ABOR SENIOR HIGH SCHOOL(ABORSCO) SUBJECT-SCIENCE(second year )

The Digestive System

The digestive system also known as the gut is essentially a long tube about 9 metres long. It starts at the mouth and ends at the anus. There are many different parts to the digestive system but each part has its’ specific function.

Oral Cavity (Mouth)

Teeth

Food enters the mouth and digestion begins with the teeth breaking down the food into smaller pieces. This serves 2 purposes:

1. Makes the food easier to swallow
2. Gives food a large surface area for enzymes to work on

A full set of adult teeth consists of 32 teeth.  But not all teeth are the same and are shaped and designed for different jobs. There are four different types of human teeth:

1. Incisors are used for cutting and biting.
2. Canines are pointed and used for piercing and tearing.
3. Pre-molars are used for grinding and crushing.
4. Molars are like pre-molars and used for crushing and chewing.

In a full set of adult teeth there are 8 incisors, 4 canines, 8 pre-molars and 12 molars which makes 32 in total.
All teeth have similar features as shown in the diagram below:

Salivary glands

The salivary glands secrete saliva which mixes with the chewed food. Saliva has two functions:

1. Saliva contains the enzyme amylase which is a carbohydrase and breaks down starch into sugar.
2. Saliva also contains mucus which lubricates the food and helps it pass down the oesophagus.

1. 

Pharynx & Oesophagus 

Swallowing

Swallowing is a reflex reaction and happens without us thinking about it. Before swallowing the tongue rolls the food into a soft ball and pushes it to the back of the mouth. The food pushes the soft palate upwards which blocks the upper pharynx and stops food going into the nasal cavity. Voluntary muscles in the face, neck and tongue push the food through the pharynx. As the food is swallowed it passes over the epiglottis which covers the opening of the respiratory system and prevents food entering it. Food passes the epiglottis and into the oesophagus which connects the pharynx to the stomach.
Now the food enters the oesophagus and is called a bolus. The oesophagus has circular muscles in the wall. These muscles contract behind the bolus to push it along and the muscles in front of the food relax. This way food passes along the oesophagus to the stomach. This movement is known as peristalsis.