27.24 : Liver Histology

The microscopic anatomy of the liver is a complex and intricate system that comprises numerous structural units known as liver lobules, each of which is comparable in size to a sesame seed. These hexagonal structures consist of plates of liver cells or hepatocytes, which are characterized by their versatility and abundance of cellular apparatus like rough and smooth ER, Golgi apparatus, peroxisomes, and mitochondria.

Hepatocytes perform a variety of essential functions. They secrete approximately 900 ml of bile daily and process bloodborne nutrients in several ways. For instance, they store glucose as glycogen and utilize amino acids to produce plasma proteins. They also play a pivotal role in detoxification, converting harmful ammonia in the blood into urea.

The liver lobule's structure is such that hepatocyte plates radiate outward from a central vein. At each corner of the lobule is a portal triad comprising a branch of the hepatic artery, a branch of the hepatic portal vein, and a bile duct. This arrangement ensures the delivery of oxygen-rich arterial blood and nutrient-laden venous blood to the liver.

Between the hepatocyte plates lie enlarged, heavily fenestrated liver sinusoids. Blood from both the hepatic portal vein and the hepatic artery proper flows through these sinusoids and empties into the central vein. Eventually, this blood enters the hepatic veins, which drain the liver and empty into the inferior vena cava.

Stellate macrophages, also known as hepatic macrophages or Kupffer cells, form part of the sinusoid walls. These star-shaped cells help filter the blood by removing debris, such as bacteria and worn-out blood cells.