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More about the digestive system
The human body is a wonderful and complex mechanism. It performs various functions within a matter of minutes, one of which is digestion.
The human digestive system includes organs that break down food into simpler substances, which are then used by our body to function properly. These organs are salivary glands, mouth, esophagus, stomach, liver, pancreas, gallbladder, small and large intestines, and rectum.
The human digestive system, otherwise known as the gut or gastrointestinal tract, is essentially a continuous muscular tube about 7 to 8metres long in adults, running from the mouth to the anus (back passage). It is designed to process food and fluids, which are consumed on a daily basis. The main processes involve ingestion, digestion, absorption and elimination.
The food we eat contains vitamins, minerals, starch, fats and proteins, such as bread, meat, and vegetables. Our food and drink must be converted to smaller molecules before they can be absorbed and carried to cells throughout the body.
The large, hollow organs of the digestive system contain muscles that enable their walls to move. This movement can propel food and liquid and can mix contents within each organ. In fact, the movement of the esophagus, stomach, and intestine is known as peristalsis, akin to the wave motion of the sea, moving through the muscle. This causes narrowing of the muscles, slowly propelling the narrowed portion down the length of the organ and pushing food and fluid in front of the organ.
Esophagus: Digestion begins in the mouth, when we chew our food into small pieces. When these pieces are small enough to swallow, they travel from the mouth, through the esophagus and into the stomach.
At the lower end of the esophagus, a one-way valve — the lower esophageal sphincter — prevents the stomach contents from going back to the esophagus. At the esophagus-stomach junction, there is a ring-like valve, closing the passage between two organs. However, as food approaches this closed ring, the surrounding muscles relax and allow it to pass.
Stomach pouch: Food then enters the stomach, which has three tasks to do. First, it must store food and liquid. This requires the upper stomach muscle to relax and accept swallowed material. The second job is to mix food with digestive juices produced by the stomach. Finally, it must empty its contents into the small intestine.
Small intestine: In the middle of the abdomen lies the twenty-foot-long small intestine. It is here that the final process of digestion and nutrient absorption takes place. Enzymes present in the pancreas and small intestine are released into this part of the digestive system to absorb carbohydrates, fat and protein. In addition, bile salts secreted from the gallbladder help with the digestion and absorption of fats and fat-soluble nutrients, such as vitamin A, D, E and K.
The small intestine is divided into three sections. The first part is called duodenum, the middle portion is jejunum and the last part is ileum. One group produces a swaying motion that churns together food and digestive juices. Another set of muscles produces a wave-like action; the waves push the contents along a few inches and then, die out.
Food molecules must encounter a large number of specialized intestinal cells to maximize absorption. For this, the walls of one’s intestines are covered with microscopic, hair-like projections called microvilli. Each square-inch of the intestine contains about 10 billion microvilli. This increases the surface area for food absorption dramatically. It takes the small intestine about four hours to process a meal. Once that is done, your gut passes the indigestible watery gruel that is left, to the last five feet of your digestive tract, the colon.
The small intestine is the primary organ involved in the absorption of nutrients. Anything that interferes with the secretion of enzymes or bile salts, or disrupts the absorptive walls of the small intestine, such as the inflammatory bowel syndrome, chronic antacid use, chronic diarrhea, pancreatic insufficiency, or celiac disease, may result in vitamin deficiencies and fat mal-absorption.
Pancreas and liver: There are also two organs, the liver and pancreas, that produce digestive juices which accelerate the process. These juices reach the small intestine through little tubes, or ducts. The liver makes bile, which is temporarily stored in the gallbladder and carried down the bile duct to mix with food. The pancreas produces enzymes, which are carried down the pancreatic duct to further aid the process of digestion. The pancreas also produces insulin to regulate the level of sugar in your blood.
Colon: This organ reclaims excess water from intestinal waste and sends it back to your bloodstream. The colon is sometimes known as the large intestine. However, because of its wider diameter, it is actually much shorter than the small intestine (about 5ft long). By the time food reaches the colon, most nutrients have already been absorbed, leaving behind indigestible fibre and water. The large intestine absorbs water, electrolytes and a few vitamins. The length of time taken for food to pass through the colon largely depends on fibre intake. Mucus is secreted to protect cells lining the colon from bacterial toxins.
The colon begins in the cecum located in the lower right portion of our abdominal cavity. At the junction of the small intestine and the cecum, there is a valve, called the ileocecal valve, that prevents digested material in the cecum from going back to the ileum.
Ascending colon: Your cecum continues as an ascending colon upwards along your right side. Just under the liver it makes a sharp turn.
Transverse colon: The colon continues across the upper abdomen as the transverse colon, only to make another sharp downturn.
Sigmoid colon: It continues straight down your left side as a descending colon and then into an S-shaped segment, called the sigmoid colon.
Rectum: The sigmoid colon connects to the last six inches, called the rectum. This continues directly into the short anal canal, which terminates with the anal sphincter. The anal sphincter is a valve that must remain closed, to prevent stool incontinence, and must open properly, to permit bowel movements. Some observers have referred to the anal sphincter muscle as the social muscle, because it is able to prevent accidental bowel movements and to distinguish between passing gas, as opposed to solids and liquids.
The hormone regulatory system and nerve regulators control the entire process. The major hormone regulators that control functions of the digestive system are produced and released by cells in the mucosa of the stomach and small intestine.
These hormones are released into the digestive tract and travel back to the heart, ultimately returning to the digestive system, where they stimulate digestive juices and cause organ movement. These hormones are gastrin, secretin, and cholecystokinin (CCK), Ghrelin and Peptide YY.
In the nerve regulatory system, two types of nerves help in controlling the action of the digestive system. Extrinsic nerves come to the digestive organs from the brain or spinal cord. They release two chemicals, acetylcholine and adrenaline.
Acetylcholine causes the muscle of the digestive organs to squeeze with more force and increase the “push” of food and juice through the digestive tract. The intrinsic nerves make up a very dense network embedded in the walls of the esophagus, stomach, small intestine and colon. They release many different substances that speed up or delay the movement of food and the production of juices by the digestive organs.
Sometimes, the digestive system can malfunction, which in turn, leads to distressing and embarrassing symptoms. Therefore, if you have persistent intestinal problems, please do consult your doctor.
The writer
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