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Functions Flashcards

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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
What is the second step in amino acid breakdown?
Oxidative deamination
26
What is the result of oxidative deamination?
Liberation of amino group as free ammonia An alpha-keto acid (eg pyruvate) which can enter Krebs cycle Ammonia which can enter urea cycle
27
What catalyses oxidative deamination?
Glutamate dehydrogenase | Co-enzymes (NAD+/NADPH)
28
Are transamination and oxidative deamination reversible processes?
Yes. They are both readily reversible.
29
Oxidative deamination is dependent upon relative concentrations of what?
1. Glutamate 2. Alpha-ketoglutarate 3. Ammonia
30
How would oxidative deamination be affected by a protein-rich meal?
Glutamate concentration high, so ammonia produced
31
In the glucose/alanine cycle, what happens in the muscle?
Glucose is turned into pyruvate by glycolysis. | Pyruvate (+ glutamate) is converted by ALT to alanine (+ alpha-ketoglutarate)
32
How does the liver participate in the glucose/alanine cycle?
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)
33
Which enzyme converts alanine to pyruvate?
PLP
34
How does muscle protein contribute to the glucose/alanine cycle?
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
35
How does glutamate contribute to the urea cycle?
Glutamate converted into NH4+ (ammonia) which combines with arginine to form urea
36
Where do amine groups (NH2) that contribute to the glucose/alanine cycle come from?
1. Dietary amino acids | 2. Alanine and glutamine from muscles
37
What are the two metabolic products from excess amino acids?
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
Give an example of an alpha-keto acid
Pyruvate
39
Where are the enzymes responsible for the urea cycle found?
In mitochondria or cytosol
40
What does one turn of the urea cycle consume?
1. 3 ATP equivalents | 2. 4 high energy nucleotides
41
What happens if some of the enzymes in the urea cycle are deficient?
Increased ammonia in blood
42
How could a deficient urea cycle result in neurotoxicity?
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
Briefly describe the Absorptive state
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
Briefly describe the post-absorptive state
1. Nutrients are no longer absorbed from the GI tract | 2. Nutrient stores must supply the energy requirements of the body
45
In the post-absorptive state, glucose is no longer being absorbed from the GI tract. What are the sources of blood glucose?
1. Glycogenolysis (hrs) 2. Lipolysis 3. Proteolysis (>hrs) (ie GLUCONEOGENESIS)
46
What is glycogenolysis, and where does it occur?
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
Where is the lactate produced by muscles converted to glucose?
In the liver
48
Why do muscles make lactate instead of glucose from glycogenolysis?
They lack the enzyme to make glucose from G6P
49
What does lipolysis involve?
Glycerol is enzymatically converted to glucose in the liver
50
What does proteolysis involve?
Amino acids taken up by the liver and converted to glucose
51
What is the term for synthesis of glucose from precursors such as glycerol and amino acids?
Gluconeogenesis
52
What is gluconeogenesis?
The process of generating new molecules of glucose from non-carbohydrate precursors
53
What are the substrates for gluconeogenesis?
1. PYRUVATE (from lactate and amino acids) 2. Glycerol (from triglyceride hydrolysis) 3. 6 ATP
54
Give some examples of substances stored in the liver
1. Iron 2. Fat soluble vitamins 3. Glycogen 4. Minerals
55
How is iron distributed? (What is it utilised by and where is it stored?)
``` Utilised by: 1. Haemoglobin 2. Myoglobin 3. Bone marrow Stored in: 1. Liver 2. Reticulo-endothelial macrophages ```
56
What is Transferrin?
The protein that transports iron in the plasma to the bone marrow so it can be incorporated into new RBCs
57
What is Ferritin?
Storage form of iron | Main source is found in the liver
58
How is iron stored?
As ferritin
59
What is the main source of ferritin?
Liver
60
What is the primary location of iron absorption?
Duodenum
61
4 main fat soluble vitamins?
A D E K
62
Where is Vitamin A stored?
In Ito cells (in space of Disse) | High levels stored in liver - prevents deficiency for 10 months
63
What is the function of Vitamin A?
1. Vision (retinal pigments) 2. Healthy skin 3. Growth and reproduction
64
Liver storage of Vitamin D prevents deficiency for how long?
3-4 months
65
What is the function of vitamin D?
1. Increases calcium reabsorption from intestinal tract | 2. Promotes intestinal phosphate reabsorption
66
What is the function of vitamin E?
Antioxidant
67
What is the function of vitamin K?
Necessary for production of clotting factors
68
Liver storage of vitamin B12 prevents deficiency for how long?
Over a year
69
What is the function of vitamin B12?
Promotes growth and RBC formation + maturation
70
What substance is required for absorption of vitamin B12?
Intrinsic factor (produced by parietal cells of stomach)
71
What is pernicious anemia?
Malabsorption of vitamin B12 due to lack of intrinsic factor produced by parietal cells of stomach
72
Where is vitamin b12 absorbed?
In the terminal ileum
73
Where is glycogen stored in the body?
1. Liver (~10% of mass) 2. Skeletal muscle (~2% of mass) (More stored in skeletal)
74
What is the function of glycogen?
Readily mobilised storage form of glucose - maintains blood glucose levels
75
Glycogen is the secondary energy reservoir. What is the primary source?
Lipids
76
Which minerals are stored in the liver?
1. Iron (as ferritin) | 2. Copper
77
How is most of the body's fat stored?
In adipocytes, which form tissues called adipose tissue
78
What are the four main body energy reserves? How many calories in each?
Blood glucose - 40kcal Glycogen - 600kcal Muscle - 25,000kcal Lipid reserve - 100,000kcal
79
What are the 4 main body energy reserves? How long does each last?
Blood glucose - few mins Glycogen - day Muscle - week Lipid reserve - month
80
What are triglycerides composed of?
3 fatty acid chains bound to a glycerol backbone
81
Triglycerides account for what percentage of the energy stored in the body? Proteins? Carbs?
TGs- 78% Proteins - 21% Carbs - 1%
82
What are the 3 main lipoproteins, and where are they synthesised?
1. HDL - liver 2. LDL - plasma 3. VLDL - hepatocytes (Also IDL)
83
What do lipoproteins do?
Transport cholesterol through the blood
84
What 3 main types of proteins are synthesised by the liver?
Plasma proteins Clotting factors Complement factors
85
What are lipids?
Esters of fatty acids and certain alcohol compounds
86
Give 3 functions of lipids
1. Energy reserves 2. Structural (part of cell membrane) 3. Hormone metabolism
87
How are dietary fats in the small intestine converted to fatty acids in cells? Give 8 steps.
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
Explain fat catabolism (ie the breakdown of fatty acids into CO2 and ATP)
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 5. Another CoA attaches to FA and cycle repeated 6. Coenzyme - 2H molecules lead to production of CO2 and ATP via Krebs cycle and OXPHOS
89
Name 2 enzymes involved in the hepatic metabolism of lipids
1. Lipoprotein lipase | 2. Hepatic lipase
90
What does lipoprotein lipase do?
Hydrolyses TGs in lipoproteins (chylomicrons, VLDL) into 2 FFAs and 1 glycerol
91
What does hepatic lipase do? Where is it expressed?
Converts IDL into LDL | Expressed in liver and adrenal glands

Liver (2 decks)

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