Digestive System

Digestive System of the Human Body.
Detailed explaination.
According to ICSE syllabus for grade 9.
This Presentation includes: The alimentary canal, organs and their functions, secretions, processes and definitions.
Based on selina publishers- Biology Part 1 grade 9.

1. DIGESTIVE SYSTEM Jhanavi purohit

2. What is digestive system? DIGESTION is the breakdown of naturally occurring foods into diffusible form so that it can be directly absorbed by the blood for distribution in the body. It converts lipids to fatty acids , proteins to simple amino acids and carbohydrates to simple sugars . DIGESTIVE SYSTEM is an organ system that helps in the process of digestion. DIGESTIVE SYSTEM Alimentary canal Digestive Glands

3. The Alimentary C anal and the Glands. The alimentary canal is an muscular tube that starts at the mouth and ends at the anus. It is approximately nine metres long. The digestive organs/glands include : Mouth, Teeth, Salivary glands, Oesophagus, Stomach, Liver, Pancreas, Gall Bladder, Small Intestine, Large Intestine.

4. The Mouth It is the space where the food we eat is chewed and mixed with the saliva. It has tongue and lips which have there own functions.

5. The Teeth They cut and break down the food into smaller bits for larger surface area so that the enzymes can act on it. Teeth Incisors Canines Premolars Molars

6. Teeth in mammals appear in two sets during life. 20 first and the gradually increasing to 32. The first set, namely the milk teeth, appear when the infant in about 7 to 8 months old. They are temporary and fall out when their roots dissolve away in the jaw. The second set appear eventually after the milk tooth has fallen. They are called the permanent teeth. They mostly grow and protrude out at the age of 12 years.

7. Structure of a Tooth

8. Salivary Glands There are 3 pairs of salivary glands: SUBLINGUAL – located below the tongue. PAROTID – located in front and beneath the ear. SUBMANDIBULAR – located near the inner side of the lower jaw on each side.

9. Saliva Saliva is a secretion from the salivary glands which helps in the following : - Moistens inner lining of the mouth to allow speaking and swallowing. - Lubricates the food by mixing in it. - Acts as a solvent for certain food particles. - Stimulates the taste buds present on the tongue. - Helps in the formation of bolus . - Digests starch and converts it into maltose. - Cleans mouth and destroys germs. - Aids in water balance in the body.

10. Oesophagus It is a tube that simply conducts the food from the throat to the stomach.

11. What is Peristaltsis ? Peristaltsis is a wave of constriction caused by the circular muscles of the gut pushing the food along. It occurs throughout the gut.

12. Stomach Our stomach is an elastic bag located below the diaphragm which can hold 2-3 litres of food. It is muscular and it churns the food thoroughly to mix it with the gastric juice secreted by its inner lining. The opening of the stomach to the intestine is called the pylorus. Sometimes when the stomach is overloaded or rather disturbed, antiperistaltsis takes place and causes vomiting, ie , throwing the food out by mouth.

13. The Gastric Juice is colourless, highly acidic and consists of water, some salts, hydrochloric acid ( HCl ) and pepsin , an enzyme. Its functions : - Kills germs presents in the food, if any. - Activates pepsinogen and converts it into pepsin to act on proteins and form peptides. Food stays in the stomach for 3 hours in a pulp-like state called chyme .

14. Small Intestine Small intestine is a tube which is 7 m long and 2.5cm wide, coiled in the abdomen like It has 3 sub regions : Duodenum , where the bile duct opens, Jejunum , 2 metres after duodenum and Ileum , next 4 metres twisted.

15. Small villi is present on the inner lining of the small intestine, which enormously increase the surface area to help in digestion. The small intestine serves for both, absorption and digestion. It receives two digestive juices, bile and the pancreatic juice.

16. Bile, yellow-green watery fluid (due to billiverdin and bilirubin) which is produce in the liver is received by the duodenum. It contain a lot of sodium bicarbonate (NaHCO 3 ) to neutralise the acid content of the food. The Pancreatic Juice is produced in the pancreas and is released into the duodenum. It contains the enzymes Amylopsin , digests leftover starch into maltose, Trypsin , which converts polypeptides into peptides and Steapsin , which converts fats into fatty acids and glycerol. The intestinal juice contains erepsin and converts – peptides to amino acids, maltose to glucose, sucrose to glucose+fructose and lactose to glucose+galactose .

17. The Large Intestine It is 1.5m long and consists of the Caecum, a blind pouch at junction of the 2 intestines which may cause appendicitis when its vermiform appendix inflames, Colon, is a little longer than a metre and Rectum, around 15 cm long, opening at the anus. Functions of the large intestines are : - To absorb the leftover water in the contents to become semi-solid faeces. - To store the faeces until defaecation.

18. Accessory Glands LIVER PANCREAS GALL BLADDER

19. Bibliography Selina publishers Biology grade ten part II Images from google