human digestive system and its function. Human digestive system starts from Mouth, buccal cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus are the parts in the human digestive system.

1. NUTRITION IN ANIMALS- PART1
HUMAN DIGESTIVE SYSTEM
CLASS –VII
CBSE
Video: Human Digestive system
https://www.youtube.com/watch?v=O1AtPbj3rGw&t=631s
Google Form Worksheet:
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Ms. NANDITHAAKUNURI

2. Human digestive system starts from Mouth, buccal cavity, pharynx,
oesophagus, stomach, small intestine, large intestine, rectum and anus
are the parts in the human digestive system.

3. Mouth, salivary glands and their functions Mouth is only an opening
of the digestive system. Taking in of food digestive system. Taking
in of food through mouth is called ingestion. The cavity or space in
the mouth is called oral cavity or buccal cavity.

4. Digestion starts in buccal cavity. Teeth, tongue and openings of three
pairs of salivary gland are present in buccal cavity. Physical and
chemical nature of the food changes when it is masticated with the
help of teeth and mixed with saliva.

5. There are four types of teeth in man- incisors, canines, premolars and
molars- each for a specific functions. The arrangement of teeth is
same on the upper and lower jaws. An adult human has thirty two
teeth – 8 incisors, 4 canines, 8 premolars, and 12 molars.

6. Tongue is muscular and pushes the food on to the teeth during
mastication. Taste buds on the tongue sense the taste of food.

7. Three pairs of salivary glands are present in the buccal cavity. They
are parotid, sub-lingual and sub-maxillary glands. Parotid glands
are present near the ear. Secretion from these glands is sent into
buccal cavity through ducts.

8. Other two pairs of glands open below the tongue through ducts.
Saliva is released when food is present in buccal cavity. It is also
released at the sight, smell and even thought of food. Saliva contains
large amount of waste small amounts of salts and mucous.

9. Saliva is slightly alkaline in nature. It contains an enzymes called
salivary. Amylase converts starch into dextrin and maltose sugar. As
the food stays only for short time in the buccal cavity, starch is
partly digested here.

10. Mucous present in the saliva makes the food sticky and helps its
passage easy through pharynx. The food in buccal cavity undergoes
mainly physical changes. Saliva is also useful as a solvent for
dissolving the chemical substance present in food.

11. Oesophagus is a narrow tube and connects pharynx and stomach. It
has both volume and involuntary muscles. These muscles are arranged
circularly and longitudinally. Internally, the wall of oesophagus is
lined with a mucous membrane which secretes mucous. Mucous acts
as a lubricant and helps in the easy and smooth passage of food.

12. Swallowing means pushing food into oesophagus, is a voluntary act.
Once food enters oesophagus, swallowing becomes an involuntary act.
When food enters into oesophagus, the muscles present in its wall
contract and relax alternately producing wave like movements. These
are called peristaltic movements.

13. They help in pushing the food down the oesophagus into the stomach. Peristaltic
movements of oesophagus are involuntary. There are no digestive enzymes in
oesophagus. Oesophagus is only a passage through which food enters into stomach.

14. Hence, food does not undergo any change in pharynx and oesophagus.
However, amylase present in the saliva continues to act on the starch
present in the food. Stomach as a muscular bag it is present on the left
side in the abdominal cavity, below the diaphragm. Part of the stomach
into which oesophagus opens is called cardiac stomach.

15. Part of the stomach that opens into duodenum is called pyloric stomach.
Opening of the pyloric stomach into duodenum is protected by pyloric
sphincter.
Muscles in the walls of the stomach are involuntary muscles. These are
arranged longitudinally, diagonally and circularly. These muscles,
contract in different directions. As a result food is churned in the
stomach.

16. Stomach has three important roles:
1. It stores the food temporarily.
2. Mixing of various components in the food thoroughly – this occurs
due to contraction and relaxation of muscles.
3. It brings about physical and chemical changes in the food.

17. Internally stomach wall is lined by mucous membrane. A number
of glands called gastric glands are present in this membrane. Each
gastric gland opens by a small pore into the lumen of stomach.
Gastric glands secrete gastric juice and mucin.

18. Gastric juice is a thick, clear and straw coloured fluid. Gastric juice
contains hydrochloric acid and enzymes. The food gets mixed with
hydrochloric acid present in the gastric juice.
Hydrochloric acid kills bacteria present in food. It also destroys the
structure of proteins, so that enzymes can digest them easily. Mucous
membrane protects stomach wall from the action of acid present in the
gastric juice.

19. Pepsin and lipase are the enzymes present in the gastric juice. When
pepsin is secreted, it is inactive and is called as pepsinogen.
Acids converts inactive pepsinogen to pepsin which is the active
form of the enzyme. Pepsin breaks down proteins into peptones and
proteases. Lipase converts fats into fatty acids and glycerol. In
children, another enzyme called rennin is secreted into the stomach.
It curdling of milk. This enzyme disappears as the child grows.

21. Food is retained in the stomach for two to four hours and is partially
digested in the stomach. As the food is undergoing changes in
stomach, the pyloric sphincter closes the opening of stomach into
duodenum. The pyloric sphincter allows only small quantities of food
into duodenum at a time. The food that enters the duodenum is called
chyme. This is acidic and very soft.

22. Duodenum, pyloric sphincter, liver, gall bladder, pancreas
Duodenum is ‘U’ shaped and connects stomach with ileum. Bile from
the live and pancreatic juice from pancreas reach duodenum through
separate ducts. The pyloric sphincter remains closed until digestion of
food in the stomach is completed.

23. It opens and allows small amounts of acidic chime to enter into
duodenum, so that entire duodenum is not filled with chyme. Pyloric
sphincter closes immediately after the chyme enters duodenum and
this prevents the back flow of chyme into stomach. Opening and
closing of pyloric sphincter is involuntary.

24. Liver
Liver is present on the right side of duodenum, below the diaphragm. It
is brown in color there are four lobes in the liver. Cells present in the
liver are called hepatocytes. Liver produce bile duct through cystic duct.

25. Gall bladder:
Gall bladder is a pear shaped dark colored sack. Bile is stored
temporarily and also concentrated – by the removal of water in the gall-
bladder. Bile from the gall-bladder is sent to bile reaches duodenum
through a duct called bile duct.

26. Bile : in human beings bile has a mixed colour of yellow and golden
brown. Bile is thick and sticky fluid it has about 86% of water, bile
salts and bile pigments.
Sodium cholate and sodium deoxycholate are the bile salts. Bilirubin
and biliverdin are the bile pigments. Bile pigments are products
during the degradation of haemoglobin. Color of bile depends on the
amount of bile pigments.

27. When the bile duct is blocked, bile gets mixed with blood and
circulates in the body. Because of this, the eyes and skin become
yellow. This is called jaundice.

28. Pancreas :
Pancreas is an yellow grey gland and is present on the left side of
duodenum, below the stomach. There are two parts in pancreas. One
of them is called exocrine pancreas. Cells of exocrine pancreas open
into ducts and secrete a juice called pancreatic juice.

29. Small intestine – structure and functions of enzymes. Small intestine
is a tube of 6 meters length and 3cm width. The anterior part is called
duodenum. The middle part is called jejunum and posterior part is
called ileum. Ileum joins large intestine. The middle part of intestine
is coiled.

30. Cells present in the intestinal wall secrete mucous and enzymes in the
form of intestinal juice. This is called succusentericus. Enter kinesis,
peptidase, lipase, sucrose, nucleotides, nucleosides are some of the
enzymes present in the intestinal juice. Partially digested food entering
the intestine mixes with the intestinal juice. Enzymes present in the
intestine completely digested the partially digested food.

31. Absorption:
Transport of the products of digestion from the intestine into blood is
called absorption. Internally, intestinal wall has a number of finger
like process called villi. The villi increase the surface area for
absorption. Blood vessels are present in the form a network in the
villi. Products of digestion are absorbed first into the villi and from
there into the blood vessels and lymph vessels.

32. Colon
The diameter of large intestine is greater than the diameter of the small
intestine. Large intestine is present between small intestine and rectum.
The wall of colon is made of involuntary muscles. Movement of these
muscles pushes the food large intestine.

33. Water and minerals salts present in the chime are absorbed in the
colon and soft, solid faeces is formed. Faeces consists of undigested
food material, dead material, bile salts and bile pigments.
By the peristaltic movements of large intestine, faeces is pushed
towards rectum. It is expelled out through the anus. This happens when
the sphincter muscles that guard anus expand. This activity is called
defecation.

34. Video : Human Digestive System
https://www.youtube.com/watch?v=O1AtPbj3rGw&t=631s
Google form worksheet:
Thank you
By
Ms.Nanditha Akunuri