Biochemical Aspects of Liver Metabolism Flashcards Preview

JL Gastrointestinal > Biochemical Aspects of Liver Metabolism > Flashcards

Flashcards in Biochemical Aspects of Liver Metabolism Deck (77):
1

Where is the first destination of most nutrients and xenobiotics absorbed from the GI tract?

Liver

2

What does the liver produce?

Bile

3

Name a plasma protein excreted from the liver?

Albumin

4

What two roles does the liver have in regulation of metabolism?

1. Carbohydrate and lipid metabolism - fuel storage
2. Amino acid metabolism - urea cycle

5

What allows seperation of proteins by size?

Electrophoresis

6

What 4 plasma proteins can be seperated by electrophoresis?

1. Albumin
2. Alpha globulins
3. Beta-globulins
4. Gamma globulins

7

What substances maintan oncotic or colloid osmotic pressure?

Plasma proteins

8

What transports hydrophobic substances like steroid hormones, free fatty acids, bilirubin and cholesterol?

Plasma proteins

9

How can plasma proteins be involved with pH buffering?

Amino-acid side chains can carry net charges

10

What plasma proteins transport lipoproteins, lipids, hormones and bilirubin?

Alpha-globulins such as ceruloplasmin

11

What alpha-globulin, other than ceruloplasmin, transports vitamin A?

Retinol binding protein

12

What does deficiency of vitamin A cause?

Visual impairment

13

What is vitamin A converted to?

Retinaldehyde, part of rhodopsin, a visual pigment

14

Name two beta-globulins?

Transferrin and fibrinogen

15

What two things does transferrin do?

Transports Fe3+
Indicator of iron deficiency

16

What is an inactive form of fibrin and is involved in clotting of blood?

Fibrinogen

17

What is the most abundant plasma protein?

Albumin

18

How would you describe albumin?

Small, negatively charged, water-soluble

19

What is the main determinant of plasma oncotic pressure?

Albumin

20

What stimulates production of albumin in the liver?

Insulin

21

What are levels of albumin like in liver disease?

Low

22

What two factors can lead to low levels of albumin?

Starvation and low protein diets

23

What does albumin have multiple binding sites for?

Hydrophobic molecules

24

What is the affinity and capacity like for albumin?

Low affinity, but high capacity because of high concentration

25

Name three endogenous lipophilic substances that albumin transports?

Fatty acids
Bilirubin
Thyroid hormones

26

What important exogenous substances does albumin carry?

Aspirin

27

What special structural feature of albumin allows it to carry hydrophobic molecules?

Hydrophilic clefts in globular domains

28

What do haemoglobin, myoglobin and cytochromes all haev which is a key component?

Iron

29

How is iron transported?

As ferric ion Fe3+ bound ti transferrin

30

How is iron stored?

In cells bound to ferritin

31

What is an essential trace element?

Copper

32

How is copper transported?

In blood bound to ceruloplasmin

33

What disease is related to a copper/ceruloplasmin deficiency?

Wilsons disease

34

What are two hydrophobic hormones?

Steroid hormones (derived from cholesterol)
T3/T4 thyroid hormones

35

How is thyroxine transported?

Bound to thyroid-binding globulin

36

How is cortisol transported?

Bound to cortisol-binding globulin

37

What do transport proteins do to steroid hormones and T3/T4 thyroid hormones?

Extend biological half-life and increased plasma concentration

38

What two substances are in teh core of lipoproteins (core of hydrophobic lipids)?

Cholesterol esters and triglycerides

39

What two substances are in the shell of a lipoprotein?

Polar lipids and apoproteins

40

What substances are involved in fat transport between organs and tissues?

Lipoproteins

41

What is the density order for lipoproteins, starting with the least dense?

Chylomicrons, VLDL, IDL, LDL, HDL

42

Where do chylomicrons originate and what is there function?

Intestine - transport of exogenous fat to liver

43

Where does VLDL originate and what is its function?

Liver - transports endogenous fat to peripheral cells

44

Where does IDL originate and what is its function?

VLDL - LDL precursor

45

Where does LDL originate and what is its function?

VLDL/IDL/liver - cholesterol transport to peripheral tissues

46

Where does HDL originate and what is its function?

Intestine/liver - reverse cholesterol transport

47

What removes excess choleeterol from cells?

HDL

48

How is cholesterol removed from cells?

Esterified with fatty acids, transported back to liver, excreted as bile salts via biliary system or faeces

49

What is the only organ capable of metabolising and excreting cholesterol?

Liver

50

What vitamin does the liver store for 10 months as retinol palmitate?

Vitamin A

51

What vitamin does the liver store for 3 weeks?

Vitamin Dq

52

What vitamin is stored in hte liver for a few years worth?

Vitamin B12

53

What is cholesterol a precursor for (3 substances)?

1. Bile acids
2. Steroid hormones
3. Vitamin D

54

What is a major component of gall stones?

Cholesterol

55

Where in cells is cholesterol synthesised?

In cytoplasm or enzymes bound to ER membranes

56

What other three organs, than the liver, are involved in cholesterol synthesis?

Intestine, adrenal cortex and gonads

57

What three things does synthesis of 1 mol of cholesterol require?

1. Source of C atoms
2. Source of reducing power
3. Significant energy

58

How many moles of acetyl-CoA is needed for 1 mol of cholesterol?

18 mol

59

How many mol of NADPH is needed for 1 mol cholesterol?

16 mol

60

How much energy is needed to make 1 mol of cholesterol?

36 mol of ATP

61

What converts HMG CoA to mevalonic acid in cholesterol synthesis?

HMG-CoA reductase

62

What does HMG-CoA reductase catalyse?

The reversible formation of mevalonic acid, so is rate limiting

63

What is the synthesis and activity of HMG-CoA reductase stimulated by?

Fasting

64

What does dietary cholesterol and high intrahepatocyte cholesterol do to HMG-CoA reductase?

Reduces activity

65

What drugs target HMG-CoA reductase?

Statins

66

What product from cholesterol has a role in the regulation of calcium and phosphorus metabolism?

Vitamin D

67

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

Vitamin D3

68

Where are corticosteroids (21 carbon atoms) synthesised?

Adrenal cortex

69

Where are androgens (19 carbon atoms) synthesised?

In testis

70

Where are oestrogens (18 carbon atoms) synthesised?

In ovaries

71

What is the main metabolic product of cholesterol?

Bile salts

72

Where are bile salts synthesised and stored?

In liver
Stored as compoennet of bile in gall baldder

73

What, once released into the duodenum, act as detergents for emulsifying ingested lipids?

Bile salts

74

What agents bind bile salts and inhibit reabsorption in the enterohepatic circulation?

Anion exchange resins - cholestyramine

75

What do anion exchange resins do to bile salt excretion and synthesis?

Increased bile salt excretion with increased synthesis of bile salts

76

When there is increased synthesis of bile salts in teh liver, what does the concentration of cholesterol do?

Decrease and number of LDL receptors of hepatic cells increases

77

When the number of LDL receptors of hepatic cells increases, what happens to the uptake of LDL cholesterol from plasma?

Increases leading to lower plasma LDL