Digestive Enzymes

By Serena (Xu Ruijia)

Digestive system

The series of the tube-like organs that convert our meals into body fuels.

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

What are DIGESTIVE ENZYMES?

Enzymes help in the breakdown of food, in a process called CHEMICAL DIGESTION.

Food contains carbohydrates, proteins and lipids, so a wide range of enzymes is needed.

Carbohydrases break down carbohydrates

Proteases break down protein

Lipases break down lipids

Let’s start to eat !

Mouth

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 (4).

Amylase

Saliva is produced by the salivary glands.

It contains mucus and the enzyme salivary amylase(2).

breaks down starch into maltose (a disaccharide)

starch amylasemaltose

What’s Next?

The food is then pushed down the oesophagus to the stomach by PERISTALSIS(4).

What is peristalsis?

Peristalsis is the contraction and relaxation of the circular muscles in the wall of the gut(4).

When the muscle contracts at the top of food, the food is pushed down

When it relaxes, the food drops down

Stomach

Now, the food is in the stomach. It is churned around by more waves of peristalsis to make it into mush , at the same time , mixes with Gastric juice(4)

COME ON ! BABE!

Gastric juice Gastric juice is produced by the gastric glands in

the stomach wall(2).

It contains:

mucus

hydrochloric acid

the inactive enzyme precursor e.g. pepsinogen

Some digestive enzymes are secreted as inactive precursors because, in their active state, they would be potentially very harmful to the exocrine gland cells that produce and secrete them.

Pepsin

Pepsinogen is activated by the hydrochloric acid, which converts it into pepsin which is an endopeptidase(2).

Pepsin converts proteins into peptides

proteinpepsin

peptides

Small intestine

The major digestive organ(3)

Neutralize acid from stomach, add digestive enzymes and bile, break proteins, carbohydrates and lipids to absorbable materials

Site of nutrient absorption into the blood

95% of food absorbed here

Three parts: duodenum, jejunum, ileum

Duodenum

The food is then released in the duodenum, which is the first part of the small intestine(4).

Ok does it produce enzymes ?

The duodenum DOES NOT produce digestive juices,

But where the juices come from?

-Pancreas

- Liver

- Duodenal glands

From Pancreas

Pancreatic juice is produced by the exocrine glands in the pancreas

It contains:

bicarbonate ions (alkaline)

enzymes, including pancreatic amylase and pancreatic lipase, endopeptidases and exopeptidases

the inactive enzyme precursor – trypsinogen, chymotrypsinogen

Pancreatic amylase

Pancreatic amylase carries out the same reaction as salivary amylase(2):

amylaseStarch Maltose

Pancreatic Lipase

Pancreatic lipase breaks down triglycerides into glycerol and fatty acids(2).

triglycerideslipase

glycerol+ fatty acids

Special problem of lipids

The breakdown of lipids by pancreatic lipase poses special problems, because lipids are insoluble in the aqueous environment of the digestive tract(2).

As food travels through the digestive tract, the lipids within them melt and coalesce into large droplets.

Lipase is water-soluble, so is unable to enter the lipid droplets and would only be able to breakdown the lipids on the surface of the droplets.

Food does not remain in the digestive tract long enough for lipase to be able to completely digest the lipids in this manner

Bile This problem is overcome by the action of BILE.

Produced by Liver

Stores in Gallbladder

When no digestion is occurring, bile backs up the

bile duct for storage in the gallbladder

When digestion of fatty food is occurring, bile is

introduced into the duodenum from the

gallbladder(2)

How does Bile work?

Bile molecules have a hydrophobic end and a hydrophilic end, so are able to interact with both the lipids and the water, causing the lipids to break up into smaller droplets. This process is called Emulsification.

This speeds up the digestion of the lipids in the small intestine(2).

Trypsin

Trypsinogen is activated by an enzyme called enteropeptidase, which is secreted by the lining of the small intestine. Enteropeptidase converts trypsinogen to trypsin(2).

Trypsin continues the breakdown of proteins.

peptides trypsin smaller peptides

From Duodenal glands

The juices contain:

Maltase which converts maltose to glucose

Exopeptidase which make short polypeptides to amino acids

Dipeptidase which make double acids to single ones

Ileum The inner linings of ileum contain very small

finger-like bumps called “villi”.

The presence of these tiny bumps on the inside of the small intestine means that the surface area is much larger than if the lining were just a flat surface.

Absorption is through diffusion, facilitated diffusion and active transport(1).

Enzymes produced by the wall of the small intestine are not secreted like the other enzymes of the digestive tract(2).

Instead, they remain attached to the plasma membrane of the cells lining the intestine, with their active sites exposed to the food in the intestine(2).

With this arrangement, the substrates can be digested and then the products of digestion can immediately be absorbed into the body(2).

Large intestine

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

Final product

Thanks for listening !

Reference1. ALP. A, Digestion and Absorption, Biology class hand-out, City

of Bath College.

2.Dewarcw.com, Digestive enzymes,

Dewarcw.wikispaces.com/file/view/Digestive+Enzymes.ppt

[Accessed at:2nd March 2013]

3. Mcvsd.org, Jan 2010, Digestive enzymes,

www.mcvsd.org/weblog/jreuther/Digestive%20Enzymes.ppt

[Accessed at:2nd March 2013]

4. Spolem.co.uk, Digestion, www.spolem.co.uk/worksheets/docs/

Digestion.ppt[Accessed at:2nd March 2013]