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DIGESTION Digestion is the process of converting complex food materials into simple absorbable forms. We get nutrients required for life activities from the food we eat. The nutrients that we should obtain through food are as follows: ❖ Carbohydrates ❖ Proteins ❖ Fat ❖ Minerals ❖ Vitamins ❖ Water These nutrients perform certain functions in the human body. NUTRIENTS FUNCTIONS Carbohydrate Supply energy Protein Body building, rectifying Fat damages Minerals Supply energy Vitamins For the growth of bones, teeth. For the activity of the nerves and Water muscles For the metabolic activities after digestion, for the health of eyes Transport of matter and materials, internal homoeostasis

DIGESTIVE SYSTEM The human digestive system consists of the alimentary canal and the associated glands.

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CHAPTER-2 FOOD INSIDE MOUTH The mouth is an opening through which the food is taken inside the body. The mouth also called the oral cavity includes teeth, tongue, salivary glands. The mouth is an important part as it is helpful for speech and communication, eating and digestion, and can also be used for breathing. The buccal cavity or oral cavity is the beginning of the alimentary canal, which leads from the pharynx to the oesophagus. The structure and arrangement of teeth is suitable to masticate the food we eat. The four types of teeth are: ❖ Incisor ❖ Canine ❖ Premolar ❖ Molar

TYPES OF TEETH FUNCTIONS Incisor Helps to bite and cut the Canine food Premolar Helps to tear the food Molar Helps to chew at the food Helps to chew the food STRUCTURE OF TOOTH Even though teeth vary in their morphology and function, they show similarities in their internal structure. The structure of tooth consists of Enamel: white in colour, the hardest part, dead tissue Dentine: living tissue which forms the tooth Pulp: soft connective tissue seen in the pulp cavity Cementum: calcium containing connective tissue

The tongue is a freely movable muscular organ attached to the floor of the oral cavity. It helps to masticate food materials and mix them with saliva. The taste buds in the tongue help in the sensation of taste. SALIVA AND DIGESTION There are three pairs of salivary glands in the mouth. The saliva secreted from the salivary glands contains mucus and enzymes like salivary amylase and lysozyme. Mucus makes the food slimy, so that it can be swallowed. Lysozyme, to an extent helps to destroy the germs that enter the body through food. Salivary amylase partially converts starch to maltose, a form of sugar.





Peristalsis in oesophagus The food reaches the stomach by wave like movement of the walls of the oesophagus. These movements are called peristalsis. Peristalsis is a series of wave-like muscle contractions that move food through the digestive tract. It starts in the oesophagus where strong wave-like motions of the smooth muscle move balls of swallowed food to the stomach.





Peristalsis in the stomach The strong peristalsis in the stomach coverts food into a paste form. The special circular muscles present in the posterior part of the stomach retain food for a specific period. Different components in the gastric juice, secreted by the glands in the stomach wall also play a very important role in the process of digestion. Components And Functions of Gastric Juice Gastric Juice Functions Pepsin enzyme Converts protein to peptones partially Gastric lipase enzyme Digests fat partially Hydrochloric acid Destroys germs in the food. Mucus Regulates pH suitable for the digestion in stomach Protects the stomach wall from the actions of digestive juices







LIVER ❖ Enzymes are absent in the bile secreted by the liver. ❖ It helps in digestion by breaking down fat into smaller particles and making the food alkaline. ❖ The bile secreted by the liver is stored in the gall bladder. PANCREAS ❖ Secretes pancreatic juice. ❖ Bile and the pancreatic juice reach the duodenum through a common duct. Liver is the largest solid organ in the body situated in the upper part of the abdomen on the right side. The main function of liver is to filter the blood coming from the digestive tract, before passing it to the rest of the body. The excess bile secreted by the liver is stored in the gall bladder. Starch PANCREATIC Maltose Protein JUICE Peptide Fat Fatty acid + Glycerol Pancreatic amylase Trypsin Pancreatic lipase When food moves forward from duodenum, it gets mixed with the intestinal juice secreted by the glands in the small intestine. Different enzymes are present in the intestinal juice, some of which convert maltose, lactose (the carbohydrate in milk) and sugar (sucrose) into simpler forms like glucose, fructose and galactose. Another set of enzymes converts peptides to amino acids.

That the digestion of fat is almost completed in the duodenum itself. So, the end products formed after digestion are as follows: Carbohydrate: glucose, fructose, galactose Protein: amino acids, glycerol Fat: fatty acid, glycerol And the nutrients that do not undergo digestion are: Water Minerals Vitamins

















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