Digestive system

© Food – a fact of life 2009

The digestion process


Organs involved in digestion

What is the route food takes through the body?

Let’s look at the body you labelled for homework


Mouth

Mastication is the action of the teeth and the jaws working together to break food down. Food needs to be chewed to be broken down into pieces small enough to swallow.

Breaking the food down also gives it a larger surface area for the digestive enzymes to work on.


Saliva

Saliva contains the enzyme amylase which breaks down starch into simple sugars.

It also moistens the food allowing easier passage through the gastrointestinal tract.

Saliva is secreted from glands found under the tongue and at the back of the mouth.

The sight, smell, taste or even the thought of food will start to increase the amount of saliva secreted.


Moving on from the mouth

Food is masticated and mixed with saliva in the mouth.

The tongue and cheeks help to push the food into the teeth and also shape the food into a ball before being swallowed.

The ball is passed through to the oesophagus.


Oesophagus

The oesophagus is similar to a conveyor belt as it transfers the food from the mouth to the stomach in 3-6 seconds.

Circular muscles in the wall of the oesophagus relax in front of the bolus whilst circular muscles behind the food contract, pushing the ball onward. This is called peristalsis.

People do not have conscious control over the muscles in the oesophagus. Even if someone is upside down, the food will be passed on to the stomach.


Stomach

The stomach is an expandable sack made up of three different layers of muscles where the ball will be churned for a few minutes or up to 2 or 3 hours.

The ball is mixed with hydrochloric acid which helps to kill any bacteria present.


Stomach

The enzyme pepsin is also active in the stomach. It starts to break down protein to form peptides and amino acids.

Alcohol and a little water is absorbed by the stomach. Alcohol is absorbed through the stomach wall and taken to the liver where it is metabolised.

When the food has been churned into a creamy mixture known as chyme, the pyloric sphincter (a ring of muscles) opens and chyme is released gradually into the small intestine.


Small intestine

Chyme passes out of the stomach through the pyloric sphincter into the small intestine.

The small intestine is a tube about 6 metres long.

The small intestine is divided into three sections, the duodenum, jejunum and the ileum.

The first section of the small intestine is the duodenum.


Bile

Bile is produced in the liver and stored in the gall bladder. This contains bile salts which emulsify fat. Fat is normally insoluble in water. The bile salts are released into the duodenum making it easier to break down fat.

The bile allows the fats to mix in with the watery digestive juices, and allows the enzyme lipase to digest the fats efficiently.

Fat can take from 3 to 5 hours to be broken down and absorbed.


Pancreatic juices

The pancreas provides alkaline pancreatic juices.

These juices contain sodium bicarbonate to neutralise the hydrochloric acid mixed into the chyme from the stomach.

Pancreatic juices also contain digestive enzymes such as:

●Trypsin and chymotrypsin – break down protein to peptides and amino acids.;●Pancreatic amylase – breaks down starch and glycogen to maltose;●Lipase – breaks down fat to fatty acids and glycerol.


Peristalsis

Peristalsis is the action of waves of muscular contractions which moves food along the digestive system.

Dietary fibre aids peristalsis because it increases the bulk of the ball or chyme being moved along.


Wall of the small intestine

The inner surface of the small intestine is folded into finger-like structures called villi, which greatly increase the surface area available for absorption.


Digestion in the wall of the small intestine

• Protease breaks down peptides to amino acids.• Maltase breaks down maltose to glucose.• Sucrase breaks down sucrose to glucose and

fructose.• Lactase breaks down lactose to glucose and

galactose.• Lipase breaks down fats to fatty acids and

glycerol.


Colon

The colon is a tube just over one meter long, which is inhabited by bacteria.

The main function of the colon is to absorb water into the bloodstream.

Bacteria in the colon ferment dietary fibre (NSP) and produce fatty acids and gas.

Other bacteria produce vitamin K, which is also absorbed.

The products of bacterial digestion, along with water and any remaining minerals are absorbed leaving a residue behind.


Colon

The watery residue moves along the colon, and the faeces are formed and stored in the rectum before being excreted through the anus.

Young children gradually learn to control this action.

It may take 12-24 hours for the faeces to pass through the colon. This time can be reduced if the diet is high in fibre.




How much did you remember?

What enzyme is in saliva?

What does that help break down?

What breaks down in the stomach?

What happens to food that can’t be digested?

What is the function of bile?


Well here’s what I got!

1)Amylase

2) That starts to break down carbohydrates

3) Proteins, by an enzyme called protease

4) It is passed out of the body through the anus

5) It allows fats and digestive juices to mix.

Well done 5/5!


So what do I get for 100%?

Sweeties! To do some of

your own digestion!

Take a look at this too!http://www.medtropolis.com/VBody.asp

(right click and open hyperlink, click on English, digestive tract and then guided tour!)

Education

Digestive system