The human digestive system

In a nutshell

The food you eat is broken down by the digestive system to be used for energy, growth and development. This summary explores the six main parts of the body involved in digestion and why food needs to be digested.

Role of the digestive system

Food, as it appears on a plate, is too large to be useful to the body. Nutrients need to be small enough to be absorbed into the blood where they can be used for energy, growth and development.

Example

Protein is a nutrient needed by the body for growth but it has to be broken down before it can be used.

Definitions

Absorb	To take up.
Waste	The leftover food that cannot be absorbed or used.
Acid	A substance that kills the bacteria in food.
Enzyme	A substance that helps to break down food in the stomach.
Nutrient	A substance obtained from food that is needed for energy, growth and development.
Chyme	A mixture of partially digested food and stomach acid.
Swallow	The action of moving food from the mouth to the stomach.
Digestion	When the body breaks down large pieces of food into smaller pieces.

Parts of the digestive system

The digestive system is a group of body parts that carry out the process of digestion. There are six main parts of the body involved in digestion.

1a. Mouth, 1b. Salivary glands, 2. Oesophagus, 3. Stomach, 4. Small intestine, 5. Large intestine, 6. Anus

Steps in digestion

Digestion begins with food entering the mouth and ends with waste being pushed out of the anus as poo.

	Body part involved	Explanation
1.	Mouth	The mouth has teeth which chew food into smaller pieces. The salivary glands make a liquid called saliva which moistens and breaks down food in the mouth before swallowing.
2.	Oesophagus	The oesophagus is a muscular tube connected to the mouth which squeezes swallowed food down into the stomach.
3.	Stomach	The stomach mixes food with acids and enzymes to break it down into a runny pulp called chyme ready to enter the small intestine.
4.	Small intestine	The small intestine is a narrow tube with special cells that absorb nutrients from chyme and transport them into the blood.
5.	Large intestine	The large intestine is a wider tube that absorbs water from chyme making the waste left behind thicker.
6.	Anus	The anus is the exit location for waste where it is pushed out of the body as poo.

Science; Animals, including humans; KS2 Year 4; The human digestive system