As the food move in the oral cavity. The teeth are organs found along the anterior and lateral edges of the mouth. These living organs and contain blood vessels and nerves under the dentin in a soft area known as the pulp. Teeth are used for cutting and grinding food into smaller pieces. The tongue is situated on the lower portion of the mouth just posterior. The outside of the tongue contains numerous coarse papillae for gripping food as it is moved by the tongue’s muscles. The taste buds on the surface of the tongue sense taste molecules in food and attach to the nerves in the tongue to send the information to the brain. The tongue helps to push food toward the posterior part of the mouth for swallowing. Surrounding the mouth are three sets of salivary glands, these are known as accessory organs that produce a watery secretion known as saliva. Saliva helps to dampen food and begins the digestion of carbohydrates. The body uses saliva to lubricate food as it passes through the mouth, pharynx, and esophagus. The pharynx, or throat, is a funnel-shaped tube attached to the posterior end of the mouth. The pharynx is responsible for the passing of the multitude of chewed food from the mouth to the esophagus. The pharynx also plays an major role in the respiratory system, as air from the nasal cavity passes through the pharynx on its way to the larynx and ultimately the lungs. The pharynx serves two diverse purposes, it contains a flap of tissue known as the epiglottis that acts as a switch to route food to the esophagus and air to the larynx (Innerbody, 2016). The esophagus is a muscular tube connecting the pharynx to the stomach that is part of the upper gastrointestinal tract. It carries swallowed multitudes of chewed food along its length. At the lower end of the esophagus is a muscular ring called the lower esophageal sphincter or cardiac sphincter. The purpose of this sphincter is to close at the end of the esophagus and trap food in the stomach. The stomach is a muscular sac that is positioned on the left side of the abdominal cavity, just lower to the diaphragm. In average human, the stomach size varies depending on the volume of food that has been consumed (Waugh and Grant, 2014 p299). This major organ acts as a storage tank for food so that the body has time to digest large meals correctly. The stomach also contains hydrochloric acid and digestive enzymes that continue the digestion of food that had began in the mouth.
The small intestine is a long, thin tube about 2.5 cm in diameter and about 3m long that is part of the lower gastrointestinal tract. It is positioned just lower to the stomach and takes up most of the area in the abdominal cavity. The whole small intestine is coiled like a hose and the inside surface is full of many ridges and folds. These folds are used to make the most of the digestion of food and absorption of nutrients. By the time food leaves the small intestine, around 90% of all nutrients have been removed from the food.
The liver is an accessory organ of the digestive system located to the right of the stomach, just lower to the diaphragm and superior to the small intestine. The liver weighs about 1.3kg and is the second largest organ in the body (Advanced Biology Notes, 2016). The liver has many different functions in the body, but the main purpose of the liver in digestion is the production of bile and its secretion into the small intestine. The gallbladder is a small, pear-shaped organ located just posterior to the liver. The gallbladder is able to store and recycle excess bile from the small intestine so that it can be reprocessed for the digestion of subsequent meals. The pancreas is a large gland. it is about 15cm long and connected to the duodenum towards the left wall of the abdominal cavity. The pancreas secretes digestive enzymes into the small intestine to complete the chemical digestion of foods. The large intestine is a long, thick tube about 6.5 cm in diameter and about 1.35m long (Rutishauser,1994). It is located just inferior to the stomach and wraps around the superior and lateral border of the small intestine. The large intestine absorbs water and contains many symbiotic bacteria that aid in the breaking down of wastes to extract some small amounts of nutrients. Faeces in the large intestine exit the body through the anal canal.
The digestive system is responsible for taking whole foods and turning them into energy and nutrients to allow the body to function, grow, and repair itself.
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