The gastrointestinal (GI) system is made up of the GI tract plus accessory organs. In essence, the GI tract is a long hollow tube that extends from your oral cavity where food enters your body, via the oesophagus, stomach, small intestine, large intestine, rectum, and finally to the anus where undigested food is expelled. The accessory organs include the salivary glands, pancreas and liver. These secrete important enzymes into the digestive tract. The gall bladder, which stores bile, is also considered part of the GI system.
The function of the GI system is to process nutrients and energy from food and fluids that you ingest. To do this, the GI system first needs to break foods down or 'digest' them into their simplest forms. The main components of food are carbohydrates, fats, proteins, vitamins, minerals and fibre. Food also contains varying amounts of water. The process of digestion breaks starch and sugars from carbohydrate-rich foods such as bread, potatoes and pasta into simple sugars such as glucose and fructose. Fats in butter, cheese, meat etc are converted into cholesterol and fatty acids. Proteins, for example in meat, eggs and fish, are broken down into amino acids.
When you eat and drink, digestion begins when you chew food to break it down into smaller pieces and enzymes within your saliva (excreted from salivary glands) begin to break the foods down into the component parts. Swallowed food and fluids travel down your throat into your oesophagus and then into your stomach. Once within the stomach, the food and fluids are mixed with strong acids that dissolve the solids, and digestive enzymes continue to break the food down. Next, the mixture passes into the small intestine where it is digested further by juices from your pancreas, liver (which produces bile) and small intestine. The nutrients are then in an accessible form and can travel through the wall of the intestine into the bloodstream (a process known as absorption) to be delivered to cells throughout your body. Undigested food in the small intestine moves into the large intestine (where some of the water is reabsorbed into the body) and is then expelled from the body as faeces or 'stools'.
In people with GI problems, these functions are impaired. Digestion of foods can be reduced, so fewer nutrients are converted into a usable form. Alternatively, food may be digested correctly but nutrients may not be absorbed into the bloodstream for use by the body. Finally, food and nutrients may be expelled too soon or specific nutrients and fluids may be lost via the faeces.
Some of the most common GI problems are constipation, diarrhoea, nausea and vomiting. These may be mild, self-limiting and temporary or may persist over the long term and affect your health. For instance, sustained constipation can lead to diverticular disease (where the intestine becomes damaged from passing hard stools and then form pocket-like sacs) and impaction (causing the intestine and rectum to become blocked). Sustained diarrhoea can make your blood pressure drop, which can lead to fainting or heart rhythm abnormalities. Nutrient and fluid loss from your body due to diarrhoea or vomiting can lead to dehydration, electrolyte imbalances, vitamin deficiencies, weight loss and malnutrition. Similarly, nausea, indigestion and constipation can reduce your appetite, and thus reduce your food intake leading to nutritional deficits. The nutritional effects of GI problems can be particularly serious for people who are already malnourished or ill.
• How common are gastrointestinal problems?
• What causes gastrointestinal problems?
• What are the symptoms and signs of gastrointestinal problems?
• How are gastrointestinal problems diagnosed?
• How are gastrointestinal problems treated?
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