 Hi welcome to Physiology Open. Try to solve this question on functions of insulin. In this question you have to state which statement is true and which statement is false. You can pause the video and think about the answers. We will come back to the question at the end of the video again. Okay now let's discuss the concepts on functions of insulin or effects of insulin on metabolism. The main function of insulin is to store the excess fuel during times of their availability for future use. Thus insulin is released in the fed state when the availability of the fuel especially carbohydrates is high. As these substrates are absorbed from gastrointestinal tract their concentration in blood rises. However with the release of the insulin they are quickly moved from the blood into their storage depots. So how does insulin promote the storage of nutrients? By affecting the entry of nutrients into cells and their metabolic cycles. Well before we go into the concepts we will just see in brief which metabolic cycles will decrease the nutrient concentration in blood and which will increase the concentration in blood. Factors which cause increase in blood glucose concentration are intake of food and then digestion and absorption of nutrients into the blood stream. Then glycogenolysis meaning breakdown of stored glycogen into glucose and then gluconeogenesis which causes synthesis of new glucose mainly from amino acids. Now factors which cause decrease in blood glucose concentration are storage of glucose as glycogen that is glycogenesis which occurs mainly in liver and skeletal muscles. Also storage of excess glucose as fatty acids this also occurs in liver and finally utilization of glucose by peripheral tissues. Similarly for fats and proteins concentration is increased by lipolysis and proteolysis respectively and decreased by promoting their entry into cells and further fatty acid synthesis and protein synthesis respectively. So logically you can tell from this that to lower nutrient concentration in blood insulin should promote glycogenesis synthesis of fats from glucose and utilization of glucose by peripheral tissues while it should decrease glycogenolysis and gluconeogenesis. Similarly it should promote fatty acid synthesis and storage and inhibit lipolysis and it should also increase protein synthesis and inhibit proteolysis. So what it is specifically does to have these effects? Well this all happens mainly in three tissues that is the liver skeletal muscles and adipose tissue. In liver it increases the activity of enzyme glucokinase which converts glucose to glucose 6 phosphate. Thus it keeps the concentration of glucose low in the liver so that glucose can enter the hepatocytes. Then it promotes glycogenesis by increasing the activity of the enzyme glycogen synthase while it inhibits glycogenolysis by inhibiting glycogen phosphorylase. Also excess glucose which has not been converted into glycogen enters into glycolysis pathway and produces acetyl coenzyme A in liver. Now this acetyl coenzyme A is used for synthesis of fatty acids. Since insulin promotes the activity of the enzyme acetyl coate carboxylase which is very important enzyme in lipogenesis and hence insulin promotes fatty acid synthesis. Also in the process of synthesis of fatty acids malonyl coase formed which inhibits carnitine palmatoil transferase enzyme that is CPT enzyme present on the membrane of mitochondria which causes entry of fatty acids into the mitochondria. So when this enzyme is inhibited beta oxidation of fatty acid doesn't occur. So what is happening only synthesis of fats is occurring from extra glucose. Well now the formed fatty acid should now go and get stored in their depose that is adipose tissue. So they are transported from liver to adipose tissue as triacetyl glycerol in VLDL via blood. Insulin increases the expression of lipoprotein lipase in the walls of capillaries of adipose tissue. This lipoprotein lipase releases fatty acids from triacetyl glycerol in a VLDL which then enter into the adipose tissue and is stored. So these were the actions of insulin in liver and some on adipose tissue. Now insulin also promotes the entry of glucose in most cells except neurons and RBCs. It does this by causing fusion of glute pore transporters which are present inside the cell to the membrane. This increases their number on the membrane. Since glucose is in higher concentration in blood it enters in those cells along its concentration gradient via these glute pore transporters by a facilitated diffusion. So most cells start using glucose as a fuel in presence of insulin and hence usage of fats as fuel is spared. We have already seen that beta oxidation is not occurring in liver right. Now note here that insulin increases the entry of glucose into apatocytes also but not by increasing these glute pore transporters instead by increasing the activity of glucokinase enzyme right. Anyways now in skeletal muscles excess glucose is also stored as glycogen while in adipose tissue the glucose which enters acts as a substrate for glycerol portion of triacetyl glycerol. We have already seen that fatty acids from VLDL enter the adipose cells. So the glycerol from glucose and fatty acids combined upon triacetyl glycerol in adipose tissue. This is how excess glucose is stored as triacetyl glycerol in adipose tissue. Also insulin inhibits hormone sensitive lipase in fat cells. This lipase breaks down stored triacetyl glycerol into fatty acids and glycerol. Thus by inhibiting hormone sensitive lipase insulin prevents hydrolysis of triglyceride in adipose tissue. So we have seen two lipases here lipoprotein lipase causing entry of fatty acids into the adipose tissue this is promoted by insulin and the one causing glycerol triacetyl glycerol from adipose tissue that is hormone sensitive lipase it is inhibited by insulin. Okay now what about this action on protein metabolism insulin also promotes amino acid uptake by cells and promotes protein synthesis simultaneously inhibiting their breakdown. Well now let's come back to our original question. In this question first and second statements are correct. We have seen that glucose is not only converted to glycogen but also to fatty acids in liver and then fatty acids are transported as triacetyl glycerol in VLDL to adipose tissue where lipoprotein lipase facilitates the entry of fatty acids into the tissue. Well the third statement is wrong since insulin spares the use of fatty acid instead it promotes its synthesis. Fourth statement is also wrong since we have seen that in liver insulin increases the activity of the enzyme glucokinase due to which glucose entry into hepatocytes is increased. Well thanks for watching the video if you liked it do not forget to subscribe to the channel Physiology Open. Thank you.