Transcript Functions of the liver

Functions of the liver
Option H.4
1. Synthesis of cholesterol
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Some cholesterol is absorbed from food in
intestines
A larger quantity in made each day in
hepatocytes (liver cells)
Some used by the liver to produce bile
Rest is transported via blood for use by cells
eg. plasma membranes
2. Synthesis of plasma proteins
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Rough er from hepatocytes produces 90% of
proteins in blood plasma
Three main types: albumin, globulin,
fibrinogen
All albumin and fibrinogen is made in the
liver.
Some globulin made in the liver and some by
lymphocytes (antibodies)
3.Storage of nutrients
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Some minerals and fat-soluble vitamins are
stored in the liver
Eg iron, retinol (vitamin A), calciferol
(vitamin D)
Carbohydrate also stored as glycogen
4. Regulation of nutrients in blood
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When there is an excess of certain nutrients in the
blood, hepatocytes absorb and store them
They are released back into the blood when levels
are too low
Eg high blood glucose levels triggers insulin to
stimulate hepatocytes to absorb glucose and convert
it to glycogen.
Eg low blood glucose levels triggers glucagon to
stimulate hepatocytes to break down glycogen and
release it into the blood
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This is necessary so as not to affect the
osmotic concentration of the blood
5. Bile secretion
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Hepatocytes secrete bile into narrow tubes
called canaliculi
Bile contains bile salts, bile pigment,
hydrogen carbonate ions (HCO3-) and
cholesterol
It drains from canaliculi into the gall bladder
Water is reabsorbed leaving it concentrated
before eventual discharge into small intestine
6. Breakdown of erythrocytes
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Erythrocytes have a short life span of 120
days
The plasma membrane becomes fragile and
ruptures releasing haemoglobin into the blood
plasma
Special Kuppfer cells lining the sinusoids in
the liver are phagocytic
They take up the haemoglobin by engulfing it
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Inside the Kupffer cells haemoglobin is split
into globin and heme groups
Globin is hydrolysed into amino acids and
released into the blood
Heme groups are broken down into iron and
bile pigment (bilirubin)
Iron is carried to the bone marrow for use in
production of new erythrocytes
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Bilirubin is used to make bile.
A build-up in the blood leads to jaundice
(yellow skin colour)
Breakdown of erythrocytes - summary
7. Detoxification
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Plants and animals often produce substances that are
toxic to prevent being eaten by predators
Such toxins eg nicotine are broken down by the liver
and excreted
Artificial substances such as alcohol and drugs are
also detoxified in the same way
The liver contains several broad specificity enzymes
for this purpose.
8. Deamination
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The body cannot store protein or amino acids
Excess amounts in the diet are broken down
by the liver for use as energy sources
Excessive alcohol consumption
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The liver has to
metabolize
excess alcohol
taken into the
body
The enzyme
pathway involved
looks like this:
ETHANOL
Alcohol dehydrogenase
ACETALDEHYDE
Aldehyde dehydrogenase
ACETIC ACID
FATTY ACIDS
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Acetaldehyde build up causes a hangover,
along with dehydration
Fatty acids accumulate in liver cells and
around the capillaries in the liver
This reduces blood flow and ultimately kills
the cells (necrosis)
Collagen fibres become deposited leading to
cirrhosis and eventual liver failure
Circulation of blood through liver
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The liver is supplied by 2 blood vessels:
Hepatic artery brings oxygen rich blood from
heart
Hepatic portal vein brings blood from the gut
to the liver
One vessel – the hepatic vein – carries blood
away.
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Inside the liver the hepatic
portal vein divides up into
vessels called sinusoids
They are wider than
normal capillaries and are
very porous due to:
Single layer of very thin
cells / no basement
membrane / large number
of fenestrations (pores)
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This allows blood flowing along sinusoids to
come into close contact with the hepatocytes
Sinusoids drain into venules that lead to the
hepatic vein, which removes blood from the
liver back to the heart along the vena cava
Branches of the hepatic artery join the
sinusoids at certain points, providing
oxygenated blood.