D3 Functions of the Liver Flashcards
What is the liver?
The liver is a lobed organ located below the diaphragm that functions to regulate the chemical composition of blood
What artery leads to the liver and what is its function?
It receives oxygenated blood via the hepatic artery, which is used to sustain liver cells (hepatocytes)
What vessel lead to the liver (not artery) and what is it’s role?
It also receives nutrient rich blood from the gut via the portal vein
What vessel leads away from the liver and what is its purpose?
Deoxygenated blood is transported from the liver via the hepatic vein
What is the general function of the liver?
The liver functions to process the nutrients absorbed from the gut and hence regulates the body’s metabolic processes
What is the liver’s role in relation to storage and release?
It is responsible for the storage and controlled release of key nutrients (e.g. glycogen, cholesterol, triglycerides)
What is the liver’s role in relation to detoxification?
It is responsible for the detoxification of potentially harmful ingested substances (e.g. amino acids, medications, alcohol)
What is the liver’s vascular role?
It produces plasma proteins that function to maintain sustainable osmotic conditions within the bloodstream
What is the liver’s function in relation to red blood cells?
It is responsible for the breakdown of red blood cells and the production of bile salts
What is the liver composed of?
The liver is composed of smaller histological structures called lobules, which are roughly hexagonal in shape
What is each lobule surrounded by?
Each lobule is surrounded by branches of the hepatic artery (provide oxygen) and the portal vein (provide nutrients)
Where do all the vessels in the liver drain into?
These vessels drain into capillary-like structures called sinusoids, which exchange materials directly with the hepatocytes
Where do sinusoids drain into and why?
The sinusoids drain into a central vein, which feeds deoxygenated blood into the hepatic vein
What is another name for liver cells and what is its role?
Hepatocytes also produce bile, which is transported by vessels called canaliculi to bile ducts, which surround the lobule
What are sinusoids?
Sinusoids are a type of small blood vessel found in the liver that perform a similar function to capillaries (material exchange)
What is a special property of sinusoids?
Sinusoids have increased permeability, allowing larger molecules (e.g. plasma proteins) to enter and leave the bloodstream
What 2 structural features cause increased permeability of sinusoids?
The surrounding diaphragm (basement membrane) is incomplete or discontinuous in sinusoids (but not in capillaries)
The endothelial layer contains large intercellular gaps and fewer tight junctions (allowing for the passage of larger molecules)
How are nutrients transported to the liver?
Nutrients absorbed by the small intestine are transported by the hepatic portal vein to the liver for metabolism
What does the liver do with transported nutrients?
The liver converts these nutrients into forms that can be stored or used and mediates their transport to various tissues
What are examples of nutrients stored in the liver?
Nutrients stored within the liver include glycogen, iron, vitamin A and vitamin D
What happens to excess glucose in the blood stream?
Excess glucose in the bloodstream (e.g. after meals) is taken up by the liver and stored as glycogen
What happens when blood glucose levels drop?
When blood glucose levels drop, the liver breaks down glycogen into glucose and exports it to body tissues
What happens when blood glucose levels are low, but there is no more glycogen?
When hepatic glycogen reserves become exhausted, the liver synthesises glucose from other sources (e.g. fats)
What substance regulates blood glucose levels?
These metabolic processes are coordinated by the pancreatic hormones – insulin and glucagon
Why does deamination occur?
The body can not store amino acids, meaning they must be broken down when in excess
What does deamination release initially?
Amino acid breakdown releases an amine group (NH2), which cannot be used by the body and is potentially toxic
What is done with the amine group formed by deamination?
The liver is responsible for the removal of the amine group (deamination) and its conversion into a harmless product
How is the amine group detoxified? What happens to it?
The amine group is converted into urea by the liver, which is excreted within urine by the kidneys
Apart from deamination, what other process relating to protein metabolism is carried out in the liver?
The liver can also synthesise non-essential amino acids from surplus stock (via transamination)
What is the liver the main site for, relating to fat metabolism?
The liver is the major site for converting excess carbohydrates and proteins into fatty acids and triglycerides
What types of lipids can the liver synthesise?
It is also responsible for the synthesis of large quantities of phospholipids and cholesterol
What happens to the lipids synthesised by the liver?
These compounds are then stored by the liver or exported to cells by different types of lipoproteins
What is the role of LDL’s?
Low density lipoprotein (LDL) transports cholesterol to cells, for use in the cell membrane and in steroid synthesis
What is the role of HDL’s?
High density lipoprotein (HDL) transports excess cholesterol from cells back to the liver (for storage or conversion)
Are LDLs or HDLs considered “bad” and why?
LDL is considered ‘bad’ as it raises blood cholesterol levels, while HDL lowers cholesterol levels and is therefore ‘good’
What happens to surplus cholesterol?
Surplus cholesterol is converted by the liver into bile salts, which can be eliminated from the body via the bowels
What type of toxins does the liver detoxify and why?
Many of these toxic compounds are fat soluble, making them difficult for the body to excrete
Generally, what is done to toxic compounds?
These compounds are converted into less harmful and more soluble forms, which are then excreted from the body
What is the first step in detoxification?
Toxins are converted into less harmful chemicals by oxidation, reduction and hydrolysis reactions
What mediates the first step of detoxification?
These reactions are mediated by a group of enzymes known as the cytochrome P450 enzyme group
What is the end product of the first step?
These conversions produce damaging free radicals, which are neutralised by antioxidants within the liver
What is done with the free radical/converted chemical produced by the first step of detoxification?
The converted chemical is then attached to another substance (e.g. cysteine) via a conjugation reaction
What is the purpose of the second main step of detoxification?
This renders the compound even less harmful and also functions to make it water soluble
What is the final result of detoxification?
The water soluble compounds can now be excreted from the body within urine by the kidneys
What are plasma proteins?
Plasma proteins are proteins present in the blood plasma and are produced by the liver (except for immunoglobulins)
What produces plasma proteins? What exports them?
The proteins are produced by the rough ER in hepatocytes and exported into the blood via the Golgi complex
What are 3 examples of plasma proteins?
albumins
globulins
fibrinogens
What is the role of albumins?
Albumins regulate the osmotic pressure of the blood (and hence moderate the osmotic pressure of body fluids)
What is the role of globulins?
Globulins participate in the immune system (i.e. immunoglobulins) and also act as transport proteins
What is the role of fibrinogens?
Fibrinogens are involved in the clotting process (soluble fibrinogen can form an insoluble fibrin clot)
What is the general structure of red blood cells and why?
In humans, red blood cells possess minimal organelles and no nucleus in order to carry more haemoglobin
What is the consequence of red blood cells being so highly specialised?
Consequently, red blood cells have a short lifespan (~120 days) and must be constantly replaced
What are the recycled components of red blood cells used for?
These components are used to make either new red blood cells or other important compounds (e.g. bile)
What are Kupffer cells?
Kupffer cells are specialised phagocytes within the liver which engulf red blood cells and break them down
What do Kupffer cells break down and what are they broken down into?
Kupffer cells break down haemoglobin into globin and iron-containing heme groups
How is globin recycled?
Globin is digested by peptidases to produce amino acids (which are either recycled or metabolised by the liver)
How are heme groups recyled?
Heme groups are broken down into iron and bilirubin (bile pigment)
What must be done to the released iron? (RBC recycling)
The released iron must be complexed within a protein in order to avoid oxidation to a ferric state
What can be done to the iron produced by the recycling of RBC? 2
Iron can be stored by the liver within a protein shell of ferritin
Iron can be transported to the bone marrow (where new haemoglobin is produced) within the protein transferrin
What is jaundice?
Jaundice is a condition caused by an excess of bile pigment – bilirubin – within the body
Where is bilirubin produced?
Bilirubin is produced as part of the natural breakdown of haemoglobin by the liver
How does the liver usually deal with bilirubin?
Normally, the liver conjugates this bilirubin to other chemicals and then secretes it in bile
What happens if there’s an excess of bilirubin?
When there is an excess of bilirubin, it may leak out into surrounding tissue fluids
What may cause jaundice? (general)
Jaundice may be caused by any condition which impairs the natural breakdown of red blood cells
What are 3 general causes of jaundice?
liver disease
obstruction of the gall bladder
damage to red blood cells
How may liver disease cause jaundice?
impaired removal of bilirubin by the liver may cause levels to build within the body
How may obstruction of the gall bladder lead to jaundice?
preventing the secretion of bile will cause bilirubin levels to accumulate
How may damage to red blood cells?
increased destruction of erythrocytes (e.g. anemia) will cause bilirubin levels to rise
What is the main consequence of jaundice?
The main consequence of jaundice is a yellowish discoloration of the skin and whites of the eyes (sclera)
What are other common symptoms of jaundice?
Other common symptoms include itchiness, paler than usual stools and darkened urine
How may jaundice be resolved?
Jaundice may be resolved by treating the underlying cause for the build up of bilirubin within the body
