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liver & friends lectures > liver as a storage organ > Flashcards

liver as a storage organ Flashcards

1
Q

how is excess glucose stored

A

in the liver as glycogen

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2
Q

what stimulates glucose storage

A

insulin releaseq

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3
Q

how much of glycogen is stored in the liver

A

around 100g

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4
Q

how much of glycogen is stored in skeletal muscle

A

300g

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5
Q

describe process of synthesis of glycogen

A
  1. Glucose is converted to Glucose-6-P by glucokinase (hexokinase in skeletal muscle)
  2. Glucose-6-P is converted to Glucose-1-P by phosphoglucomutase
  3. Glucose-1-P is then converted to UDP-Glucose
  4. Finally UDP-glucose is added to the glycogen chain within the liver either by glycogen synthase or branching enzym
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6
Q

what are the lipid soluble vitamins

A

A, D, E , K

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7
Q

where are lipid soluble vitamins stored

A

in the liver

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8
Q

how is vitamin A stored

A

stored within stellate cells in the liver as retinyl ester

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9
Q

what is the active form of vitamin A

A

retinol

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10
Q

how is the active form of vitamin A converted to the storage form

A

by lecithin:retinol acyltransferase.

this provides an easily retrievable source of Vitamin A and regulates its availability for other pathways

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11
Q

what is retinol recycling

A

vitamin A may be stored or removed from storage several times a day, regulating the amount in circulation and preventing damage that may occur as a result of excess

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12
Q

functions of vitamin A (4)

A
  1. Formation of the photoreceptor rhodopsin
  2. Signalling molecule within gene transcription
  3. Normal function of the immune system
  4. Mobilisation of iron stores for red blood cell production
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13
Q

sources of vitamin D

A

either produced in body - (cholecalciferol)

or

found in food - (ergocalciferol)

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14
Q

what happens to vitamin D in the liver

A

it must be metabolised in the liver before becoming the active form

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15
Q

functions of vitamin D (3)

A
  1. Maintaining normal serum calcium and phosphate concentrations
  2. Increased absorption of calcium in the kidneys and intestines
  3. Increased mobilisation of calcium from bone , activating osteoclasts to release more calcium
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16
Q

what is vitamin E

A

a family containing various chemicals, including anti-oxidants.

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17
Q

where is vitamin E stored

A

in either the liver or adipose tissue

18
Q

functions of vitamin E (3)

A
  1. Antioxidant
  2. Preventing propagation of free radicals
  3. Protects Vitamin A
19
Q

how many forms of vitamin K are there

A

there are two forms of Vitamin K depending on whether they are obtained from plant or meat sources.

20
Q

functions of vitamin K (2)

A
  1. Important for synthesis of clotting factors II, VII, IX and X
  2. Co-factor for enzymes
21
Q

where is vitamin B12 typically found

A

in animal products

22
Q

how much of vitamin B12 is stored in the body

A

2-5%

with around 50% of this being in the liver

23
Q

functions of vitamin B12 (3)

A
  1. Production of DNA and RNA
  2. Maintaining healthy neurones
  3. Red blood cell production – alongside Vitamin B9
24
Q

which minerals are stored in the liver

A

iron and copper minerals

25
Q

why is excess iron stored in the liver

A

because iron levels within the body need to be tightly regulated

26
Q

where is most iron within cells stored

A

in ferritin - a protein produced by the liver.

All cell types within the liver can store iron however the majority is stored within hepatocytes.

27
Q

what happens in severe iron overload

A

the ferritin storage becomes saturated and so excess becomes stored within haemosiderin.

However haemosiderin is a large, insoluble complex and iron stored within it is difficult to mobilise effectively.

28
Q

why do water-soluble vitamins require more regular intake than fat-soluble vitamins

A

because they pass more readily through the body

29
Q

why is iron essential

A

used in haemoglobin, myoglobin & bone marrow

30
Q

sources of iron

A

meat, liver, shell fish, egg yolk, beans, nuts and cereals

31
Q

where is homeostatic control of iron balance

A

in the intestinal epithelium, in the DUODENUM - which actively absorbs IRON from ingested foods

32
Q

how much of ingested iron is absorbed into blood stream

A

about 10% each day

33
Q

how are iron ions transported to duodenum

A

via active transport
into the duodenal intestinal epithelial cells

34
Q

what happens to iron ions in duodenum

A

some iron ions are incorporated into FERRITIN - acts as an intracellular store for iron

Most of the iron bound to ferritin in the intestinal epithelial cells is released back into the intestinal lumen when the cells at the tips of the villi disintegrate, and the iron is then excreted in the faeces

35
Q

what does iron absorption depend on

A

the body’s iron content

36
Q

what happens when the body has stored enough iron

A

the increased concentration of free iron in the plasma and intestinal
epithelial cells leads to an increased transcription of the gene encoding for ferritin

and thus an increased synthesis of ferritin protein.

results in an increased
binding of Fe in the intestinal epithelial cells and a reduction in the amount of iron released into the blood

37
Q

what happens when body has low iron levels

A

the production of intestinal ferritin
decreases resulting in a decrease in the amount of iron bound to ferritin thus
increasing the unbound iron released into the blood

38
Q

what happens to unbound iron released into the blood

A

it circulates around the body bound to the plasma protein TRANSFERRIN

Transferrin transports iron in the blood plasma to the bone marrow to be
incorporated into new erythrocytes

Once iron has entered the blood, the body has very little means of excreting it meaning it accumulates in tissues, most of the iron is stored in the LIVER in liver ferritin within KUPFFER CELLS (reticulo-endothelial macrophages)

39
Q

how much of total iron is haemoglobin

A

50%

40
Q

how much of iron is in heme containing proteins (mainly cytochromes)

A

25%

41
Q

how much of iron is in liver ferritin

A

25%

liver & friends lectures (7 decks)

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