LECTURE 4: NUTRITION IN HUMAN BEINGS (CLASS X)

CLASS X   |    SCIENCE    |    LIFE PROCESSES

      Notes prepared by Subhankar Karmakar

---

click to access other class notes

SCIENCE: CLASS X: CBSE (CLASS NOTES)

FOR 1 TO 1 ONLINE CLASSES OVER ZOOM PLATFORM AT REASOBLE PRICE

BOOK YOUR CLASS, CALL AT 7002561074

---

• HUMAN DIGESTIVE SYSTEM

The various organs of the human digestive system in sequence are:

Mouth, Oesophagus, Stomach, Small Intestine and Large Intestine. The glands which are associated with the human digestive system and form a part of the human digestive system are : Salivary glands, Liver and Pancreas. 

• Alimentary Canal:

Human alimentary canal which runs from mouth to anus is about 9 metres long tube. The ducts of various glands open into the alimentary canal. 

• 1. INGESTION

The organ for human ingestion is called mouth.

• 2. DIGESTION 

In human beings, digestion of food begins in the mouth itself. 

• A. Buccal Cavity:

The mouth cavity is also known as buccal cavity. It contains teeth, tongue and  salivary glands. The teeth cut the food, chew and grind it. Tongue mixed the small pieces of food mixed with saliva. Saliva contains an enzyme called Salivary Amylase, which converts Starch into sugar. Hence, Salivary glands helps chemical digestion by secreting enzymes. But due to short period of time the digestion remains incompleted. 

• B. Oesophagus

The food pipe is known as oesophagus. It carries food to the stomach. 

• Peristaltic movement
• The walls of the food pipe/oesophagus have muscles which can contract and expand alternatively. When slightly digested food enters the food pipe, the walls of the food pipe start contraction and expansion movements. This contraction and expansion movements of the food pipe walls are known as  peristaltic movement. 
• Peristaltic movement moves the food in all digestive organs throughout the alimentary canal. 

• C. Stomach
• Stomach is a J shaped organ present in the left side of the abdomen. Here food is broken down into a semi-solid paste. 

• Gastric Juice

Stomach wall contains three tubular glands which secrete gastric juice. The gastric juice contains hydrochloric acid, the pepsin enzyme and mucus. The gastric juice is acidic in nature. 

• Function of Pepsin enzyme

In the acidic medium pepsin breaks down the proteins into smaller molecules, often into amino acids. Therefore, the digestion of proteins start at stomach. 

• Function of Hydrochloric acid

Pepsin is only activated in an acidic medium. The function of the Hydrochloric acid in stomach is to make the gastric juice acidic, so that pepsin can start digesting proteins molecules. Another function of the hydrochloric acid is to kill any bacteria that may enter into the stomach through the food. 

• Function of mucus

The mucus helps to protect the stomach walls from its own secretion of hydrochloric acids. If mucus is not secreted, hydrochloric acid will cause the erosion of the inner lining of stomach leading to the formation of ulcers in the stomach. 

• Sphincter Muscle

The partially digested food from stomach passes to the small intestine. The exit of food from stomach is regulated by a gate called sphincter muscle which releases it in small amounts into the small intestine. 

• D. Small Intestine

The small intestine is the largest part of the alimentary canal of about 6.5 m long in an adult man. It is very narrow hence, it is called small intestine. It is arranged in a coil form. The small intestine in human beings is the site of complete digestion of food like carbohydrates, proteins and fats. 

Difference in small intestine in Herbivores and Carnivores

Herbivores eat cellulose which is difficult to digest. Hence, herbivores have longer small intestine, whereas carnivores eat meat which is easier to digest so they have relatively shorter small intestine. 

Secretions from two glands in small intestine: Liver and Pancreas

• Liver : Liver is a gland that secretes bile. Bile is a greenish yellow liquid made in the liver and stored in the gall bladder. Bile is alkaline in nature and conatains salts which helps to break the fats/ lipids present in the food. 

Functions of Bile

Bile performs two functions. 

• (i) it makes the acidic food coming from the stomach alkaline so that pancreatic enzymes can act on it.
• (ii) Bile salts break the fats present in the food into small globules so that enzymes can act and digest it. 

• Pancreas

Pancreas is a large gland which lies parallel to and beneath the stomach. Pancreas secretes pancreatic juice which contains digestive enzymes like pancreatic amylase, trypsin and lipase. 

Pancreatic amylase breaks down the starch.

Trypsin digests the proteins and lipase breaks down the emulsified fats. 

Functions of intestinal juice

• The intestinal juice contains many enzymes which converts complex carbohydrates into glucose, proteins into simple amino acids and fats into fatty acids and glycerol all of which are water soluble small molecules. 
• The chemical digestion of food is brought about by biological catalysts called enzymes. 

• 3. ABSORPTION

• The small intestine is the main region for the absorption of digested food. After digestion, the molecules become so small that they can pass through the walls of the small intestine which contain blood capillaries and go to our blood. 
• The inner surface of small intestine has millions of tiny finger like projections called villi.  The presence of villi gives the inner walls of small intestine a very large surface area which helps in the rapid absorption of digested food. 

• 4. ASSIMILATION

• The blood carries the digested food to all the parts of the body where it becomes assimilated as part of the cells and it is used by the body cells for obtaining energy as well as for growth and repair of the body. 
• The unused part of the food is stored in the liver in the form of a carbohydrate known as glycogen. The stored glycogen can be used when it is needed. 

• 5. EGESTION

• A part our food which can not be digested passes from small intestine to a wider tube which is called large intestine. It is called large as it is wider. 
• The walls of the large intestine also have villi which absorb most of the water from the undigested part of the food and hence, it becomes solid. 
• The last part of the large intestine is called rectum which stores the undigested food for some time and then be expelled from our body as stool. This process is known as Egestion or defecation and it is controlled by anal sphincter. 

Dental Caries

1. The hard, outer covering of a tooth is called Enamel. It is harder than bones. 

2. The part of tooth below enamel is called Dentine. Dentine is similar to bone. 

3. Inside the dentine, there is pulp cavity, which contains nerves and blood vessels. 

4. Formation of small cavities in the teeth due to the action of acid forming bacteria and improper dental care is called dental caries. 

5. If the teeth are not cleaned regularly, they become covered with a sticky, yellowish layer of foid particles and bacteria cells called dental plaque. 

Extra Notes:

The long, tube-like organ that is connected to the small intestine at one end and the anus at the other is called large intestine. The large intestine has four parts: cecum, colon, rectum, and anal canal. Partly digested food moves through the cecum into the colon, where water and some nutrients and electrolytes are removed. The remaining material, solid waste called stool, moves through the colon, is stored in the rectum, and leaves the body through the anal canal and anus.