Digestion – The breakdown of complex components of food into simpler substances
Digestion in Humans
- Digestive tract and the associated glands together constitute the digestive system.
- They are secreted by the inner walls of the stomach, small intestine & other glands
- Help in the breakdown food from complex substance into simpler substances
Parts of the digestive tract
- The food passes through a continuous tract called alimentary canal
- It can be divided into various parts:
- The buccal cavity,
- Food pipe or oesophagus,
- Small intestine,
- Large intestine ending in the rectum
- The anus.
Mouth and buccal cavity
- Ingestion – The process of taking food into the body
- 4 types of tooth: Incisor, Canine, Pre-molar, and Molar
- Cutting and biting teeth - Incisor
- Piercing and tearing teeth - Canine
- Chewing and grinding teeth - Pre-molar, and Molar
- Saliva breaks down starch into sugars
- Tooth decay –
- Normally bacteria are present in our mouth
- They break down the sugars present from the leftover food and release acids
- The acids gradually damage the teeth and this is called tooth decay
- By brushing our teeth, we prevent tooth decay
- Runs along the neck and the chest
- Food is pushed down by movement of the wall of the foodpipe
- Widest part of the alimentary canal
- Its inner linings secrete mucous, hydrochloric acid and digestive juices
- The mucous protects the lining of the stomach
- The acid kills many bacteria that enter along with the food and also makes the medium in the stomach acidic which helps the digestive juices to act.
- The digestive juices break down the proteins into simpler substances.
- A reddish brown gland situated in the upper part of the abdomen on the right side
- Largest gland in the body
- Secretes bile juice that is stored in a sac called the gall bladder
- Bile plays an important role in the digestion of fats
- About 7.5 metres long
- Receives secretions from the liver and the pancreas and also secretes juices
- Food gets digested here:
- Carbohydrates get broken into simple sugars such as glucose,
- Fats are reduced to fatty acids and glycerol,
- Proteins are converted into amino acids
- Inner walls of the small intestine have numerous finger-like outgrowths called villi
- The villi increases the surface area for absorption of the digested food
- Digested food then passes into the blood vessels through the villi. This process is called absorption
- The absorbed substances are transported via the blood vessels to different organs
- They are used to build complex substances. This is called assimilation
- The food that remains undigested and unabsorbed enters into the large intestine
- About 1.5 meter long but wider than small intestine
- Absorbs water and some salts from the undigested food material
- The remaining waste passes into the rectum
- The faecal matter is removed through the anus by the process of egestion
Digestion in grass-eating animals
- Such animals swallow the grass and store it in a part of the stomach called rumen
- Here the food is partially digested and is called cud
- Later the cud returns to the mouth in small lumps and the animal chews it
- This process is called rumination and these animals are called ruminants.
Digestion of cellulose in ruminants
- The grass is rich in cellulose, a type of carbohydrate
- The cellulose in the food is digested in the rumen by the action of certain bacteria
- These bacteria are not present in humans.
Feeding and digestion in amoeba
- Amoeba is a microscopic single-celled organism found in pond water
- It constantly changes its shape by pushing out one, or more finger-like projections, called pseudopodia or false feet
- This is for movement and for capturing the food
- Amoeba pushes out pseudopodia around the food particle and engulfs it.
- The food becomes trapped in a food vacuole
- Digestive juices are secreted into the food vacuole.
- They act on the food and break it down into simpler substances.
- Gradually the digested food is absorbed and The undigested residue of the food is expelled outside by the vacuole