Digestive System Of Human Body

Digestive System Of Human Body

Digestive system is a group of organs & associated digestive glands that take part in ingestion, digestive absorption of food & egestion of undigestible matter. Digestive organs from a continuous canal called alimentary canal.

Alimentary Canal Contains Following Parts:
Alimentary Canal in man is 9 metres long & consists of the following parts

Ingestion:
Food is taken into the body through the mouth, and is chewed. We have different types of teeth, which help us in breaking down food into smaller pieces.

Mouth:
Transverse slit like aperture.

Oral Cavity:
It is bounded by lips & has cheeks, gums, teeth & tongue.
The food taken inside oral cavity is masticated i.e. mechanically broken into smaller particles before being swallowed. The floor of the buccal cavity has a tongue bearing taste buds. Man possesses teeth on both the jaws, there are 32 teeth of four different types, namely incisors, canines, premolars & molars.

Tongue:
The tongue is a fleshy muscular organ present in the mouth. It helps to mix saliva with the food while chewing. The tongue is also a very important sense organ and has taste buds, which help to sense four different tastes, namely, sweet, salty, bitter, and sour.

Dental Formula:

Pharynx:
It is short conical region that lies after the mouth cavity.

Oesophagous:
It is a long narrow muscular tube which leads to the stomach. No digestive gland are present.

Stomach:
It lies below the diaphragm on the left side of abdominal cavity is J-shaped.

Small Intestine:
It is convoluted tube and differentiated into 3 regions, viz. Duodenum which is the first part of small intestine & is curved C-shaped; Jejunum, comparatively longer & more coiled and Ileum, which is the last part of small intestine whose inner surface is folded to form villi, which absorbs the products of digestion.

Large Intestine:
It is much shorter & wider than small intestine & is differentiated into three regions viz;
Caecum which is small rounded blind sac from which vermiform appendix arises;
Colon is the inverted U-shaped tube
The rectum opens to exterior through anus.
No digestion takes place in large intestine, only absorption of water takes place.
In herbivores like horse, rabbit digestion of cellulose takes place in caecum.

Digestion:
The process of digestion starts in the mouth itself where the food is mixed with saliva.
Saliva, secreted by the salivary glands, contains digestive juices that help in the breakdown of starch into sugar. Saliva also makes the food slimy so that it can be easily swallowed.

Once swallowed, the food passes from the mouth into a long tube called the oesophagus (also called food pipe). The walls of the oesophagus contract and relax to produce wave-like movements (called peristaltic movements). These movements help to move the food down into a large sac-like muscular organ called the stomach.

Further digestion of food takes place in the stomach. The inner wall of the stomach secretes digestive juices, hydrochloric acid, and mucus. The digestive juices help in the breakdown of proteins into simpler forms. The hydrochloric acid kills microorganisms and provides an acidic medium for effective digestion. From the stomach, the semi-digested food called the chyme passes into the small intestine.
Further digestion of food takes place in the small intestine where the secretions of the liver and pancreas are released.

The liver secretes bile, which plays an important role in the digestion of fats. Bile is stored in an organ called gall bladder before being released in the small intestine. The secretions of the pancreas called pancreatic juice help in the breakdown of carbohydrates into sugars, proteins into amino acids, and fats into fatty acids and glycerol. Thus, the digestion of various components of food is completed in the small intestine.

Absorption:
In the small intestine (ileum) absorption of all digested materials takes place. Even though digestion continues in the small intestine, the main job of the small intestine is to absorb the nutrients obtained as a result of digestion. The lining of the small intestine has finger-like projections called villi (singular: villus) that increase the surface area of the lining. This makes absorption more efficient. Each villus has a network of fine blood vessels. Nutrients are absorbed into the blood present in these fine blood vessels. The chyme now passes into the large intestine, where water and minerals are absorbed.

Assimilation:
It is the process of utilisation of absorbed food for various body functions. The absorbed nutrients are utilised to resynthesise complex molecules like carbohydrates, protein & fats inside the cells. Man cannot digest cellulose. The nutrients that are absorbed in the blood are transported to the rest of the body. The final product of carbohydrate digestion, i.e., glucose, is broken down into carbon dioxide and water in the cells with the help of oxygen, to release energy. Amino acids are used for repairing worn out cells and tissues. Fatty acids and glycerol act as energy reserves and are stored for further use.

Egestion:
After absorption of water and minerals in the large intestine, the undigested food becomes semi-solid. It is then stored in the rectum until it is removed through the anus. It is the process of elimination of undigested food formed in the cells, or in the lumen of large intestine (colon & rectum) through the anus. Voluntary cotraction of abdominal muscles help in egestion of faeces.

Table: Summary Of Digestion Enzymes Of Various Glands With Their Secretions And End Products Of Digestion In Man

Activity

Aim: To study the effect of saliva on food.
Materials needed: Bread, watch glass, petridish, iodine solution, and saliva from your mouth.
Method:

1. Break off a small piece of bread and test it for starch using iodine solution. If it turns blue- black, starch is present.
2. Now take a piece of bread in the petridish.
3. Put four drops of saliva on the bread and leave it for some time.
4. After some time, test for starch again on the portion where saliva was added.

Observation: The piece on which saliva was put shows no change in colour.
Conclusion: As starch has been converted to sugar by the digestive juices in saliva, the test for starch is negative.