The Lovely Liver

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Basic Histology of Liver

The Liver consists of lots of tissue consisting of liver cells and Kupffter cells. 

Liver cells:

  • Simple Cuboidial shape. 
  • Have many microvilli on the surface. 
  • Dense cytoplasm due to the liver carrying out many functions. 

Kupffer cells:

  • Specialised macrophages.
  • Involved in the breakdown and recycling of old red blood cells
  • One of the products is bilirubin, which is the brown pigment in faeces. 
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Humans need roughly 4-6 tablespoons of protien a day. However what happens to the rest of it? Well the amine group is actually toxic in large quantites so it needs to be excreted, However the amino acid group actually has a lot of energy so we need to ensure that we only excrete the amino group. 

The first stage of this process is known as deamination which is a reletively simple reaction:

Amino Acid + Oxygen --> Keto Acid + Ammonia.

A keto acid is any acid with a ketone group on a carbon seperate to the carbon with the carboxylic acid group. 

However we have to do another process after this because Ammonia is both soluble and toxic (yep remember that next time you die your hair). So we have to then process the ammonia to make Urea via the Ornithine cycle

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The Ornithine Cycle

As we learnt from the previous card, the deamination process makes a keto acid and ammonia. Ammonia however is very toxic and thus must be converted to a less toxic form quickly. This is done via the ornithine cycle. 

This does sound slightly complex however if you remember A Catch An Ugly Otter then you'll remember that the cycle goes Citrulline, Arginine, Urea and finally Ornithine before it goes back to the start. The cycle always contines as long as there is ammonia to be converted. The cycle in general can be summerised as simply:

Ammonia + Carbon dioxide --> Urea (CO(NH2)2 ) and water. 

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The liver is clever . It can detox hydrogen peroxide into safer substances and can do the same for alcohol. It can do this via a series of chemical reactions with enzyme catalysts (see As if you forgot what enzymes were). 

For this card we'll take ethanol or the alcohol that you may drink on a saturday night. Because of the bonds present, ethanol actually has alot of chemical potential energy, which can be used for respiration. To do this we have to do alot of oxidation. 

Ethanol is a primary alcohol (for non-chemists this means that there is only one carbon attached to the carbon with the OH group present) this means that in the presence of ethanol dehydrogenase, it is reduced to ethanal (an aldehyde). Any aldehyde can be oxidised further to make a carboxylic acid and Ethanal is no different, in the presence of ethanal dehydrogenase (really original) it is oxidised to ethanoic acid (vinegar to you). Ethanoic acid then reacts with a spare coenzyme A to form acetyl coenzyme A which is then used in repriration. The hydrogens that are lost in the oxidation process then react with NAD to make reduced NAD  which is used to break down fatty acids. 

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Quick summery (or last minute panic card).

  • Liver cells have lots of microvilli and are a basic cuboidal shape.  Used in protien synthesis, transformation/storage of carbohydrates, synthesis of cholestrol and bile and detoxification. 
  • Kupffer cells are involved in the breakdown/ recycling of old red bllod cells. One product is bulirubin which is the brown pigment in faeces
  • Urea is formed via a 2 stage process: deamination followed by the ornithine cycle.
  • In deamination an amino acid reacts with oxygen to make keto-acid and ammonia.
  • The ammonia is the converted via the ornithine cycle. 2 molecules of ammonia react with carbon dioxide to make urea and water. 
  • Ethanol is detoxified via lots of oxidation reactions. Firstly in the presence of ethanol dehydrogenase, it is oxidised to ethanal. The ethanal is the oxidised in the presence of ethanal dehydrogenase to make ethanoic acid. The ethanoic acid then reacts with coenzyme A to make acetyl coenzyme A
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