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Saturday, July 29, 2017

ABDOMEN—Gross Anatomy of the Liver


The liver is an accessory organ of the gastrointestinal tract. It is a peritoneal organ, positioned in the right upper quadrant of the abdomen, and is the largest visceral structure in the abdominal cavity.
The liver performs a wide range of functions, including synthesis of bile, glycogen storage and clotting factor production.
Diagram
Image result for liver

Anatomical Position and Relations

The liver is located in the right hypochondrium and epigastric areas, extending into the left hypochondrium.
During embryological development, the liver is formed within part of the ventral mesentery, which suspends the foregut organs from the anterior abdominal wall. This is useful for remembering the anatomical relations of the liver:
  • Anterior to the liver is the anterior abdominal wall and ribcage.
  • Superior to the liver is the diaphragm (separating the abdominal cavity from the thoracic cavity)
  • Posterior to the liver are the oesophagus, stomach, gallbladder, first part of the duodenum (the foregut-derived organs).

Liver Surfaces

The external surfaces of the liver can be classified by the structures they lie in close proximity to. There are two liver surfaces – the diaphragmatic and the visceral.
The diaphragmatic surface refers to the anterosuperior surface of the liver. It is smooth and convex, fitting snugly beneath the curvature of the diaphragm. A section of this surface is not covered by visceral peritoneum, known as the ‘bare area’ of the liver.
The visceral surface covers the posteroinferior aspect of the liver. It is moulded by the shape of the surrounding organs, making it irregular and flat. It lies in contact with the oesophagus, right kidney, right adrenal gland, right colic flexure, duodenum, gallbladder and the stomach.

Ligaments of the Liver

There are various ligaments that attach the liver to the surrounding structures. These are formed by a double layer of peritoneum.
Falciform ligament – attaches the  anterior surface of the liver to the anterior abdominal wall. The free edge of this ligament contains the ligamentum teres, a remnant of the umbilical vein.
  • Coronary ligaments (left and right) – attach the superior surface of the liver to the diaphragm.
  • Triangular ligaments (left and right) – attach the superior surface of the liver to the diaphragm.
  • Lesser omentum – consists of the hepatoduodenal ligament (extends from the duodenum to the liver), and the hepatogastric ligament (extends from the stomach to the liver).
In addition to these supporting ligaments, the posterior surface of the liver is secured to the inferior vena cava by hepatic veins and fibrous tissue.

Hepatic Recesses

The hepatic recesses are spaces between the liver and surrounding structures. They are of clinical importance, as infected fluids can collect in these areas, forming an abscess.
  • Subphrenic spaces (left and right) –  located between the diaphragm and liver, either side of the falciform ligament.
  • Subhepatic space – located between the inferior surface of the liver and the transverse colon.
  • Morison’s pouch – the posterosuperior aspect of the right subhepatic space, located between the visceral surface of the liver and the right kidney. This is the deepest part of the peritoneal cavity when supine (lying flat), and this is where fluid is likely to collect in a bedridden patient.

Arterial Supply and Venous Drainage

  • Hepatic artery proper – supplies the liver with arterial blood. It is derived from the coeliac trunk.
  • Hepatic portal vein – supplies the liver with deoxygenated blood, carrying nutrients absorbed from the small intestine. This is the dominant blood supply to the liver parenchyma and allows the liver to perform its gut-related functions, such as detoxification.
Venous drainage of the liver is achieved through three hepatic veins, which drain into the inferior vena cava.
Image result for liver

Nerve Supply

The parenchyma of the liver is innervated by the hepatic plexus, which contains sympathetic (from the coeliac plexus) and parasympathetic (vagus nerve) nerve fibres. These fibres enter the liver at the porta hepatis and follow the course of branches of the hepatic artery and portal vein.

Lymphatic Drainage

The lymphatic vessels of the liver drain into hepatic lymph nodes. These lie along the hepatic vessels and ducts in the lesser omentum, and empty in the coelic lymph nodes.

Clinical Relevance:

Percutaneous Liver Biopsy

A percutaneous liver biopsy is procedure used to obtain a sample of liver tissue. A needle is inserted through the skin to access the liver.
The biopsy is required in several clinical scenarios:
  • Abnormal LFTs of unknown cause.
  • Hepatitis C – Assessment for severity of liver fibrosis and disease progression.
  • Other liver conditions (such as Hereditary Haemochromatosis and Autoimmune Hepatitis).
  • Following liver transplantation.
During the procedure, the liver is located via ultrasound. Local anaesthetic is injected on the mid-axillary line, where on percussion there is dullness. The patient is asked to deeply expire (avoiding damage to the lungs), and the needle biopsy is taken during held expiration.
If a patient has abnormal clotting (a contraindication for the procedure), a transvenous liver biopsy can be attempted. This involves cannulating the internal jugular vein, and passing the biopsy needle through to the hepatic veins, allowing for a biopsy sample to be taken.
Liver Cirrhosis;   is often considered to be a form of liver disease and may be the only liver-related condition that many people have heard of. In fact, cirrhosis is a condition that results from permanent damage or scarring of the liver. It is the end stage of many different forms of liver disease and is known to cause a number of other health problems, including variceal bleeding, ascites and hepatic encephalopathy.
Many types of liver disease still have unknown causes but the most frequent liver diseases are generally caused by one of the following factors:
  • Viral hepatitis
    Caused by viruses that attack the liver, viral hepatitis comes in many forms. The most common forms world-wide are hepatitis A, B and C. Although hepatitis A and B can be prevented by vaccine, there is no vaccine for hepatitis C. In Canada, hepatitis C is the leading cause of liver transplants.
  • ObesityThe leading cause of liver disease in Canada is fatty liver disease linked to obesity.
  • Alcohol
    Factors such as gender, age, nationality, weight and health can affect how a person’s liver metabolizes alcohol. When the liver has too much alcohol to handle, normal liver function may be interrupted leading to a chemical imbalance. If the liver is required to detoxify alcohol continuously, liver cells may be destroyed or altered resulting in fat deposits (fatty liver) and more seriously, either inflammation (alcoholic hepatitis) and/or permanent scarring (cirrhosis). Liver cancer can also result from alcohol induced liver disease.
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