Food is something you probably think about often during the day. You look forward to eating some foods, and hope that your favourite foods are served up for dinner. Food provides your body with all its building materials and the energy you need for all your activities. However, you cannot use food until after your digestive system has been to work on it.

The need for body systems

Your body is organized at several different levels. Cells come in many types, such as skin cells and muscle cells. Cells of the same type that carry out the same job in the body are grouped together to form tissues, such as muscles and nerves. At the next level of organization, tissues are grouped to form organs, such as the stomach or brain.

An organ is a structure that contains at least two different types of tissue that work together to complete a task. Organs are arranged into organ systems that have two or more different organs that work together.

The systems of your body all have their own jobs to do:

• The respiratory system takes in oxygen.
• The digestive system makes food available in a form the body can use.
• The circulatory system carries the food and oxygen to the cells where it is needed.
• The excretory system gets rid of wastes.
• The skeletal system supports the body and enables it to move.

The digestive system

Digestion is the process of breaking down food into a usable form and making the nutrients available.

Digestion takes place in your digestive system. Your digestive system consists of:

• a digestive tract, the pathway that the food takes though a series of organs. The first part of the digestive tract is the mouth
• organs off to the side of the digestive tract that produce chemicals to assist with digestion.

Types of digestion

There are two different types of digestion:

• Mechanical digestion
• Chemical digestion

Mechanical digestion is when the food is broken down into smaller pieces. It is like cutting a slice of bread or a piece of meat into smaller pieces. Mechanical digestion is a physical change because no new substances are made.

In chemical digestion the large, complex substances in the food are broken down into simpler chemicals. This produces new, smaller chemicals that the body can absorb. Chemical digestion is a chemical change because new substances are produced.

In the mouth

Types of Teeth

The process of digestion starts with your teeth.

• Incisors- bite off parts of your food
• Canines- they are used for tearing apart meat
• Premolars- These are for grinding up food into smaller parts and cutting them
• Molars- these are used for grinding food

The incisors are the four pairs of teeth at the front.Their job is to bite offpieces small enough to chew. The tongue then pushes the food back to the premolars and molars. These teeth grind the food into smaller and smaller pieces as you chew.

In humans, the canine teeth have no significant function or job. However, in animals such as lions or wolves that catch live prey, the long canines are used to hold onto the food as it is torn apart.

Biting and chewing food is a form of mechanical digestion but chemical digestion also takes place in the mouth. As the food is being digested mechanically, it is mixed with saliva. Saliva is a watery liquid produced by your salivary glands.

Saliva contains a chemical that starts to change any starch (a complex sugar) in the food into glucose (a simple and easily absorbed sugar). Saliva also moistens the food, making it slippery, slimy and easy to swallow. The tongue rolls the food into a ball (called a bolus), which is pushed down into the next part of the system, the oesophagus.

Swallowing

Food travels down the Oesophagus into the stomach. Muscles push these down the bolus down the oesophagus. This is the process known as Peristalsis.

Stomach

The stomach contains gastric juice, which is produced by special cells in the stomach wall. Gastric juice contains:

• hydrochloric acid-a strong acid that kills many of the bacteria that may have entered the body with the food
• mucus-creates a layer on the lining of the stomach and prevents the stomach digesting itself
• digestive juices -contain chemicals that start the digestion of protein, the main nutrient found in meat.

Small intestine

The small intestine is a very long, narrow tube. It is the longest part of your digestive tract- up to 6m. ( the small intestine is so long because it is required to absorb water and nutrients, and the longer the small intestine the greater the amount of nutrients and water it can absorb

The duodenum is the first part of the small intestine. Two tubes entering the duodenum carry chemicals important for digestion. These tubes come from the pancreas and the liver.

The pancreas is not part of the digestive tract. It is an organ that is connected to it and produces pancreatic juice. Pancreatic juice contains chemicals that help digest carbohydrates (starches and sugars), fats and protein.

The nutrient uptake increased considerably through hair like structures known as Villi.

The nutrients that pass from the small intestine are:

• fatty acids and glycerol produced from the digestion of fats
• amino acids from the digestion of proteins
• glucose from the digestion of carbohydrates.

Liver

The liver is the body’s largest internal organ and performs over 500 different chemicals processes. YOU CANNOT LIVE WITHOUT THIS ORGAN- IT IS VITAL.

The process in the liver that is important for digesting is the production of bile. Bile is a greenish liquid responsible for chemical digestion of fats.

Large intestine

The large intestine is the final section of your digestive tract. At 1.5 meters, it is shorter than the small intestine, but it is wider, being 6 to 7 cm in diameter.

Digestive disorder

• Vomiting
• Diarrhea
• Heartburn
• Appendicitis