Digestive System : Parts and Digestive Glands

Posted under Category : Health Fundas

Introduction to the Basics of Digestive System

Food is required for getting energy. Food contains carbohydrates, proteins and fats. They are present in complex form and do not give the energy directly. They need to be converted into simpler forms like glucose, aminoacids and fatty acids which give energy. This conversion is done by the digestive enzymes which are produced by various glands of the digestive system.

Digestive system helps in the digestion of the food.The alimentary canal is wide in some places and narrow at some places. The alimentary canal is lined internally by the mucous membrane.

Parts of the Digestive System:

Digestive system consists of the alimentary canal and the digestive glands. Alimentary canal contains many parts. The important parts of the alimentary canal are mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.

Mouth:

Mouth is the first part (front opening) of the alimentary canal and begins with upper and lower lips. Upper lip and lower lip are protective in function. Mouth opens into a spacious mouth cavity or oral cavity and is bounded by upper and lower jaws.

There is a thick muscular tongue with taste buds on the floor of the mouth cavity. The function of the tongue is to chew the food and to feel different tastes with the help of taste buds.

Thirty two teeth are present in the mouth cavity. Four types of teeth are present in the oral cavity namely incisors, canines, molars and premolars which are arranged in an order like incisors (2/2), canines (1/1), premolars (2/2) and molars (3/3). in the upper and lower jaws. This arrangement of teeth is called as dental formula.The teeth are arranged in the sockets of the upper and lower jaws on each side. Sixteen teeth are present on the upper jaw and sixteen are on the lower jaw.

The function of the incisors is to cut the food into pieces. The canines are almost round in shape in the human beings. There are two premolars next to the canines and the last three are molars whose function is to grind the food. The last molar teeth are called as wisdom teeth and come out of the jaws between the age of seventeen and twenty five.

Structure of the tooth:

The part of the tooth that is enclosed in the jaw bone is known as root and which is exposed is known as crown and is covered by a shiny enamel. The tooth is made up of a substance called as dentine and it is harder than bone. There is a cavity inside inside the tooth and is filled with blood vessels and nerve fibres and is known as pulp cavity.

The teeth which are developed first in the children are known as milk teeth. They are dropped at the age of eight or nine years and new set of teeth called permanent teeth are developed. Children will have only twenty teeth.

Salivary Glands:

There are three pairs of salivary glands in the oral cavity. These salivary glands secrete saliva into the buccal cavity. The three types of salivary glands are parotid glands, submandibular glands and sublingual glands. Parotid glands are the largest salivary glands. Submandibular glands are located beneath the lower jaws and sublingual glands are located below the tongue. The saliva contains the enzyme ‘ptyalin’ which digests the food partly in the buccal cavity.

Then the food is pushed into pharynx.

Pharynx

Behind the mouth cavity lies the funnel like structure known as pharynx. Pharynx is a wide and muscular chamber that opens into the oesophagus and helps in swallowing. The partly digested food from pharynx enters into oesophagus with the help of the tongue. .

Oesophagus

Oesophagus is a long and narrow muscular structure. Mucous is secreted by the glands which are present in the walls of the oesophagus that helps in the easy passage of the food. It passes through the neck, chest cavity and enters into the abdomen where it opens into the stomach. On the top of oesophagus, a flap like tissue named as epiglottis is present. It prevents food from entering into trachea during swallowing.

Stomach

Stomach is located on the left side of the abdomen below the diaphragm. The diaphragm is a thin layer that separates the body cavity into an upper chest cavity and lower abdominal cavity. Stomach is a sac like structure consisting of numerous tiny glands called as gastric glands that secrete gastric juice. The stomach opens into the small intestine.

It is a bag like structure present beneath the oesophagus. The innerwalls of the stomach are folded and churn the food and make the food smooth. This food is called chyme.

Glands in Stomach:

The glands which are present in the stomach are called gastric glands which secrete gastric juice. Enzymes are present in the gastric juice and parietal cells in the stomach secrete hydrochloric acid which kills the bacteria present in the food. Proteins are digested and converted to simpler forms like peptones and peptides. This food then enters into the small intestine.

Small intestine

Small intestine is about 7 metres long and the first part of it is uncoiled and is called as the duodenum and lies parallel to the stomach. The coiled second part is known as ileum. The opening of the stomach into the duodenum is guarded by the pyloric sphincter that acts as a valve and allows only little quantities of food at a time from the stomach into the duodenum. There are finger like folds in the wall of small intestine which helps to increase the surface area for absorption. The ileum opens into the large intestine.

Small intestine is a thin muscular structure and starts with duodenum. Duodenum is a ‘U’ shaped structure. The next part of the small intestine is ileum. The ducts from the liver and pancreas open into the loop of the duodenum. Bile juice is secreted by the liver and pancreatic juice is secreted from the pancreas. B(beta) cells of islets of langerhans of pancreas secrete insulin and alpha cells secrete glucagon which maintain sugar levels in the blood. The enzymes present in these intestinal juices digest most of the food. The digested food is absorbed mostly from the small intestine into the blood circulation and undigested food reaches the large intestine.The food which is present in the small intestine is called as ‘chyle’.

Large intestine

Large intestine is about 1.5 metres long. The first part of the large intestine is known as caecum and the opening of the ileum into the caecum is guarded by a sphincter which acts as a valve. There is a finger like appendix at the base of the caecum. Appendix is a vestigial organ in the humans and is reduced and functionless. Caecum is well developed in grazing animals like rabbit and horse and helps in digesting cellulose that is present in the food. The second part of the large intestine is colon and has an ascending limb, a transverse limb and a descending limb.

Digestion does not take place in the large intestine as it does not contain the digestive glands. Water is absorbed from the large intestine. Undigested food is excreted as the faecal matter.

Rectum and Anus

Rectum is the terminal part of the colon and opens to the outside through the anus. Undigested food is sent out through the anus.

Digestive glands:

There are two digestive glands namely liver and pancreas that secrete juices for the digestion of food.

Liver

The liver is the largest gland in the body and is located on the right side in the upper part of the abdominal cavity. It is reddish brown in colour and weighs about 1.5 kg. The liver has right and left lobes. The structural and functional units of the liver are hepatic cells. The liver secretes bile juice and it is stored through bile duct in a sac called as gall bladder. From the gall bladder bile is released into the duodenum.

Pancreas

Pancreas are located below the stomach and it is a leaf shaped gland with several lobes. Pancreas secrete pancreatic juice that contain digestive enzymes. A specialised group of cells called islets of langerhans are present in the pancreas that secrete insulin which regulates the blood sugar levels. The deficiency of insulin leads to diabetes and excess sugar goes out of the body through urine.

The ducts of liver and pancreas unite into a common duct and open into the duodenum.

Basic Introduction to The Islets of Langerhans

The pancreas contain many hundreds and thousands of clusters of cells which are randomly distributed called as islets of langerhans. Each of the little cell clumps contain millions of cells, which is a microscopic endocrine gland.

Hormones secreted by islets of langerhans:

These glands secrete the hormone insulin and if it is not functioning properly it leads to diabetes mellitus. The islets of langerhans secretes insulin and also glucagon. Both these hormones are essential for maintaining the glucose in the blood stream and the rate at which it is to be used by the body. Glucose is essential to get energy for life and living processes. When the secretion of these hormones get disturbed, the cells’ ability to absorb and use sugar is restricted. The sugar becomes unutilized and it passes out of the body in urine. Now the insulin has been manufactured and is available for the diabetics. It is to be taken in regulated doses and the person can lead a normal life.