Learning outcomesAt the and of the lesson, you should be able to:

1.Identify the part of the digestive system where the formation of faeces takes place.

2.Describe the formation of faeces and problems related to defaecation.

3.Explain the role of microorganisms in the colon and the effect of antibiotics on them.

4.Explain defaecation and the importance of high fibre diets.

Faeces After absorption of nutrients has taken place in

the small intestine. The intestinal contents enter the colon.

The intestinal contents are now a mixture of water, undigested food substances and indigestible fibre, most of which is cellulose from plant cell walls.

Their movements are very slow and helped by peristalsis.

Cont…Recovery of water from the undigested

remains in the colon results in the formation of faeces, which are now semi-solid waste.

Faeces also contain dead cells shed from the intestinal lining as well as waste products like bile pigments and toxic substances which have to be eliminated from the body.

Figure of large intestine (colon)

Microorganisms vs antibioticsThe colon also serves as a habitat for a

flourishing population of bacteria.

The presence of beneficial microorganisms plays an important role in maintaining a stable environment in the alimentary canal.

What happens if a person is sick and goes to see a doctor?

Cont…In most cases, the doctor will prescribe

antibiotics to treat various infections.

However, overuse of antibiotics can reduce the microbial population.

Bio facts…

Bio FactsE. coli is one of the most common intestinal

bacteria.

They synthesise several types of vitamins B and K.

It provides a valuable supplement to our dietary intake, especially vitamin K, which is deficient in a normal diet.

Defaecation The wall of the colon secretes mucus which binds

the faeces and lubricates the movement of faeces along the colon.

After 12 to 24 hours in the colon, the faeces pass to rectum.

Pressure in the rectum increase, causing a desire to expel the faeces from the body.

This is called defaecation.

This process is controlled by muscles around the anus.

Figure of large intestine (colon)

What is the relationship between these two figure?

Constipation Lots of fruits and vegetable

Problems related to defaecationWhat will happen if defaecation is not regular?

Have you experienced constipation before?

This condition is caused by the faeces moving too slowly through the colon.

As a result, a greater amount of water is reabsorbed in the colon, making the faeces hard!

This will cause painful defaecation.

What should I do?Constipation can be avoided by drinking a lot of

water.

The daily diet should contain sufficient amounts of fibre.

The presence of fibre helps move food along the intestinal tract.

Chronic constipation is associated with haemorrhoids and in some cases can lead to colon cancer.

Bacteria used in industry