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.
The liver comprises several histological components, such as hepatocytes, bile canaliculi, and sinusoids.
Hepatocytes are specialized epithelial cells that are arranged in highly branched, irregular, three-dimensional plates called hepatic laminae.
Their primary function is to assist in blood detoxification and to secret bile.
Hepatocytes secrete bile into small ducts called bile canaliculi. From here, bile flows into bile ductules and subsequently into larger bile ducts.
Present on the edge of the laminae is a collection of bile ducts, branches of hepatic arteries, and hepatic portal veins called a portal triad.
Liver sinusoids, present between the rows of hepatocytes, collect blood from the portal triads, eventually emptying into the central vein.
Blood enters the hepatic veins from the central veins, which empty into the inferior vena cava.
The sinusoid walls also have stellate or hepatic macrophages that filter blood by removing debris and worn-out blood cells.
There are many anatomical ways in which hepatocytes, portal triad, and sinusoids can be arranged the most accepted of which is the hepatic acinus.
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