Digestion in humans

Humans take food through the mouth, digest the food and finally, the undigested food is removed from the body. The food passes from the oral cavity and finally, the undigested food is defecated through the anus.

It is a complex process involving the following steps:

Ingestion:

Ingestion refers to the intake of food

Ingestion takes place through Mouth

Digestion:

Digestion refers to the breakdown of ingested food into simpler forms

Teeth, Stomach, Small intestine and secretion from various glands help in Digestion

Absorption:

Absorption refers to the process in which digested food absorbed into the body fluids (Blood & lymph)

Small intestine plays a major role in Absorption

Assimilation:

Assimilation refers to the process in which absorbed food is transported to different cells of the body

Egestion:

Egestion refers to the process of removal of undigested food from the body

Large intestine plays a major role in Egestion

Parts of the digestive tract in humans:

The digestive tract in humans starts from the mouth and ends at the anus. It is also called the alimentary canal.

 Human Digestive tract

The parts of the digestive tract are:

1. Mouth and buccal cavity

2. Food pipe/Oesophagus

3. Stomach

4. Small intestine

5. Large intestine

6. Rectum

7. Anus

There are some associated glands that secrete enzymes that help in the digestion of food. These include:

1. Salivary glands

2. Liver

3. Pancreas

The digestive tract and the associated glands together constitute the digestive system.

Mouth and Buccal cavity

We take the food through our mouth.

Ingestion: It is the process of taking food into the body.

Salivary glands: Our mouth has three pairs of salivary glands. They secrete saliva.

Saliva: Saliva acts upon starch and break down into sugars.

 Mouth showing teeth and tongue

Teeth and its types

Teeth help in chewing our food. Each tooth is placed in separate sockets in the gums. There are different types of teeth that perform different functions.

There are two sets of teeth, one set is called milk teeth which grow during infancy and they fall between the age of six to eight years.

The second set of teeth is called permanent teeth which replace milk teeth and they remain throughout our life. They fall during old age.

Tooth decay:

1. Improper cleaning of teeth leads to the growth of harmful bacteria that produce acids from the leftover food present in our mouth, which damages our teeth leading to tooth decay.

2. We can avoid it by brushing teeth twice a day, rinsing our mouth properly after meals, avoiding uptake of sweets, dental floss, etc.

Experiment to show the effect of saliva on starch

1. Two test tubes were taken and were labeled A and B.

2. In test-tube, A one teaspoon full of boiled rice was kept.

3. In test-tube B one teaspoon full of boiled rice which was chewed for 3-5 minutes were kept.

4. 3-4 ml of water was added to both the tubes.

5. Then 2-3 drops of iodine solution were added to both test tubes A and B.

Observation:

The test tube A shows blue-black color whereas test tube B does not show this color.

Conclusion:

Since test tube B has boiled rice which was chewed for 3-5 minutes, the saliva present in the mouth has acted upon starch to break down into sugars. So it does not show any color in the presence of an iodine solution. Boiled rice in test tube A has not been exposed to saliva, so the starch is present which is indicated by blue-black color on the addition of iodine solution.

Tongue

The tongue is a fleshy muscular organ which is free at its front end and is attached at the back of the floor of the buccal cavity. It can move in all directions.

Functions:

1. It mixes saliva with food while chewing.

2. It plays an important role while talking. The taste of the food can be known due to different taste buds present in our tongue. It helps in swallowing our food.

Experiment to identify the position of taste buds in the tongue of humans

Four different solutions were made – sugar solution, salt solution, solution of neem leaf juice and lemon juice. Four clean earbuds were taken which were dipped inside the above solutions separately. These buds were then rubbed on different areas of the tongue separately.

Observation:

The bud dipped in sugar solution taste sweet at the tip of the tongue. The bud dipped in salt solution tastes salty in the area just behind the tip of the tongue. The bud dipped in lemon juice tastes sour at the two sides of the tongue. The bud dipped in neem juice tastes bitter at the back portion of the tongue.

Different taste buds located on the tongue