Human Digestive System

Digestion – The process by which complex food substances are converted into simple absorbable food substances so that they can be used by the body, is called digestion.
The organ system that is related to the digestive system is called the digestive system. It is divided into two parts –
1. alimentary canal 2. digestive glands

1. Diet – The alimentary canal of man is complete. It is like a tube extending from the mouth to the anus. It is divided into the following parts-

i. Mouth – The teeth in the mouth break the food into small particles and the tongue mixes the food well with the help of saliva and makes the food sticky. Here the enzymes present in saliva convert salivary amylase or tylin starch or starch particles into sugar.

ii. The pharynx is the pharynx below the oral cavity. The pharynx is the place where both the respiratory system and the digestive system open. There is no digestion here.

iii. Esophagus – The peristaltic motion is found in this, through which food reaches the stomach. There is no digestion in the esophagus.

iv. Stomach- The stomach expands when food comes in. And the gastric juices are mixed with the food by the gastric glands and the food is mixed well. Gastric glands secrete hydrochloric acid (HCl), pepsinogen and prorenin etc. HCl prepares the acidic medium and converts pepsinogen into active pepsin and prorenin into active renin. Pepsin digests proteins and renin digests casein, a protein present in milk.

v. Small intestine – The small intestine is the longest part of the esophagus. Its length is about 5-6 meters. Food enters the small intestine from the stomach. Pancreatic juice and bile juice are mixed in the food that enters the small intestine. Bile juices make the food alkaline so that pancreatic juice can act on it. Apart from this, bile juices break the fat into small granules so that digestion of fat can be done easily with the help of lipase enzyme. This process is called emulsification or emulsification of fat.
Enzymes secreted by the small intestine are also added to the food, which digest proteins into amino acids, complex carbohydrates into glucose and fats into fatty acids and glycerol. These digested substances are absorbed through the small intestine wall. There are many finger-like growths on the inner lining of the small intestine, which are called long hairs. It increases the surface area of absorption.
Blood vessels are abundant in large follicles, which carry the absorbed food to every cell of the body. Here it is used to obtain energy, in the formation of new tissues and in the repair of old tissues.

vi. Colon (Large Intestine) – The undigested food is sent to the colon where most of the large intestine absorbs the water present in it. The rest of the material is expelled out of the body through the anus in the form of feces, this process is called ejection.

Acidity – The mucous layer of the stomach protects the stomach wall from HCl. Sometimes the secretion of HCl starts increasing due to which we start getting sour belching, this condition is called acidity.
It can be got rid of by the use of alkaline substances like Milk of Magnesia, Eno etc. Many medicines also provide relief from this.

Tooth decay- Tooth decay or dental caries occurs due to gradual softening of enamel and dentine. It begins when bacteria react with sugar to form acid, then the enamel softens or demineralizes. Many bacterial cells mix with food particles to form dental plaque by sticking to the teeth. Plaque covers the teeth so saliva cannot reach the dental surface to neutralize the acid and microorganisms enter the medulla (cavity) causing irritation and infection.
Therefore, brushing after meals can remove plaque and it does not attack bacteria.