Different ways of taking food
All animals require food for obtaining energy, growth, repair of damaged parts, and functioning of the body. The process of taking food by an animal and its utilisation in the body is called animal nutrition.
Starfish: It is a marine animal that is covered by hard shells of calcium carbonate. It has a unique mode of nutrition. It opens the shell of its prey and pops out its stomach through its mouth surrounding the soft body of its prey. The starfish after capturing its prey brings back its stomach inside its own body.
Carbohydrates, fats, and proteins are large insoluble substances that cannot pass through the walls of our intestine and get absorbed in that form. Therefore, these substances are broken down into small water-soluble substances. This is done by the process of digestion.
Digestion in Humans
Alimentary canal: The food components pass through a continuous canal and get digested in each compartment. This is called an alimentary canal, it is ‘the tract or canal running from mouth to anus of human being where digestion and absorption of food take place.
The alimentary canal can be divided into various compartments:
- The buccal cavity
- Food pipe or oesophagus
- Stomach
- Small intestine
- Large intestine ending in the rectum
- The anus
The main digestive glands which secrete digestive juices are
- salivary gland
- liver
- pancreas
The process of taking food into the body is called ingestion.
The process by which the food containing large insoluble substances is broken down into small water-soluble substances is called digestion.
There are two methods of digesting food, i.e. physical method (including chewing and grinding of food in the mouth) and the chemical method (addition of digestive juices to the food by the body itself).
The process by which the digested food passes through the intestinal wall into the bloodstream is called absorption.
The process by which the absorbed food is taken into body cells and used for energy, growth, and repair is called assimilation.
The process by which the undigested food is removed from the body is called egestion.
The Digestive System - The alimentary canal and the digestive glands together form a system in the human body which is responsible for the digestion of food in the body. This system is called the Digestive System.
The Mouth or Buccal Cavity:
The food is chewed with the help of teeth, saliva and the tongue present in the mouth.
The tongue present in the mouth helps in mixing the food with the saliva and helps in swallowing it inside the mouth. It also has taste buds which help in identifying the taste of anything that we eat.
Different types of teeth
Milk Teeth - In early childhood a set of teeth grows in children that then fall off after certain age of 6 to 8 years. These teeth are called Milk Teeth.
Permanent Teeth - The teeth that grow after milk teeth fall off are called Permanent Teeth. They generally remain during the lifetime of a person or at least until old age.
Tooth Decay –
- Gradual damage of teeth is often called tooth decay.
- Tooth decay is caused mainly because of eating food with high sugar content, soft drinks, and chocolates.
Prevent tooth decay:
- Clean your teeth with a brush or dental floss at least twice a day.
- Rinse your mouth after every meal you eat.
- Do not put a dirty finger or any unwashed food items in your mouth.
Food Pipe or Oesophagus
- The food pipe starts from the neck region and runs until the chest area in animals.
- The food, when chewed, moves through the food pipe and reaches the stomach through this path.
- The food moves in the downward direction in the food pipe.
The Stomach
It is the widest part of the alimentary canal. It's a bag-like structure in a flat U shape. The stomach is connected with the food pipe and the small intestine.
The stomach’s inner lining produces three things:
- Mucous: It protects the stomach lining
- Hydrochloric Acid: It kills the bacteria present inside the stomach and activates the digestive juices
- Digestive Juices: They help in digestion of the food by breaking down the proteins present in the food into simple substances (olympiads)
Small Intestine
- It is a highly coiled structure.
- The liver and pancreas release digestive juices into the small intestine.
- The inner lining of the intestine also secretes some digestive juices on its own.
- The small intestine breaks the carbohydrates into glucose, fats into fatty acids and proteins into amino acids.
The Pancreas
- It is a cream-coloured gland present in the human body.
- It secretes pancreatic juice that helps in the digestion of fats, carbohydrates, and proteins.
Villi in the intestine: the small intestine contains small finger-like structures called villi. They increase the surface area of the intestine thereby increasing the amount of absorption. The digested food gets into the blood vessels through the villi and then reaches the whole body.
The Large Intestine
- Any food that is left undigested passes through the small intestine and enters the large intestine.
- It is a wide tube-like structure.
- The main function of the large intestine is to absorb water and salts from undigested food.
- The rest of the waste, undigested food passes through the rectum.
Diarrhea: A condition when watery stools appear frequently is called Diarrhea.
Food poisoning and infection are two main causes of diarrhea.
Digestion in Grass-Eating Animals
Digestive System in Cow:
Rumen - It is a sac-like structure present between the food pipe and the small intestine in grass-eating animals like cows and buffaloes.
Cud: The partly digested food present in the rumen is called Cud.
Rumination: The cud returns to the mouth in these animals and then they chew it. This is called Rumination.
Ruminants: The animals that swallow their food at first and then chew it, later on, are called Ruminants.
Grass-eating animals can digest cellulose while several other animals cannot. These animals have different type of bacteria present in the stomach that helps in digesting the cellulose.
Feeding and Digestion in Amoeba
The Amoeba is a microscopic organism which is made up of only one cell. The Amoeba is capable of changing its shape and position on its own.
The Amoeba has a cell membrane, cytoplasm, a nucleus that is round and dense, and small vacuoles which are like bubbles present all over it.
The Amoeba also secretes out waste products or undigested food out of its body.
Amoeba uses false teeth called pseudopodia to take in the food present in the surroundings. Whenever it wants to intake the food the pseudopodia or finger-like projections come out of its body.
The pseudopodia engulf the food and the food gets stored in the food vacuoles. Then it secretes some digestive juices inside the vacuoles that help in the digestion of the food.
The food of Amoeba are microscopic organisms like tiny plants and animals present in pond water.
