Human Physiology
Production of plasma proteins
Detoxification
Regulation of nutrient levels
Storage of nutrients in excess
Formation of bile
Breakdown of the RBCs
Jaundice
Liver cells absorb toxic substances from the blood and convert them into non- toxic or less toxic substances, using a range of chemical conversions.
alcohol is converted into a less toxic substance by the enzyme ethanol dehydrogenase
The liver converts toxic ammonia into urea
Hepatocytes are the most numerous cells in the liver, and are the most active in removing and processing chemical toxins from the blood. They extract toxins from the plasma and begin a process to eliminate the toxins.
They chemically modify the toxin to make it less destructive
They add chemical components that make the (now modified) toxin water soluble
The water-soluble modified substance can be added back into the blood in order to be eliminated by the kidneys as a component of urine
One of the main functions of the liver is to regulate the quantity of nutrients circulating in the blood
It plays a key role in the regulation of circulating glucose by either storing glucose as glycogen or breaking glycogen down to glucose
body cannot store proteins or amino acids, excess quantities of these in the diet are broken down in the liver to be utilised as energy sources
very low density lipoproteins (VLDL) are synthesised in hepatocytes. Their purpose is to transport the triglycerides synthesised in the liver into blood plasma for storage or use in the body
when the blood glucose level is too high, insulin stimulates hepatocytes to absorb glucose and convert it to glycogen for storage
When the blood glucose level is too low, glucagon stimulates hepatocytes to break down glycogen and release glucose into the blood
Nutrients like:
Vitamin A
Vitamin D
Iron
are stored in the liver when they are in surplus and released when there is a deficit in the blood
Hepatocytes convert surplus cholesterol into bile salts
These bile salts are added to bilirubin to make the substance bile
When bile is secreted into the small intestine, the bile salts emulsify droplets of lipid, greatly speeding up lipid digestion by lipase
The liver is responsible for the breakdown of red blood cells and recycling of its components
These components are used to make either new red blood cells or other important compounds (e.g. bile)
Kupffer cells in the walls of sinusoids in the liver are specialised macrophages that absorb and break down damaged red blood cells by phagocytosis and recycle their components.
The hemoglobin is split into iron containing heme groups and globins.
The iron atom is removed from each heme group.
The globins are hydrolyzed to amino acids by peptidases, which are either recycled by being released into the blood or metabolized by the liver.
Some of this iron is stored within the liver and some is sent to bone marrow to be used in the production of hemoglobin for new red blood cells
Once iron has been removed from the haem group, what remains of the molecule is a yellow colored substance called bile pigment (bilirubin)
This is absorbed by the nearby hepatocytes and becomes a key component of bile
Jaundice is a condition caused by an excess of bile pigment bilirubin within the body
Consequences
Causes
Liver disease
Impaired removal of bilirubin by the liver may cause levels to build within the body. Obstruction of the gallbladder or bile duct
Preventing the secretion of bile, which will cause bilirubin levels to increase.
Damage to red blood cells-Increased destruction of erythrocytes (e.g. anemia) will cause bilirubin levels to rise.
Other causes include hepatitis, liver cancer and gallstones
The main consequence of jaundice is a yellowish discoloration of the skin and whites of the eyes (sclera) due to an accumulation of bilirubin in blood plasma and skin tissues
Other common symptoms include itchiness, paler than usual stools and darkened urine.
If bilirubin levels in blood plasma remain elevated for long periods in infants, a serious consequence could be a form of brain damage that results in deafness and cerebral palsy
Types
Fibrinogens
Albumins
helps regulate blood osmotic pressure and acts as a carrier for bile salts and some other fat-soluble substances.
when converted to fibrin forms the mesh component of a blood clot.
Organelles involved
Golgi apparatus in hepatocytes
Endoplasmic reticulum in hepatocytes
The rough endoplasmic reticulum of hepatocytes produces 90% of the proteins in blood plasma, including all of the albumin and fibrinogen.
Plasma proteins are processed by the Golgi apparatus in hepatocytes before being released into the blood
Brief process
DNA within the nucleus of a hepatocyte synthesizes messenger RNA for a particular protein (transcription)
mRNA exits the nucleus through a nuclear pore
mRNA binds a ribosome located on rough endoplasmic reticulum
Plasma protein is synthesized
Plasma protein is transported by a vesicle to the Golgi apparatus
The Golgi apparatus possibly modifies the protein and surrounds the protein with another vesicle
the vesicle goes to the plasma membrane for exocytosis (secretion)
The plasma protein enters the blood plasma
