The Digestive System II
Now take another look at the description of the digestive system and this time pay attention to the importance of enzymes.
The digestive system
In the mouth, food is taken into the body and teeth chew it, breaking it up into small pieces. This increases the surface area for digestive enzymes, like amylase, to work on. Amylase is contained in the saliva and breaks down starch. Amylase belongs to a group of enzymes, called carbohydrases that break down carbohydrates into sugars. For example, starch is broken down glucose. The tongue helps form food into a ball called the bolus. This gets coated in saliva, which lubricates it and makes it easier to swallow.
In the oesophagus, a muscular tube between the mouth and stomach, muscles contract in waves to squeeze the food down towards the stomach. This is called peristalsis.
The stomach, a muscular bag that makes enzymes (mainly ones that digest proteins called proteases, for example pepsin) and acid churns the food up in these juices by peristalsis to make a thick paste. Proteins are broken down into amino acids.
The small intestine, a long, coiled muscular tube contains lots of digestive enzymes made by the pancreas and it also makes its own enzymes. In here, large insoluble food molecules are broken down into smaller soluble molecules. The latter ones are absorbed into the blood using finger-shaped projections called villi, which contain capillaries. Food is moved along by peristalsis.
The pancreas is an organ that makes digestive enzymes and releases them into the first part of the small intestine.
The large intestine is a thin, wide, thin-walled tube where undigested food passes into after the small intestine. Water diffuses into the blood leaving the waste material (faeces) behind.
The undigested food passes out of the body through the anus.
The digested food that has dissolved into the blood plasma is taken to the liver to be processed. The liver makes bile, which helps the digestion of fats. Bile contains lipases, enzymes that break down fats. Fats are also called lipids and are broken down into fatty acidsand glycerol. Some molecules are broken down even more in the liver and some others are built into larger molecules again.
The gall bladder is a small organ that stores the bile made by the liver and releases it into the small intestine when it is needed.
You must have noticed the importance of enzymes in digestion. They break down large insoluble molecules into smaller soluble molecules. This way they aid absorption of food molecules and act as catalysts, speeding up reactions. Enzymes are very specific; an enzyme only breaks down one type of molecule. They work by using an active site, where molecules (substrate) bind to and are thus, broken down.
(a) Describe the roles of the enzymes involved in digestion.