Digestion is the process whereby food substances are converted into soluble and diffusible forms. Digestion may be physical or chemical. Physical digestion is the mechanical breakdown of food into smaller particles. This increases the surface area of the food for enzyme action. Chemical digestion refers to the enzymatic hydrolysis of food substances.
What are enzymes?
Enzymes are biological or organic catalysts, i.e. substances that are protein in nature and can alter the rate of chemical reactions without themselves being chemical changed at the end of the reactions. Enzymes can/are:
Digestion starts in our mouth. There we chew up our food and our tongue will have special sense cells to help us select suitable foods. Saliva is secreted through the three salivary glands namely the, parotid gland, the sublingual gland, and the submandibular gland. The saliva excreted contains amylase, which breaks starch into maltose. The tongue then rolls the food into balls and pushes them down our oesophagus. Our epiglottis will then close up the trachea.
The Small Intestine
The liver plays a vital role in the functioning of the body:
Production of bile
The gall excreted is stored in the gall bladder before use.
The liver keeps the amount of glucose in the blood constant. Blood normally contains about 70-90mg glucose. After a heavy meal, this glucose content rises. As the blood passes through the liver the excess glucose is converted into insoluble glycogen and stored. The blood leaving the liver contains a fairly constant amount of glucose. When the tissue cells of the body are in need of glucose, they obtain it from the blood. As a result the glucose level in the blood drops. This induces the liver to convert the glycogen in it back to glucose that enters the blood. In this way, the glucose level in the blood rises to normal. The deposition and mobilisation of glycogen is under the control of the hormones insulin and adrenaline.
Excess amino acids are brought to the liver when their amino groups are removed and converted to urea. The remains of the deaminated amino acids are converted into glucose in the liver. Any excess glucose formed in this way is converted to glycogen.
Harmful substances may be absorbed into the blood from the
alimentary canal. The substances such as benzoic acid, picric acid, chloroform are
rendered harmless by the liver cells. The process of converting harmful substances into
harmless ones is known as detoxication.
Heat is produced as a result of numerous chemical activities occurring in the liver and is distributed by the blood to other parts of the body, thus maintaining the body temperature.
Here, water and mineral salts are absorbed by our body and undigested matter moves along this passage and is stored in the rectum as faeces, until it is ready to be excreted through.
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