Food: Food is a basic requirement of all living beings. Food provides energy for different activities in the body. Food also provides organic materials for growth and repair. Carbohydrates, proteins and fats are the major components of food and hence these are called macronutrients. Vitamins and minerals are required in small quantities and hence are called micronutrients. Water plays an important role in various metabolic processes. Water also prevents dehydration of the body.
Digestion: The macromolecules in food cannot be utilised by our body in their original form. They need to be broken down and converted into simple substances so that they could be absorbed. The process of converting complex food into absorbable forms is called digestion. Various mechanical and biochemical methods are involved in digestion of food.
The human digestive system consists of the alimentary canal and the associated glands.
Alimentary Canal: The alimentary canal begins with the mouth and ends in the anus. Mouth is situated at the anterior part and anus is situated at the posterior part of the body. The alimentary canal can be divided into five main parts, viz. mouth, oesophagus, stomach, small intestine and large intestine.
Buccal Cavity: The mouth opens into the buccal cavity or oral cavity. A muscular tongue and a number of teeth are present in the buccal cavity.
Thecodont: Each tooth is embedded in a socket of jaw bone. This type of attachment is called thecodont.
Dentition: The arrangement of different types of teeth in the jaws of an animal is called dentition. Two sets of teeth form during the lifetime of a human being. A set of temporary milk teeth or deciduous teeth are formed when the child is about 6 months old. These teeth are replaced by a set of permanent teeth when the child is about 10 years of age.
Diphyodont: The type of dentition in which an animal gets two sets of teeth during its lifetime is called diphyodont. This type of dentition is present in most of the mammals.
Heterodont Dentition: When different types of teeth are present, this arrangement is called heterodont dentition.
Dentition in Humans: An adult human has four different types of teeth, viz. incisors (I), canine (C), premolars (PM) and molars (M). There are 32 permanent teeth in an adult human being.
Dental Formula: In human beings, each half of the upper and lower jaw has teeth in the order I, C, PM, M as represented by following dental formula:
Tongue: Tongue is a freely movable muscular organ. It is attached to the floor of the buccal cavity by the fernulum. Small projections; called papillae are present on the upper surface of the tongue. Some of the papillae bear the taste buds.
Pharynx: The oral cavity leads into the pharynx. The pharynx serves as a common passage for food and air.
Oesophagus: The oesophagus is a long tube which connects the buccal cavity to the stomach. A muscular sphincter; called gastrooesophageal sphincter regulates the opening of oesophagus into the stomach. A cartilaginous flap; called epiglottis; prevents the entry of food into the glottis during swallowing.