Transcript H4: Functions of the Liver

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The largest gland in the body
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The second largest organ (after the skin)
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About 1.5 kg in mass
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Located just below the diaphragm and over
the upper portion of the stomach
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The liver receives blood from 2 major blood
vessels and blood leaves the liver by 1 blood
vessel
The HEPATIC ARTERY is a branch of the aorta
It carries oxygenated blood (from the heart)
to the liver tissues.
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The HEPATIC PORTAL VEIN brings
deoxygenated blood from the digestive tract
to the liver
This blood is rich in absorbed nutrients from
the villi of the small intestine.
The hepatic artery and hepatic portal vein
carry blood into the “capillaries” of the liver,
called the sinusoids.
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All sinusoids are then drained by a central
vein which is a branch of the HEPATIC VEIN,
which is the sole blood vessel that takes
blood away from the liver and delivers it to
the vena cavas so it may return to the heart.
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The blood delivered to the liver via the
hepatic portal vein is unique (in comparison
to the type of blood that is usually delivered
to an organ) because:
It is low pressure, deoxygenated blood
because it has already been through a
capillary bed.
It has a high quantity of nutrients
(particularly glucose) – though this is based
on the types of food and the timing of
digestion and absorption
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A major function of the liver is to remove
some things from the blood and to add
others to it.
This is done by hepatocytes (liver cells)
O2-rich blood from the hepatic artery, and
(sometimes) nutrient-rich blood from the
hepatic portal vein, both flow into the
sinusoids of the liver.
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Sinusoids are where the exchange of
materials occur between blood and
hepatocytes.
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Kupffer Cells: cells that line the sinusoids.
They ingest foreign particles and are involved
in the breakdown of old erythrocytes (rbc)
The hepatocytes produce bile.
Bile will move in the opposite direction of the
blood, towards the bile ducts.
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Sinusoids differ from a typical capillary bed in
the following ways:
Sinusoids have larger lumens
Sinusoids have Kupffer cells that breakdown
rbc for recycling
Sinusoids are lined by endothelial cells with
gaps between them.
 These gaps allow large molecules (like proteins) to be
exchanged between hepatocytes and the bloodstream
 Hepatocytes are in direct contact with blood
components making all exchanges with the
bloodstream more efficient
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Each type of solute dissolved in blood plasma
has a normal homeostatic range.
Concentrations below or above this range
creates physiological problems in the body.
The liver helps regulate the levels of nutrients
in the blood and maintain homeostatic
ranges.
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Ex: after a meal, blood glucose will be
converted into glycogen by the hepatocytes.
When blood glucose levels are low, the
hormone glucagon tells the hepatocyte to
release the glycogen so it may be converted
back into glucose.
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The liver is the main organ for detoxification.
Pesticides, medicines, food additives, alcohol,
and other toxins are removed from the blood
stream and broken down in the hepatocytes of
the liver.
The liver does not extract all excess glucose,
toxins etc in a single trip through the sinusoids,
The chemicals within the blood will be acted on
by hepatocytes multiple times as blood
continuously makes circuits through the liver.
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After drinking alcohol, each time blood
passes through the liver, hepatocytes attempt
to remove the alcohol from the bloodstream.
The breakdown of alcohol produces free
radicals and other reactive molecules that
damage proteins, lipids and DNA.
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The liver breaks down alcohol in the following
way:
Alcohol  acetaldehyde  acetic acid  carbon dioxide
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Long term alcohol abuse seems to interfere
with normal liver metabolism of proteins, fats
and carbohydrates
Long term alcohol abuse can result in:
cirrhosis, fat accumulation, inflammation
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The scar tissue left
when areas of
hepatocytes, blood
vessels and ducts
have been destroyed
by exposure to
alcohol.
Areas of the liver,
showing cirrhosis no
longer function
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“Fatty liver”
Damaged areas of the liver will build fat in
place of normal liver tissue thus decreasing
function.
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This is swelling of damaged liver tissue due
to alcohol exposure
Sometimes referred to as alcoholic hepatitis
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Inflammation of the liver
Often leads to jaundice, lack of appetite, and
general discomfort
Most cases are cause by a hepatitis virus; can
also be caused by the ingestion of toxins
(such as alcohol)
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Acute infectious disease of the liver, caused
by a hepatitis A virus.
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Transmission: oral-fecal route from
contaminated water or infected individual.
Greater risk of contracting virus in a
developing country (because of inadequate
water treatment)
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Symptoms: fever, nausea, fatigue, loss of
appetite, jaundice
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Caused by hepatitis B virus
Sexually transmitted diseased (transmitted in
body fluids: semen, blood, vaginal secretions)
Symptoms: liver inflammation, jaundice,
vomitting, death in rare cases, chronic cases
may result in cirrohosis
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Caused by the hepatitis C virus
Transmission: blood (transfusions,
unsterilized lab equipment)
Symptoms: asymptomatic (no symptoms)
however, if it becomes chronic, cirrhosis, liver
cancer, and liver failure may result.
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As mentioned, carbohydrates are stored in
the liver in the form of glycogen.
The liver also stores iron, vitamin A, and
vitamin D
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Hemoglobin is an important component of
rbc and it contains iron
Iron is present in food, however it is hard for
the body to absorb.
After red blood cells are broken down, their
iron is stored in the liver until it can be used
again.
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The main vitamins stored in the liver are fat
soluble vitamins A and D
VITAMIN A:
◦ found in dairy products; associated with good
vision
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VITAMIN D:
◦ often found as an additive in dairy products
◦ made by the skin in the presence of UV light
◦ Important in the uptake of calcium
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Plasma Proteins: (blood proteins)
◦ ALBUMIN – regulates osmotic pressure of fluids in
the body
◦ FIBRINOGEN – involved in forming blood clots.
◦ GLOBULINS – antibodies (defend the body from
foreign invaders)
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Cholesterol
◦ Some cholesterol is ingested and some is made by
the liver
◦ Used to produce bile
◦ Used to make cell membranes
◦ Used to make lipid based hormones
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Erythocytes have a life span of about 120
days
They do not have a nucleus so, they are
destroyed (do not undergo mitosis –
remember, new rbc come from bone marrow)
When rbc get to 120 days, their cell
membranes become weak and eventually
ruptures
This usually occurs in the spleen
Fist sized organ that
regulates and stores
red blood cells.
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The spleen removes old rbc from circulation
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When a rbc ruptures, it released millions of
hemoglobin
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molecules that now will circulate in the blood
stream and eventually pass through the liver.
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As these molecules make their way through
the liver, they are absorbed by the Kupffer
cells via phagocytosis
Hemoglobin is broken down into heme group
(the iron and non amino acid component) and
globin (the amino acid component)
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Contains the iron component
The iron is stored in the liver before being
transported back to the bone marrow to be
reused in new erythrocytes
The remainder of the heme group become
biliverdin (a green bile pigment), which is then
converted into bilirubin (a yellow pigment) that is
secreted into the small intestine via bile duct with
bile.
Bilirubin turns to stercobilin in the colon an is
what gives feces its characteristic colour reddish
brown colour
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Gives the reddish brown colour to feces
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Gives the yellow colour to urine
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When the liver isn’t functioning properly, high
amounts will circulate in the blood and give
your skin the yellowish appearance known as
jaundice.
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Broken down into amino acids
These amino acids can then be reused to
make other proteins
They can also be broken down for energy