Transcript Lesson 3 liver functionx

The Function
of the Liver
Objectives
• Describe the formation of urea in the liver,
including an outline of the ornithine cycle.
• Describe the roles of the liver in
detoxification.
Macrophages called
Kupfer cells
Alcohol, Drugs,
Ammonia
Detoxification
of…
Controls levels
of….
Lipid (storage in
adipose)
Glucose
Amino acids
Plasma proteins
(inc clotting factors)
Red blood cells (in
foetus)
What does
the liver
do?
Removal of….
Bile
Glucose
Cholesterol and
lipoproteins
Heat
Stores….
Glucose as glycogen
Minerals Cu and Fe
Bilirubin (haem
group from old RBC
Key Vitamins A, D,
E, K and B12
Used hormones e.g.
sex hormones
Saturated fat
Role of Liver in digestion
• Produces bile that is stored in the gall
bladder between meals and released into
small intestines:
• Bile salts - emulsify fats
• Important for absorption of fat soluble
vitamins from digested food (Vit. D,E,K & A)
• Neutralisation of excess acidity from
stomach
• Bactericidal role (defence)
Formation of Urea
• XS aa in the diet cant be stored as the amine
group makes them toxic so the aa is deaminated
forming a keto acid and ammonia
amino acid
ammonia + keto acid
deamination
• The keto acid can enter respiration directly to
release energy – gluconeogenesis
Formation of Urea
• Deamination forms ammonia which is highly
toxic
• The ammonia enters the ornithine cycle to
form less toxic, soluble urea for excretion by
the kidneys
amino acid
ammonia + keto acid
deamination
urea
ornithine cycle
The ornithine Cycle
The ornithine cycle
• Ammonia combines with carbon dioxide to
produce urea.
• Urea is reabsorbed back into the blood and
transported to the kidneys where it is filtered
into the urine.
• Urine is stored in the bladder until it is
released from the body.
2NH3 + CO2
CO(NH2)2 + H2O
Detoxification
• Toxins may be produced by our body (e.g.
hydrogen peroxide), may be taken in via our
diet (e.g. alcohol), or may be consumed
recreationally/medicinally (e.g. drugs).
• Toxins can be oxidised, reduced, methylated
or combined with another molecule to make
them harmless.
• Liver cells contain many enzymes that make
toxins less toxic e.g. catalase breaks down
hydrogen peroxide into ……..
Detoxification of Alcohol
• Ethanol (alcohol) depresses nerve
activity.
• It contains energy so can be respired.
• It is broken down by hepatocytes to
ethanal by the enzyme ethanol
dehydrogenase.
• Ethanal dehydrogenase then breaks the
ethanal down into ethanoate.
• Ethanoate combines with coenzyme A to
form acetyl coenzyme A which can enter
the respiratory pathway.
Detoxification of Alcohol
• The H+ions released during this process are
used to reduce the coenzyme NAD to form
reduced NAD.
• NAD is also used in respiration to break down
fatty acids.
• If the liver has to detoxify too much alcohol
it has insufficient NAD to deal with the fatty
acids and so these are converted back to
lipids to be stored in the liver. This leads to
the “fatty liver” condition and can lead to
hepatitis or cirrhosis.
Ethanol
Ethanal
NAD Reduced
NAD
Ethanoic Acid
NAD Reduced
NAD
Acetyl Coenzyme A
To
respiration
Summary: 9 Basic Functions
1. Bile Synthesis – aids in fat digestion
2. Gluconeogenesis (when carbohydrate stores are
depleted)
3. Storage of Fe, Cu and soluble vitamins (A,D,E,K)
4. Site of the ornithine cycle
5. Production of plasma proteins
6. Detoxification of poisons
7. Synthesis of cholesterol from acetyl co-A
8. Metabolism - amino acids, fats, carbohydrates
9. Phagocytosis of worn out red blood cells
Stretch and Challenge
What do other animals do?
other mammals and amphibians make urea like us!
Birds, reptiles and insects
turn urea into uric acid
and excrete it in faeces,
but this uses LOTS of
energy so WHY?
Fish and aquatic
invertebrates simply
excrete their ammonia
into the sea.
Why is it OK?
Brown bears & Hibernation
Describe the similarities and differences between
the metabolism of nitrogen-containing compounds in
inactive brown bears, as described in the passage,
and in humans.
During winter, the brown bear, Ursus arctus, enters a long
period of inactivity. During which it undergoes various
physiological changes, such as a decrease in core body
temperature and a decrease in resting heart rate. There are
also changes in the brown bear’s metabolism of protein and
lipids.
During periods of inactivity, the brown bear reabsorbs all
urea molecules from the filtrate in its kidneys and from the
bladder. Urea is transported in the blood to the large
intestine where Bacteria convert urea to ammonia and CO2,
which diffuse back into the blood. When the ammonia
reaches the liver, it is converted into amino acids which are
then used to synthesise proteins in the body, especially in the
liver and muscle cells.
Brown bears & Hibernation
Describe the similarities and differences between
the metabolism of nitrogen-containing compounds in
inactive brown bears, as described in the passage,
and in humans.
This
a very good
discriminator,
Mostwas
candidates
appreciated
that as
1
2
3
4
similarities
production of urea ;
urea transported in blood ;
urea filtered from blood ;
synthesis of proteins from amino acids
differences (assume refs are to brown bears
unless otherwise stated)
5
amino acids synthesised from ammonia
6
all urea reabsorbed ;
7
from kidney and bladder ;
8
urea converted to ammonia by bacteria
9
AVP ; e.g. (humans) less tolerant to high
ammonia (in blood)
max 5
only
the and
mostbears
able candidates
were in
able
humans
use amino acids
to
score
the five
available,
the
synthesis
of marks
proteins
and many
despite
much
of the
stated the
thatfact
ureathat
would
be produced
in
information
had been
to them
both mammals.
Therepresented
were fewer
inreferences
the preceding
text. the
Weaker
to either
transport of
candidates
failed
to
use
this
material,
urea in the bloodstream or to
the
despite
being
directed
to regard
do so intothe
filtration
of urea.
With
the
stem
of the question.
they
differences,
a numberInstead
of vague
concentrated
on their
knowledge
statements were
seen,own
such
as the of
the
metabolism
of nitrogenous
conversion
of urea
to ammonia without
compounds
in
humans,
details
of
mention of the role ofgiving
bacteria
in this
deamination
and the ornithine
cycle,
process or precisely
where reabsorption
neither
which
wasplace.
relevant.
of ureaofwould
take
Better
Furthermore,
some candidates
neglected
candidates understood
that amino
acids
to
put
their
responses
under
the
could be synthesised from ammonia in
appropriate
headings
‘similarities’
and
bears although
some of
believed
that this
‘differences’,
thereby
marks for
would also take
place losing
in humans.
otherwise correct statements.