Anatomy And Physiology

Anatomy Physiology



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The liver is a very important organ in the human body due to its pivotal role in monitoring homeostasis and keeping constant environment in the body.  This importance is manifested by the many functions that it has in the body such as proteins synthesis in addition to many other functions that will be discussed sequentially.


The liver in humans is situated in the right side of the abdomen below the diaphragm.  It is a unique structure in the body due to its unique blood supply.  The liver in contrast to other organs in the body has dual or two sources of blood supply.  These are:  The hepatic artery and the portal vein. 


The hepatic artery is a branch of the aortic artery that brings blood that is full of oxygen to the liver from the lungs which is required for liver cells reparation.  The portal vein is a vein which comes from the gastrointestinal tract including the intestine and the digestive organs such as the pancreas. 


This vein carries nutrients to the liver that are digested and degraded and absorbed in the small intestine.  In addition, any toxic material and microbes that succeed to penetrate the epithelial barrier of the digestive tract are entered into the liver sinuses where they are trapped and neutralized by the immune system of the liver that is located in the blood sinuses that are typical of the liver.  These toxic materials and microbes are trapped by macrophage cells that neutralize these offensive agents.   


The liver has many functions in the body that it is not possible for humans to live without it.  The normally functional liver can be removed up to 80% of its size and yet conserve its functional capacity to normal.  One of the important functions of the liver is the synthesis of proteins from amino acids. 


Proteins such as the important class of immunoglobolins  are synthesized in the liver such as the protein alpha1 antitrypsin which has a clinical significance in the lung disease of emphysema.  Especially important is the synthesis and secretion of the protein albumin.  Albumin is an important protein in the blood due to its role or function in maintaining an appropriate osmotic colloid pressure within the arteries.


In the case of liver pathology in which proteins synthesis is diminished this deficiency in the blood causes decreased colloid osmotic pressure in the blood which can cause edema in the body.  Therefore if a patient suffers from skin edema one should suspect liver disease in addition to the other possible causes of hypertension and inflammation. 


The liver also synthesizes proteins which are responsible for the the clotting of blood.  These proteins are important to maintain hemostasis in the case of bleeding.  In addition the liver synthesizes an important hormone which stimulates platelets formation and which is called thrombopoietin.   For this reason the lack of these clotting factors in the case of liver dysfunction can lead to bleeding disorders in the body so that one person can bleed easily. 


The liver is also the site of of glucose storage in the body.  It is stored there in the form of the polymer glycogen which is degraded upon stimulation of hypoglycemia or upon stimulation by the sympathetic nervous system.  The process of glucose synthesis from amino acids occurs also in the liver in addition to the kidney.  Fatty acids metabolism and oxidation also occur in the liver in an energy producing process that leads to the formation of energy rich molecules that are called ATP.


The liver is also known for its role in the synthesis of bile which is secreted from the liver to the gallbladder.  Bile includes the pigment bilirubin which is produced in the liver and in cases of red blood cells hemolysis from the molecule hemoglobin.  The liver is usually enlarged in pathologic conditions which have clinical significance.    

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