Digestive System

Digestive System
Digestive System

Important point

(1) Digestive system – A system consisting of many organs, glands, etc., work in harmony from the ingestion of food to the excretion. This is called the digestive system.

 (2) Digestion – The process of converting complex nutrients and large molecules into simple, small and soluble substances with the help of various chemical reactions and enzymes is called digestion.

 (3) Alimentary Canal – It is also called nutritional canal. Its length is about 8 – 10 meters. Following are the major parts of the alimentary canal              

 (4) Digestive glands – These are of three types –

 (i) salivary gland

(ii) liver gland

(iii) Pancreas

(5) Sphincters – At different levels, the pectoral muscles control the movement of food, digested food, juices and waste.

 (6) Teeth – Four types of teeth are found in the mouth –

1. Incisors

2 . Carines

3. Premolars

4. molars

The position of gums and teeth in humans is called thecodont. Diphyodont and orthodontic teeth are found in humans. 32 teeth are found in the oral cavity. (16 in the upper jaw and 16 in the lower jaw)

 (7) Pharynx by its structure ensures that food does not enter the windpipe and air does not enter the esophagus. The pharynx is divided into three parts –

 (i) nasopharynx

(ii) Orophar ynx

(iii) Laryng opharynx

(8) Stomach – Its shape is like J. It can hold 1 to 3 liters of food. The stomach is divided into three parts –

(i) cardiac or gastric part

(ii) gastric excretory part

(iii) Fundis portion

(9) Small Intestine – Most of the digestion and absorption of food takes place in the small intestine. The small intestine is divided into three parts – the duodenum, the forebrain and the small intestine.

(10) Large Intestine – It mainly absorbs water and mineral salts and excretes undigested food from the anus. The large intestine is also divided into three parts –

 (i) cecum or blind canal

(ii) colon

(iii) rectum

(11) Digestive Glands – Some digestive glands are also found in the digestive system, such as – salivary gland, liver and pancreas. These glands help in digestion of food through digestive juices. Small intestine etc. Organs also secrete digestive juices.

 (12) Salivary gland – Saliva is secreted by them. The main function of saliva is to digest starch present in food, to make food smooth and soluble and to clean the teeth, oral cavity and tongue. There are three types of salivary glands –

 (i) pre ear gland

(ii) hypodermic/subcutaneous salivary gland

( iii ) the thyroid gland

Detailed description

Human beings get the necessary energy and body material through food. Food is made up of various components like proteins, carbohydrates, fats, vitamins, minerals and salts etc. Most of these components in food are complex. are in condition. They are simplified for absorption in the body. To carry out this process, from the ingestion of food to the excretion, a system consisting of many organs, glands, etc., works in harmony. This system is called the digestive system. In digestion, complex nutrients and large molecules of food are converted into simple, small and soluble substances with the help of various chemical reactions and enzymes.

Human digestive system

The following are the organs and glands involved in the digestive system:

 (a) organ

( 1 ) Mouth

( 2 ) Pharynx

( 3 ) Esophagus ( Oesophagus )

(4) Stomach

(5) Small intestine

(6) Large intestine

( 7) Rectum

(b) glands

(1) Salivary gland

(2) Liver

(3) Pancreas

All the organs together form the alimentary canal which starts from the mouth and goes to the anus. It is about 8 – 10 m. Till long. It is also called the digestive canal.

The alimentary canal has three main functions –

 (a) Digestion by simplifying the diet

(b) absorption of digested food

(c) passing food from the mouth to the anus

The digestive juices produced by the glands found in the alimentary canal or the glands present elsewhere are responsible for carrying out the digestive function. These digestive juices simplify the food by various chemical reactions and convert it into a form that the body can accept. Many components are found in digested food juices such as proteins, carbohydrates, fats, minerals, salts, vitamins, water etc. These nutrients are absorb by various components of the alimentary canal with the help of specialized cells. The food ingested from the mouth moves through the contraction and expansion of various muscles in its long journey. Sphincters at different levels control the movement of food, digested food, juices and waste.

Organs used in Digestive System

As you are aware that in the work of digestion, from the mouth to the anus, many organs work (picture). Now we will discuss these parts in detail.

1. Mouth

The front part of the esophagus starts from the mouth and opens into the oral cavity. It is a bowl shaped organ. Above it are found hard and soft palate below. In the mouth cavity itself, the muscle-made tongue that can move around is found. The tongue is attached to the base plane in the posterior part of the oral cavity by the frenulum lingual or tongue annulum and goes to the central part of the oral cavity.

The mouth is surrounded by two muscular lips, which are helpful in opening and closing the mouth and catching food. There are 16 – 16 teeth in one jaw each in the upper and lower part of the mouth. All the teeth are located in a mold found in the jaw.

This mold is called gum. This condition of the gums and teeth is called Thecolout. Diphyodont teeth system is found in humans, in which two types of teeth – temporary (milk teeth) and permanent are found in life.

There are four types of teeth –

(a) Incisors – These are the front teeth. Who does the work of munching and cutting. They emerge at the age of six months.

 (b) Canines – These teeth do the work of tearing food. They emerge at the age of 16 – 20 months. These are 2 – 2 in each jaw. They are more developed in carnivorous animals.

 (c) Premolars – These are helpful in chewing food and are found in each jaw. They are fully developed at the age of 10 – 11 years.

 (d) Molars – These teeth are also helpful in chewing food and 6 – 6 are found in each jaw. They first emerge at the age of 12 to 15 months.

2. Pharynx

The oral cavity is connected to a small sac or flask shaped pharynx at the back of the tongue and palate. Through the pharynx, food goes into the alimentary canal or esophagus and air into the trachea. The pharynx ensures by its structure that in no case food can enter the trachea and air can not enter the food pipe. The mouths of these two drains are on the lower side of the pharynx – the trachea is located in the front part and the esophagus is located in the back part. The structure of the pharynx is divided into three parts –

(a) Nasopharynx

(b) Oropharynx

(c) Laryngopharynx or Hypopharynx

The function of chewing food and mixing it with saliva is performed in the oral cavity. The mucus in saliva lubricates the food particles and helps them to stick. Food now reaches the esophagus from the pharynx and from the esophagus to the stomach by peristalsis in the form of bolus. Gastro-esophageal sphincter controls the entry of food into the stomach. The enzyme tylen or amylase present in saliva starts the hydrolysis of carbohydrates in the oral cavity itself. Here about 30 percent of the starch is decomposed into maltose. Three types of secretions are found in the stomach – mucus, proenzyme pepsinogen and hydrochloric acid. Mucus is secreted by mucous cervical cells. The proenzyme pepsinogen is converted into the active enzyme pepsin in an acidic environment prepared by hydrochloric acid. And breaks down the proteins present in the food. In newborns, an enzyme called renin is also found in gastric juice along with pepsin. It helps in digestion of milk protein.

Oxyntic cells secrete hydrochloric acid. Food remains stored in the stomach for a few hours and by muscular contraction mixes with gastric juice to form chyme.

Food reaches the small intestine from the stomach. Most of the digestion process takes place in the duodenum. Here pancreatic juice, bile salts and intestinal juices are released by various ducts. , These juices contain various enzymes that digest the various nutrients present in the food.

Bile does the emulsification of fats. , This fat is essential for digestion. It also activates bile lipase enzymes. Simplified substances in the duodenum are absorbed in the small intestine and small intestine. Absorbed substances are transported in the blood with the help of various cells. Undigested and unabsorbed substances go from the small intestine to the large intestine. The main function of the large intestine is the absorption of water and salts and the excretion of the remaining undigested part. The undigested part becomes solid and remains temporarily in the rectum. Ejection of faeces from the anus occurs due to a neural reflex.