D.3 Functions of the liver Flashcards
Blood arrives at the liver from which two sources?
Hepatic artery and hepatic portal vein
Where does the hepatic artery come from and what blood does it bring?
- branches off from the aorta
- bringing oxygen-rich blood from the heart
What is majority of the blood circulating in the liver from?
From the hepatic portal vein
Where does the hepatic portal vein come from and what blood does it bring?
- brings blood from the stomach and the intestine to the liver
- blood can be rich in nutrients that have been absorbed from digested blood depending on how revently the individual has eaten
- Because the blood travelled from the heart to the stomach or intestine first, the oxygen content is relatively low
Why is the oxygen content relatively low in the blood from the haptic portal vein?
The blood travelled from the heart to the stomach or intestine first
Why is the oxygen content relatively low in the blood from the haptic portal vein?
The blood travelled from the heart to the stomach or intestine first
Within the liver, the vein subdivides into what?
into subdivisions called sinusoids
What are sinusoids like?
Like capillaries but are wider and the walls are not continuously lined with cells
What does the sinusoid allow for?
- Blood flowing through to come in contact with the hepatocytes (liver cells)
- allow proteins such as albumin to enter and leave the blood
What do hepatic artery subdivide into?
into arterioles, which join with the sinusoids at various points to provide oxygenated blood
What joins the sinusoid to provide oxygenated blood?
Arterioles subdivided from hepatic artery
What do sinusoids merge with?
with venules that lead to the hepatic vein
Why does the sinusoid merge with venules from the hepatic vein?
to carry the blood away fromthe liver to the vena cava
What is one of the main functions of the liver?
to regulate the quantity of nutrients circulating in the blood
* e.g. glucose -> glycogen -> glucose
How does the liver treat proteins?
- the body cannot store proteins or amino acids
- excess quantities are broken down in the liver and utilized as energy sources
- the liver processes the resulting nitrogenous waste
How does the liver respond to lipids?
- liver is responsible for managing circulating lipids which arrive in a variety of forms
- the liver processes lipids in one form and distributes it in other forms
How does the liver treat chylomicrons?
Some forms such as chylomicrons arriving from the intestine are broken down in the liver
How dos the liver transport tryglycerides?
Very low density lipoproteins (VLDL) are synthesized in the hepatocytes. Their purpose is to transport the triglycerides synthesized in the liver into blood plasma for storage or use in the body
What does the liver do to surplus cholesterol?
convert it into bile salt
How does the liver respond to high and low levels of glucose in the blood?
High
* release insulin
* insulin stimulates hepatocytes to take up the glucose and store as glycogen
Low
* hormones such as glucagon is released
* breakdown of glycogen, glycerol, amino acids and fatty acids in the liver
* release glucose to the blood stream
What minerals are stored in the liver in excess?
Iron, retinol (vitamin A), calciferol (vitamin D)
* released when there is a deficit in the blood
What is the typical lifespan of an erythrocyte?
(red blood cell)
in an adult, about 120 days
What changs do old and damaged erythrocytes undergo?
changes in their plasma membrane which make them susceptible to recognition by macrophages
What happens at the end of erythrocytes’ lifespan?
- removed from circulation
- broken down in the spleen and liver
- Liver breaks down the erythrocytes and hemoglobin
- most of the breakdown products are recycled
What do red blood cells do as they age?
Swell
What happens to some swelling red blood cells?
They are engulfed by Kupffer cells, which are marcrophages which line the sinusoids in the liver
What happens to some swelling red blood cells?
They are engulfed by Kupffer cells, which are marcrophages which line the sinusoids in the liver
What are Kuppffer cells?
Macrophages which line the sinusoids in the liver
What happens inside the Kupffer cell after engulfing a red blood cell?
- hemoglobin molecule is split into globin chains and a heme group
- Amino acids from the globin chains are recycled, while the heme group is further broken down into iron and bilirubin
What is a red blood cell initially split into by a Kupffer cell?
Hemoglobin molecule -> globin chains and a heme group
What gets recycled from the globin chain split from a hemoglobin molecule?
Amino acids
What gets recycled from the globin chain split from a hemoglobin molecule?
Amino acids
How is the heme group further broken down into after in the Kupffer cell?
Into iron and bilirubin
What does the Kupffer cell do to the bilirubin from the heme group?
Release into the blood
What does the Kupffer cell do to the iron from the heme group?
The iron is obund to transferrin and transported to the liver and spleen for storage or to the bone marrow to be used in the synthesis of new red blood cells
Why would iron be sent to the bone marrow?
to be used in the synthesis of new red blood cells
What are Kupffer cells capable of?
Phagocytosis, whereby they trap and engulf foreign particles and substances
What are filopodia?
Kupffer cell’s long arm-like extensions of cytoplasm
Where is hemoglobin synthesized?
In red blood cells
How is iron that was recycled from old red blood cells used?
They aare carried to the bone marrow and added to the heme group of new red blood cells
Why is iron essential for red blood cell function?
Because it is a component of the hemoglobin molecule
What is iron at high concentrations?
Toxic
What is iron at high concentrations?
Toxic
What is transferrin?
It is a protein that is bound to iron either absorbed from the intestine or released during the breakdown of damaged red blood cells.
It is transferred in the blood
How does iron enter cells?
- bound to transferrin
- cells have receptors for the transferrin molecule
- once bound, the receptor-iron complex enters the cell
- iron is either incorporated into the heme molecule or it is transferred to a storage molecule called feritin
What are red blood cells formed from in the bone marrow?
From stem cells in the bone marrow
When would there be a relarively high levels of transferrin receptors?
When developing red blood cells
What is ferritin?
A storage molecule where iron in cells can be stored
What is bilirubin?
A yellow pigment
* released from the breakdown of other proteins such as myoglobin and cytochrome
What is the role of cytochrome P450?
- Breaks down various medicinal and recreational drugs
- Is also involved in respiration (ETC) so its role in the breakdown of drugs can interfer with repiration and cause unanted side effects
What is the product of breaking down myoglobin and cytochrome?
Bilirubin
How are bilirubin produced outside of the liver transported to the liver?
Bound to the protein albumin
Is bilirubin soluble?
No, bilirubin is relatively insoluble
What happens in the liver so that bilirubin is soluble?
It is reacted with glucaronic acid to make it soluble
Where is the water soluble form of bilirubin secreted into?
Into passages called canaliculi along with water, electrolytes, bicarbonate, cholesterol, phospholipids and salts
This mixture is called bile
What makes up bile?
The water soluble form of bilirubin, water, electrolytes, bicarbonate, cholesterol, phospholipids and salts
What do hepatocytes secrete?
A green-brown fluid called bile
What do hepatocytes secrete?
A green-brown fluid called bile
How does bile make its way from the liver to the gallbladder?
Bile is drained away from the liver through a dense netowrk of bile canaliculi towards the gall-bladder
* after a meal, bile is expelled from the gallbladder and enters the duodenum for breakdown and digestion of fatty compounds
How does bile make its way from the liver to the gallbladder?
Bile is drained away from the liver through a dense netowrk of bile canaliculi towards the gall-bladder
* after a meal, bile is expelled from the gallbladder and enters the duodenum for breakdown and digestion of fatty compounds
What happens when a disease interferes with the normal metabolism or excretion of bilirubin?
It can build up in the blood and result in a condition known as jaundice
What is jaundice?
A conition in which the skin and eyes are discoloured due to the deposition of excess bilirubin (pigment) in skin tissues
* yellow eyes and skin
What is jaundice?
A conition in which the skin and eyes are discoloured due to the deposition of excess bilirubin (pigment) in skin tissues
* yellow eyes and skin
if jaundice is not a disease in itself what is it?
It is a symptom of many disorders of the liver and biliary system
What is jaundice due to in liver diseases?
Such as hepatitis or liver cancer
* can occur due to obstruction of the bile ducts by gallstones or pancreatic cancer
How common is jaundice in newborns?
Relatively common
What are the different causes of jaundice in newborns?
- Newborns have a relatively high turnover of red blood cells
- A new born’s liver is often still developing and may not be able to process the bilirubin fast enough
- Some newly born infants do not feed properly and the lack of intestinal contents means that excreted bilirubin can be reabsorbed
What are some treatments to jaundice?
exposure to ultraviolet light either uner a special ‘bili’ lamp or by exposing the skin to the sun
How does ultraviolet light treat jaundice?
The ultraviolet light converts the excess bilirubin into products that can be excreted
The eyes are covered to prevent any possible damage to the retina
Why is treatment of jaundice important to infants and not as much in adults?
Babies:
Extended periods of elevated serum bilirubin in infants including a form of neurological damage called kernicterus in which brain damage results in deafness and cerbral palsy
Adults:
normally just experience itchiness
Where can we get cholesterol in our daily life?
- Absorbed from food in the intestine
- Large quantity also synthesized each day by hepatocytes
What is cholesterol and why is it needed in large amounts?
Choleterol is a raw material needed for:
* the synthesis of vitamin D
* synthesis of steroid hormones
* It is a structural component of membranes
* used in the production of bile
How does the liver regulate the amount of circulating lipids such as cholesterol and lipoproteins?
Either synthesizing them as required, or breaking them down and secreting cholesterol and phospholipids in the bile
How does your diet affect the amount of cholesterol synthesized by the body?
The body varies to some degree with diet.
Excess saturated fat in the diet increases the production of cholesterol
How are lipids transported in the blood?
In vesicles known as lipoproteins
How many types of lipoprotein are there?
5
What are lipoproteins composed of?
- a hydrophilic exterior of phospholipids
- proteins
- cholesterol
- a core of cholesterol and fats (tryglycerides)
What is an example of a lipoprotein?
Chylomicrons transport lipids from the intestine to the liver
Others are synthesized in the liver
Why do some lipoproteins change their density?
As molecules are selectively removed from them
What of hepatocytes within the liver produce 90% of the proteins in blood plasma?
The rough endoplasmic reticulum
What proteins in blood plasma does the RER of hepatocytes produce?
Fibrinogen and albumin
What is albumin?
Carrier protein that binds to such things as bilirubin
For this reason it is referred to as a transport protein
Though is also plays a role in maintaining osmotic balance in the blood
What is fibrinogen?
A protein that is essential for clotting
What explains the characteristic appearance of hepatocytes?
The fact that hepatocytes are actively involved in protein synthesis
What are some characteristic appearance of hepatocytes?
- extensive network of ER and Golgi body providing high levels of protein synthesis
- Estimated that there are 13 million ribosomes attached to the ER of a typical liver cell
What is an important role of the liver besides dealing with nutrients, red blood cells, conversion of cholesterol to bile salts and production of plasma proteins?
Detoxifcation
What does the liver do for detoxificiation?
- Liver cells absorb toxic substances from the blood and convert them into non-toxic or less toxic substances, using a range of chemical conversions
- one mean why which the liver does this is to convert hydrophobic compounds into more easily excreted hydrophilic ompounds
How is alcohol converted into a less toxic substance?
By the enzyme ethanol dehydrogenase
What does the liver convert toxic ammonia into?
Urea
What is the word equation for deamination?
Amino acid + oxygen -> Keto acid + ammonia
What is the ammonia produced by deamination converted to?
CO2 + NH3 -> urea
What is the remaining keto acid from deamination used in?
used directly in respiration (directly enter the kreb cycle for energy ATP) to release energy or it may be converted to a carbohydrate or fat for storage
What biochemicals do the liver also detoxify?
Biochemicals which are foreign to the organism’s normal biochemistry such as poisons or drugs
What are the functions of the liver? (6)
- processing of nutrients
- Storage of nutrients
- recycling of red blood cells
- conversion of cholesterol to bile salts
- production of plasma proteins by hepatocytes
- Detoxification
