The liver is a wedge-shaped, reddish-brown organ that is considered the second largest organ in the human body after the skin. It is located below the diaphragm, to the right of the stomach. It occupies most of the right upper quadrant (right hypochondrium) and epigastrium, often extending as far as the left upper quadrant (left hypochondrium). The size and weight of the liver varies according to sex, age, and body size. In an adult individual, it weighs an average of 1.5 kg, which accounts for approximately 2.5% of the adult body weight.
Functionally, the liver serves as a gland and performs many metabolic activities required for homeostasis, nutrition, and immune defense. It also secretes bile, a yellow-brown or dark green fluid that helps in the emulsification of fat in the small intestine.
The liver has both a diaphragmatic surface that runs in anterior, superior, and posterior directions; and a visceral surface that runs in an inferior direction. The diaphragmatic surface is smooth and domed. This is related to the concavity of the inferior surface of the diaphragm, which separates it from the pleurae, the lungs, the pericardium, and the heart.
The visceral surface, unlike the diaphragmatic surface, bears multiple fissures. It is molded by the shape of the organs surrounding it, resulting in an irregular and flat shape. The visceral surface reflects the liver’s relation with the esophagus, the right kidney, the right adrenal gland, the right colic flexure, the lesser omentum, the duodenum, the gallbladder and the stomach.
There are various ligaments formed by a double layer of peritoneum that attach the liver to its surrounding structures. The falciform ligament attaches the anterior surface of the liver to the anterior abdominal wall. The hepatogastric ligament connects the liver to the stomach, the hepatoduodenal ligament connects the liver to the duodenum, and the triangular and coronary ligaments connect the liver to the diaphragm. Moreover, fibrous tissue and hepatic veins secure the posterior surface of the liver to the inferior vena cava.
Divisions and relations
The liver is covered by a fibrous capsule termed the Glisson’s capsule. Its ligaments and surface depressions divide the liver into four lobes. The falciform ligament divides the liver into a right and left lobe. The right lobe is larger than the left; it has the accessory quadrate and caudate lobes arising from it. The quadrate lobe is located on the lower anterior part of the visceral surface. It is bounded on the left by the fissure for the ligamentum teres, and on the right by the gallbladder fossa. Functionally, it is related to the left lobe. The caudate lobe is located on the upper posterior aspect of the visceral surface. It is bounded on the left by the fissure for the ligamentum venosum, and on the right by the groove of the inferior vena cava. Between the quadrate and caudate lobes is a deep fissure termed the porta hepatis. The porta hepatis serves as a point of entry for all the vessels, nerves, and ducts of the liver.
In terms of neurovasculature, liver is unique. This organ receives more venous blood than arterial blood, and this is due to the fact that it helps clean the blood via detoxification. The portal vein transports deoxygenated, nutrient-rich blood from the gastrointestinal tract, and blood from the spleen, pancreas and gallbladder to the liver.
While the right and left hepatic arteries, which originate from the celiac trunk, provide the arterial blood, the venous drainage of the liver flows primarily through three hepatic veins, which drain into the inferior vena cava.
The liver has dual innervation supplied by the hepatic nerves arising from the hepatic plexus, containing sympathetic and parasympathetic vagal fibers; and the branches arising from the lower intercostal nerves.