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1. GI > Biochemistry of the Liver > Flashcards

Biochemistry of the Liver Flashcards

1
Q

What is the role of Cytochrome p450?

A

metabolises potentially toxic compounds, including drugs and products of endogenous metabolism such as bilirubin principally in the liver

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2
Q

Roles of the liver?

A 
First destination of most nutrients and xenobiotics absorbed from the GI tract
Bile production
Elimination of unwanted molecules
Secretion of plasma proteins
    e.g. albumin 
Storage of important molecules
    e.g. fuels, iron, vitamins
Regulation of metabolism
   carbohydrate and lipid metabolism - fuel storage
   amino acid metabolism - urea cycle
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3
Q

How are proteins seperated by size?

A

Electrophoresis

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4
Q

What are the main functions of plasma proteins?

A

Maintenance of oncotic or colloid osmotic pressure
- don’t exit into interstitial fluid
- prevents loss of plasma proteins
Transport of hydrophobic substances
- steroid hormones, free fatty acids, bilirubin, cholesterol
pH buffering
- amino acid side chains can carry net charges
Enzymatic
- e.g. blood clotting
Immunity

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5
Q

How does the oncotic force act?

A

draws fluid from body compartments to the blood

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6
Q

What controls oncotic pressure?

A

Albumin

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7
Q

What is the role of alpha gobulin?

A

transport lipoproteins, lipids, hormones and bilirubin
retinol binding protein - ceruloplasmin
- transports vitamin A

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8
Q

What does vitamin A deficiency result in?

A

visual impairment

lipid soluble alcohol, converted to retinaldehyde, part of rhodopsin, a visual pigment

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9
Q

Name two types of beta gobulins?

A

transferrin

  • transports Fe3+
  • indicator of iron deficiency

fibrinogen

  • inactive form of fibrin
  • clotting of blood
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10
Q

What is the most abundant plasma protein?

A

Albumin

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11
Q

How much Albumin does the liver normally make each day?

A

14 g/day

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12
Q

What stimulates Albumin production? What can cause it to drop?

A

insulin stimulates production

starvation/low protein diet causes decrease of levels - levels are low in liver disease

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13
Q

Which endogenous and exogenous substances does Albumin transport?

A

transports important endogenous lipophilic substances e.g. fatty acids, distribution of energy-rich substrates, bilirubin, breakdown product of haem, thyroid hormones

transports important exogenous substances e.g.
drugs like aspirin (any drug that has a weak hydrophobic capacity)

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14
Q

Describe the transport mechanisms of Albumin?

A

Multiple binding sites for hydrophobic molecules
hydrophobic clefts in globular domains
low affinity, but high capacity because of high concentration
Transports endogenous and exogenous substances

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15
Q

How is iron transported?

A

as ferric ion Fe3+

bound to transferrin

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16
Q

How is iron stored in cells?

A

bound to ferritin

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17
Q

How is copper transported in the blood?

A

bound to ceruloplasmin

18
Q

What is Wilson’s Disease?

A

Copper deficiency

19
Q

Are Steroid hormones and the T3/T4 thyroid hormones hydrophobic or hydrophillic?

A

hydrophobic

20
Q

How is thyroxine transported in the blood?

A

bound to thyroid-binding globulin

21
Q

How is cortisol transported in the blood?

A

bound to cortisol-binding globulin

22
Q

Describe the make up of lipoproteins?

A 
Core of hydrophobic lipids
     cholesterol esters
     triglycerides
Surrounded by shell
      polar lipids (phospholipids)
      apoproteins
Free cholesterol dispersed throughout
23
Q

What is the function of HDL?

A

Removes excess cholesterol from cells

  • cholesterol is esterified with fatty acids
  • transported back to liver
  • excreted as bile salts via biliary system or faeces
24
Q

Which organ can control cholesterol levels?

A

liver

25
Q

What is cholesterol a precursor of?

A

bile acids
steroid hormones
vitamin D

26
Q

What is cholesterol metabolism important for?

A

etiology of cardiovascular disease

major component of gall stones

27
Q

Where is cholesterol stored?

A

lipid droplets

28
Q

How is cholesterol transported in water?

A

30 % of circulating cholesterol is in free form
Majority is esterified to a wide range of long-chain fatty acids
- through hydroxyl group
- even less soluble in water

29
Q

How is cholesterol solubilised?

A

is incorporated into lipoproteins

30
Q

Where is the main and lesser sites of cholesterol synthesis?

A
  1. liver

Lesser: intestine, adrenal cortex, gonads

31
Q

What does the synthesis of 1 mol cholesterol require?

A 
source of C atoms
    18 mol of acetyl-CoA
source of reducing power
    16 mol of NADPH
significant amounts of energy
    36 mol of ATP
32
Q

What is the role of HMG-CoA reductase?

A

Catalyses the irreversible formation of mevalonic acid

33
Q

What reduces HMG-CoA reductase activtiy?

A

Dietary cholesterol and high intrahepatocyte cholesterol

34
Q

What stimulates HMG-CoA reductase activity?

A

fasting

35
Q

What is the most abundant form of vitamin D in the circulatory system?

A

Vitamin D3

36
Q

What is the role of vitamin D?

A

regulation of calcium and phosphorus metabolism

37
Q

What are the three groups of steroid hormones?

A

corticosteroids
androgens
estrogens

38
Q

Where are corticosteroids, androgens and estrogens released?

A

corticosteroids - adrenal cortex
androgens - testis
estrogens - ovary

39
Q

How are primary bile salts converted to secondary bile salts?

A

bacteria in the intestine

40
Q

Describe the life cycle of bile salts?

A

Synthesised and secreted by liver
Stored as component of bile in the gall bladder
Once released into the duodenum, act as detergents for emulsifying ingested lipids
Recycled by enterohepatic circulation

41
Q

How is cholesterol excretion manipulated?

A

Anion exchange resins (e.g. cholestyramine) bind bile salts and inhibit reabsorption in the enterohepatic circulation
Increased bile salt excretion and synthesis of bile salts
Concentration of cholesterol in the liver is decreased
The number of LDL receptors of hepatic cells increases
Uptake of LDL cholesterol from plasma increases
Lower plasma LDL and therefore cholesterol

1. GI (61 decks)

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