Transcript 1.4 digestion

LEARNING
OUTCOMES
ALL MUST…
Know that enzymes are used
in the digestion of food in the
body, which can then be
absorbed into the
bloodstream
LEARNING
OUTCOMES
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
Digestion
Egestion
faeces
Ingestion
Absorption
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.
Surface area = 24 cm2
2cm
Volume = 8 cm3
2cm
SA : V ratio = 24:8 = 3:1
2cm
Surface area = 6 cm2
Volume = 1 cm3
1cm
1cm
SA : V ratio = 6:1
1cm
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
LEARNING
OUTCOMES
ALL MUST…
Label a diagram of the
component parts of the
digestive system and identify
their function.
LEARNING
OUTCOMES
to include:
• buccal cavity - the mechanical
digestion by teeth and the
chemical digestion of starch
by amylase;
LEARNING
OUTCOMES
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
Add gall bladder,
bile duct, sphincter
Buccal cavity
Salivary gland
Oesophagus
Liver
Stomach
Duodenum
Pancreas
Ileum
Colon
Appendix
Anus
Rectum
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
Muscles in wall contract
FOOD
PERISTALSIS
Oesophagus wall
Food moves
forwards
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.
LEARNING
OUTCOMES
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
LEARNING
OUTCOMES
to include:
• duodenum - enzyme
production by the pancreas
and the duodenal wall to
include carbohydrases,
lipases and proteases
LEARNING
OUTCOMES
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;
LEARNING
OUTCOMES
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 in
the 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.
bile made in the liver
passes into the gall bladder
gall bladder
digestive enzymes
produced in pancreas
bile duct
pancreatic
duct
duodenum
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
network of
blood
capillaries
lacteal
absorbs
fatty acids
single
layer of
epithelial
cells
villus
muscle
layer
arteriole
venuole
A villus
sugar
ileum wall
Made of epithelial cells
amino acids
fatty acids
blood
capillaries
lacteal
to liver
• 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.
LEARNING
OUTCOMES
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
descending
colon
ascending
colon
appendix
rectum
anus
Summary
bbc learning zone
clip 4180
dvd
Cut & stick
activity