Metabolism

All chemical changes occurring in a living cell are called metabolism. Metabolism may be anabolism or catabolism. Anabolism is the process of synthesis of complex chemical molecule from simpler ones. Photosynthesis is an example of anabolism. Catabolism is the process of breaking down of a large and a complex molecule into the simple form. Respiration and digestion are the example of catabolism .

Anabolism and catabolism together are called metabolism . Anabolism is called a constructive process and catabolism is called the destructive process. Metabolism is indicated by the following processes taking places in the body.

a.      Formation of the necessary cells and tissues takes place in the body  as a result of the chemical reaction of various nutritious food.

b.      The blood cells and tissues  become useless  in the body .

Nutrition in the Human body:

Human beings like other animals are unable to prepare their own food so, the nutrition in the human beings is heterotropic. The human being depend on plants directly or indirectly for their food.

Digestive System in Human:

Digestion is a catabolic process or the process of breaking down of complex food materials into simple forms which can  be directly absorbed by the body. The organs concerned with digestion is called digestive system. The digestive system of human body consist of mouth, alimentary canal and the anus.

Mouth:

It is an opening through which food is taken inside the body. The food mixes with saliva inside the mouth and here the mechanical break down food occurs by the help of teeth and tongue. Saliva contains the enzyme ptyalin which helps to break down the carbohydrate partially to the glucose.

Alimentary Canal:

The alimentary canal is basically a long tube extending from the mouth to anus. It is necessary to move the foods in a regulated manner along the digestive tube so that it can be processed properly in each part .  The linings of canal have muscles that contract rhythmically in order to puss the food forward. These peristaltic movements occur all along the gut. Alimentary canal has the following parts:

a.      Food pipe or oesophagus

b.      Stomach

c.       Small intestine

d.      Large intestine

e.      Anus

Food Pipe or Oesophagus:

The food after chewing in the mouth passes to stomach through the food pipe or oesophagus.

Stomach:

The stomach is a large organ which expands when the food enters in it. The muscular walls of stomach helps in mixing the food thoroughly with more digestive juices. The digestive functions are carried out by the gastric glands present in the wall of stomach. The gastric gland release:

a.      Hydrochloric acid

b.      A protein digesting enzyme called protein

c.       Mucus

The hydrochloric acid creates an acidic medium which facilates the action of enzyme pepsin. It also kills the bacteria present in the food.