July 10, 2014
Human Digestion Summary
The digestive system is a group of organs that work together to convert food into energy and nutrients to feed the body. In a healthy person, the process of digestion can take 24 to 72 hours to fully digest food. This transit time could vary based on factors such as composition of the diet, level of physical activity, gender, stress level, medications, and illnesses that affect the gastrointestinal tract. At about 30 feet in length, the digestive system begins in the mouth and ends at the anus. Digestion begins in the mouth before the first bite of food is taken. When the aroma of the food is sensed or even when the taste of food is imagined, the salivary glands begin producing saliva. As food is chewed, more saliva is produced, moistening it for easy swallowing. In the saliva, the digestive enzyme amylase starts to break down some of the starches and sugars before it is swallowed. When swallowed, the food passes through the pharynx down through the esophagus and into the stomach.
The stomach serves as a storage tank, allowing enough time for the body to properly digest large meals. The muscles within the stomach churn and mix the food with hydrochloric acids and digestive enzymes, which continue to break down food into smaller, more digestible pieces. These smaller pieces, also referred to as chyme, are then emptied into the small intestine.
Once in the small intestine, the chyme is mixed with digestive juices from the pancreas (enzymes), liver (bile) and intestine that aids in the process of further digestion. The small intestine has three segments that each performs an important role in the absorption of nutrients. The duodenum is where the chyme is first received and exposed to secretions such as bile salts, enzymes and bicarbonate. The bile salts created by the liver help digest fats and fat-soluble vitamins. The pancreatic enzymes help digest carbohydrates and fats. The chyme is then passed down to the middle of the small intestine, the jejunum. Mainly in the first half of the jejunum, the majority (about 90%) of nutrient absorption occurs involving proteins, carbohydrates, vitamins, and minerals (Your Digestive System, n.d.). From the jejunum, the remaining chyme enters the ileum, which leads to the large intestine. The ileum is responsible for the absorption of water, bile salts and vitamin B12. The walls of the small intestine absorb the digested nutrients into the bloodstream; from here the nutrients are carried throughout the rest of the body.
After processing in the small intestine is complete, the large intestine receives the liquid residue remaining after the digestion and absorption has taken place. This waste consists mostly of water as well as other nutrients that were not digested. The large intestines main function is to reabsorb the water back into the body system to avoid dehydration. It also contains symbiotic bacteria that aids in breaking down the small pieces of waster to extract any small amounts of nutrients that remain. The remaining waste is then passed through the colon into the rectum and is ultimately excreted through the anus in the form of feces.
Throughout the digestive process proteins, fats and carbohydrates are broken down in various stages. Proteins, which are needed to build and repair body tissues, are first broken down in the