Food is an important source for human beings to derive nutritional energy. Carbohydrate, protein and fats are the major component of food. Human-beings cannot utilize these major components in their complex form or in the natural form. So, the digestive system in the human- beings helps to convert these complex biomolecule into the simpler substances. The alimentary canal and digestive glands are the parts of the digestive systems.
Ø Alimentary glands are associated with the digestive glands in the human digestive system. There are following glands which play an important role in digestion. These are:
a) Salivary glands:
Salivary glands are exocrine glands which pour their secretion directly into the extra- cellular fluid. The main function of salivary glands is to produce saliva along with enzymes ptyalin; starch hydrolyzing enzyme secreted by salivary glands in human beings. It is also called as salivary amylase. Ptyalin secreted in the mouth brings about digestion of starch in the mouth brings about digestion of starch in the mouth itself. It hydrolyzes starch into disaccharide like maltose and isomaltose and other small dextrins called as limit dextrins. Ptyalin hydrolyzes at about 30% of the starch in the mouth itself. Saliva has many functions in the digestive process. These are as follows:
Ø Saliva is used to lubricate the mouth.
Ø Helps to swallow the food.
Ø Helps to protect the teeth from bacterial infection.
Ø Aid in the food digestion.
Salivary glands consist of following three pairs:
i. Parotid Glands: These are located on the inside of the cheeks.
ii. Submandibular glands: These are located under lower jaw bone of the mouth.
iii. Sublingual glands: These are located in the mouth below the areas of the front end of the tongue.
· Liver is reddish brown gland and plays an important role in the digestive system.
· It is the largest gland of the human body.
· It is located in the upper part of the abdomen on the right side.
· Liver secrete bile juice that is stored in a sac like structure called gall bladder. It helps in the emulsification of fats.
· The liver is connected to the two following large blood vessels:
i. Hepatic vein: It is used to carry the blood which is rich in oxygen.
ii. Portal vein: It is used to carry the blood which is rich in digested nutrients.
· Liver consists of two hepatic globules which are made up of hepatic cells. Hepatic lobules are the structural and functional unit of the liver. Each lobule is overlaid by Glisson’s capsule which is a thin connective tissue.
· Hepatic cells secrete the bile and pass into the gall bladder through the hepatic ducts where it is stored and concentrated. The hepatic ducts from the liver and cystic ducts from the gall bladder form the common bile duct.
· The bile duct and the pancreatic duct open together into the duodenum as the common hepato- pancreatic duct which is guarded by a sphincter called the sphincter of oddi.
· Pancreas is a large cream coloured gland located just below the stomach or between the limbs of the U- shaped duodenum.
· Pancreas secreted pancreatic juice which acts on carbohydrates and proteins and converts them into simpler forms from their complex forms.
· The partially digested food now reaches to the lower part of the small intestine where the intestinal juice (succus entericus) completes the digestion of all components of food.
· Gland which has two functional units to secrete both endocrine and exocrine enzymes located between the duodenum limbs. It consists of two portions:
i. Endocrine portion: This portion of pancreas is used to secrete the hormones, insulin and glucagon which circulate into the blood stream.
ii. Exocrine portion: Exocrine portion is used to secrete the alkaline digestive enzymes into the small intestine which are called as pancreatic juice.
d) Gastric glands:
It secretes HCl, pepsinogen, mucous. Gastric juice is a secretion of gastric glands located in the lining of the stomach. It is mainly made up of electrolytes, mucous, enzymes, HCl, intrinsic factor etc. Chief cells secrete pepsinogen which helps in the digestion of proteins after getting activated into pepsin by HCl. Enzyme of the gastric juice bring about digestion of different components of the food. Gastric lipase helps in emulsification of lipids in the stomach. Partially digested food in the stomach is known as chyme and this is further pass into the small intestine.
e) Intestinal glands:
These are present in the inner lining of small intestine. These glands secrete various enzymes which help in the digestion of all the components of food. Maltase, Sucrase and Lactase bring about digestion of maltose, sucrose and lactose.
Alimentary is a long hollow tube in humans which runs from mouth to anus. Different layers line the alimentary canal.It involves mechanical and chemical breakdown of food.
Peristalsis is an involuntary movements of the circular and longitudinal muscles to push the food into the stomach. This is done by peristaltic waves which are generated to pass the food.
Protein is a large biomolecule that is digested by HCl, pepsin, trypsin and chymotrypsin. Later protein is absorbed by small intestine and remaining parts are excrete out in the form of faeces.
The energy value of a food indicates how much energy the human body can gain through metabolism. The energy value specified in KJ/100gm.
Gastrointestinal hormones are chemical messenger that regulate the physiological functions. Gastrointestinal hormone includes gastrin, secretin, motilin, GIP, ghrelin, VIP, BBS.