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liver & friends lectures > protein synthesis in the liver > Flashcards

protein synthesis in the liver Flashcards

1
Q

which proteins does the liver produce (3)

A
  • plasma proteins
  • clotting factors
  • complement factors
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2
Q

examples of plasma proteins (7)

A
  • albumin
  • globulins
  • fibrinogen
  • CRP (an infection marker)
  • Clotting factors – Factors II, VII, IX and X are Vitamin K dependent
  • Thrombopoietin
  • Angiotensinogen
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3
Q

what is the most abundant plasma protein

A

albumin

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4
Q

what stimulates protein synthesis

A

insulin and growth hormone

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5
Q

role of the plasma proteins synthesised by the liver (2)

A
  1. play an important role in maintaining the amino acid equilibrium in the blood.

in times of tissue amino acid depletion, these proteins can be degraded and released back into the blood as amino acids for tissues to use in protein synthesis.

  1. provide oncotic pressure in the blood, meaning they hold water in the plasma.
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6
Q

functions of albumin (2)

A
  1. binding & transport of large, hydrophobic compounds such as bilirubin, fatty acids, hormones & drugs (NSAIDS & warfarin)
  2. maintenance of colloid osmotic pressure
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7
Q

what is colloid osmotic pressure

A

the effective osmotic pressure across blood vessel walls which are permeable to electrolytes but NOT large molecules.

It is almost entirely due to plasma proteins

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8
Q

how does albumin maintain osmotic pressure

A

albumins presence in the plasma means that the water concentration of the blood plasma is slightly lower than that of the interstitial fluid meaning there is a net flow of water
OUT OF the interstitial fluid INTO the blood plasma

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9
Q

how does fluid move across the capillary wall

A

there are 4 opposing forces called Starling forces

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10
Q

what are the 4 Starling forces

A
  1. Capillary hydrostatic pressure (favouring fluid movement out of the
    capillary)
  2. Interstitial hydrostatic pressure (favouring fluid movement into the
    capillary
  3. Osmotic force due to plasma protein concentration (favouring fluid
    movement into the capillary)
  4. Osmotic force due to intestinal fluid protein concentration (favouring
    fluid movement out of the capillary
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11
Q

what results in in bulk filtration of fluid OUT OF the capillaries

A

at the arterial ends of the capillaries the hydrostatic pressure from the
capillary is 38 mmHg - greater than that from the interstitial fluid
(which is virtually zero since there is very little fluid in the interstitial spaces
since it quickly picked up by the lymphatics etc.)

and the interstitial fluid protein concentration is 3mmHg

and the osmotic pressure due to plasma proteins is 28mmHg

so net outward pressure EXCEEDS the net inward pressure

causing bulk filtration of fluid out of the capillaries

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12
Q

what results in bulk absorption of fluid INTO the capillaries

A

at the venous end, the only difference in Starling forces is the capillary hydrostatic pressure which has decreased from 35 to around
15mmHg due to the resistance encountered as blood flow through the
capillary wall.

The other three forces are virtually the same as above

so the net inward pressure EXCEEDS the net outward pressure

so bulk absorption of fluid INTO the capillaries occurs

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13
Q

impact of reduced albumin due to liver failure

A

liver failure
reduction in albumin
less albumin in blood - (hypoalbuminaemia)

causes decrease in capillary oncotic pressure
since there will be less of a
difference in the concentration of water between plasma and interstitial fluid

causes the accumulation of water in the interstitial fluid
resulting in oedema. Hypoalbuminaemia = Oedema

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14
Q

what can cause albumin to decrease (4)

A
  • nephrotic syndrome
  • haemorrhage
  • gut loss
  • burns
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15
Q

what is nephrotic syndrome

A

where there is an increased glomerular
permeability

which allows proteins to filter through the basement membrane

meaning the loss of up to several grams of protein a day can occur

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16
Q

what is gut loss

A

a rare syndrome in which the wall of the gut is unusually permeable to large molecules resulting in albumin loss

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17
Q

how do burns reduce albumin

A

extensive tissue damage with damage to capillaries can cause loss of protein through the walls of the capillaries

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18
Q

what are globulins

A

a group of proteins in the blood made by the liver and the immune system

19
Q

what are the 3 types of globulins

A
  • Alpha (1 and 2)
  • Beta
  • Gamma
20
Q

where are alpha and beta globulins made

A

in the liver

21
Q

where are gamma globulins made

A

in the immune system

22
Q

function of alpha and betta globulins

A
  1. Blood transport of:
    - Lipids by lipoproteins
    - Iron by transferrin
    - Copper by caeruloplasmin
  2. work as enzymes
  3. a few have antibody functions
23
Q

function of gamma globulins

A

vital role in natural and acquired immunity to infection.

immunoglobulins (antibodies) - help to fight off infection

24
Q

which clotting factors does the liver produce

A

all of them except
calcium (IV)
and
von Willebrand factor (VIII)

also produces bile salts

25
Q

why does the liver produce bile salts

A

they are essential for vitamin K absorption and digestion because it is fat soluble

26
Q

what happens in biliary obstruction

A

Vitamin K is not appropriately absorbed

so the Vitamin K dependant clotting factors are not adequately synthesized,

so more bleeding.

27
Q

why does liver disease lead to a tendency of bleeding

A

as fewer clotting factors are produced

28
Q

what is essential in order to produce clotting factors

A

vitamin K is essential to the carboxylase enzyme that is used to make clotting factors II (prothrombin), VII, IX, X and protein C
(10,9,7,2)

29
Q

what are complement factors

A

plays an important role in the immune response to pathogens,

a plasma protein which sticks to pathogens, that is recognised by neutrophils, it helps mark pathogens to kill

30
Q

describe the route of albumin

A
  • leaves circulation via interstitium
  • collected by lymphatics
  • returned via thoracic duct
  • the rate is the transcapillary escape rate
31
Q

what causes albumin to decrease

A
  • decreased synthesis
  • increased catabolism
  • increased loss
32
Q

consequences of lower albumin

A
  • decreased colloid oncotic pressure
  • decreased ligand banding
33
Q

what is protein turnover

A

the continuous degradation and re-synthesis of all cellular proteins

34
Q

describe the rate of protein turnover

A

turnover is very variable and reflects usage/demand

35
Q

what causes an increase in the rate of protein turnover

A
  1. when tissues are undergoing structural re-arrangement e.g.
    when tissue is damaged due to trauma
  2. due to severe burns since there attempts at re-modelling the
    skin, its complicated by the fact that significant amounts of protein can be lost in the exudate from the damaged tissue
36
Q

what are the primary methods of protein breakdown

A
  1. Lysosomal Pathway
  2. Ubiquitin- Proteasome Pathway
37
Q

where is lysosomal breakdown carried out

A

out in the reticulo-endothelial system of the liver

this is comprised of the sinusoidal endothelial cells, Kupffer cells & pit cells

38
Q

what do Sinusoidal endothelial cells do

A

remove soluble proteins and fragments from the blood

through the sieve plates on their luminal surface -they are
important for removing; fibrin, fibrin degradation products, collagen & IgG
complexes.

Once in the liver these proteins are then fused into lysosomes containing lysozyme which are hydrolytic enzymes that break down the protein into amino acids

39
Q

what do kuppfer cells do

A

they are the livers resident macrophages and perform a similar function

except there phagocytose particulate matter thereby packaging them in to
phagosomes in the cell which contain hydrolytic enzymes which will break down the protein into amino acids

40
Q

where does the Ubiquitin-Proteasome Pathway occur

A

in cytoplasm of cells

41
Q

which proteins are degraded quicker

A

those that are defective because of incorrect amino acid sequences or because of damage to normal function (denatured)

42
Q

why do different proteins degrade at different rates

A

depends on the structure of
the protein - a denatured (unfolded) protein is more readily digested than a protein with an intact conformation

43
Q

how does Ubiquitin-Proteasome degradation occur

A

Proteins are targeted for degradation by the attachment of a small peptide called ubiquitin to the protein.

This peptide directs the protein to a protein complex called a
proteasome - “the cellular executioner”,

which unfolds the protein and breaks it
down into small peptides

liver & friends lectures (7 decks)

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