When we start eating, food enters our mouth and the process of digestion starts in our mouth. We start chewing the food. Food is crushed and ground during the mastication or chewing process. Salivary glands start secreting and lubricates the food that we chew. The food is pushed around by the tongue and within a minute or so, food becomes crushed, ground, soft and moist mass, which is called bolus. Each bolus is swallowed through the throat, which is also technically referred as the pharynx. Swallowed bolus is passed on into the esophagus.
We have four different types of teeth, each having a different role. Pointed canines are designed for tearing. At the front are chisel shaped incisors with sharp edges for cutting purposes. The premolars and molars are for crushing and grinding. Premolars have two ridges on the top but molars are flatter compared to the premolars. Molars are the largest and strongest of all teeth.
The portion of teeth above the gum is called the crown and the part which is embedded in the gum or the jawbones is called the root of the teeth. The area between the two, near the gum surface is called the neck. The technical name for gum is gingiva. Outer layer of the crown is made of a tough bone-like material called enamel. Enamel is the hardest substance in the body. If body happens to burn, what is left is teeth. That is the reason sometimes identification is made through dental records. Beneath the enamel lies softer but still very strong tissue called the dentin. It is mainly shock-absorbing. Dentin covers the whole teeth, including crown, the root and the neck. In the center of teeth lies the soft dental pulp, which has blood vessels and nerves. Below gum, another bone-like hard tissue the cementine, covers the dentin. Periodontal ligament tissues under the gum secure teeth in the jawbone.
Teeth can not crush food properly without support from the tongue. Try pulling the tongue in and chew without the tongue, you will soon realize the importance of the tongue in chewing. It keeps pushing food out towards the teeth. Three pairs of salivary glands produce saliva in the mouth. Parotid gland is in front of and just below each ear. The submandibular glands are on the inner side of the lower jawbones and the sublingual glands are on the floor of the mouth below the tongue. Saliva is mostly water (99.5%), but it has some important enzymes that start the digestion process in the mouth. Amylase begins the breakdown of starches and salivary lipase begins the digestion of fats. This is one of the reasons, chewing food thoroughly is essential as it will jump-start the digestion process. Saliva also has disinfectant and antibacterial chemicals. Saliva not only helps moisten food, but it also keeps the mucous membrane of mouth moist between periods of eating.
Once the food has been chewed properly and has been moistened by saliva, it is in the bolus form and ready to be pushed by the rest of the tongue to the back of the mouth. This is the beginning of the voluntary process of swallowing. Swallowing soft and moist bolus is easy but to swallow a solid item such as medicine pill or tablet without chewing is hard and demands focus. Liquid is not chewed and is gulped down directly right after it is put into the mouth, which is why it is easier to swallow pills with water. Once bolus is pushed down on the back of the mouth, automatic reflexes take over the later stages of swallowing, as the muscles of throat contract and push the bolus further back and down, and squeeze bolus into the top of the esophagus. A cartilage flap known as the epiglottis prevents food from going down the 'wrong way' into the larynx and the trachea and thus prevents possible choking.
The throat is a dual purpose passageway. It lets breathing air pass through as well as food, drink and saliva while eating. Muscles of the throat (pharynx), tongue, mouth, larynx and upper esophagus run under nerve signals from brain to prevent food from entering the windpipe or trachea. The cartilage flap of epiglottis is crucial in covering larynx mouth when food or drink is going down along the throat. Complex muscle movement of swallowing is a voluntary reflex triggered by the contact of solid matter to the sensors at the back of the mouth. If food is accidentally inhaled, the irritation of the windpipe triggers coughing reflex to expel inhaled particles and prevent choking.The next stage of the digestive tract is esophagus, through which bolus enters the stomach.
Source by Rimas Sony
