A closer look at the digestive system of humans for Year 8 Science.

1. FUNCTIONING ORGANISMS.
02. Digestive system.
Ian Anderson
Saint Ignatius College Geelong

2. KEY NUTRIENT GROUPS.
The foods that we eat supply the nutrients and energy
we need to carry out the important processes of life,
including
Cellular respiration & other metabolic reactions,
Grow,
Repair or replace damaged tissue,
Reproduce,
Move, etc.

3. KEY NUTRIENT GROUPS.
The nutrients we require can be broken down into 5
main groups.
Proteins,
Carbohydrates,
Fats & oils,
Vitamins & minerals,
Water (not really a nutrient, but essential for chemical
reactions in the body).

4. KEY NUTRIENT GROUPS.
Nutrient Role in our body Where chemically digested
Proteins Growth and repair
of cells.
Stomach and small intestine.
Carbohydrates
(sugars, starch,
fibre (cellulose),
etc.)
Main sources of
energy.
Mouth and small intestine.
(Fibre is not digested, but
assists in movement of food
through digestive system)
Fats & oils Stored as an
energy reserve and
also used for
making cell
membranes.
Small intestine
Vitamins &
minerals
Required in small
amounts for vital
cellular functions.
Do not need to be broken
down.

5. DIGESTIVE SYSTEM.
 Responsible for
Breaking down food into
smaller particles (molecules).
Absorption of nutrients and
water into bloodstream.
Elimination of wastes.
Source: http://www.cakechooser.com/

6. DIGESTIVE SYSTEM.
Digestion.
Breakdown of food into smaller particles/molecules.
 e.g. Proteins  amino acids; Starch  sugars.
Two types of digestion:
1. Physical digestion = breakdown of food by physical means.
 Teeth.
 Churning of food in stomach.
2. Chemical digestion = breakdown of food by digestive juices,
including enzymes and acid.
 Mouth – saliva contains enzymes.
 Stomach – gastric juices contain enzymes and acids.
 Small intestine – bile & pancreatic juices released into small
intestine contain enzymes.

7. DIGESTIVE SYSTEM.
Chemical digestion cont/.
Most chemical reactions occurring in our body would
occur too slowly to be useful without the presence of
enzymes.
Enzymes are biological catalysts that speed up the rate
of a chemical reaction.
 They are not reactants in the reaction.
 They are not used up (consumed) during the reaction and are
available to be reused over and over again.
 Enzymes are very specific to a particular reaction.
 e.g. Pepsin will only speed up the breakdown of protein;
amylase will only speed up the breakdown of starch.
 Enzymes are very sensitive to the conditions in which they
work.
 e.g. Pepsin will only work in an acidic environment.

8. DIGESTIVE SYSTEM.
Absorption.
Nutrients (simple sugars, amino acids, vitamins &
minerals) and water are absorbed through the walls of
the small & large intestines into the blood vessels of the
circulatory system.

9. DIGESTIVE SYSTEM.
Digestive system.
All the organs involved with the digestion and absorption
of food.
Alimentary canal (digestive tract).
The organs of your digestive system through which food
passes during digestion.
 From your mouth to your anus.

10. Source: Cash et al. (2013)
Teeth & mouth.
Physical
breakdown of food.
Saliva contains
enzymes that
commence
chemical
breakdown of food.
 Enzymes are
chemicals that
speed up the rate of
a chemical reaction.
DIGESTIVE SYSTEM.

11. Source: Cash et al. (2013)
Oesophagus.
Muscular tube
running from mouth
to stomach that
food moves through
via peristalsis.
 Peristalsis =
coordinated
muscular
contractions.
DIGESTIVE SYSTEM.

12. Source: Cash et al. (2013)
Stomach.
Muscular ‘bag’ that
squeezes and
churns food with
gastric juices,
producing chyme.
 Gastric juices
contain HCl &
pepsin which digest
protein.
 Stomach has a
mucous lining which
protects it from the
acid environment.
DIGESTIVE SYSTEM.

13. Source: Cash et al. (2013)
Liver & gall bladder.
Liver produces bile
which is then stored
in gall bladder.
Bile is released into
small intestine
where it neutralises
stomach acid &
digest fats.
DIGESTIVE SYSTEM.

14. Source: Cash et al. (2013)
Pancreas.
Produces
pancreatic juices
that are released
into small intestine.
 Pancreatic juices
contain enzymes.
DIGESTIVE SYSTEM.

15. Source: Cash et al. (2013)
Small intestine.
Digestion of food
continues.
Absorption of most
nutrients.
Long length (4-6m)
allows sufficient time for
all the nutrients to be
processed as the chyme
passes through.
Lining of small intestine
has villi, which
increases surface area
available for absorption
of nutrients.
DIGESTIVE SYSTEM.

16. Source: Cash et al. (2013)
Large intestine.
Absorption of
vitamins &
remaining water.
Shorter than small
intestine (~1.5m).
DIGESTIVE SYSTEM.

17. Source: Cash et al. (2013)
Rectum & anus.
Rectum stores any
remaining
undigested chyme
prior to elimination
as faeces through
the anus.
DIGESTIVE SYSTEM.

18. Source: Cash et al. (2013)
Alimentary canal.
Mouth.
Oesophagus.
Stomach.
Small intestine.
Large intestine.
Rectum.
Anus.
DIGESTIVE SYSTEM.

19. DIFFERENT DIGESTIVE SYSTEMS.
The digestive system of mammals are specialized
according to their diet.
Herbivores.
 Eat plant material.
 e.g. kangaroos, koalas, cows, etc.
Carnivores.
 Eat meat.
 e.g. Tasmanian devil, quolls, tigers, lions, etc.
Omnivores.
 Eat both plants and meat.
 e.g. humans, bush rat, chimpanzees.

20. DIFFERENT DIGESTIVE SYSTEMS.
Herbivores.
Plant matter is difficult
to digest (breakdown).
Have a long digestive
tract allowing greater
time for nutrients to be
absorbed from digested
food.
Herbivores have a large
caecum that contains
bacteria which help
breakdown the plant
matter.
Source: Cash et al. (2012)

21. DIFFERENT DIGESTIVE SYSTEMS.
Carnivores.
A diet high in protein.
Protein is easier to
digest than plant
matter, so carnivores
have a simple digestive
system, with a long
small intestine and a
very small caecum (or
none at all).
Source: Cash et al. (2012)

22. DIFFERENT DIGESTIVE SYSTEMS.
Omnivores.
A diet made up of both
plant matter and meat
(protein).
Will often have a long
small intestine, shorter
large intestine.
Depending on type of
diet, the caecum may
be well developed.
Source: Cash et al. (2012)

23. BIBLIOGRAPHY.
Cash, S., Quinton, G., Tilley, C., & Craven, E. (2013).
Oxford Big Ideas. Science 8: Australian
Curriculum. Melbourne: Oxford University Press.

24. http://sickscience8.wikispaces.com/