LEARNINGOUTCOMES

ALL MUST…

Know that enzymes are used in the digestion of food in the body, which can then be absorbed into the bloodstream

LEARNINGOUTCOMES

ALL MUST…

Know that enzymes are needed to break down (digest) large, insoluble molecules into small, soluble ones:

View the photograph on the next slide and jot down

• Where you would find it

• What produced it

• What it is

The Human Digestive System

The process of digestion has 5 functions:

Ingestion: taking food into the body

Digestion:breakdown of insoluble substances into soluble ones

Absorption: uptake of soluble substances into cells

Assimilation: how cells use food

Egestion: removal of undigested waste

Absorption

Ingestion

Digestion

Egestion

faeces

Food is broken down into smaller

pieces by biting, chewing,

churning, bile action.

These pieces are not soluble but have

a large surface area for enzymes to

work on.

2cm

2cm

2cm

Surface area = 24 cm2

Volume = 8 cm3

SA : V ratio = 24:8 = 3:1

1cm

1cm

1cm

Surface area = 6 cm2

Volume = 1 cm3

SA : V ratio = 6:1

Digestive enzymes break chemical bonds to make insoluble food

particles soluble.

Carbohydrases break down carbohydrates into sugars

Proteases break down proteins into amino acids

Lipases break down fats (lipids) into fatty acids and glycerol

model gut experiment

boiling tube

LEARNINGOUTCOMES

ALL MUST…

Label a diagram of the component parts of the digestive system and identify their function.

LEARNINGOUTCOMES

to include:• buccal cavity - the mechanical

digestion by teeth and the chemical digestion of starch by amylase;

LEARNINGOUTCOMES

to include:

• stomach - the production of gastric juice containing protease enzyme and acid, and the digestion of proteins;

Pin the pancreas on the body

What do you

remember

Salivary gland

Buccal cavity

Oesophagus

Stomach

Liver

Ileum

Appendix

Pancreas

Colon

Rectum

Duodenum

Anus

Add gall bladder, bile duct, sphincter

Mechanical: chewing, biting

Chemical: Saliva from the salivary glands contains the enzyme CARBOHYDRASE.

Starch + carbohydrase sugar (maltose)

The ball of food is called a bolus

NO FOOD IS BROKEN DOWN HERE

Muscles in the wall of the oesophagus contract, pushing food down to the

stomach. This is called PERISTALSIS

peristalsis

FOOD

Oesophagus wall

Food moves forwards

Muscles in wall contract

PERISTALSIS

The strong muscle walls contract to churn and mix food with stomach juices

called GASTRIC JUICES.

Cells in the stomach wall produce a protease enzyme that digests

proteins, breaking them down into amino acids.

The stomach cells also produce hydrochloric acid HCl, which

• Lowers the pH for the protease enzyme to work• Kills bacteria• Stops salivary amylase from working

A circular, sphincter muscle at the exit of the stomach opens to allow food into the small

intestine.

It controls release of food from the stomach.

LEARNINGOUTCOMES

to include:

• liver - the production of bile, its storage in the gall bladder and its actions in the duodenum in neutralisation of acids and emulsification of fats

LEARNINGOUTCOMES

to include:

• duodenum - enzyme production by the pancreas and the duodenal wall to include carbohydrases, lipases and proteases

LEARNINGOUTCOMES

to include:• ileum - relate its structure to its function

of absorption of digested food molecules and the ways it is adapted: large surface area (length, folds and villi), good blood supply, and thin and permeable membranes;

LEARNINGOUTCOMES

SOME MAY…

explain how the structure of a villus (finger-like shape, single layer of surface cells, capillary network and lacteal) is adapted for the efficient absorption of digested food molecules.

Bile, made in the liver and stored inthe gall bladder passes along the

bile duct into the duodenum.

Bile breaks fats into very small droplets, increasing the surface area

for enzymes to work on.This is called emulsification.

Bile is alkaline and therefore also neutralises acid from the stomach.

gall bladder

bile duct

pancreatic duct

digestive enzymes produced in pancreas

duodenum

bile made in the liverpasses into the gall bladder

ENZYMES are added to the duodenum from:• The pancreas

• The wall of the duodenum

Carbohydrases break down starch to sugars

Proteases break down protein to amino acids

Lipase breaks down fat to fatty acids and glycerol

Main function is absorption.

The walls are adapted for efficient diffusion of the soluble products of

digestion.

ridge covered with villi

villus

musclelayer

network of blood capillaries

lactealabsorbs fatty acids

arteriole venuole

single layer of epithelial cells

A villus

ileum wallMade of epithelial cells

bloodcapillaries

to liver

sugar

amino acids

lactealfatty acids

• Long length (5m), folds and villi increase the surface area for absorption

• Villi contain blood vessels to carry away absorbed nutrients

• Villi contain lacteals to carry away absorbed fats

• The walls are thin, one cell thick, and permeable to form a short diffusion distance

The absorbed nutrients, amino acids and sugars are carried in the blood to the

liver in the

HEPATIC PORTAL VEIN.

LEARNINGOUTCOMES

to include:

• colon - large surface area for water absorption;

• rectum & anus - storage and removal of faeces.

NO DIGESTION OCCURS HERE

The colon has a large surface area for the absorption of water

from the fluid we drink, food we eat, mucus and digestive juices.

It also absorbs mineral salts.

Solid waste made up of undigested food, bacteria and cells from the

gut

forms faeces,

which is stored in the rectum before passing out of the body through the

anus.

transverse colon

ascending colon

descending colon

appendixrectum

anus

Summary

bbc learning zoneclip 4180

dvd

Cut & stick activity