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Option D: Human Physiology
D.3 Functions of the Liver
http://www.youtube.com/watch?v=Q-kBd2YgpRw
http://click4biology.info/c4b/h/h4.htm
D.3
• Essential idea: The chemical composition of
the blood is regulated by the liver.
D.3.A2 Dual blood supply to the liver and differences between sinusoids and capillaries.
Hepatic vein carries blood from
the liver on to the heart with
levels of food adjusted
Liver
How much oxygen would
be in the blood coming in
from the portal vein?
Very little since it has
already delivered oxygen
the stomach and intestines
Blood arrives at the liver
from two sources:
2 Hepatic artery brings
oxygenated blood to the liver
1
Hepatic portal vein carries
blood containing digested
food from the intestines to the
liver
D.3.A2 Dual blood supply to the liver and differences between sinusoids and capillaries.
Capillary
vs.
Sinusoid
Narrow
Wide
Continuously
Spaces between
lined with cells
cells
*fenestrated epithelium
= an endothelium that
is full of holes
1
3
7
2
4
5
6
(space between
hepatocyte and a
sinusoid)
(store
Vitamin A)
D.3.U1 The liver removes toxins from the blood and detoxifies them.
Every day you ingest many toxic substances. The liver
functions to remove toxins and detoxify (convert into nontoxic or less toxic substances) them.
Examples:
• Alcohol is converted into a less toxic
substance by the enzyme ethanol
dehydrogenase
• Ammonia is converted into urea and
transported to the kidneys where it is
filtered out of the blood and released in
the urine
Other toxic substances include pesticides,
herbicides, preservatives, medications, etc.
http://www.panna.org/pesticides-big-picture/pesticides-101
D.3.U7 The liver intercepts blood from the gut to regulate nutrient levels. AND D.3.U8 Some
nutrients in excess can be stored in the liver.
D.3.U7 The liver intercepts blood from the gut to regulate nutrient levels. AND D.3.U8 Some
nutrients in excess can be stored in the liver.
Stored in liver
when in excess
and released
when there is a
deficit in the
blood.
D.3.U5 Surplus cholesterol is converted to bile salts.
Hepatocytes break down surplus
cholesterol into bile salts and
use it to make bile.
(carry bile from hepatocytes
to bile duct)
(bilirubin)
D.3.U6 Endoplasmic reticulum and Golgi apparatus in hepatocytes produce plasma proteins.
In addition to producing bile, the hepatocytes
also produce plasma proteins.
90% of plasma proteins are produced here, but two well
documented proteins include:
1. Albumin – helps regulate blood osmotic pressure
and is a carrier for bilirubin (bile salts from blood to
liver) and some other fat-soluble substances
2. Fibrinogen – gets converted to fibrin to form the
mesh component of a blood clot
Platelet/Cell Damage
clotting factors
Thrombin
Fibrinogen
(soluble)
Fibrin
(fibrous)
Captures erythrocytes
Clot
 High levels of protein synthesis!
D.3.U6 Endoplasmic reticulum and Golgi apparatus in hepatocytes produce plasma proteins.
In addition to producing bile, the hepatocytes also produce plasma proteins.
Review of protein synthesis and secretion:
1) DNA within the nucleus of the hepatocyte synthesizes mRNA for a
particular protein (transcription)
2) mRNA exits nucleus through a nuclear pore
3) mRNA finds a ribosome located on rough ER
4) Plasma protein is synthesized (translation)
5) Plasma protein is transported by vesicle to Golgi apparatus
6) The Golgi apparatus may
modify the protein and then it
is surrounded with another
vesicle
7) Vesicle goes to plasma
membrane for exocytosis
(secretion)
8) Plasma protein enters blood
 High levels of protein synthesis!
D.3.U3 The breakdown of erythrocytes starts with phagocytosis of red blood cells by Kupffer cells.
The liver also functions to breakdown and recycle erythrocytes.
The life span of a erythrocyte (red
blood cell) is about 4 months, or 120
days.
The do not contain a nucleus
(anucleate) and must be made by
the bone marrow and not mitosis.
When they are at the end of their
lifespan, the cell membrane
becomes weak and the cell bursts
open. This results in hemoglobin
being released into the blood. (There
is about 280 million hemoglobin
molecules in each RBC!)
http://image.slidesharecdn.com/rbcjothi2151022022843-lva1-app6891/95/rbc-jothi-2-5-
D.3.U3 The breakdown of erythrocytes starts with phagocytosis of red blood cells by Kupffer cells.
The liver also functions to breakdown and recycle erythrocytes.
As they age and swell, erythrocytes
may also be taken in by Kupffer cells
through phagocytosis. Here they are
broken down.
Kupffer cells are a type of macrophage
(type of leucocyte – WBC)
D.3.U2 Components of red blood cells are recycled by the liver. AND D.3.U4 Iron is carried to the
bone marrow to produce hemoglobin in new red blood cells.
The liver also functions to breakdown and recycle erythrocytes.
Hemoglobin in the blood is also ingested through phagocytosis by
Kupffer cells in the sinusoids:
• Four globin proteins (alpha & beta chains) are hydrolyzed into
amino acids
• Amino acids are released into bloodstream & can be used for
protein synthesis
• Iron atom is removed from each of the 4 heme groups. Some is
stored in the liver & some is sent to bone marrow to produce
hemoglobin in new RBCs
• Bilirubin remains & is absorbed by hepatocytes to make bile
D.3.U2 Components of red blood cells are recycled by the liver. AND D.3.U4 Iron is carried to the
bone marrow to produce hemoglobin in new red blood cells.
D.3.U2 Components of red blood cells are recycled by the liver. AND D.3.U4 Iron is carried to the
bone marrow to produce hemoglobin in new red blood cells.
Iron is essential but can be toxic if concentrations are too high.
Therefore, maintaining homeostasis of iron levels in the blood
is important.
Iron is transported in the blood by a protein called transferrin.
Iron can be stored in hepatocytes or transported to the bone
marrow where RBCs are made from stem cells.
Hemoglobin is synthesized in RBCs. When iron is bound to
transferrin it can bind to receptors on the surface of developing
RBCs and enter the cell. There the iron can be incorporated
into the heme groups or stored in a storage molecule called
ferritin.
D.3.U2 Components of red blood cells are recycled by the liver. AND D.3.U4 Iron is carried to the
bone marrow to produce hemoglobin in new red blood cells.
Overview of iron homeostasis.
Nancy C. Andrews Blood 2008;112:219-230
©2008 by American Society of Hematology
http://www.bloodjournal.org/content/112/2/219?sso-checked=true
D.3.A1 Causes and consequences of jaundice.
Jaundice is a condition characterized by having too
much bilirubin in the blood and within the tissues.
Bilirubin is a yellow pigment
which causes individuals with
jaundice to have a yellow tinge
to their skin and yellowing of
the whites of their eyes.
There are two main types of jaundice:
Infant jaundice & Adult jaundice
http://www.nhs.uk/conditions/Jaundice/Pages/Introduction.aspx
D.3.A1 Causes and consequences of jaundice.
1. Infant Jaundice
Causes: Typically occurs in premature
babies because their liver is not yet
capable of fully processing bilirubin to
bile. Another cause is that some
newborns do not feed properly and the
lack of intestinal contents means the
bilirubin can be reabsorbed.
Consequences: A brain condition called
acute bilirubin encephalopathy –
excessive levels of bilirubin are toxic to
brain cells
Treatment: Exposure to sunlight or the
use of a “bili” lamp which uses UV light –
blue and green portion of the light
spectrum changes the shape of bilirubin
allowing it to be excreted
http://kidshealth.org/EN/images/galleries/babyJaundice_enGL.jpg
D.3.A1 Causes and consequences of jaundice.
2. Adult Jaundice
Causes: Many causes: liver diseases
such as hepatitis or liver cancer;
Obstruction of bile duct by gallstones or
pancreatic cancer
Consequences: A brain condition called
acute bilirubin encephalopathy –
excessive levels of bilirubin are toxic to
brain cells; Itching; other consequences
associated with the underlying cause
Treatment: Depends on the underlying
cause
http://www.nytimes.com/health/guides/disease/cirrhosis/print.html