What is Digestive System In Human CBSE [Latest 2020]

What is Digestive System In Human: The digestive system in human consists of: (a) alimentary canal and : (b) associated digestive glands. The alimentary canal consists of buceal cavity, oesophagus, stomach, duodenum, ileum (small intestine), colon and rectum (large intestine). Glands associated with the digestive system are salivary glands, liver and pancreas.

(a) Alimentary Canal In Human

The human alimentary canal is nearly a 9 metre long tube, extended from the mouth to the anus.

Buccal Cavity

• Mouth opens into a chamber or cavity called buccal cavity. The floor of this cavity is formed by a muscular tongue, which helps in ingestion and swallowing of food.
• Both upper and lower jaws are provided with four different kinds of teeth, L.e., incisors, canines, premolars and molars. Teeth chew the food to make it soft for easy swallowing.
• The buccal cavity receives the secretion of three pairs of salivary glands through their ducts. The human saliva contains an enzyme ptyalin, which digests starch into maltose. Thus, carbohydrate digestion begins in the buccal cavity itself.

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Pharynx

• Buccal cavity opens into a small funnel-shaped pharynx, which leads to a long and tubular oesophagus. Nasal cavity (from nose) also opens into the pharynx.
• Posteriorly, pharynx contains two tubes-trachea and oesophagus. Trachea goes to the lungs, while oesophagus opens into the stomach. 

Oesophagus

It is a tube like structure, which connects pharynx to the stomach. The wall of oesophagus is highly muscular but it contains no digestive glands. Therefore, no digestion occurs in it.

Stomach

• It is a large, spacious, J-shaped organ. It is present on the left side of the abdomen. Upper part of stomach is called cardiac stomach, middle is called fundus, and lower part is called liquid. It is present in entire alimentary pylorus (or pylorie stomach).
• The innermost layer of the wall of stomach is called mucosa. It contains many branched and tubular glands. These glands are of three types. The secretion of these glands is called gastric juice. It contains digestive enzymes like pepsin and rennin (for protein digestion), HCl acid and mucus. A small amount of gastric lipase enzyme is also present to digest small amount of fats. But there is no carbohydrate digesting enzyme in the gastric juice.
• In this way, the digestion of proteins begins in the stomach. But in stomach, there is no carbohydrate

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Small Intestine

• The small intestine is a coiled and narrow tube. It is the longest part of alimentary canal.
• Small intestine is divided into three regions:
• (a) duodenum (proximal part)
• (b) jejunum (middle part)
• (c) ileum (distal part).
• Duodenum is a 'U shaped structure. It is attached to pylorus (lower part of stomach). It receives the openings of common duct (which brings the secretions of liver and pancreas).
• The wall of the small intestine has many long finger-like projections. These are called villi (sing= villus). These villi increase the surface area of the inner lining of intestine. This enhances the capacity of digestion and absorption of food.
• Small intestine contains many glands, which secrete digestive juices, collectively called succus entericus.
• Small intestine is the place where digestion of the food is completed. It is also the main site for the absorption of digested food.

Large Intestine

• The small intestine opens into the large intestine. It is smaller than small intestine, but its diameter is larger. It is divided into three parts : 
• (a) caecum (small pouch like part)
• (b) colon (middle longer part)
• (c) rectum (broad distal part)
• Rectum opens to outside through anus. Large intestine serves to absorb water and minerals from the food.
• Undigested food is sent to rectum, where from it is passed to outside through anus.

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(b) Associated Digestive Glands

Liver

• It is the largest gland of the body. It is placed in the upper right side of the abdomen.
• Liver secretes a watery, alkaline secretion, known as bile. It contains bile pigments and bile salts. The bile secreted by the liver cells is concentrated and stored in gall bladder.
• Bile does not contain any enzyme But it serves to alkaline the medium of duodenum. It also helps to emulsify fats (Emulsification means breaking of fat molecule into small globules).

Pancreas

• It is the second largest gland of the body. It is a mixed gland because it has exocrine part (enzyme secreting) as well as endocrine part (hormone secreting).
• Panereas lies beneath the stomach.
• Exocrine region of panereas secretes digestave enzymes (like trypsin, chymotrypsin and beta amylase etc.) and the endocrine region secretes hormones (like insulin and glucagon).
• Both bile and pancreatie juice enter duodenum through a common duct.
• The enzymes of pancreas Le., trypsin, chymotrypsin and beta amylase work in alkaline medium

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How To Digestive System Parts Work

The process by which large and complex components of the food are simplified to there small and simple forms is called digestion. It occurs in the alimentary canal, with the help of various enzymes. The complete process involves-ingestion, digestion, assimilation and egestion. The process of intake of food material is called ingestion. Inside the alimentary canal, food is digested and absorbed (assimilated). The undigested food is eliminated out from the body. This process of elimination of undigested food is called egestion.

Food consists of carbohydrates, fats, proteins, vitamins, minerals and water. But out of these, vitamins, minerals and water are not digested. These are absorbed as such from the intestine. So digestive process occurs only on carbohydrates, fats and proteins.

When the food is in buccal cavity, it is chewed and masticated with the help of teeth and tongue. Saliva contains an enzyme ptyalin, which converts carbohydrates (starch) into maltose. But there is no digestion of proteins and fats in the buccal cavity. When food reaches stomach, the digestion of proteins begins. Gastric juice, secreted by stomach wall. contains HCI and various enzymes like pepsin and rennin, which partially digest the proteins. HCI serves to activate these enzymes and also makes the medium acidic.

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Gastric lipase may digest a little fat, but there is no digestion of carbohydrates in stomach. Now the food goes to the small intestine. In duodenum, bile juice and pancreatic juices get mixed with the semi-digested food. Bile makes the medium alkaline and also emulsifies the fats. Pancreatic juice contains beta amylase, which converts remaining carbohydrates (starch) to maltose. Trypsin and chymotrypsin of pancreatic juice converts partially digested proteins to polypeptides.

In ileum, intestinal juice plays the final role. It contains enzymes which convert maltose and all other disaccharides monosaccharides like glucose and fructose. Similarly, enzymes like peptidases convert all polypeptides into amino acids. Intestinal lipase acts on emulsified fat and converts it into fatty acids and glycerol. In this way, all componenta of the food get digested completely in small intestine

The digested food is absorbed by the finger shaped villi. Each villus is richly supplied with blood capillaries. So it can quickly absorb the digested food from the intestine. Remaining undigested food is sent to the large intestine. In large intestine, water and minerals are absorbed. The remaining waste is called faces, which is sent to the rectum. From rectum it is eliminated to pout side through anus. This removal is called egestion or defecation. This process is regulated by anal sphincter.

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