.liver.

Gall BladderGall Bladder

The gallbladder is a small pouch that sits just under The gallbladder is a small pouch that sits just under the liver. The gallbladder stores bile produced by the the liver. The gallbladder stores bile produced by the liver. After meals, the gallbladder is empty and flat, liver. After meals, the gallbladder is empty and flat, like a deflated balloon. Before a meal, the gallbladder like a deflated balloon. Before a meal, the gallbladder may be full of bile and about the size of a small pear.may be full of bile and about the size of a small pear.

In response to signals, the gallbladder squeezes In response to signals, the gallbladder squeezes stored bile into the small intestine through a series of stored bile into the small intestine through a series of tubes called ducts. Bile helps digest fats, but the tubes called ducts. Bile helps digest fats, but the gallbladder itself is not essential. Removing the gallbladder itself is not essential. Removing the gallbladder in an otherwise healthy individual typically gallbladder in an otherwise healthy individual typically causes no observable problems with health or causes no observable problems with health or digestion yet there may be a small risk of diarrhea digestion yet there may be a small risk of diarrhea and fat malabsorptionand fat malabsorption

AbsorptionAbsorption

Absorption is the movement of Absorption is the movement of moleculesmolecules across the across the gastrointestinalgastrointestinal (GI) tract into (GI) tract into the circulatory system. Most of the end-the circulatory system. Most of the end-products of digestion, along with products of digestion, along with vitaminsvitamins, , minerals, and water, are absorbed in the minerals, and water, are absorbed in the small intestinal lumen by four mechanisms small intestinal lumen by four mechanisms for absorption: (1) active transport, (2) for absorption: (1) active transport, (2) passive diffusion, (3) endocytosis, and (4) passive diffusion, (3) endocytosis, and (4) facilitative diffusion. Active transport facilitative diffusion. Active transport requires requires energyenergy..

Large IntestineLarge Intestine

The large intestine (colon) extends The large intestine (colon) extends from the cecum to the anus and from the cecum to the anus and includes the ascending colon, the includes the ascending colon, the transverse colon, the descending transverse colon, the descending colon, the sigmoid colon, and the colon, the sigmoid colon, and the rectum. rectum.