DIGESTIVE SYSTEM

Our digestive system is uniquely constructed to perform its specialized function of turning food into the energy we need to survive and packaging the residue for waste disposal. The first part of the change that occurs during digestion is mechanical. This phase involves the chewing of food in the mouth and mixing brought about by the muscular movement of the walls of the digestive organs. The breakdown of food into small particles and the thorough mixing with various juices aid the second phase of digestion, which is chemical. This phase is accomplished by digestive enzymes that are presents in various secretions produced by the digestive glands.

The Structure and functions of Digestive System

Mouth

The mouth is an organ of sensation and of speech, but its chief function is to prepare food for digestion. The hard palate forms the roof of the mouth in the chewing area. It is consist of the bony structure covered with several membranes. The soft palate lies just behind the hard palate. It is formed by the folded membranes that extended from the near portion of the hard palate and

fastens along the sides of the tongue.

The mouth is the beginning of the digestive tract; and, in fact, digestion starts here when taking the first bite of food. Chewing breaks the food into pieces that are more easily digested, while saliva mixes with food to begin the process of breaking it down into a form your body can absorb and use.

There are three major pairs of salivary glands that send their juices by way of ducts to the mouth. Saliva contains the enzymes salivary amylase, which begins the process of starch digestion. The disaccharide maltose is a typical end product of salivary amylase digestion.

Once food has been reduced to a soft mass, it is ready to be swallowed. The tongue pushes this mass—called a bolus—to the back of the mouth and into the pharynx. 

Esophagus
Located in your throat near your trachea (windpipe), the esophagus receives food from your mouth when you swallow. By means of a series of muscular contractions called peristalsis, the esophagus delivers food to your stomach.

The digestive and respiratory passages come together in the pharynx an then separate. When food is swallowed, the soft palate, the rear portion of the mouth’s roof, moves back to close off the nasopharynx. A flap of tissue called the epiglottis covers the glottis, an opening into the trachea. Now the bolus must move through the pharynx into the esophagus because the air passages are blocked.

Stomach
The stomach is a hollow organ, or "container," that holds food while it is being mixed with enzymes that continue the process of breaking down food into a usable form. Cells in the lining of the stomach secrete a strong acid and powerful enzymes that are responsible for the breakdown process. When the contents of the stomach are sufficiently processed, they are released into the small intestine.

The wall of the stomach has deep folds (rugae) that disappear as the stomach fills to an approximate capacity of one liter. Therefore, humans can periodically eat relatively large meals and spend the rest of their time at other activities.

Small intestine

Made up of three segments — the duodenum, jejunum, and ileum — the small intestine is a 22-foot long muscular tube that breaks down food using enzymes released by the pancreas and bile from the liver. Peristalsis also is at work in this organ, moving food through and mixing it with digestive secretions from the pancreas and liver. The duodenum is largely responsible for the continuous breaking-down process, with the jejunum and ileum mainly responsible for absorption of nutrients into the bloodstream.

Contents of the small intestine start out semi-solid, and end in a liquid form after passing through the organ. Water, bile, enzymes, and mucous contribute to the change in consistency. Once the nutrients have been absorbed and the leftover-food residue liquid has passed through the small intestine, it then moves on to the large intestine, or colon.

Colon (large intestine)

The colon is a 6-foot long muscular tube that connects the small intestine to the rectum. The large intestine is made up of the cecum, the ascending (right) colon, the transverse (across) colon, the descending (left) colon, and the sigmoid colon, which connects to the rectum. The appendix is a small tube attached to the cecum. The large intestine is a highly specialized organ that is responsible for processing waste so that emptying the bowels is easy and convenient.

Stool, or waste left over from the digestive process, is passed through the colon by means of peristalsis, first in a liquid state and ultimately in a solid form. As stool passes through the colon, water is removed. Stool is stored in the sigmoid (S-shaped) colon until a "mass movement" empties it into the rectum once or twice a day. It normally takes about 36 hours for stool to get through the colon. The stool itself is mostly food debris and bacteria. These bacteria perform several useful functions, such as synthesizing various vitamins, processing waste products and food particles, and protecting against harmful bacteria. When the descending colon becomes full of stool, or feces, it empties its contents into the rectum to begin the process of elimination.

Digestive wastes ( feces ) eventually leave the body through the anus, the opening of the anal canal. Feces are about 75% water and 25 % solid matter.

Rectum

The rectum (Latin for "straight") is an 8-inch chamber that connects the colon to the anus. It is the rectum's job to receive stool from the colon, to let the person know that there is stool to be evacuated, and to hold the stool until evacuation happens. When anything (gas or stool) comes into the rectum, sensors send a message to the brain. The brain then decides if the rectal contents can be released or not. If they can, the sphincters relax and the rectum contracts, disposing its contents. If the contents cannot be disposed, the sphincter contracts and the rectum accommodates so that the sensation temporarily goes away.

Anus

The anus is the last part of the digestive tract. It is a 2-inch long canal consisting of the pelvic floor muscles and the two anal sphincters (internal and external). The lining of the upper anus is specialized to detect rectal contents. It lets you know whether the contents are liquid, gas, or solid. The anus is surrounded by sphincter muscles that are important in allowing control of stool. The pelvic floor muscle creates an angle between the rectum and the anus that stops stool from coming out when it is not supposed to. The internal sphincter is always tight, except when stool enters the rectum. It keeps us content when we are asleep or otherwise unaware of the presence of stool. When we get an urge to go to the bathroom, we rely on our external sphincter to hold the stool until reaching a toilet, where it then relaxes to release the contents.

The three accessory Organs of Digestive system

1. Pancreas

   The pancreas secretes digestive enzymes into the duodenum, the first segment of the small intestine. It is elongated and somewhat flattened organ that has both endocrine and exocrine function. As an endocrine gland, it secretes insulin and glucagon hormones that help the blood glucose level within its normal limits. As an exocrine functions, it produces pancreatic juice which contains sodium bicarbonate and digestive enzymes for all types of food. Sodium bicarbonate neutralizes acid chime from the stomach. Pancreatic amylase digest starch, trypsin digest protein, lipase digests fats. 
2. Liver

   The liver has multiple functions, but its main function within the digestive system is to process the nutrients absorbed from the small intestine. Bile from the liver secreted into the small intestine also plays an important role in digesting fat. In addition, the liver is the body’s chemical "factory." It takes the raw materials absorbed by the intestine and makes all the various chemicals the body needs to function. The liver also detoxifies potentially harmful chemicals. It breaks down and secretes many drugs.
3. Gallbladder

   The gallbladder stores and concentrates bile, and then releases it into the duodenum to help absorb and digest fats.

A pear shaped, muscular sac attach to the surface of the liver. About 1000 ml of bile are produced by the liver each day, and any excess is stored in the gall bladder. When needed, bile leaves the gall bladder and proceed to the duodenum via the common bile duct.

The cholesterol content of the bile can come out of solution and form crystals. If the crystal grow in size, they form gallstones. The passage of the stone from the gallbladder may block the common bile duct and cause obstructive jaundice. Then, the gallbladder must be removed.

Common Digestive System Disorders

Colon and Rectal Cancer

Colon and Rectal cancer is also referred to as colorectal cancer.This type of cancer is a malignant cell that is found in the colon or rectum region of the body. The large intestine is made up of the colon and the rectum. Colon and rectal cancers share so many common features that they are referred to as the same cancer which is how the name colorectal cancer came about.

Stomach Cancer

Stomach cancer is also called, gastric cancer. This cancer affected approximately 21,700 Americans during 2001. The majority of those individuals were in their 60s and 70s. The risk factors for developing stomach cancer are Helicobacter pylori infection and a diet that consists of the following: eating large amounts of smoked foods, salted fish and meat, foods that are high in starch and low in fiber, pickled vegetables, and foods and beverages that contain nitrates and nitrites.

Diarrhea

Diarrhea is watery stool, or an increased frequency in stool, or both as compared to the normal amount of stool passed by the individual. Diarrhea can be short-term or it can be related to a bacterial or viral infection, or it can be long-term which is usually related to a functional disorder or intestinal disease

Gas in the Digestive Tract

You get gas in your digestive tract by swallowing air or during the breakdown process of certain foods by the bacteria that is present in the colon. Everyone has gas. It can be uncomfortable and certainly embarrassing to pass the gas. The average person produces 1 to 3 pints of gas a day and pass gas through their rectums about 14 times each day.

Heartburn

Heartburn is what most of us get from time to time. Chronic heartburn is a digestive disorder called gastroesophageal reflux disease (GERD). GERD is caused by gastric acid that flows from the stomach and into the esophagus.

Hepatitis

This is an inflammation of the liver that can result in liver cell damage. There are two types of hepatitis – acute and chronic and six main types of the hepatitis virus.

Irritable Bowel Syndrome

Irritable bowel syndrome – more commonly referred to as IBS – is an intestinal disorder that causes cramping, gassiness, bloating and changes in the bowel habits of the individual with the disorder.

Gastritis

Gastritis a condition in which the lining of the stomach becomes irritated or inflamed and peptic ulcers (sores or holes) form in the lining of the stomach or duodenum causing pain and/or bleeding. Both of these conditions can be relieved with medication.

Stomach and Duodenal Ulcers

Ulcers are open sores or lesions. They are found in the skin or mucous membranes of areas of the body. A stomach ulcer is called a gastric ulcer and an ulcer in the duodenum is called a duodenal ulcer. Lifestyle, stress and diet used to be thought to cause ulcers. These factors may have a role in ulcer formation; however they are not the main cause of them. Scientists now know that ulcers are caused by hydrochloric acid and pepsin that are contained in our stomach and duodenal parts of our digestive system and that these acids contribute to ulcer formation.