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Topic: Structure and functions of digestive system.
Subtopics: - The Mouth and Pharynx
- The Structure Of Teeth
- Taste Buds on the Tongue
Goal: To understand the functions of the parts of human digestive system.
Objectives: At the end of this session students will be able to
- Know the function of the mouth and pharynx.
- Describe the structures of the teeth.
- Name the types of teeth.
- Describe the structure and function of tongue.
Activities and Lecturing:
Structure and Functions of Digestive Organs
The Mouth and Pharynx
Food enters the body through the mouth, where both mechanical breakdown and chemical digestion occur. Chunks of food are bitten off with the teeth and ground into pieces small enough to swallow. The tongue moves and shapes the food mass in the mouth.
As food is chewed, it is mixed with saliva, which is secreted into the mouth by three pairs of salivary glands. There are actually two types of saliva produced. One is a thin, watery secretion that wets the food. The other is a thicker, mucus secretion that acts as a lubricant and causes the food particles to stick together to form a food mass, or bolus. Saliva also contains a digestive enzyme called ptyalin, or salivary amylase. This enzyme breaks down starch, which is a polysaccharide, into maltose, which is a disaccharide.
When the food has been chewed sufficiently, it is pushed by the tongue to the back of the throat, or pharynx. This initiates the automatic swallowing reflex, which forces food into the esophagus, the tube leading to the stomach. However, air as well as food passes through the pharynx. The air must pass through the voice box, or larynx, and down the trachea to the lungs. To prevent food and liquids from entering the larynx, it is automatically closed off during swallowing by a flap of tissue called the epiglottis. At the same time, breathing stops momentarily, and the passageways to the nose, ears, and mouth are blocked. When a person "swallows the wrong way" and food enters the trachea, it is brought back up into the throat by violent coughing.
The Structure Of Teeth
The permanent teeth are arranged in the same way in upper and lower jaws. The two flat front teeth are called incisors. They have sharp edges for cutting food. Next to the incisors, at the corner of your lips on either side, is a large cone-shaped tooth. This tooth is called the canine. Behind the canine tooth are the premolars. There are two on either side. Next are the molars. You have three molars on either side if you have cut your wisdom teeth; if not, you have two. Premolars and molars have flat surfaces which are good for grinding and crushing. A tooth has three general areas. The part above the gum is called the crown. A narrow part at the gum line is called the neck. The root is the part beneath the surface. The root is held in a socket in the jawbone. A fibrous periodontal membrane anchors it firmly in the jaw socket. Different kinds of teeth have differently shaped roots. Some are long and single. Some have two, three, or four projections.
The covering of the root is called cementum. It holds the tooth firmly together. The crown has a hard white covering called enamel.
If a tooth is cut lengthwise, you can see the dentine beneath the enamel and cementum. Dentine is very hard, but somewhat softer than the enamel and cementum. It forms the bulk of the tooth. The pulp cavity is in the center of the tooth. The pulp cavity contains blood vessels and nerve fibers.
The tongue lies along the floor of the mouth, but it begins in the throat. This muscular organ has several important functions.
It helps you chew
Your tongue helps you swallow
The tongue is essential to speech
Your tongue keeps the inner surface of your teeth clean
It acts as an organ of taste.
Notice that the surface of your tongue is covered with tiny bumps. These bumps hold taste buds, which have nerve endings at their bases. When you eat, the food in your mouth touches these bumps. This stimulates the nerve endings to send "taste" messages to your brain.
There are four types of taste buds. Each reacts to a different group of chemicals in food to produce a taste. The four tastes are sweet, sour, bitter, and salty. But the flavor of food does not come from taste alone. Flavor is a mixture of taste, texture, and odor