The Liver and Glucose Homeostasis Flashcards
Energy for the synthesis of ATP can be derived from oxidation of 3 main body fuels, what are they?
1 - glucose (stored as glycogen)
2 - long chain fatty acids (stored as triacylglycerol)
3 - amino acids (mainly present in proteins)
As the body requires a continous supply of energy meal times are insufficient to maintain this. Therefore, what is the body able to do to accomadate the need for continous energy?
- store energy in the body for when its needed
- be able to release energy in a controlled manner
In the phases of assimilation following a meal we haver the immediate absorptive stage. The liver and adipose tissue import the nutrients from these meals and do what?
- glucose is used as the major energy source for all tissues
- fat, amino acids and excessive carbohydrate are stored as fat (adipose tissue) and glycogen (liver)
In the phases of assimilation in the post-absorptive events, between meals, what does the liver do?
- the cells of the liver and adipose tissues = export nutrients
- this is called mobilisation, where glycogen stores are used to maintain availability of nutrients in the blood
One of the functions of the liver is to taken carbohydrates and other substrates and store them in the liver as what?
- glycogen
One of the functions of the liver is to taken carbohydrates and other substrates and store them in the liver as glycogen. It is then able to do what with this glycogen when blood glucose levels are low?
- glycogenolysis mobilise glycogen and release into plasma as glucose
One of the functions of the liver is to take non-carbohydrate substrates and turn them into glucose for wha purpose?
- when blood glucose levels are low
One of the functions of the liver is to deaminate surplus amino acids and convert them into what so they can be transported out of the body as what?
- urea
One of the functions of the liver is to synthesise fatty acids from glucose and secrete them as what?
- triglycerides in VLDLs
One of the functions of the liver is to metabolise drugs and is also involved in what?
- elimination of drugs and toxic substances
One of the functions of the liver is to act as a storage site for fay soluble what?
- vitamins
One of the functions of the liver is to synthesise cholesterol and also do what with cholesterol?
- remove cholesterol from the body through bile
One of the functions of the liver is to synthesise ketone bodies for what?
- secrete ketones into the blood for energy by other tissues
The liver can create 3 different types of ketones that can be synthesised by the liver and secreted into plasma as energy. What are these 3 ketone bodies?
1 - acetoacetate
2 - b-hydroxybutyrate
3 - acetone
The liver can create 3 different types of ketones that can be synthesised by the liver and secreted into plasma as energy. The 3 ketone bodies are acetoacetate, b-hydroxybutyrate and acetone. Although the liver can synthesis the ketones, can it use them as an energy source?
- no
The liver is able to initiate gluconeogenesis, what is this?
-sugars are produced for catabolic reactions from non-carbohydrate precursors (fats and proteins)
What are the 2 places in the body that take up most of the glucose from the blood?
1 - brain
2 - RBCs
What organ in the body is most susceptible to hypoglycaemia?
- brain
What are neurological cells unable to do in terms of glucose?
- store glucose in significant amounts or synthesise glucose
- metabolise substrates other than glucose or ketone bodies
- extract sufficient glucose from the extracellular fluids at low concentrations because glucose entry into the brain is not facilitated by hormones
What is glycogenolysis that occurs in the liver?
- mobilisation of liver glycogen stores into glucose
What hormones in the body can control and can increase the rate of gluconeogenesis (glucose from non-carbohydrate substrates) and glycogenolysis (glucose from liver glycogen stores)?
- glucagon released by alpha cells in pancreas
- catecholamines (noradrenalin and adrenaline)
- cortisol
- growth hormone
What is glycolysis?
- oxidation of glucose into ATP for energy
If there is a lot of glucose and/or fat, what does the body do with this?
- converted into glycogen and fat for storage
Glycolysis and the storage of glucose and fat come under the control of what hormone?
- insulin
- both are increased in the prescence of insulin
Insulin and glucagon try to maintain a normal blood glucose level. What is the normal blood glucuose levels?
- between 6.0 – 7.8 mmol/L
In the pancreas we have the islets of langerhans. They are able to secrete 3 hormones through the alpha, beta and delta cells, what does each cell secrete?
- alpha = glucagon
- beta = insulin
- delta = somatostatin
Insulin is secreted by beta cells found in the islets of langerhans of the pancreas. Insulin secretion requires ATP, therefore what has to enter the beta cell for this to occur and how does it enter the beta cell?
- glucose
- enters using GLUT-2 glucose transporter
Once glucose enters the beta cell in the build up to insulin secretion, what has to happen to the glucose to create ATP?
oxidative phosphorylation which includes
- glycolysis (can be anaerobic only making pyruvate)
- citric acid cycle
- electron transport chain
Once glucose enters the beta cell in the build up to insulin secretion when blood glucose levels are high, the glucose undergos oxidative phosphorylation which includes glycolysis, citric acid cycle and the electron transport chain and creates 30-32 ATP. What does this ATP do to the K+ channel and the cell?
- K+ channels increasing the charge in the cell causing depolarisation
- Ca2+ channels open
- insulin is secreted
Once glucose enters the beta cell in the build up to insulin secretion when blood glucose levels are high, the glucose undergos oxidative phosphorylation which includes glycolysis, citric acid cycle and the electron transport chain and creates 30-32 ATP. The high ATP causes K+ channels to close and depolarisation of the cell. What does this then trigger to open?
- voltage gated Ca2+ channels open
- insulin is secreted
Once glucose enters the beta cell in the build up to insulin secretion when blood glucose levels are high, the glucose undergos oxidative phosphorylation which includes glycolysis, citric acid cycle and the electron transport chain and creates 30-32 ATP. The high ATP causes K+ channels to close and depolarisation of the cell causing Ca2+ channels to open. What does this then cause the beta cell to do?
- secrete insulin
- insulin leaves beta cells via exocytosis
What is the main source of glucose during food deprivation or fasting?
- gluconeogenesis
What type of membrane receptor are insulin receptors?
- tyrosine kinase receptor
Once insulin has bound with the alpha unit of the insulin receptors, what happens to the beta subunits?
- 2 seperate tyrosine kinase receptors come together, this is called dimerisation
- beta subunits undergo phosphorylation and become active
Once insulin has bound with the alpha unit of the insulin receptors, 2 seperate tyrosine kinase receptors come together, which is called dimerisation. The beta subunits undergo phosphorylation and become active. A signal is sent to the insulin receptor substrate triggering a cascade. What are the 2 first things this does?
1 - inhibits lipolysis (fat breakdown)
2 - promotes the transfer of intracellular vesicles containing GLUT-4 to the cell surface
- both of these increase glucose uptake
The pentose phosphate pathway is an important metabolic pathway parallel to glycolysis that generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-phosphate. which is an important precursors for the synthesis of nucleotides (DNA/RNA). What is the very first step of the pentose phosphate pathway?
- Glucose 6-Phosphate formed in early glycolysis
- formed from glucose by hexokinase using ATP
The pentose phosphate pathway is an important metabolic pathway parallel to glycolysis that generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-phosphate. which is an important precursors for the synthesis of nucleotides (DNA/RNA). Glucose 6-Phosphate formed in early glycolysis is shunted off into this pathway and is then used to form what 2 products?
- ribose phosphate used to synthesize RNA and DNA
- NADPH used for biosynthesis and to maintain redox balance of the cell (shuttle of electrons in metabolism)
Away from the liver and adipose tissue, are cells in the body involved heavily in the pentose phosphate pathway (PPP)?
- no
- instead PPP intermediates (glyceraldehyde-3-phosphate and fructose-6-phosphate) are recyled back into glycolysis
Once glucose has been absorbed by the GLUT-4 in cardiac and skeletal muscle, what are the 2 main things that could happen initially?
1 - glycogenesis stores glucose as glycogen
2 - glucose is phosphorylated into glucose-6-phosphate (G-6-P) and glycolysis begins
Once glucose has been absorbed by the GLUT-4 in cardiac and skeletal muscle, it can either be stored as glycogen or glucose can be phosphorylated into glucose-6-phosphate (G-6-P) and glycolysis begins. If the glucose enters glycolysis, what is the end product of glycolysis?
- pyruvate
- can be turned into lactate (anaerobically)
- can be turned into acetyl-CoA and enter Krebs cycle (aerobically)
Once glucose has been absorbed by the GLUT-4 in cardiac and skeletal muscle, it can either be stored as glycogen or glucose can be phosphorylated into glucose-6-phosphate (G-6-P) and glycolysis begins. If the cells are working aerobically, pyruvate is created as the end product of glycolysis. What then happens to the pyruvate?
- coenzyme A convertes pyruvate from a 3 carbon molecule into a 2 carbon molecule reducing NAD+ to NADH
- 2 carbon molecule is called acetyl CoA
- acetyl CoA can then enter the citric acid cycle
Once glucose has been absorbed by the GLUT-2 in the liver, there are a number of different things that it can be used for. What are generally they first 2 things that can happen to the glucose?
- can be stored as glycogen through glycogenesis
- can be phosphorylated into glucose-6-phosphate (G-6-P) and enter the penthose phosphate pathway (creates nucleotides and NADPH) or glycolysis
Once glucose has been absorbed by the GLUT-2 in the liver, there are a number of different things that it can be used for. it can either be stored as glycogen or glucose can be phosphorylated into glucose-6-phosphate (G-6-P) and enter the penthose phosphate pathway. It can also continue through glycolysis forming 2 different things if aerobic or anaerobic, what are they?
- aerobic or anaerobic = pyruvate
- anaerobic = lactate
Once glucose has been absorbed by the GLUT-2 in the liver, there are a number of different things that it can be used for. it can either be stored as glycogen or glucose can be phosphorylated into glucose-6-phosphate (G-6-P) and enter the penthose phosphate pathway. It can also continue through glycolysis forming pyruvate (aerobic) or lactate (anaerobic). If the cells are working aerobically, pyruvate is created as the end product of glycolysis. This can be converted to acetly-CoA, what 2 things can then occur to the acetly-CoA in the liver?
- enter the citric acid cycle (only if aerobic)
- lipogenesis = acetyl-CoA can be made into triglycerides
Once glucose has been absorbed by the GLUT-1 and 3 in the brain, there are 2 major things it can be used for, what are these?
1 - enter glycolysis and citric acid cycle and used as energy
2 - glucose-6-phosphate (G-6-P) from glycolysis can enter the penthose penthose phosphate pathway (NADPH can be used to synthesis fat)
Once glucose has been absorbed by the GLUT-4 in adipoe tissue, what are the 3 main things that it can be used for?
1 - energy (enters glycolysis and citric acid cycle)
2 - pentose phosphate pathway (nucleotides and NADPH)
3 - fat storage (enters glycolysis, citric acid cycle, but shunted to fat storage)
What is the fate of glucose in the main body tissue, such as RBCs once it has entered the cells through the GLUT-1 pathway?
- energy (glycolyis but anaerobically creating lactate as they have no mitochondria so cannot use oxidative phosphorylation)
- enters the pentose phosphate pathway
