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Liver > Functions > Flashcards

Functions Flashcards

1
Q

What are the main types of plasma proteins?

A

Albumin
Globulin
Fibrinogen

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2
Q

Which is the most common plasma protein?

A

Albumin

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3
Q

What are the functions of albumin?

A
  1. Maintenance of colloid osmotic pressure
  2. Binding and transport of large, hydrophobic compounds
  3. Antioxidant
  4. Anticoagulant and anti thrombotic effects
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4
Q

Give 4 examples of large, hydrophobic compounds that albumin binds to

A

Bilirubin
Fatty acids
Hormones
Drugs

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5
Q

What are Starling forces?

A

The opposing hydrostatic and oncotic pressures that determine net filtration pressure of a fluid across the capillary wall

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6
Q

How does albumin increase movement of water into the capillary from the interstitial fluid?

A
  1. Pores of capillaries are impermeable to plasma proteins - low conc of plasma proteins in interstitial fluid
  2. Higher conc of plasma proteins (eg albumin) in plasma
  3. Lower relative water conc in plasma means net movement of water out of interstitial fluid and into plasma
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7
Q

How does liver failure lead to oedema?

A

The liver produces albumin, so liver failure means less albumin in blood (HYPOALBUMINAEMIA)
Decreased oncotic pressure in capillary, so water accumulates in interstitial fluid (OEDEMA)

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8
Q

What are the two main functions of globulins?

A
  1. Antibody functions

2. Blood transport of lipids (lipoproteins), iron (transferrin) and copper (caeruloplasmin)

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9
Q

Which clotting factors are produced by the liver?

A

All except calcium (IV) and vWF(VIII)

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10
Q

Aside from directly producing clotting factors, how does the liver contribute to clotting?

A

Produces bile salts, which are necessary for intestinal absorption of Vit K. Vitamin K is required to produce numerous clotting factors

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11
Q

The liver synthesises complement factors. What is their function?

A

Important part of the immune response to pathogens

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12
Q

What happens to cellular proteins? (Metabolically)

A

Continuous degradation and re-synthesis

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13
Q

What percentage of liberated amino acids are re-utilised to make proteins?

A

70-80%

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14
Q

When (and where) is an increase in the rate of protein metabolism seen?

A
  1. Trauma (in damaged tissue)

2. Starvation (in skeletal tissue) - gluconeogenesis

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15
Q

What are the 2 primary methods of protein metabolism?

A
  1. Lysosomal pathway

2. Ubiquitin-proteosome pathway

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16
Q

What happens when there is a surplus of amino acids?

A

Degradation

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17
Q

What does amino acid catabolism involve? What are the products?

A

Requires removal of alpha-amino group.

Produced nitrogen, carbon skeleton and ammonia

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18
Q

How are the products of amino acid catabolism used?

A
  1. Nitrogen - incorporated into other compounds or excreted
  2. Carbon skeleton - metabolised
  3. Majority released as ammonia
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19
Q

What are the 2 main processes in amino acid breakdown?

A
  1. Transamination

2. Oxidative deamination

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20
Q

What does transamination involve?

A

Transfer of alpha-amino group from amino acid to alpha-ketoglutarate

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21
Q

What is produced by transamination?

A
  1. Alpha-keto acid (eg pyruvate)

2. Glutamate (undergoes oxidative deamination/ amino group donor for synthesis of non-essential amino acids)

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22
Q

What is the catalyst for transamination?

A

Aminotransferase enzymes

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23
Q

Under what conditions would the following occur:

  1. Amino acid degradation
  2. Amino acid synthesis
A
  1. After a protein-rich meal

2. If dietary supply isn’t reaching cellular demand

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24
Q

What is the equation for transamination?

A

alpha-ketoglutarate + L-amino acid L-glutamate + alpha-keto acid

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25
Q

What is the second step in amino acid breakdown?

A

Oxidative deamination

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26
Q

What is the result of oxidative deamination?

A

Liberation of amino group as free ammonia
An alpha-keto acid (eg pyruvate) which can enter Krebs cycle
Ammonia which can enter urea cycle

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27
Q

What catalyses oxidative deamination?

A

Glutamate dehydrogenase

Co-enzymes (NAD+/NADPH)

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28
Q

Are transamination and oxidative deamination reversible processes?

A

Yes. They are both readily reversible.

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29
Q

Oxidative deamination is dependent upon relative concentrations of what?

A
  1. Glutamate
  2. Alpha-ketoglutarate
  3. Ammonia
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30
Q

How would oxidative deamination be affected by a protein-rich meal?

A

Glutamate concentration high, so ammonia produced

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31
Q

In the glucose/alanine cycle, what happens in the muscle?

A

Glucose is turned into pyruvate by glycolysis.

Pyruvate (+ glutamate) is converted by ALT to alanine (+ alpha-ketoglutarate)

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32
Q

How does the liver participate in the glucose/alanine cycle?

A

Blood alanine is taken up by the liver.
Alanine (+ alpha-ketoglutarate) is converted to pyruvate (+ glutamate) by PLP
Gluconeogenesis occurs, converting the pyruvate into glucose which can then enter the bloodstream for use by other tissues (eg muscle)

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33
Q

Which enzyme converts alanine to pyruvate?

A

PLP

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34
Q

How does muscle protein contribute to the glucose/alanine cycle?

A
  1. Muscle protein broken down into amino acids
  2. Amino acids broken down to produce ammonia
  3. Ammonia converted to glutamate.
  4. Glutamate used by ALT to produce alpha-ketoglutarate and alanine from pyruvate
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35
Q

How does glutamate contribute to the urea cycle?

A

Glutamate converted into NH4+ (ammonia) which combines with arginine to form urea

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36
Q

Where do amine groups (NH2) that contribute to the glucose/alanine cycle come from?

A
  1. Dietary amino acids

2. Alanine and glutamine from muscles

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37
Q

What are the two metabolic products from excess amino acids?

A
  1. Alpha-keto acid - used in Krebs

2. Ammonia - mainly excreted, but some used in biosynthesis of amine containing substances (eg amino acids, nucleotides)

38
Q

Give an example of an alpha-keto acid

A

Pyruvate

39
Q

Where are the enzymes responsible for the urea cycle found?

A

In mitochondria or cytosol

40
Q

What does one turn of the urea cycle consume?

A
  1. 3 ATP equivalents

2. 4 high energy nucleotides

41
Q

What happens if some of the enzymes in the urea cycle are deficient?

A

Increased ammonia in blood

42
Q

How could a deficient urea cycle result in neurotoxicity?

A

Increased ammonia.
Crosses BBB readily;
1. Converted to glutamate (by glutamate dehydrogenase)
2. Decrease in alpha-ketoglutarate in brain
3. Decrease in oxaloacetate
4. Krebs cycle stops
Leads to irreparable cell damage and neural cell death

43
Q

Briefly describe the Absorptive state

A
  1. Ingested nutrients are absorbed from the GI tract into the blood
  2. A proportion of nutrients are catabolised and used
  3. Remainder are converted and stored for future use
44
Q

Briefly describe the post-absorptive state

A
  1. Nutrients are no longer absorbed from the GI tract

2. Nutrient stores must supply the energy requirements of the body

45
Q

In the post-absorptive state, glucose is no longer being absorbed from the GI tract. What are the sources of blood glucose?

A
  1. Glycogenolysis (hrs)
  2. Lipolysis
  3. Proteolysis (>hrs)
    (ie GLUCONEOGENESIS)
46
Q

What is glycogenolysis, and where does it occur?

A

Hydrolysis of glycogen stores in liver (and skeletal muscle - although in muscle, lack enzyme to make glucose from G6P so lactate is produced, which is taken up by liver and converted to glucose)

47
Q

Where is the lactate produced by muscles converted to glucose?

A

In the liver

48
Q

Why do muscles make lactate instead of glucose from glycogenolysis?

A

They lack the enzyme to make glucose from G6P

49
Q

What does lipolysis involve?

A

Glycerol is enzymatically converted to glucose in the liver

50
Q

What does proteolysis involve?

A

Amino acids taken up by the liver and converted to glucose

51
Q

What is the term for synthesis of glucose from precursors such as glycerol and amino acids?

A

Gluconeogenesis

52
Q

What is gluconeogenesis?

A

The process of generating new molecules of glucose from non-carbohydrate precursors

53
Q

What are the substrates for gluconeogenesis?

A
  1. PYRUVATE (from lactate and amino acids)
  2. Glycerol (from triglyceride hydrolysis)
  3. 6 ATP
54
Q

Give some examples of substances stored in the liver

A
  1. Iron
  2. Fat soluble vitamins
  3. Glycogen
  4. Minerals
55
Q

How is iron distributed? (What is it utilised by and where is it stored?)

A 
Utilised by:
1. Haemoglobin
2. Myoglobin
3. Bone marrow
Stored in:
1. Liver
2. Reticulo-endothelial macrophages
56
Q

What is Transferrin?

A

The protein that transports iron in the plasma to the bone marrow so it can be incorporated into new RBCs

57
Q

What is Ferritin?

A

Storage form of iron

Main source is found in the liver

58
Q

How is iron stored?

A

As ferritin

59
Q

What is the main source of ferritin?

A

Liver

60
Q

What is the primary location of iron absorption?

A

Duodenum

61
Q

4 main fat soluble vitamins?

A

A
D
E
K

62
Q

Where is Vitamin A stored?

A

In Ito cells (in space of Disse)

High levels stored in liver - prevents deficiency for 10 months

63
Q

What is the function of Vitamin A?

A
  1. Vision (retinal pigments)
  2. Healthy skin
  3. Growth and reproduction
64
Q

Liver storage of Vitamin D prevents deficiency for how long?

A

3-4 months

65
Q

What is the function of vitamin D?

A
  1. Increases calcium reabsorption from intestinal tract

2. Promotes intestinal phosphate reabsorption

66
Q

What is the function of vitamin E?

A

Antioxidant

67
Q

What is the function of vitamin K?

A

Necessary for production of clotting factors

68
Q

Liver storage of vitamin B12 prevents deficiency for how long?

A

Over a year

69
Q

What is the function of vitamin B12?

A

Promotes growth and RBC formation + maturation

70
Q

What substance is required for absorption of vitamin B12?

A

Intrinsic factor (produced by parietal cells of stomach)

71
Q

What is pernicious anemia?

A

Malabsorption of vitamin B12 due to lack of intrinsic factor produced by parietal cells of stomach

72
Q

Where is vitamin b12 absorbed?

A

In the terminal ileum

73
Q

Where is glycogen stored in the body?

A
  1. Liver (~10% of mass)
  2. Skeletal muscle (~2% of mass)
    (More stored in skeletal)
74
Q

What is the function of glycogen?

A

Readily mobilised storage form of glucose - maintains blood glucose levels

75
Q

Glycogen is the secondary energy reservoir. What is the primary source?

A

Lipids

76
Q

Which minerals are stored in the liver?

A
  1. Iron (as ferritin)

2. Copper

77
Q

How is most of the body’s fat stored?

A

In adipocytes, which form tissues called adipose tissue

78
Q

What are the four main body energy reserves? How many calories in each?

A

Blood glucose - 40kcal
Glycogen - 600kcal
Muscle - 25,000kcal
Lipid reserve - 100,000kcal

79
Q

What are the 4 main body energy reserves? How long does each last?

A

Blood glucose - few mins
Glycogen - day
Muscle - week
Lipid reserve - month

80
Q

What are triglycerides composed of?

A

3 fatty acid chains bound to a glycerol backbone

81
Q

Triglycerides account for what percentage of the energy stored in the body? Proteins? Carbs?

A

TGs- 78%
Proteins - 21%
Carbs - 1%

82
Q

What are the 3 main lipoproteins, and where are they synthesised?

A
  1. HDL - liver
  2. LDL - plasma
  3. VLDL - hepatocytes
    (Also IDL)
83
Q

What do lipoproteins do?

A

Transport cholesterol through the blood

84
Q

What 3 main types of proteins are synthesised by the liver?

A

Plasma proteins
Clotting factors
Complement factors

85
Q

What are lipids?

A

Esters of fatty acids and certain alcohol compounds

86
Q

Give 3 functions of lipids

A
  1. Energy reserves
  2. Structural (part of cell membrane)
  3. Hormone metabolism
87
Q

How are dietary fats in the small intestine converted to fatty acids in cells? Give 8 steps.

A
  1. Bile salts and phospholipids emulsify dietary fats in the small intestine forming MICELLES
  2. Intestinal lip adds degrade TGs
  3. FAs are taken up into intestinal mucosa and converted into TAGs
  4. TAGs + cholesterol + apolipoproteins -> chylomicrons
  5. Chylomicrons move through lymphatic system and bloodstream into tissues
  6. Lipoprotein lipase converts TAGs to FAs and glycerol
  7. FAs enter cells
  8. FAs oxidised as fuel or re-esterified for storage
88
Q

Explain fat catabolism (ie the breakdown of fatty acids into CO2 and ATP)

A
  1. Coenzyme A links to carboxyl at end of FA
  2. ATP -> AMP + 2Pi
  3. Beta-oxidation of Acetyl CoA
  4. 2H+ transferred to coenzymes
  5. H+ from coenzymes enter OXPHOS to form ATP
  6. Another CoA attaches to FA and cycle repeated
  7. Coenzyme - 2H molecules lead to production of CO2 and ATP via Krebs cycle and OXPHOS
89
Q

Name 2 enzymes involved in the hepatic metabolism of lipids

A
  1. Lipoprotein lipase

2. Hepatic lipase

90
Q

What does lipoprotein lipase do?

A

Hydrolyses TGs in lipoproteins (chylomicrons, VLDL) into 2 FFAs and 1 glycerol

91
Q

What does hepatic lipase do? Where is it expressed?

A

Converts IDL into LDL

Expressed in liver and adrenal glands

Liver (2 decks)

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