o ral cavity

1. Food enters into the digestive tract through the oral cavity. The oral cavity consists of many important structures like palate, tongue, teeth and opening of salivary glands. Each part performs a specific function. Four functions are performed by the oral cavity. 1. Selection of Food 2. Grinding of Food 3. Lubrication 4. Digestion 1. Selection of Food First function of the oral cavity is to select the food by taste. A food with bad taste is rejected. In the selection of food sight and smell play an important role. Social and psychological factors are also involved in preferring a certain type of food over the other. 2. Grinding of Food Once the food is inside the mouth cavity, it is subjected to the grinding action. Teeth, tongue and cheeks all take part in the physical and quick breakdown of food into smaller pieces. Enzymes can easily work on smaller food particles. 3. Lubrication The process of lubrication and digestion starts as the food is broken down into smaller pieces. Three pairs of the salivary glands secrete saliva which has three ingredients: 1. Water and mucus 2. Sodium bicarbonate and other salts 3. Enzyme--Amylase or ptyalin Water and mucus Water and mucus together make slimy liquid which mainly moistens and lubricates the ingested food. The food can be chewed efficiently to allow the digestive juices to enter the food mass. Sodium bicarbonate Sodium bicarbonate and other salts stabilize the pH of the food although they are slightly antiseptic. Fresh saliva is alkaline with a pH 8 but quickly loses carbon dioxide and gets to pH 6. Amylase Amylase (Ptyalin) is a carbohydrate enzyme which hydrolyzes starch and glycogen to maltose. Thus softened, partially digested food is now arranged into small oral lumps called boluses. The boluses are pushed to pharynx by the combined efforts of the check muscles, the floor of the buckle cavity and the tongue. oral cavity

2. stomach 1. stores the food we eat 2. breaks down the food into a liquidly mixture called chyme3.Mixes with Enzymes which is a chemical that breaks down food. 4. and slowly emptys that liquidly mixture into the small intestine.

3. esophagus The tube that connects the pharynx (throat) with the stomach. The esophagus lies between the trachea (windpipe) and the spine. It passes down the neck, pierces the diaphragm just to the left of the midline, and joins the cardiac (upper) end of the stomach. In an adult, the esophagus is about 25 centimeters (10 inches) long. When a person swallows, the muscular walls of the esophagus contract to push food down into the stomach. Glands in the lining of the esophagus produce mucus, which keeps the passageway moist and facilitates swallowing. Food is passed through the esophagus by using the process of peristalsis. Specifically, it connects the pharynx, which is the body cavity that is common to the digestive factory and respiratory system with the stomach, where the second stage of digestion is initiated.

4. pharynx The role of the pharynx is to facilitate the passage of the food bolus into the esophagus. The pharynx is designed to direct the food bolus in this direction. It is here where the second phase of swallowing takes place. After the moistened food bolus is moved to the back of the mouth by the tongue, an involuntary swallowing reflex is triggered which prevents food from entering the respiratory tract. The tongue closes off the mouth, the soft palate blocks the nose, and the larynx rises such that the epiglottis closes off the trachea. Food then moves from the pharynx into the esophagus.