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Liver n Proteins n glucose Flashcards

1
Q

The liver is a major producer of proteins

A

It produces plasma proteins, clotting factors & complement factors

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2
Q

What is the most abundant plasma protein

A

Albumin

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3
Q

Function of Albumin

A

Binding & transport of large, hydrophobiccompounds such as bilirubin, fatty acids, hormones & drugs (NSAIDS & warfarin)
n
Maintenance of colloid osmotic pressure

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4
Q

What is colloid osmotic pressure

A

Colloid osmotic pressureis the effective osmotic pressureacross blood vessel walls which are permeable to electrolytes but NOT large molecules. It is almost entirely due to plasma proteins

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5
Q

How does albumin maintain osmotic pressure

A

Albumin maintains osmotic pressure due to the fact that its 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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6
Q

What are the stalling forces and give all 4

A

Opposing forces act to move fluid across the capillary wall,

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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7
Q

How is tissue fluid formed at arterial end of capillaries

A

At the arterial ends of the capillaries the hydrostatic pressurefrom the capillary is 38 mmHg which is 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 28mmHg thusnet outward pressureEXCEEDS the netinward pressure resulting in bulk filtration of fluid OUT OF the capillaries

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8
Q

What happens to tissue fluid at venous end of capillaries

A

However, 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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9
Q

What happens to tissue fluid when there is liver failure

A

When there is liver failure there is a reduction in albumin resulting in less albumin in the blood (hypoalbuminaemia). This in turn will mean there will be a decreases in capillary oncotic pressure, since there will be less of a difference in the concentration of water between plasma and interstitial fluid resulting in the accumulation of water in the interstitial fluid, resulting in oedema. Hypoalbuminaemia = Oedema

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10
Q

Other than liver failure what are causes of albumin decrease

A

Nephrotic syndrome: 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

  • Haemorrhage
  • Gut loss: a rare syndrome in which the wall of the gut is unusually permeable to large molecules resulting in albumin loss
  • Burns: Extensive tissue damage with damage to capillaries can cause loss of protein through the walls of the capillaries
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11
Q

What are globulins

A

Antibody functions (most are gamma-globulins NOT MADE IN LIVER, but some are alpha/beta globulins which ARE MADE IN LIVER)

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12
Q

How are lipids, iron and copper transported

A

Blood transport of:

  • Lipids by lipoproteins
  • Iron by transferrin
  • Copper by caeruloplasmin
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13
Q

How is copper transported in the blood

A

caeruloplasmin

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14
Q

Liver produces all clotting factors except

A

calcium (IV) & von Willebrand factor (VIII)

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15
Q

Liver produces bile salts what is this important for

A

The liver also produces bile salts which are essential for vitamin Kabsorption (fat soluble). Vitamin K is essential for the synthesis of numerous clotting factors - 10,9,7,2 (1972)

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16
Q

Need Vitamin K for what clotting factors

A

clotting factors - 10,9,7,2 (1972)

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17
Q

What are complement factors and what is their function

A

-Plays an important role in the immune response to pathogens, its a plasma protein which sticks to pathogens, that is recognised by neutrophils, essentially help markpathogens to kill

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18
Q

What is protein turnover

A

Protein turnover refers to the continuous degradation and re-synthesis of all cellular proteins

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19
Q

The rate of protein turnover is very variable and reflects usage/demand
when is an increase seen (2)

A

Increase is seen when tissues are undergoing structural re-arrangement e.g. when tissue is damaged due to trauma, uterine tissue during pregnancy in skeletal muscle during starvation - gluconeogenesis. In starvation the skeletal muscle is degraded and the liberated amino acids are used in gluconeogenesis

It also increases 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

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20
Q

There are 2 primary methods of protein breakdown;

A

Lysosomal & Ubiquitin-Proteasome Pathway

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21
Q

Lysosomal protein breakdown carried out where

A

Carried out in the reticulo-endothelial system of the liver

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22
Q

What is the reticulo-endothelial system of the liver made of

A

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

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23
Q

Process of Lysosomal protein breakdown

A

Sinusoidal endothelial cells removesoluble proteins and fragments from the bloodthrough the fenestrations known as 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 lysosomescontaining lysozyme which are hydrolytic enzymes that break down the protein into amino acids
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24
Q

What do kupffer cells do in the Process of Lysosomal protein breakdown

A

Kupffer cells 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

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25
Where does Ubiquitin-Proteasome Pathway occur
occurs in cytoplasm of cells
26
Different proteins degrade at different rates why
this depends on the structure of the protein - a denatured (unfolded) protein is more readily digested than a protein with an intact conformation Rapidly degraded proteins include those that are defective because of incorrectamino acid sequences or because of damage to normal function (denatured
27
Ubiquitin-Proteasome Pathway
Proteins can be 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
28
AMINO ACID DEGRADATION & CATABOLISM where does this occur
these reaction occur in the hepatocytes of the liver
29
what is catabolism
Catabolism is the break down of complex substances to simpler ones accompanied by the release of energy
30
What happens to unseeded amino acids
Any amino acids that are not required as building blocks for protein synthesis mustundergo degradation (degraded to specific compounds)
31
What does catabolism entail and produce
* Amino acids contain nitrogen atoms (in their amino group) in addition to carbon, hydrogen and oxygen atoms * Amino acid catabolism requires the alpha amino group (nitrogen containing) to be removed * It produces:-Nitrogen - which is incorporated in other compounds or excreted-Carbon skeleton - which can then be metabolised and used in the Kreb’s cycle
32
There are 2 main catabolism processes;
oxidative deamination & transamination
33
What Is Oxidative Deamination
The liberation of an amino group as free ammonia (NH3)
34
What is the only amino acid that goes rapid oxidative deamination
Glutamate
35
Steps of oxidative deamination
- Amino acid gives rise to a molecule of ammonia (NH3) and is replaced by an oxygen atom from water to form a alpha - keto acid e.g. alpha-ketoglutarate -Reaction results in the formation of an alpha - keto acid (e.g alpha-ketoglutarate) & ammonia-The alpha-keto acid can then be used in the Kreb’s cycle for use in glucose production - GLUCONEOGENESIS - essentially reversing Krebs + glycolysis to start NOTE: the ammonium (NH4+) produced quickly disassociates to form ammonia(NH3) which can then be converted to urea, via the urea cycle since it is very toxic
36
Which enzyme catalyses oxidative deamination
glutamate dehydrogenase
37
`what coenzyme involved in oxidative deamination
The co-enzyme involved is NAD+ (forwards reaction)/NADPH (backwards reaction)
38
oxidative deamination is reversible what does this depend on
The process is readily reversible and is dependent on concentrations of; glutamate, alpha-ketoglutarate & ammonia - if the amino acid at the start is glutamate - the most abundant amino acid in the body
39
Because oxidative deamination is reversible what happens when there is excess ammonia (NH3)
when there is EXCESS ammonia (NH3+) it can easily cross the blood-brain barrier and then react with alpha-ketoglutarate(thereby meaning there will be a decrease in ATP - DANGEROUS in the brain)
40
After a protein rich meal what does the conc of glutamate result in
After a protein rich meal, the glutamate concentration will be high, oxidative deamination will degrade the amino acid glutamate resulting in ammonia formation
41
What is transamination
Transfer of an alpha-amino group from amino acid to a keto-acid to form an alpha-keto-acid
42
What happens when the amino acid transaminate in alanine
If the amino acid alanine is transaminated then the amino group from it is transferred to the keto-acid called alpha-ketoglutarate and results in the formation of pyruvate (for use in the Kreb’s cycle for use in GLUCONEOGENESIS) and glutamate (amino acid, which can then be oxidatively deaminated) look at pic
43
What enzyme is used in transamination and where is tis found
aminotransferase, they are found in the cytosol of the mitochondria throughout the body and particularly in the kidneys & liver. If alanine is being transaminated then the enzyme used is known as alanine aminotransferase (ALT)
44
If alanine is being transaminated whats the enzyme
alanine aminotransferase (ALT)
45
Each aminotransferase is specific to how many amino group donors
Each aminotransferase is specific to one or a few amino group donors
46
Is transamination reversible?
This reaction is readily reversible, degradation will occur after a protein-rich mealand amino acid synthesis will occur depending on dietary supply and cellular demand
47
What is nitrogen balance
A measure of the equilibrium of protein turnover
48
Anabolic nitrogen balance
positive balance i.e net gain in amino acids
49
catabolic nitrogen balance
negative balance i.e. net loss in amino acids
50
Whats a healthy nitrogen balance
People can be defined as healthy if their nitrogen balance is in equilibrium
51
If any of the essential amino acids (i.e. those the body cannot synthesise of which there are nine) are missing from our diet what does this mean nitrogen balance wise
a negative nitrogen balance (loss greater than gain) results
52
Positive nitrogen balance [ANABOLIC]: nitrogen intake > nitrogen loss Common cause
Pregnancy is the most common cause of a positive nitrogen balance
53
What is the recommended daily amino acid intake to remain in nitrogen balance
The recommended daily intake of amino acids to remain in nitrogen balanceis 0. 8g/kg bodyweight (in normal man and women), 1. 3g/kg bodyweight (in pregnant women) & 2. 4g/kg bodyweight (in first few months of live)
54
Negative nitrogen balance [CATABOLIC]: nitrogen intake < nitrogen loss 2 common causes
- Malnutrition is the most common cause | - Multiple trauma or extensive trauma where there is a lot of tissue damage can result in a negative nitrogen balance
55
How is alanine produced in muscles
In muscles there are aminotransferases such as alanine aminotransferase (ALT)that utilise pyruvate (produced from glycolysis) as an alpha-keto acid for transamination. This produces alanine as the amino acid product and alpha-ketoglutarate as the alpha keto acid product which can then be used in the Kreb’s cycle to produce glucose via gluconeogenesis (essentially reverse transamination of alanine)
56
1) What happens to excess alanine after transamination in the muscles
Excess alanine is released into the bloodstream and transported into the liver look at pic pls
57
2) What happens to excess alkaline once its back in the liver
Once in the liver, the alanine is converted back to pyruvate by transamination (reverse reaction of that above) look at pic pls
58
3) when the transamination in the liver produces pyruvate what happens then
The pyruvate can be used as a source of carbons for glucose production via gluconeogenesis look at pic pls
59
4) what happens to the glucose that is produced in the liver as a result of transamination
The glucose then enters the blood and can be used in the muscles which in turn can produce pyruvate via glycolysis which canthen be used again to remove excess ammonia (NH3) - this is the glucose-alanine cycle look at pic pls
60
5) what happens to the gluatamate produced as a result of the glucose alanine cycle
The glutamate produced can then be converted to ammonium (NH4+) via oxidative deamination producing ammonium (NH4+) which then rapidly disassociates into ammonia (NH3) which in turn can be converted to urea via the urea cycle look at pic pls
61
Where are all the enzymes involved in the urea cycle found
All the enzymes involved are found in the liver in either the mitochondria or cytosolof hepatocytes
62
Step 1 of urea cycle | arginine..
arginine either from the diet or protein breakdown, is cleaved by arginasegenerating urea & ornithine look at pic
63
Step 2 of urea cycle NH3...
Then ammonia (NH3) and CO2 is built on the ornithine to form citrulline look at pic
64
Step 3 of urea cycle NH3...
Another molecule of ammonia (NH3) is then added to citrulline to regeneratearginine and enable the cycle to go around again look at pic
65
What does one reaction of the urea cycle produce
The reactions of one turn of the cycle consume:-3 ATP equivalents-4 high energy nucleotides (PO4-)
66
What is the only product of the urea cycle
Urea is the ONLY compound generated by the cycle, all the other components are recycled
67
What happens if theres a deficiency in any of the enzymes that are needed in the urea cycle
Deficiencies of ANY of the enzymes involved is associated with higher levels of ammonia in the blood, ABSENCE of them is NOT COMPATIBLE WITH LIFE
68
Why are higher levels of ammonia associated with neurotoxicity
- Ammonia is able to cross the blood brain barrier VERY easily - Once inside it is converted to glutamate under the action of the glutamate dehydrogenase enzyme - This means there is a depletion in alpha-ketoglutarate -As alpha-ketoglutarate falls so does oxaloacetate ultimately resulting in the Kreb’s cycle coming to a halt - This results in IRREPARABLE CELL DAMAGE & neural cell DEATH - This is the reason why ammonia is neurotoxic
69
glucose reg | Absorptive state: 4)+(4
- Ingested nutrients are absorbed from the GI tract into the blood - A proportion of nutrients are catabolised and used - The remainder are converted and stored for future use - During the absorptive state: * Glucose is used to generate ATP * Amino acids are converted to proteins * Glycerol & fatty acids are converted to lipids * Glucose is converted to glycogen
70
Post-absorptive state:
- Nutrients are no longer absorbed from the GI tract | - Nutrient stores MUST supply the energy requirements of the body
71
Glucose regulation in the post-absorptive state:
- Glucose is no longer being absorbed from the GI tract - Yet it is essential to maintain the plasma glucose concentration due to the fact that the CNS is always using it for fuel - In the post-absorptive state there are 3 main sources of glucose
72
What are the three main sources of glucose in post-absorbative state
1 GLYCOGENOLYSIS 2 LIPOLYSIS 3 PROTEIN
73
What is glycogenolysis in the post absorptive state
-The hydrolysis of glycogen to monomers of glucose-6-phosphate In the liver; glucose-6-phosphate is enzymatically converted to glucose which then enters the blood
74
Where does glycogenolysis in the post absorptive state occur
Occurs in the liver & skeletal muscles
75
Whats the first line of defence in maintaining glycogen levels in a post absorptive state
Hepatic glycogenolysis begins within seconds of an appropriate stimulus, such as sympathetic nervous system activation. Consequently it is the first line of defence in maintaining the plasma glucose concentration within a homeostatic range
76
How long can hepatic glycogen supply glucose in a post absorptive state
The amount of glucose available from the liver can only supply the bodies requirements for only several hours before hepatic glycogen stores are nearly depleted
77
What holds more glycogen stores | liver or skeletal muscles?
glycogenolysis Also occurs in skeletal muscles, which contains the same amount of glycogen as the liver BUT ITS NOT A SOURCE OF BLOOD GLUCOSE!! WHY?
78
Why is skeletal muscle not source of blood glucose?
unlike the liver, skeletal muscle does not possess the enzymenecessary to from glucose from the glucose-6-phosphate formed during glycogenolysis, thus muscle glycogen is not a source of blood glucose Instead, the glucose-6-phosphate undergoes glycolysis within muscle to yield ATP, pyruvate & lactate
79
What happens to the products of skeletal muscle, post absorptive, glycogenolysis
The ATP & pyruvate are used directly bythe muscle cell - However, some of the lactate enters the blood and circulates to the liver and is converted into glucose which can then leave the liver cells to enter the blood - Thus, muscle glycogen contributes to blood glucose indirectly by way of the livers processing of lactate
80
What is lipolysis
The catabolism of triglycerides in adipose tissue via the hydrolysis of triglycerides to produce glycerol and fatty acids
81
How is lipolysis carried out
Glycerol and fatty acids enter the blood via diffusion -The glycerol enters the liver which in turn enzymatically converts it through a series of steps into glucose
82
How is Protein a source of blood glucose
- A few hours into the post-absorptive state, protein becomes another source of blood glucose - Large quantities of protein in muscle and tissues can be catabolised without significant cellular malfunction
83
Process of protein as blood glucose source
-The proteins supply amino acids, which enter the blood and are taken up by the liver where they can be converted via the alpha-keto acid pathway to glucose, which can then be released into the blood
84
The synthesis of glucose from such precursors as amino acids and glycerolis known as
gluconeogenesis •Thus glycogenesis is the process of generating new molecules of glucose from non-carbohydrate precursors 21

LIVER & FRIENDS (11 decks)

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