What is digestion?

Digestion is the breakdown of large insoluble molecules into smaller soluble molecules which can pass through the wall of the gut into the blood.

Wow, sounds complicated.

Really, it’s not. Let us tell you about it.

How does it start?

Well first you chew something with your teeth. Which makes it have a larger surface area, then and enzyme in your saliva called amylase starts breaking the carbohydrate into sugar.

Oh, I see, what happens then?

The food is then pushed down the oesophagus to the stomach by PERISTALSIS.

What is peristalsis?

Glad you asked that! Here I’ll explain it to you.

Peristalsis is the contraction and relaxation of the circular muscles in the wall of the gut.

When the muscle relaxes

the food drops down and

when it contracts at the

top the food at the bottom is pushed down

I see, what happens then?

The food is then in the stomach, the food is churned around by more waves of peristalsis to make it into mush, and it mixes with gastric juice.

What on earth is that?

Gastric juice contains and enzyme called protease which breaks down, yup you guessed it, protein, into amino acids.

It also contains hydrochloric acid which kill bacteria and makes the optimum PH for this enzyme, meaning it will work at its best at a lower PH.

I think I got that.

The food is then released a little bit at a time into the duodenum, which is the first part of the small intestine.

Ok does it have an enzyme too?

The duodenum DOES NOT

produce any digestive juices,

but has 2 poured into it!

*Did you know the small intestine is 6m long?*Whoa that’s really long!

One of the juices comes from the pancreas. It contains carbohydrase, protease and lipase.

I know the other two but what does lipase do?

It breaks down lipids.

What are they?

They are fats and oils.

Where does the other digestive juice come from?

The other digestive juice is call bile. Which is made by the liver and stored in a bag called the gall bladder. It is NOT AN ENZYME, but it neutralises the acid that was added in the stomach. This helps the small intestine work more effectively.

Bile also helps emulsify the fats.

What’s emulsify mean?

It means to make the fats into smaller blobs to make their surface area larger. So that the lipase can digest quicker.

The food is now a semi-

liquid like a smoothie! And

it passes into the second part of the small intestine called the ileum.

The walls of the ileum make a digestive juice which contains

carbohydrase, protease and lipase.

What does this do?

These enzymes complete the digestion of fats to fatty acids, glycerol, (carbohydrate) to simple sugars and protein to amino acids.

Oh I see, what then?

The ileum is specially adapted for absorption, passing digested food into the blood. It is very long to allow time for digestion

It has a very large surface area due to the presence of villi (finger like projections) and microvilli

This allows rapid diffusion

of the products of digestion.

Aren’t villi walls only one cell thick?

Yes, well done, this helps speed up the diffusion.

Each Villus has a blood vessel and a lymph vessel to carry the food away.

Is that all?

Not quite, all the food which cannot be digested ends up in the large intestine. It enters into the colon where most of the water is reabsorbed into the blood.

The indigestable remains form a semi solid faeces which is stored in the rectum. Eventually it is passed out the anus.

So you might need one of these…

How much did you remember?

What enzyme is in saliva?

What does that help break down?

What type of food is broken 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 neutralises the acid that was added in the stomach. This helps the small intestine work more effectively.

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!)