Digestion

Digestion

Food components must be broken

down into their building blocks before

they can be absorbed

Chemical and mechanical digestion

helps this process

Digestion

Some single cell organisms such as

mould secrete digestive enzymes on

to food outside the organisms

(Saprotrophic)

You are a tube inside a tube…

The tube starts

here:

And although

there are a few

twists and turns

along the way…

It comes out here:

Anything that goes

in the top hole

(mouth) does not

become part of the

body until it is

absorbed (taken in)

in a part called the

small intestine.

This tube is

called the GUT.

A closer look at absorption…

Food is absorbed (taken in) to the body in the small

intestine. The wall of the small intestine has small holes in

it. Only small particles can pass through it:

starch

starch

starch

starch G

G

G

GUT INSIDE THE

BODY (BLOOD) Large particles

(e.g. starch) are

left in the gut and

small particles

(e.g. glucose) go

through into the

blood. G

G

G

BUT large particles can be broken down into small particles. This is called DIGESTION

TASK: Copy and complete this diagram

underneath Question 7 on your worksheet:

starch

starch

starch

starch G

G

G

GUT INSIDE THE

BODY

(BLOOD)

G

G

G

BEFORE ABSORPTION

GUT INSIDE THE

BODY

(BLOOD)

AFTER ABSORPTION

What is the gut?

The gut is a coiled tube where food is

broken down (digested) and absorbed

into the body.

Any waste food is passed out of the

body through the anus.

The digestive system is really

one long tube with an opening

at each end.

Stretched out it is a 9m tube!

Parts of the Gut

Mouth

Oesophagus

Stomach

Small Intestine

Large Intestine

Anus

Teeth

Teeth are needed to tear, rip and

chew food to physically break it into

smaller pieces.

This is mechanical digestion

These glands (a special type of tissue) produce

saliva, a sticky liquid.

As mentioned, the saliva has two jobs.

Being a liquid, it softens the food and allows the digested food to be rolled into

a ball just before it is swallowed.

It also contains a chemical known as an enzyme.

biological catalysts.

made from proteins

specific for each substrate

Saliva

The enzyme fits over

the substrate

perfectly – like a key

fits a lock.

It holds the starch

molecule in place as

a water molecule

breaks the bond

between two glucose

particles

Starch

molecule

Amylase

enzyme

This continues until

the molecule has

been broken down

completely

Digestive Enzymes

There are 3 main types of digestive

enzymes:

Amylase breaks starch down into

glucose.

Protease breaks protein down into

amino acids.

Lipase breaks fats down into fatty

acids and glycerol

Digestive Enzymes

Amylase

Starch

Glucose

Protease

Protein

Amino

Acids

Digestive Enzymes

Gly

ce

rol

Fatty Acid

Fatty Acid

Fatty Acid

Lipase

Fat Fatty Acids

and Glycerol

What factors affect the rate

of reaction of enzymes

How do you think you can speed up the rate of an enzymatic reaction? (Hint: It’s the same as any other reaction!)

Temperature

pH

Concentration

Inhibitors

Enzymes

Enzymes catalyse all chemical

reactions of the body.

This is referred to as metabolism

Enzymes

Metabolism includes

Anabolism

• Building up complex molecules

• Photosynthesis

Catabolism

• Breaking down complex molecules

• Respiration

Enzymes and temperature

Enzymes work best at 37˚C

Enzymes and pH

Enzymes work best at one pH. This

pH is different for each different

enzyme.

If the pH goes too low (more acidic) or

too high (more alkaline), the enzyme

will not work as effectively.

However, changes to pH will NOT

denature enzymes.

Enzymes and pH

Enzymes and pH

Answer the questions at the bottom of

the graph

Enzymes in Industry

Imagine your

favourite shirt

has a blood

stain on it…

The protease enzymes

in biological washing

powders, break down

the Haemoglobin

It is stained

because blood

contains the red

protein

Haemoglobin

These smaller

molecules are not

coloured and dissolve

easily in water. They

can be washed away.

Protease

Enzymes in Industry

Enzymes are also used in many other processes in industry e.g.

Pectinase to extract juice from fruit

Protease to break down the proteins in baby food to make it easier for the baby to digest

Cellulases to soften vegetables

Amylases to make syrup from starch

Research one of these uses for homework

Swallowing and Peristalsis

Food is shaped into a ball called a

bolus.

Bolus moves through the pharynx

Epiglottis blocks the trachea

Swallowing and Peristalsis

Food is shaped into a ball called a

bolus.

Bolus moves through the pharynx

Epiglottis blocks the trachea

Swallowing and Peristalsis

Bolus moves down the oesphagus

through the process of peristalsis

Swallowing and Peristalsis

Peristalsis is a wavelike

motion of the

oesophagus.

A ring of circular muscles

contraction behind the

bolus while the muscles

ahead of it relax.

How it gets down the gullet

Swallowing and Peristalsis

During vomiting the propulsion of food

comes from contractions of the

abdominal muscles

Peristalsis does not reverse in the

oesophagus

The stomach is basically a muscular bag, filled with hydrochloric acid (HCl).

cross section of stomach

food enters from

the gullet

glandular tissue makes:

hydrochloric acid, mucus

and protease enzyme

muscle tissue

The basics on the stomach

liquids mix with the food digested food leaves

…attacks any microbes (bacteria) that may have been swallowed

accidentally when the food was eaten.

The food is then subjected to a

coordinated attack.

Firstly the

the hydrochloric acid

When the food enters the stomach. The sphincter

contracts behind it.

Gastric processes:

HCl

Food bolus

Microbes

These enzymes begin digesting the proteins in the swallowed food.

These proteins are broken down to release the amino acids.

protease protein

Secondly, the hydrochloric acid provides the perfect conditions for

protease enzyme.

Protease enzymes work best under acidic conditions (pH < 7).

Protein digestion

amino

acids

Thirdly, the muscular tissue of the stomach has the ability to contract and

relax and in doing so, physically grinds the food inside it.

Mucus is produced to protect the lining of the stomach from the acid. If the

mucus were not present, the hydrochloric acid would actually digest the

tissue that had made it!

Mucus and muscles

presence of

HCl

The hydrochloric acid, mucus, food and enzyme solution is given the

name - gastric juice.

muscle and

glandular tissue

layer of

mucus

wall of stomach

is protected

Making gastric juice

The stomach

Chyme is formed

(food is liquefied);

highly acidic

Smooth muscles mix

food (3-5 hours)

muscular tissue

of stomach

protease enzyme and

hydrochloric acid

sugars

amino

acids

carbohydrates

proteins

fats

fat

protein

carbohydrate

sugar

physical

digestion

chemical

digestion

The stomach’s digestive action - summary

The duodenum

The first part of

the small intestine

is called the

duodenum.

The duodenum

The food is now a semi liquid, highly

acidic mush.

It needs to be neutralised and

digestion needs to be continued…

Liver

Gall bladder

Duodenum

Pancreas

Stomach

The bile and the fat meet within the small intestine.

The bile emulsifies the fat. This basically means the fat is physically broken

into smaller pieces.

emulsification by bile

Notice that the fat has not been chemically digested, only physically. The

result is a greater surface area over which the enzyme, lipase, can

attack the fat.

liver produces bile

bile is released from the gall bladder

and passes down through the bile duct

A whole lot of bile

fat within the gastric

juice

The small intestine

The small intestine produces 3

enzymes to complete digestion:

Amylase breaks starch down into

glucose.

Protease breaks protein down into

amino acids.

Lipase breaks fats down into fatty

acids and glycerol

Pancreas

Secretes

digestive

enzymes into the

small intestine

Pancreatic

juice: amylase,

protease,

lipase

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate

Pancreas Duodenum

Amino Acids

Fat

Pancreas

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose

Pancreas Duodenum

Amino Acids

Fat

Small intestine

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose Salivary glands

Pancreas Duodenum

Small Intestine

Amino Acids

Fat

Small intestine

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose Salivary glands Mouth

Pancreas Duodenum

Small Intestine Small Int.

Amino Acids

Fat

Small intestine

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose Salivary glands Mouth

Pancreas Duodenum

Small Intestine Small Int.

Protease Amino Acids

Fat

Small intestine

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose Salivary glands Mouth

Pancreas Duodenum

Small Intestine Small Int.

Protease Protein Amino Acids

Fat

Small intestine

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose Salivary glands Mouth

Pancreas Duodenum

Small Intestine Small Int.

Protease Protein Amino Acids Stomach

Pancreas

Small Intestine

Fat

Small intestine

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose Salivary glands Mouth

Pancreas

Duodenum Duodenum

Protease Protein Amino Acids Stomach Stomach

Pancreas Duodenum

Small Intestine Duodenum

Fat

Small intestine

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose Salivary glands Mouth

Pancreas Duodenum

Small Intestine Duodenum

Protease Protein Amino Acids Stomach Stomach

Pancreas Small Int.

Small Intestine Small Int.

Lipase Fat

Small intestine

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose Salivary glands Mouth

Pancreas Duodenum

Small Intestine Small Int.

Protease Protein Amino Acids Stomach Stomach

Pancreas Small Int.

Small Intestine Small Int.

Lipase Fat Glycerol

Fatty Acid Small intestine

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose Salivary glands Mouth

Pancreas Duodenum

Small Intestine Small Int.

Protease Protein Amino Acids Stomach Stomach

Pancreas Small Int.

Small Intestine Small Int.

Lipase Fat Glycerol

Fatty Acid

Pancreas

Small intestine

Enzyme summary

Enzyme Substrate Product Where it is

produced

Where it acts

Amylase Carbohydrate Glucose Salivary glands Mouth

Pancreas Duodenum

Small Intestine Small Int.

Protease Protein Amino Acids Stomach Stomach

Pancreas Duodenum

Small Intestine Duodenum

Lipase Fat Glycerol

Fatty Acid

Pancreas Duodenum

Small intestine Duodenum

Absorption

The digested food begins to be

ABSORBED in the ileum

Absorption

The digested food is ABSORBED

through the wall of the small intestine

into the blood stream.

To do this effectively, the small

intestine needs to have a large

surface area.

Absorption 1

The tube is over 6 meters long

The inner wall of the tube has bends in it

The wall is covered in villi (small finger like

structures)

Outer wall

Inner wall

Pathway

for Food

Absorption 2: Villi

Absorption takes place

through villi.

These are small finger

like structures that

stick out into the small

intestine tube.

They help to increase

the surface area of the

small intestine.

Absorption 2: Villi

Outer wall

Inner wall

Pathway

for Food

Absorption 2: Villi

The digested food

passes through the wall

of the villi (epithelium).

Why does the epithelium have

to be thin?

The glucose and amino

acids pass into the blood

capillary. From here they

go to the liver

Absorption 2: Villi

The fatty acids and glycerol go

into one of these lymphatic

vessels in the villus.

ileum

By the time the

contents leave the

ileum all nutrients,

vitamins, minerals

and water has

been absorbed

Large intestine

Compaction of

solid waste

Bacterial

breakdown of

proteins; vitamin

formation

Absorption of the

remainer water,

ions, vitamins

Defecation

The blood reabsorbs the excess water that is mixed with the waste food.

Getting back excess water

LARGE

INTESTINE

B

L

O

O

D

Egestion

Any indigestible food (e.g. fibre) passes into the large intestine (colon).

Water is absorbed back into the body.

Where has this water come from?

The food becomes a solid waste called faeces.

Faeces are stored in the rectum and removed through the anus. This removal is called EGESTION.

Applications to health

Peptic ulcer- craterlike lesion caused by exposure to gastric juices.

Vomiting- forcible expulsion of the contents of the upper GI tract (stomach and duodenum).

Peritonitis- acute inflammation of the peritoneum.

Hepatitis- inflammation of the liver caused by viruses, drugs, or chemicals.

Gallstones- crystallization of cholesterol due to insufficient bile salts.

Appendicitis- inflammation of the appendix caused by an obstruction of the lumen.

We have now finished our journey through the digestive system. We have

seen the chemical and physical digestion of large & insoluble into small &

soluble food.

It is important to remember that the digestive system relies heavily on the

presence of two important types of body tissue.

Through constant contraction

and relaxation, the food is kept

moving through the system,

from the mouth to the anus.

2. Muscular tissue

This is responsible for the

production of the digestive

enzymes.

1. Glandular tissue

Important body tissues in digestion

Complete

the Tour

map

Thank you for travelling

along Alimentary Canal.

Have a nice day…