liver as a storage organ Flashcards
how is excess glucose stored
in the liver as glycogen
what stimulates glucose storage
insulin releaseq
how much of glycogen is stored in the liver
around 100g
how much of glycogen is stored in skeletal muscle
300g
describe process of synthesis of glycogen
- Glucose is converted to Glucose-6-P by glucokinase (hexokinase in skeletal muscle)
- Glucose-6-P is converted to Glucose-1-P by phosphoglucomutase
- Glucose-1-P is then converted to UDP-Glucose
- Finally UDP-glucose is added to the glycogen chain within the liver either by glycogen synthase or branching enzym
what are the lipid soluble vitamins
A, D, E , K
where are lipid soluble vitamins stored
in the liver
how is vitamin A stored
stored within stellate cells in the liver as retinyl ester
what is the active form of vitamin A
retinol
how is the active form of vitamin A converted to the storage form
by lecithin:retinol acyltransferase.
this provides an easily retrievable source of Vitamin A and regulates its availability for other pathways
what is retinol recycling
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
functions of vitamin A (4)
- Formation of the photoreceptor rhodopsin
- Signalling molecule within gene transcription
- Normal function of the immune system
- Mobilisation of iron stores for red blood cell production
sources of vitamin D
either produced in body - (cholecalciferol)
or
found in food - (ergocalciferol)
what happens to vitamin D in the liver
it must be metabolised in the liver before becoming the active form
functions of vitamin D (3)
- Maintaining normal serum calcium and phosphate concentrations
- Increased absorption of calcium in the kidneys and intestines
- Increased mobilisation of calcium from bone , activating osteoclasts to release more calcium
what is vitamin E
a family containing various chemicals, including anti-oxidants.
where is vitamin E stored
in either the liver or adipose tissue
functions of vitamin E (3)
- Antioxidant
- Preventing propagation of free radicals
- Protects Vitamin A
how many forms of vitamin K are there
there are two forms of Vitamin K depending on whether they are obtained from plant or meat sources.
functions of vitamin K (2)
- Important for synthesis of clotting factors II, VII, IX and X
- Co-factor for enzymes
where is vitamin B12 typically found
in animal products
how much of vitamin B12 is stored in the body
2-5%
with around 50% of this being in the liver
functions of vitamin B12 (3)
- Production of DNA and RNA
- Maintaining healthy neurones
- Red blood cell production – alongside Vitamin B9
which minerals are stored in the liver
iron and copper minerals
why is excess iron stored in the liver
because iron levels within the body need to be tightly regulated
where is most iron within cells stored
in ferritin - a protein produced by the liver.
All cell types within the liver can store iron however the majority is stored within hepatocytes.
what happens in severe iron overload
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.
why do water-soluble vitamins require more regular intake than fat-soluble vitamins
because they pass more readily through the body
why is iron essential
used in haemoglobin, myoglobin & bone marrow
sources of iron
meat, liver, shell fish, egg yolk, beans, nuts and cereals
where is homeostatic control of iron balance
in the intestinal epithelium, in the DUODENUM - which actively absorbs IRON from ingested foods
how much of ingested iron is absorbed into blood stream
about 10% each day
how are iron ions transported to duodenum
via active transport
into the duodenal intestinal epithelial cells
what happens to iron ions in duodenum
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
what does iron absorption depend on
the body’s iron content
what happens when the body has stored enough iron
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
what happens when body has low iron levels
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
what happens to unbound iron released into the blood
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)
how much of total iron is haemoglobin
50%
how much of iron is in heme containing proteins (mainly cytochromes)
25%
how much of iron is in liver ferritin
25%
