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Medicine Year 1 - Semester 2 - Part 1 > Metabolic Stores > Flashcards

Metabolic Stores Flashcards

1
Q

What is metabolism ?

A

Mechanisms which couple the demand for energy (which is constant), with the fuel supply (which is intermittent)

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2
Q

Describe absorptive/fed state

A

Nutrients are plentiful - fuels broken down and excess stored (anabolism)

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3
Q

What is the aim of the absorptive/fed state ?

A

To store nutrients in mobilizable form, for times of need.

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4
Q

Function of insulin

A

Promotes :

  • Glucose uptake
  • Fatty acid synthesis
  • Protein synthesis
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5
Q

Describe post-absorptive / fasting state

A

Storage molecules broken down for energy (catabolism) - biosynthesis slows down

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6
Q

What is the aim of the post absorptive / fed state ?

A

To provide metabolites for cellular respiration and ATP synthesis.

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7
Q

What is the primary aim / goal of the post absorptive state ?

Blood glucose levels

A

TO maintain blood glucose levels within homeostatic range of 70-110 mg/dl or 4-7 mmol/L

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8
Q

Describe interconversion of fuels

A

Metabolic storage molecules are interconvertible as their pathways are linked by key intermediates.

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9
Q

What effector organs control the release/interconversion of fuels ?

A

Liver
Adipose
Muscle

Mobilisation of glucose, triglycerides and amino acids

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10
Q

Where does blood glucose come from in the post absorptive state ?

A

Glycogenolysis
Gluconeogenesis

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11
Q

Where does glucogenesis occur ?

A

Occurs mainly in the liver

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12
Q

Describe glycogenolysis

Liver and Muscle

A

Liver glycogen (around 100g) –> enough for about 3-5 hours activity.

Mucle glycogen is only utilised within muscle

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13
Q

What is glycogenolysis ?

A

Breaks down glycogen to release glucose
Stimulated by low blood glucose

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14
Q

What is gluconeogenesis ?

A

Formation of glucose from non-carbohydrate molecules.

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15
Q

Describe gluconeogenesis

A

Lipolysis of fatty acids to generate glycerol, which generates glucose.

Catabolism of muscle protein - deamination of amino acids –> glucose

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16
Q

What does it mean when blood glucose levels are :

<53 mg/dL and <3 mmol/L

A

Severe Hypoglycaemia
Metabolic Consequences

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17
Q

What does it mean when blood glucose levels are :

<70 mg/dL and <3.9 mmol/L

A

Hypoglycaemia

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18
Q

What does it mean when blood glucose levels are :

<125 mg/dL and <7 mmol/L

A

Normal

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19
Q

What does it mean when blood glucose levels are :

<200 mg/dL and <10 mmol/L

A

High

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20
Q

What does it mean when blood glucose levels are :

> 200mg/dL and >10 mmol/L

A

High-Metabolic Consequences

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21
Q

What is glycogen ?

A

A branched polysaccharide storage molecule for glucose.

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22
Q

Where are the main glycogen storage reservoirs ?

A

Liver and Skeletal muscle atrophy the main glycogen reservoirs.

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23
Q

Function of the liver

A

Maintains blood glucose levels

Enough glycogen for 3-5 hours of moderate exercise or 12 hours overnight fast

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24
Q

Function of muscle (in relation to glycogen)

A

Stores glycogen for muscle contraction - channeled into glycolysis

(not released in the bloodstream)

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25
Q

What promotes glycogenesis ?

A

Insulin

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26
Q

What promotes glycogenolysis ?

A

Promoted by glucagon, adrenalin, cortisol and growth hormone.

IN muscle, there are no glucagon receptors and so responds mainly to adrenalin.

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27
Q

What enzymes are involved in glycogenesis ?

A

Glucose residues formed by alpha1,4-glycoside linkages

Branching occurs via alpha1,6-glycosidic linkages

28
Q

What enzymes are involved in glycogenolysis ?

A

Glycogen phosphorylase - alpha1,4 linkages

De-branching enzyme : alpha1,6, linkages

29
Q

Describe glycogenolysis in the liver

A

Glycogen –> G-1-P –> G-6-P –> Glucose

Released into the bloodstream (Glut2), for uptake by all cells, but especially brain and RBCs.

30
Q

Describe glycogenolysis in muscle

A

No G-6-Pase enzyme, G-6-P enters glycolysis

31
Q

State other sources of energy other than glycogen

A

Lipids are the major form in which energy is stored.

Triglycerides can produced 6 times as much energy as glycogen.

32
Q

Describe glucogenesis

A

Formation of glucose from non-carbohydrate sources :

Glycerol from triglycerides

Glucogenic amino acids (alanine & glutamine)

Lactate

33
Q

What is the importance of glucogenesis ?

A

Crucial for survival : i.e. tissues whose primary source of energy is glucose

  • Brain
  • RBCs
  • Renal Medulla
  • Lens
34
Q

Where does glucogenesis mainly take place ?

A

The liver (and kidneys in prolonged fasting)

35
Q

What is lipogenesis ?

A

Formation of fat

36
Q

How is most fat stored ?

A

Stored as triglycerides = triacylglycerols

37
Q

How are triglycerides formed ?

A

Glycerol molecule undergoes condensation with 3 fatty acids.

38
Q

Describe lipids (fatty acids)

A

Hydrocarbon chain, usually 14-24 carbon atoms - most common FAs 16-18 carbons

39
Q

What are triglycerides ?

A

Esters formed by the reaction of an alcohol and organic acid

40
Q

Describe lipolysis

A

Fat breakdown into glycerol and fatty acids

REVERSE of Lipogenesis

41
Q

Where does lipolysis occur ?

A

Fatty acids and glycerol are released from adipose tissue and metabolised mainly by the liver.

42
Q

What happens to the glycerol produced from lipolysis ?

A

Glycerol feed into gluconeogenesis but can also be utilised by most cells -

converted into glyceraldehyde-3-phosphate -> glycolysis

(1/2 glucose = 15ATP aerobically)

43
Q

What happens to the fatty acids produced from lipolysis ?

A

Undergo beta oxidation

44
Q

Describe beta oxidation

A

Fatty acids are broken down into 2-carbon acetic acid and fused to coenzyme A –> acetyl-CoA

FAD and NAD+ are reduced and feed into the electron transport chain

Acetyl CoA –> Citric Acid Cycle

45
Q

Describe the production of ketone bodies

A

When carbohydrate intake is inadequate and beta-oxidation product : acetyl-CoA is in XS (for citric acid cycle metabolism), ketone bodies are formed.

46
Q

What is the limiting factor in gluconeogenesis ?

A

Oxaloacetate îs the limiting factor when glucose low, as converted to pyruvate in gluconeogenesis.

47
Q

Where are ketone bodies formed ?

A

Acetyl-CoA converted to ketone bodies in the liver :

  • Acetoacetate
  • 3-hydroxybutyrate
  • Acetone
48
Q

Describe the role of ketone bodies in diabetes

A

In diabetes acetoacetate is produced faster than metabolised.

Ketone bodes accumulate in blood (potential acidosis) and fruity smell of acetone on breath.

49
Q

Describe protein metabolism

A

Excess protein cannot be stored

Amino acids are oxidised for energy OR converted to fat.

50
Q

What is transamination ?

A

Process by which come amino acids can be converted to keto acids

51
Q

What is deamination ?

A

Removal of an amine group (NH2) prior to oxidation or storage.

52
Q

Give an example of transamination

A

Amine group is transferred to keto-glutamate = glutamic acid

Modified keto acids generate pyruvate or keto acid intermediates fr the citric acid cycle

OR

Converted to glucose (gluconeogeneis)

53
Q

Explain the need for deamination and transamination of amino acids in cellular metabolism

A

Excess protein cannot be stored

Amino Acids are oxidised for energy or converted to fat

54
Q

State the function of the hepatic portal system

A

HPS ensures liver has ready access to absorbed nutrients

Major metabolism centre, orchestrating interconversion of CHO, proteins&fats, plus lactate.

Maintains blood glucose levels

55
Q

State the function of the brain

A

60% of all glucose is used by the brain (around 120g per day)

No stores of glycogen or glucose

Can use ketone bodies in starvation

56
Q

State muscle (metabolic stores)

A

Resting muscle uses fatty acids as fuel, also glucose and ketone bodies

Large glycogen reserves 3/4 of body stores

57
Q

Simple definition of glycolysis

A

Converts glucose to pyruvic acid

58
Q

Simple definition of glycogenesis

A

Polymerises glucose to form glycogen

59
Q

Simple definition of glycogenolysis

A

Hydrolyses glycogen to glucose monomers

60
Q

Simple definition of gluconeogenesis

A

Forms glucose from noncarbohydrate precursors

61
Q

What is formed during aerobic respiration when electrons are passed down the electron transport chain ?

A

Water

62
Q

What is the net gain of ATP from the full oxidation of 2 molecules of glucose ?

A

60

63
Q

Which mechanism generates the energy for creating the electrochemical gradient between the mitochondria matrix and inner membrane ?

A

Oxidation and reduction of cytochrome complexes

64
Q

What is the process of generating glucose from glycogen called ?

A

Glycogenolysis

65
Q

Which effector organ is primarily involved in gluconeogenesis ?

A

Liver

66
Q

Which intermediate is a rate limiting factor of the citric acid cycle ?

A

Oxaloacetate (keto acid)

67
Q

Metabolism

A

The sum of anabolic and catabolic reactions within the cells

Medicine Year 1 - Semester 2 - Part 1 (51 decks)

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