Liver

External structure and surfaces

Anatomically, the liver is a voluminous organ that traditionally features two main surfaces:

1. Diaphragmatic surface (facies diaphragmatica). It is completely smooth, convex, and closely matches the shape of the diaphragmatic dome, which it firmly adheres to. This surface clearly shows the division of the organ into the right and left lobes (lobus hepatis dexter et sinister). The boundary between them is the falciform ligament (lig. falciforme hepatis). Also located here are the coronary ligament (lig. coronarium hepatis) and the paired triangular ligaments (ligg. triangulare dextrum et sinistrum).
2. Visceral surface (facies visceralis). Facing downward toward the abdominal organs, it has an uneven relief with impressions from neighboring structures. It is characterized by a complex system of fissures: the groove for the inferior vena cava (sulcus venae cavae), the fissure for the round ligament of the liver (sulcus ligamenti teretis), and the fissure for the ligamentum venosum (sulcus ligamenti venosi).

Porta hepatis and lobes of the visceral surface

The central landmark of the visceral surface is the porta hepatis (porta hepatis). This is a peculiar "checkpoint" through which major vascular pathways pass.

Structures entering the organ through the porta hepatis:

• portal vein (v. portae);
• proper hepatic artery (a. hepatica propria);
• nerve plexuses.

Structures exiting the porta hepatis:

• common hepatic duct (ductus hepaticus communis);
• lymphatic vessels.

The system of fissures on the visceral surface divides the liver tissue not into two, but into four lobes. In addition to the classic right and left lobes, the quadrate lobe (lobus quadratus) and the caudate lobe (lobus caudatus) are clearly distinguished.

Internal structure and hepatic lobule

Externally, the organ is protected by a serous membrane (tunica serosa), beneath which lie the subserous layer and the dense fibrous capsule (tunica fibrosa). This connective tissue not only covers the organ but also penetrates its parenchyma through the porta hepatis and the fissure of the round ligament. Accompanying the bile ducts and blood vessels, it forms the perivascular fibrous capsule (capsula fibrosa perivascularis), creating a robust internal framework.

The structural and functional unit of the organ is the hepatic lobule (lobulus hepaticus). This is a microscopic structure measuring only 1–2 mm. It is formed by liver cells (hepatocytes) arranged in rows — hepatic plates (laminae hepaticae).

Blood flow in the lobule is uniquely arranged. Interlobular arteries and veins run along the periphery, giving rise to capillaries. These transition into sinusoidal vessels (vasa sinusoidea) located between the plates. It is within the sinusoids that the crucial process of mixing oxygen-rich arterial blood and nutrient-dense venous blood from the portal vein takes place. The mixed blood heads toward the center of the lobule and collects into the central vein (v. centralis). Subsequently, the central veins merge into sublobular veins, which in turn form the right, middle, and left hepatic veins.

Segmental anatomy of the liver

The external division into anatomical lobes does not coincide with the internal distribution of blood flow. Modern surgical anatomy uses the concept of segmentation, which is based on the branching of intraorgan portal system vessels and bile ducts.

First-order branches of the portal vein divide the organ into the right, left, and posterior parts. The boundaries between them are hidden internally and project onto the gallbladder fossa and the groove for the inferior vena cava.

Second-order branches supply isolated areas:

• right medial and right lateral areas;
• left medial and left lateral areas.

Segments are formed from these areas. The right and left lateral areas are further divided into anterior and posterior segments. Meanwhile, the left medial area consists of only a single segment. The posterior part of the organ, which anatomically corresponds to the caudate lobe, also constitutes a single independent segment.

Topography and syntopy

The liver occupies a vast space in the upper storey of the abdominal cavity: it is located in the right hypochondriac region, occupies the epigastrium, and extends with its left edge into the left hypochondriac region.

Skeletotopy of the liver:

• Upper boundary: on the right along the midclavicular line, it reaches the level of the 4th intercostal space, and on the left, its highest point is at the level of the 5th intercostal space.
• Lower margin: on the right along the midclavicular line, it descends to the 10th intercostal space, then runs along the right costal margin, crosses the epigastrium, and passes under the left costal margin at the level of the 8th left costal cartilage.
• Posterior boundary: on the right along the scapular line, it projects between the 7th intercostal space and the upper margin of the 11th rib.

Syntopy (relation to adjacent organs): With its smooth diaphragmatic surface, the liver is in contact with the right and partially left domes of the diaphragm. The visceral surface is in contact with a number of organs: the cardia, body, and pylorus of the stomach, the superior part of the duodenum, the right kidney, and the right colic flexure and right end of the transverse colon. In addition, the gallbladder closely adheres to the inner surface of the right lobe.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Histological structure of hepatic plates and hepatocytes
• Detailed diagram of portal system vessel branching within segments
• Ligamentous apparatus of the liver and its peritoneal reflections
• Features of bile formation and drainage via intrahepatic ducts
• Formation of the right, middle, and left hepatic veins

Other topics in "Splanchnology / Digestive System"

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