Overview of Liver Physiology

Liver physiology centers mainly around metabolism of important biomolecules in the body such as glucose, in addition to metabolism of medications and drugs that are administered for therapeutic purposes and which are detoxified in the liver there are certain types of liver cells such as kupffer cells and hepatocytes.

The liver blood supply is unique in comparison  to blood supply for other organs in the body.  There are two blood supplies to the liver.  One through the hepatic artery which carries oxygenated blood from the lungs to the liver.  This artery does not have an apparent role in supplying the liver with nutrients.

The other blood supply to the liver is from arteries that originate from the intestine and other organs  and which supply nutrients to the liver in addition to other harmful compounds, which are absorbed in the intestine such as medications.

In the liver these harmful compounds and bacteria that succeed to enter the circulation via the intestinal wall are trapped in the liver sinuses  where they are metabolized  by the immune cells of the liver which are called kupffer cells. 

The liver is the main site for the metabolism of glucose in the body.  Glucose is metabolized in the liver by a process which is called glycolysis and which generates energy rich molecules called ATP.

The excess glucose in the blood such as occurs after a meal that is rich in carbohydrates is converted to the biopolymer glycogen.  Glycogen is stored in the liver and is degraded back to its glucose units upon stimulation by the sympathetic nervous system when there is a state of hypoglycemia or low blood levels of glucose such as occurs in starvation.

The level of glucose in the blood is mainly monitored in the liver by a hormone that is called glucagon.  This hormone is secreted by the pancreas in response to low level of glucose in the blood.  This hormone stimulates the degradation of glycogen into glucose units. 

Along with this hormone that is secreted by the pancreas there is also another hormone which is called insulin and which is also secreted by the islet cells of the pancreas.  Insulin is an antagonist to the action of glucagon and functions by removing excess glucose in the blood by converting it to its polymer glycogen. 

In the case of deficient levels of glucose in the blood the liver in addition to the kidney uses a mechanism that is called gluconeogenesis.  This mechanism produces glucose from metabolizing amino acids to glucose. 

In the case of hepatorenal failure or insufficiency a state of hypoglycemia can occur due to the lack of this mechanism in both the liver and the kidney. 

The liver also metabolizes fatty acids into ketone bodies in the case of diabetes.  Therefore, one of the symptoms of diabetes in affected individuals is that they have a urine sample that smells like acetone. 

In addition to its role in metabolism the liver has a role in synthesis of important  proteins such as immunoglobulins.  In addition clotting factors are also synthesized in the liver.  A sign of liver failure is obtained when there is a hemorrhage or skin purpura.

The liver also synthesizes the important protein albumin.  This protein is important for maintaining the blood oncotic pressure.  Its deficiency as occurs in hepatic failure can lead to  low oncotic pressure which can lead subsequently  to the accumulation of fluid in the interstitial space between the cells, the so called edema.

Bile is also synthesized in the liver and is secreted to the small intestine through the gallbladder canals.  Bile helps in the digestion process of food in the intestine by emulsifying lipids there.