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Overview of the Liver

• The liver is capable of regeneration, particularly interesting because it involves tissues studied through mitosis and the cell cycle.

• Unlike skin, liver cells (hepatocytes) do not turnover as frequently, but they can regenerate when necessary.

• The liver may become quiescent (inactive) for a period but can stimulate growth if a portion is removed.

Location and Size

• The liver is primarily located in the upper right quadrant of the abdomen. It sits low on the right side and is the largest solid organ, weighing approximately 3.3 pounds.

• It is often referred to as the largest gland, although not everyone categorizes it as a gland due to varied structural functions.

Anatomical Structure

• The liver has two main lobes (right and left) separated by a significant ligament known as the falciform ligament.

• The round ligament is a remnant of the umbilical cord that connects to the lower abdominal wall, anchoring the liver in place.

• The anatomy can be complex due to its three-dimensional structure, making it easier to understand with a 3D model rather than a 2D diagram.

Posterior vs. Anterior Views

• A posterior view reveals structures like the gallbladder and inferior vena cava.

• The gallbladder can help identify the quadrate lobe, positioned adjacent to it. The caudate lobe is found near the inferior vena cava.

Ligaments Supporting the Liver

• The coronary ligament supports the liver's connection to the upper abdominal wall and diaphragm, preventing it from dropping into the pelvis.

• The peritoneum is a multi-layered covering that provides protection and reduces friction.

Histological Structure

• Liver tissue comprises repeated units called lobules, each with a portal triad consisting of a portal vein, hepatic artery, and bile duct.

• Sinusoids are specialized blood vessels where oxygen-rich blood from the hepatic artery and nutrient-rich blood from the portal vein mix, allowing hepatocytes to process nutrients.

Blood Input into the Liver

• The liver receives two blood supplies:

  • Hepatic artery (oxygen-rich blood)

  • Hepatic portal vein (nutrient-rich, deoxygenated blood from the intestines)

• The liver processes these nutrients, detoxifies blood, stores glycogen, and produces bile.

Functions of the Liver

• Carbohydrate Metabolism: The liver stores glucose as glycogen (via glycogenesis) and can convert non-carbohydrate sources back into glucose (gluconeogenesis).

• Protein Metabolism: The liver produces vital proteins like albumin and clotting factors, stores amino acids, and is involved in the conversion of excess amino acids to urea for excretion.

• Lipid Metabolism: The liver synthesizes cholesterol and lipoproteins for hormone production and bile formation.

• Drug Metabolism: The liver modifies and activates many medications, with an important process called the first pass effect, where drugs are metabolized before entering systemic circulation.

Bile Production and Pathway

• Bile is produced from the breakdown of red blood cells (and bilirubin) in hepatocytes and travels through bile canaliculi into the bile ducts.

• Bile flows from the right and left hepatic ducts, merging into the common hepatic duct, and can go towards the duodenum or be stored in the gallbladder.

• The gallbladder stores bile until needed, at which point it is released into the common bile duct, mixing with pancreatic juices for digestion in the small intestine.

Pathology of the Liver

• Liver failure poses significant health risks due to extensive metabolic responsibilities. High alcohol intake can lead to liver damage.

• Functions tested through liver panels (checking enzyme levels) can indicate liver function and damage extent. Elevated enzymes typically signal liver distress.

Understanding Viruses

• Viruses are obligate pathogens dependent on a host for replication and survival.

• They have a nucleic acid core (DNA or RNA) surrounded by a capsid and may have an envelope made from lipids.

• Viruses attach to host cells using specific receptors and complete a series of steps to replicate, infect other cells, and spread infection.

Tissue Tropism in Virology

• Tissue tropism refers to a virus's specific affinity for infecting certain cell types, such as hepatitis viruses primarily targeting liver cells.

• Understanding this concept can help in identifying how specific viruses propagate and affect the body.