Liver Function 5, Protein metabolism

so we're now thinking about the functions of the liver in terms of protein metabolism now the liver cells are able to change one form of amino acid into another form of amino acid at least on some occasions with some types of amino acids now the amino acids are the subunits of proteins so there's one amino acid unit and then the something called a peptide bond which connects it to another amino acid unit and then another amino acid and they string together to form long peptide chains which form proteins so these are the amino acids now human proteins contain 20 different amino acids and all of these need to be available for the processes of growth and repair as these are synthesized into bigger molecules and they have a primary structure and they fold round into secondary and tertiary structures to give three-dimensional shapes now of these twenty required amino acids ten can be produced in the liver from other amino acids so the twenty the liver is able to synthesize ten from other amino acids but the other ten can't be converted therefore the ten which cannot be converted from other amino acids must be present in the diet because the liver can't synthesize them if health is to be maintained they must be present in the diet the ten dietary essential amino acids and these are the ten which cannot be produced in the liver therefore they are essential now the amino acids which can be produced by the liver by conversion are called non-essential amino acids not because they're not necessary for normal physiology but because health can be maintained even if they're not part of the diet as long as there are adequate amounts of other amino acids to transfer into the amino acids that we need and this process of conversion of one amino acid to another is a fundamental function of the liver and that's called transamination so transamination is changing what I mean acid into another so essential amino acids can be converted into non-essential amino acids but of course the non-essential can't be converted into the essential amino acids because they are essential as part of the diet now if more proteins are consumed than are required the accessory no acids are utilized for their energy yielding content but before the proteins can be used to produce carbohydrate or fat they must first be chemically broken down and this process is called DME ination so DME ination is the breaking down of amino acids into things that can be used as substrates for fuels like carbohydrates and fats and again like these other liver functions this is occurring in the individual hepatocyte s' that make up the liver and the products of this process of DME ination can be used for energy immediately or they can be converted into glycogen or into fats for longer-term storage now another essential function of the liver is that it forms and excretes plasma proteins so plasma proteins are made in the liver and they are excreted into the plasma and this includes the clotting proteins so formation of plasma proteins and formation of the clotting proteins in fact the liver forms I think all of the plasma proteins except the immunoglobulins the antibodies they're produced by the B lymphocytes now albumin is the most abundant plasma protein and is produced by the hepatocytes and then released into the blood as you would expect an albumin is a very large protein in fact a chicken albumin you'll have seen when you eat an egg because it's made that is the white part of the egg is made of albumin but of course this is human Albert because has been produced by a human liver and human hepatocyte and the albumin is a particularly large protein and it's essential for the maintenance of the osmolarity of the plasma which is needed to facilitate osmotic reabsorption of the tissue fluids this is sometimes called the colloidal osmotic pressure or the oncotic pressure it's thick the reabsorption that we need so you probably remember that in the capillaries we have capillary endothelial cells with small gaps and that the tissue fluid is going to be formed at the arteriole end of the capillary and it needs to be reabsorbed at the venous end of the capillary so it's formed the arteriole end of the capillary because the hydrostatic pressure is greater than the osmotic pressure and it's reabsorbed at the venous end because the osmotic pressure is greater than the hydrostatic pressure and sucks it back in but of course if were short of plasma proteins particularly the albumin produced by the liver then this is not going to be sucked back in and we'll be left with edema so patients who are hypo protein emic often become a demitasse because they're not sucking this back in this is why you have seen pictures of malnourished children who have swollen tummies and they are a demitasse because they don't have the plasma proteins to suck the fluid back in so the child needs to be fed proteins and the proteins will be broken down in the digestive tract to amino acids the amino acids will go to the liver and the liver is more than capable of producing all the albumin that's required as long as we have these essential amino acids then yet tragically we get malnourished children who are a demitasse so simple but so tragic now albumin is also described as a carrier molecule transporting sub substances around in the circulatory system for example some drugs are transported bound to albumin it's called protein binding of drugs now clotting proteins the liver cells produce several of the clotting protein factors such as Prout thrombin and fibrin agent so fibrinogen is present in the blood and it but then when there's the right trigger the fibrinogen precipitates into long sticky strands of fibrin that stick to each other but because they're sticky the blood cells will also were stick to the sticky strands of fibrin forming a blood clot which of course is essential for hemostasis if there's any form of trauma causing hemorrhage so if liver function is compromised production of these plasma clotting proteins is going to be reduced and this rapidly leads to hemorrhagic problems as patients are no longer able to form blood clots so patients with liver failure can have contusions and bruises and hemorrhage problems because they lack these clotting proteins and another protein that we've mentioned in previous videos is is angiotensinogen to remember the angiotensinogen part of the angiotensin renin how the steer own system and then for the regulation of blood pressure then you might remember that the young Geo tense Inogen unless acted on by renin is converted into angiotensin so we see that these amazing hepatocytes are converting one form of amino acid into another in this process of transamination they're breaking amino acids down to form energy and this protest of DME ination and they're producing a wide range of proteins which essential systemic physiological functions

Channel: Dr. John Campbell

Views: 11,404

Rating: 4.9702601 out of 5

Keywords: liver, proteins, protein metabolism

Id: CwgdIJTcIP8

Length: 8min 55sec (535 seconds)

Published: Wed Jun 12 2019