Digestive System - Notes, Biology | IBPS PO Prelims & Mains Preparation - Bank Exams PDF Download

Digestive System in Humans : 

• The process of converting food into energy giving substances is carried out by this system.
• The digestive system comprises the alimentary canal and the associated digestive glands like liver and pancreas.

1. Buccal Cavity

• In the mouth salivary glands secrete saliva which contains the enzyme Ptyalin (or salivary amylase)
• Here the food is called bolus.
• Also contains Lysozyme which kills bacteria.

Teeth

• Teeth : They are produced in two sets – Temporary and Permanent.
• The teeth are of four types :
  • Incisors,
  • Canines,
  • Premolars and
  • Molars.

Dental Formula: 2123 / 2123.

• This means that there are 2 incisors, 1 canine, 2 Premolars and 3 molars in half of the upper jaw and exactly the same arrangement in half of the lower jaw.
• This figure is doubled to get the full number, i.e. 32.
• The premolars and the molars are called the grinding teeth. The last molars are called the wisdom teeth.
• In elephants, incisors of the upper jaw grow into huge tusks.
• Canines are very large in predators such as cat, dog and lion.

Structure of a Tooth: 

A tooth consists of 3 Regions :

• Crown, Neck and Root:
• The crown is the exposed part. It is covered by a shining material called Enamel.
• Enamel is the hardest substance in the human body

2. Pharynx

• Links Buccal Cavity to Oesophagus.
• Food is carried by peristaltic movement [Peristalsis is a series of wave of contraction that passes from end to other and is meant for pushing the food].
• Trachea opens into Pharynx through an aperture called Glottis.
• It also receives the opening of the Eustachian Tubes from the middle ear through an Aperture called Gullet.

4. Stomach

• Oesophagus opens into it.
• The opening is guarded by a valve which checks the regurgitation of food.
• In stomach, the food is called chyme.
• Has 3 Parts :
  • Fundus
  • Cardiac
  • Pyloric
• It is a warehouse where food can be stored to await the main process of digestion.
• Gastric juices produced in the stomach help in digestion of food.
• Also contains HCI which kills bacteria and provides acidic medium.
• Besides it activates pepsinogen to pepsin and prorennin to rennin.
• It is a warehouse where food can be stored to await the main process of digestion.
• Gastric juices produced in the stomach help in digestion of food.
• Also contains HCI which kills bacteria and provides acidic medium.
• Besides it activates pepsinogen to pepsin and prorennin to rennin.

5. Small Intestine (Duodenum + Jejenum + Ileum)

• Here the food from the stomach is mixed with bile (from liver) and pancreatic juice (from pancreas) and moves forward by peristaltic movement.
• Duodenum receives the bile – pancreatic duct formed by the union of bile duct and pancreatic duct.
• Both jejunum and ileum have numerous figure like projections called the villi.
• The villi contain blood vessels to receive the products of digestion after they have been absorbed.
• Bile doesn’t take direct part in digestion of fat; it just makes the food alkaline. (It is stored in gall bladder)
• Pancreatic juice contains several enzymes, which act on proteins, carbohydrates and fats.

6. Large Intestine (Caecum + Colon + Rectum)

• It receives undigested material from the small intestine and absorbs water.
• Caecum is the diverted part of intestine.
• Cellulose digestion takes place in it.
• It is very large in herbivores.
• Vermiform appendix is a part of caecum, which produces antibodies. Both caecum and appendix are vestigial in humans.
• The remaining waste material is sent to rectum and discharged through anus.

Pancreas

Intestinal Glands