In previous classes you've learnt about the structure of human, animal and plant bodies.
There are key maintenance functions that must go on in all living organisms to keep the body functioning.
To keep the body working, our organs need energy. This energy is acquired in the form of food - which is chemical energy and then broken down into usable forms of energy in a process known as nutrition.
The whole process of acquiring food and using it for bodily functions can be broken down into 4 broad steps.
Click on the buttons below to see the four steps!
*Click on each new button to reveal the next step
We will study the four steps for plants and animals in this chapter.
Nutrition can be acquired in two ways - autotrophic or heterotrophic. Autotrophic nutrition involves the process of photosynthesis and hence is not applicable to human beings.
Human beings acquire their nutrition through heterotrophic means.
The food we eat has chemical energy stored in it.
You must have heard that a healthy diet involves eating food which provides you with adequate amounts of carbohydrates, protiens, vitamins and minerals.
Carbohydrates- are compounds which are made of carbon, hydrogen and oxygen atoms. When you eat sugary or starchy food, you are getting a healthy dose of carbohydrates!
In order to break down the food into simpler chemical substances the food needs to be digested.
The process of digestion begins with mastication(chewing) in the mouth. Our teeth break down food from solid to semi solid form.
Salivary glands secrete a fluid called saliva which mixes with the food and makes it easier to swallow.
Saliva contains an enzyme called amylase which helps to break down starch (a complex sugar) into simple sugar.
The lining of the alimentary canal(digestive system) has muscles that contract and relax rhytmically to move food through the canal.
From your mouth, the food travels down the food pipe or the oesophagus to the stomach.
The stomach is a fairly flexible organ. It expands when food enters it.
The walls of the stomch help in mixing the chewed food with enzymes which help break down the food even further.
Inside the stomach are gastric glands which line the inner wall of the stomach.
These glands release fluids essential for the digestion process.
They release hydrochloric acid, pepsin and mucus.
The hydrochloric acid creates an acidic medium in the stomach which facilitates the action of pepsin.
Specifically, the hydrochloric acid lowers the pH of the stomach to 1.5 -2. The low pH then activates the pepsin.Pepsin then helps in breaking down complex protiens into simpler peptides.
Because such low pH can be harmful to the stomach, mucus creates a protective layer for the inner lining of the stomach.
After the digestion in the stomach, the food enters the small intestine.
The small intestine is actually quite long but it is coiled to fit into our body.
The small intestine is the site of complete digestion of carbohydrates, protiens and fats.
Protiens are converted to amino acids.
Complex carbohydrates are converted to glucose.
and fats are converted to fatty acids and glycerol.
The walls of the small intestine contains glands which secrete intestinal juices which helps in digestion.
The small intestine also recives secretions from the liver and pancreas which aid in this digestion.
Because the food coming from the stomach can be quite acidic, bile juice from the liver helps to make the food more alkaline.
Bile also acts on fat globules and breaks them down into smaller globules.
The pancreas secretes pancreatic juice which helps in breaking down protiens and emulsified fats.
Once the food has been digested in the small intestine, it is absorbed by the walls of the intestine.
The walls actually contain a large amount of finger like projections called villi.
The villi have a rich supply of blood vessels. These blood vessels absorb the digested food and transport it to each and every cell in the body, thus providing each cell, muscle and organ with the energy they need to keep our body working!
The remaining unabsorbed food is then passed on to the large intestine.
The wall of the large intestine then absorbs water from the remaining food, while the rest is removed from the body via the anus.
Phew! That's a long process isn't it?
Usually it takes upto 6-8 hours after you eat for food to pass through your stomach and small intestine! Your body is continously working to digest the food you eat.