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NME Emma copy and edit > The Liver and Glucose Homeostasis > Flashcards

The Liver and Glucose Homeostasis Flashcards

1
Q

Energy for the synthesis of ATP can be derived from oxidation of 3 main body fuels, what are they?

A

1 - glucose (stored as glycogen)

2 - long chain fatty acids (stored as triacylglycerol)

3 - amino acids (mainly present in proteins)

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2
Q

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?

A
  • store energy in the body for when its needed
  • be able to release energy in a controlled manner
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3
Q

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?

A
  • 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)
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4
Q

In the phases of assimilation in the post-absorptive events, between meals, what does the liver do?

A
  • 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
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5
Q

One of the functions of the liver is to taken carbohydrates and other substrates and store them in the liver as what?

A
  • glycogen
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6
Q

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?

A
  • glycogenolysis mobilise glycogen and release into plasma as glucose
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7
Q

One of the functions of the liver is to take non-carbohydrate substrates and turn them into glucose for wha purpose?

A
  • when blood glucose levels are low
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8
Q

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?

A
  • urea
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9
Q

One of the functions of the liver is to synthesise fatty acids from glucose and secrete them as what?

A
  • triglycerides in VLDLs
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10
Q

One of the functions of the liver is to metabolise drugs and is also involved in what?

A
  • elimination of drugs and toxic substances
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11
Q

One of the functions of the liver is to act as a storage site for fay soluble what?

A
  • vitamins
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12
Q

One of the functions of the liver is to synthesise cholesterol and also do what with cholesterol?

A
  • remove cholesterol from the body through bile
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13
Q

One of the functions of the liver is to synthesise ketone bodies for what?

A
  • secrete ketones into the blood for energy by other tissues
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14
Q

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?

A

1 - acetoacetate

2 - b-hydroxybutyrate

3 - acetone

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15
Q

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?

A
  • no
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16
Q

The liver is able to initiate gluconeogenesis, what is this?

A

-sugars are produced for catabolic reactions from non-carbohydrate precursors (fats and proteins)

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17
Q

What are the 2 places in the body that take up most of the glucose from the blood?

A

1 - brain

2 - RBCs

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18
Q

What organ in the body is most susceptible to hypoglycaemia?

A
  • brain
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19
Q

What are neurological cells unable to do in terms of glucose?

A
  • 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
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20
Q

What is glycogenolysis that occurs in the liver?

A
  • mobilisation of liver glycogen stores into glucose
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21
Q

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)?

A
  • glucagon released by alpha cells in pancreas
  • catecholamines (noradrenalin and adrenaline)
  • cortisol
  • growth hormone
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22
Q

What is glycolysis?

A
  • oxidation of glucose into ATP for energy
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23
Q

If there is a lot of glucose and/or fat, what does the body do with this?

A
  • converted into glycogen and fat for storage
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24
Q

Glycolysis and the storage of glucose and fat come under the control of what hormone?

A
  • insulin
  • both are increased in the prescence of insulin
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25
Q

Insulin and glucagon try to maintain a normal blood glucose level. What is the normal blood glucuose levels?

A
  • between 6.0 – 7.8 mmol/L
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26
Q

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?

A
  • alpha = glucagon
  • beta = insulin
  • delta = somatostatin
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27
Q

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?

A
  • glucose
  • enters using GLUT-2 glucose transporter
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28
Q

Once glucose enters the beta cell in the build up to insulin secretion, what has to happen to the glucose to create ATP?

A

oxidative phosphorylation which includes

  • glycolysis (can be anaerobic only making pyruvate)
  • citric acid cycle
  • electron transport chain
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29
Q

Once glucose enters the beta cell in the build up to insulin secretion, it undergos oxidative phosphorylation which includes glycolysis, citric acid cycle and the electron transport chain. How many ATP can be created from one glucose molecule?

A
  • 30-32 ATP
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30
Q

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?

A
  • K+ channels increasing the charge in the cell causing depolarisation
  • Ca2+ channels open
  • insulin is secreted
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31
Q

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?

A
  • voltage gated Ca2+ channels open
  • insulin is secreted
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32
Q

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?

A
  • secrete insulin
  • insulin leaves beta cells via exocytosis
33
Q

What are the 3 sources of glucose during the day?

A

1 - diet

2 - glycogenolysis (glycogen is catabolised)

3 - gluconeogenesis (glucose is built from non-carbohydrate substrates)

34
Q

What is the main source of glucose during food deprivation or fasting?

A
  • gluconeogenesis
35
Q

When we are sleeping we deplete what source of glucose supply?

A
  • glycogenolysis
  • refilled by breakfast or first meal
36
Q

What is the major and most important metabolic effect of insulin?

A
  • allow glucose entry into cells
37
Q

What sort of lipid bilayer transporter facilitates glucoseentry into the cells?

A
  • GLUT transporters
  • via facilitated diffusion (i.e. a carrier-mediated process) with glucose entering the cells down its concentration gradient when glucose levels in the blood are high
38
Q

Glucose transporter proteins or GLUTs are structurally related but are encoded by different genes that are expressed in a tissue specific manner. This means that each tissue type will have a specific type of GLUT. How many different GLUT are there?

A

1 - Glut 1 = erythrocytes, muscle, brain, kidney, colon, placenta, foetal tissue

2 - Glut 2 = liver and pancreatic b cells

3 - Glut 3 = the brain

4 - Glut 4 = skeletal muscle and adipose tissue (Insulin-sensitive)

5 - Glut 5 = small intestine (fructose not glucose transporter)

39
Q

Glucose transporter proteins or GLUTs are structurally related but are encoded by different genes that are expressed in a tissue specific manner. This means that each tissue type will have a specific type of GLUT. There are 5 different types of GLUT, but which one is Insulin-sensitive?

A
  • GLUT 4
40
Q

GLUT- 1 is often referred to as the universal glucose transporter as they are present throughout the body in a lot of tissue. In order to ensure glucose makes its way into the tissues with GLUT-1, what does GLUT-1 have?

A
  • a high affinity for glucose
  • will be absorbed when blood glucose is at 1mM or above
  • this maintain normal blood glucose
41
Q

GLUT- 2 is present in the liver and beta cells in the pancreas. Does GLUT-2 have a high or low affinity for glucose?

A
  • low affinity
  • glucose is conserved for other tissues
  • only when glucose is between 15-20mM will it be absorbed, occurs after meal, especially high sugar content
42
Q

GLUT- 3 is primarily present in neuronal cells. Does GLUT-3 have a high or low affinity for glucose?

A
  • a high affinity for glucose
  • will be absorbed when blood glucose is at 1mM or above
  • this maintain normal blood glucose
43
Q

GLUT- 4 are insulin sensitive receptors and are primarily present in skeletal muscle, the heart and adipose tissue. Does GLUT-4 have a high or low affinity for glucose?

A
  • moderate affinity for glucose
  • controlled by blood glucose levels
  • if blood glucose is high insulin increase the number of GLUT-4
44
Q

What type of membrane receptor are insulin receptors?

A
  • tyrosine kinase receptor
45
Q

Once insulin has bound with the alpha unit of the insulin receptors, what happens to the beta subunits?

A
  • 2 seperate tyrosine kinase receptors come together, this is called dimerisation
  • beta subunits undergo phosphorylation and become active
46
Q

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. What does this then do intracelluarly?

A
  • sends a signal to the insulin receptor substrate
  • this triggers a cascade
47
Q

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?

A

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
48
Q

In addition to insulin signalling that is able to increase the number of GLUT-4 molecules on skeletal muscle and adipose tissue, what other day to day activity can increase the number of GLUT-4 receptors?

A
  • exercise
49
Q

The short term, immediate effects of insulin is increased uptake of glucose by cells. When glucose levels are high there are 4 main longer lasting effects of insulin that can occur over several hours that involve the expression of genes, what are these?

A

1 - increased expression of liver enzymes that synthesize glycogen

2 - increased expression of adipocyte enzymes that synthesize triacylglycerols

3 - inhibition of lipolysis in adipose tissue by inactivating hormone-sensitive lipase

4 - functions as a growth factor for some cells e.g. fibroblasts

50
Q

What is the pentose phosphate pathway?

A
  • metabolic pathway parallel to glycolysis
  • it generates NADPH and pentoses (5-carbon sugars) as well as ribose 5-phosphate
  • important precursors for the synthesis of nucleotides (DNA/RNA)
51
Q

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?

A
  • Glucose 6-Phosphate formed in early glycolysis
  • formed from glucose by hexokinase using ATP
52
Q

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?

A
  • 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)
53
Q

Which tissues are rich in the enzymes involved in the penthose phosphate pathway biosynthesis?

A
  • liver and adipose tissue
54
Q

Away from the liver and adipose tissue, are cells in the body involved heavily in the pentose phosphate pathway (PPP)?

A
  • no
  • instead PPP intermediates (glyceraldehyde-3-phosphate and fructose-6-phosphate) are recyled back into glycolysis
55
Q

Once glucose has been absorbed by the GLUT-4 in cardiac and skeletal muscle, what are the 2 main things that could happen initially?

A

1 - glycogenesis stores glucose as glycogen

2 - glucose is phosphorylated into glucose-6-phosphate (G-6-P) and glycolysis begins

56
Q

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?

A
  • pyruvate
  • can be turned into lactate (anaerobically)
  • can be turned into acetyl-CoA and enter Krebs cycle (aerobically)
57
Q

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. Pyruvate is created if the cells are working aerobically, but what is created if the cells are working anaerobically?

A
  • lactate
58
Q

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?

A
  • 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
59
Q

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?

A
  • 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
60
Q

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?

A
  • aerobic or anaerobic = pyruvate
  • anaerobic = lactate
61
Q

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?

A
  • enter the citric acid cycle (only if aerobic)
  • lipogenesis = acetyl-CoA can be made into triglycerides
62
Q

Nicotinamide adenine dinucleotide phosphate (NADPH) is created in the penthose phosphate pathway. Is NADPH used in the anabolic or catabolic energy metabolism?

A
  • Anabolic pathways that need energy Adding to it
  • it is used to make things
63
Q

Is nicotinamide adenine dinucleotide (NADH) used in the anabolic or catabolic energy metabolism?

A
  • Catabolic pathways that Create energy
64
Q

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?

A

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)

65
Q

Once glucose has been absorbed by the GLUT-4 in adipoe tissue, what are the 3 main things that it can be used for?

A

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)

66
Q

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?

A
  • energy (glycolyis but anaerobically creating lactate as they have no mitochondria so cannot use oxidative phosphorylation)
  • enters the pentose phosphate pathway
67
Q

Using the mnemonic Big Fat Boys, how can this help me remember where GLUT-1 receptors are located?

A
  • Blood = RBCs
  • Fetus
  • Blood Brain Barrier
68
Q

Using the mnemonic Kill Small Little Pansies, how can this help me remember where GLUT-2 receptors are located?

A
  • Kill = Kidney
  • Small = Small Intestines
  • Little = Liver
  • Pansies = Pancreas
69
Q

Using the mnemonic Producing Nervous Kids, how can this help me remember where GLUT-3 receptors are located?

A
  • Producing = Placenta
  • Nervous = Neuronal cells
  • Kids = Kidneys
70
Q

Using the mnemonic Mad Fathers, how can this help me remember where GLUT-3 receptors are located?

A
  • Mad = Muscle
  • Fathers = Fat
71
Q

Which transporter takes up glucose only in the brain

A

Glut 3 (“special”

72
Q

Which glucose transporter is present across multiple body tissues?

A

Glut1

Glut 1Many tissues e.g. erythrocytes, muscle, brain, kidney, colon, placenta, foetal tissue.

73
Q

What is the most insulin dependant glucose transporter

A

Glut 4 for skeletal muscle, adipose tissue

(Insulin-sensitive)

74
Q

Which glucose transporter is unique for liver and pancreatic B cells

A

Glut 2 → liver, pancreatic b cells

75
Q

Which glut transporter does not transport Glucose?

A

Glut 5 → Small intestine, fructose not glucose transporter

76
Q

Insulin can induce both immediate and long-term cellular responses

What are the Immediate effects:

A

• ­ in the rate of glucose uptake in muscle and adipocytes•• modulation of the activity of enzymes involved in glucose metabolism•

These effects:

• occur within minutes• do NOT require protein synthesis• occur at insulin concentrations of 10-9 to 10-10 mols/L

77
Q

Continued exposure to insulin produces longer-lasting effects:

what are they?

A
  • increase­ expression of liver enzymes that synthesize glycogen
  • increase ­ expression of adipocyte enzymes that synthesize triacylglycerols
  • Inhibits lipolysis in adipose tissue by inactivating hormone-sensitive lipase which mobilizes fatty acids from TG stores• functions as a growth factor for some cells e.g. fibroblasts

These effects:

• occur over several hours• require continuous exposure to insulin at around 10-8 mol/L

78
Q

How does insulin inhibit lipolysis

A

Insulin inhibits lipolysis in adipose tissue by inactivating hormone-sensitive lipase which mobilizes fatty acids from TG stores

79
Q

which cells secrete insulin and glucagon?

A

•Pancreas secretes these hormones in response to blood glucose levels: b-cells secrete insulin, a-cells secret glucagon

NME Emma copy and edit (61 decks)

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