Download Digestion - RGA

AS Level Biology
• Biol 1 = Biology & Disease (1 hour 15 mins)
• Biol 2 = The Variety of Living Organisms (1 hour 45
mins)
– 33.3% AS marks
– 16.7% A level
• Unit 3 Investigative Practical Skills
– Practical and written paper
– 20% AS marks
– 10% A level
AS Level Biology
• Knowledge
• Application of knowledge to unknown
biological examples
• How Science Works
• Data Interpretation
• Practical Skills
• Structured answers
How to do well?
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Actively take part in lessons
Ask if you are unsure
Make clear and concise notes
Use the specification
Read around the subject
Try past exam questions
Unit 1 Biology and Disease
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The Digestive System
Proteins
Enzymes
Carbohydrates
Absorption
Active Transport
Pathogens
Cholera
Immunology
Digestion
K.Ripping
2011
The Digestive
System
Label
your
diagram
of the
digestive
system
The Digestive System 2
• The major parts of the digestive system
are the:
•
•
•
•
Oesophagus
Stomach
Small intestine (duodenum, jejunum, ileum)
Large intestine (colon, caecum, rectum)
• Other organs around the gut produce
digestive secretions
• Liver/gall bladder
• Pancreas
Adaptations - Oesophagus
• In most parts of the gut,
the epithelium is only a
single cell thick but in the
oesophagus, where
physical protection is
needed, it is several
layers thick.
• The mucosa is folded to
allow expansion
• Mucus-secreting glands
help to lubricate the
passage of food.
Answer the following question:
• How does the structure of the
oesophagus aid food in getting to the
stomach quickly?
[4]
•Answer:
–The muscle layers [1] enable peristalsis [1]
to occur, which pushes food along. Mucus
secretions [1] help food to slide [1] along
Stomach facts!
• Can hold up to 5 Litres!
• Extra Muscle layer helps
with churning.
• Gastric glands secrete
600ml of gastric juice per
meal.
• Contains 0.15M HCl
• If the
enzymes(endopeptidases)
were not found in their
inactive form, they would
self-digest the cells of the
stomach!
Adaptations - Stomach
• Temporary storage of food
• Folded mucosa
• Mucus-secreting cells to protect from
acid & enzyme action
• Gastric glands secrete acid & pepsin
(enzyme which breaks down proteins)
• Many nerve cell bodies to control
secretion of gastric juices
• Muscularis externa is 3 three layers
thick & churns the contents into chyme
The Small Intestine
• Long, coiled tube
about 5-6m long
• First 30cm is the
duodenum into which
open the bile &
pancreatic ducts. Most
digestion here.
• Ileum forms most of
small intestine.
Absorption of
digested food here.
The Duodenum
Important secretions added:
i)alkaline secretions from glands
at base of villi to neutralise acid
ii)mucus-secreting glands in
epithelium to protect from acid
damage
iii)bile salts from liver (stored in
gall bladder) to emulsify fats
iv)digestive secretions from
pancreas containing enzymes
Adaptations for Absorption
Like the oesophagus & stomach,
the small intestine is folded.
However it also has millions of
finger-like projections or VILLI
(20 – 40 per mm2 , each extending
0.5 – 1.5 mm into the lumen). The
epithelial cells of the villi
themselves have MICROVILLI,
forming a BRUSH BORDER to
further increase the surface area
for absorption.
Adaptations 2
Enzymes for digestion come
from three sources:
i) Pancreatic secretions
ii) Cells in the folds between
the villi
iii) Enzymes embedded within
the cell membranes of the
epithelial cells themselves
The epithelium is one cell layer
“thick” providing a short
distance for absorption.
Absorbing Food 1
Again, lipids are absorbed slightly
differently to glucose & amino acids.
Processes involved:
simple diffusion (lipids)
active transport (glucose, AA)
facilitated diffusion (glucose, AA)
Destinations:
blood (glucose, AA)
lacteals/lymph (lipids)
Absorbing Food 2
A. Sodium is pumped out of the
cell by ACTIVE
TRANSPORT (against its
concentration gradient,
requiring energy)
C. Glucose diffuse s
across the cell & moves
into the blood with the
help of a channel
protein. This is
facilitated diffusion
B. Sodium & glucose/amino
acids bind to a carrier
protein. The sodium
diffuses into the cell down
its concentration gradient,
carrying the glucose with it.
Glucose & sodium leave the
carrier protein
The whole point of digestion is to break down our food so
that we can get the bits we need from it…
The digestive system
The main foods
affected are
CARBOHYDRATES –
these are broken down
into GLUCOSE.
Starch
molecule
Glucose
molecules
1) In the mouth food
is
2) mechanically
In the stomach
broked
down
by the
food
chemically
3) Inisthe
small
teeth
and
chemically
broked
down
by
intestine
enzymes
4) In the
large
broken
down
by
enzymes
and
acid is
complete
the
intestine
excess
5)
The waste
faeces
enzymes
in
saliva
produced
to
kill
digestion
process
and
water
is absorbed
are removed
through
bacteria
andother
help the
glucose
and
into
the
blood
the anus
enzymes
work
small foods
are
absorbed into the
bloodstream.
Digestion
Other facts to digest...
The liver produces bile
to help digest fat
The gall bladder stores
bile before releasing it
into the small intestine
via the bile duct
The pancreas produces
lots of enzymes