Human Digestion Process Explained - Colon Health Digest
Published in Digestion Process on 30th April 2013
When you eat foods– such as bread, meat, and vegetables– they are not in a form that the body can use as nourishment. Food and drink must be changed into smaller molecules of nutrients before they can be absorbed into the blood and carried to cells throughout the body. Digestion is the process by which food and drink are broken down into their smallest parts so the body can use them to build and nourish cells and to provide energy.
Digestion is the complex process of turning the food you eat into the energy you need to survive. The digestion process also involves creating waste to be eliminated.
The digestive tract (or gut) is a long twisting tube that starts at the mouth and ends at the anus. It is made up of a series of muscles that coordinate the movement of food and other cells that produce hormones and enzymes to aid in the breakdown of food. Along the way are three other organs that are needed for digestion: the liver, gallbladder, and the pancreas.
Food’s Journey Through the Digestive System
The mouth is the beginning of the digestive system, and, in fact, digestion starts here before you even take the first bite of a meal. The smell of food triggers the salivary glands in your mouth to secrete saliva, causing your mouth to water. When you actually taste the food, saliva increases.
Other mechanisms come into play once you start chewing and breaking the food down into pieces small enough to be digested. More saliva is produced to begin the process of breaking down food into a form your body can absorb and use. In addition, “juices” are produced that will help to further break down food. Chew your food more– it helps with your digestion.
Also called the throat, the pharynx is the portion of the digestive tract that receives the food from your mouth. Branching off the pharynx is the esophagus, which carries food to the stomach, and the trachea or windpipe, which carries air to the lungs.
The act of swallowing takes place in the pharynx partly as a reflex and partly under voluntary control. The tongue and soft palate– the soft part of the roof of the mouth– push food into the pharynx, which closes off the trachea. The food then enters the esophagus.
The esophagus is a muscular tube extending from the pharynx and behind the trachea to the stomach. Food is pushed through the esophagus and into the stomach by means of a series of contractions called peristalsis.
Just before the opening to the stomach is an important ring-shaped muscle called the lower esophageal sphincter (LES). This sphincter opens to let food pass into the stomach and closes to keep it there. If your LES doesn’t work properly, you may suffer from a condition called GERD, or reflux, which causes heartburn and regurgitation (the feeling of food coming back up).
Stop 3: The Stomach and Small Intestine
In addition to holding food, it serves as the mixer and grinder of food. From there, food moves to the small intestine.
Made up of three segments– the duodenum, jejunum, and ileum– the small intestine also breaks down food using enzymes released by the pancreas and bile from the liver. The small intestine is the ‘work horse’ of digestion, as this is where most nutrients are absorbed. Peristalsis is also at work in this organ, moving food through and mixing it up with the digestive secretions from the pancreas and liver, including bile. The duodenum is largely responsible for the continuing breakdown process, with the jejunum and ileum being mainly responsible for absorption of nutrients into the bloodstream.
A more technical name for this part of the process is “motility,” because it involves emptying or moving food particles from one part to the next. This process is highly dependent on the activity of a large network of nerves, muscles, and hormones. Problems with any of these components can cause a variety of conditions.
While food is in the small intestine, nutrients are absorbed through the walls and into the bloodstream. What’s leftover (the waste) moves into the large intestine (large bowel or colon).
Everything above the large intestine is called the upper GI tract Everything below is the lower GI tract.
Stop 4: The Colon, Rectum, and Anus
The colon (large intestine) is a five- to seven -foot -long muscular tube that connects the small intestine to the rectum. It is made up of the ascending (right) colon, the transverse (across) colon, the descending (left) colon and the sigmoid colon, which connects to the rectum.
Stool, or waste left over from the digestive process, passes through the colon by means of peristalsis, first in a liquid state and ultimately in solid form. As stool passes through the colon, any remaining water is absorbed. Stool is stored in the sigmoid (S-shaped) colon until a “mass movement” empties it into the rectum, usually once or twice a day.
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.
The rectum is an eight-inch chamber that connects the colon to the anus.The rectum:
Lets the person know there is stool to be evacuated.
Holds the stool until evacuation happens.
When anything (gas or stool) comes into the rectum, sensors send a message to the brain. If the contents can not be expelled, the sphincters contract and the rectum accommodates so that the sensation temporarily goes away.
The anus is the last part of the digestive tract. It consists of the muscles that line the pelvis (pelvic floor muscles) and two other muscles called anal sphincters (internal and external).
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 anal sphincters provide fine control of stool. The internal sphincter is always tight, except when stool enters the rectum. It keeps us continent (not releasing stool) when we are otherwise unaware or asleep of the presence of stool. We rely on our external sphincter to keep the stool in until we can get to the toilet when we get an urge to defecate (go to the bathroom).
Among other functions, the pancreas is the chief factory for digestive enzymes that are secreted into the duodenum, the first segment of the small intestine. These enzymes break down protein, fats, and carbohydrates.
The liver has multiple functions, but two of its main functions within the digestive system are to make and secrete an important substance called bile and to process the blood coming from the small intestine containing the nutrients just absorbed. The liver purifies this blood of many impurities before traveling to the rest of the body.
Bile made in the liver travels to the small intestine via the bile ducts. If the intestine doesn’t need it, the bile travels into the gallbladder, where it awaits the signal from the intestines that food is present.
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