The Liver is considered as an accessory digestive organ, together with the pancreas and the gallbladder. Although it has other metabolic and regulatory roles, when talking about the digestive system it is classified as an accessory. The main function of the liver with respect to digestion is the production of bile, a fat emulsifier, which helps in the breakdown of fat so it is easier for the digestive enzymes to further break down the fats and making it ready for absorption.
The functional unit of the liver is called the liver lobules. It has the size same as that of a sesame seed. The liver lobules have a distinctive hexagonal structure and within this structure lies the hepatocytes or liver cells. In each corner of the hexagonal structure of the lobule, the portal triad can be seen. It is named as such because the hepatic artery, hepatic portal vein and a bile duct are always present in the area.
Liver sinusoids are enlarged, leaky capillaries found in between hepatocyte plates. The blood coming from the hepatic artery and the hepatic portal vein seep towards the triad regions by way of these sinusoids which then empties into the central vein. The blood collected in the central vein will then enter the hepatic veins, drains the liver and then finally empties into the inferior vena cava.
Kupffer cells are star-shaped hepatic macrophages which functions to removes debris such as worn-out blood cells and bacteria as the blood flow past.
Large amounts of both smooth and rough endoplasmic reticulum, mitochondria and peroxisomes can be found in the hepatocytes, thus allowing them to function in a versatile way. Aside from the production of bile, the hepatocytes can also make use of amino acids for the body to make plasma proteins. They can also store glucose as glycogen. The hepatocytes are also active in the storage of fat-soluble vitamins and play a critical role in detoxification.
Detoxification by the hepatocytes is done by converting the free ammonia to urea. With all of the functions and actions mentioned, the blood that leaves the liver contains fewer nutrients and fewer waste materials compared to the time it entered the liver.
The rich supply of blood to the hepatocytes enables the liver to regenerate back to its former size even after a loss of over 70% of its normal size. This is possible due to the abundance of blood supply to the hepatocytes, allowing them to release VEGF or vascular endothelial growth factor during liver injury. The VEGF then binds to specific receptors in the sinusoids. The endothelial cells, found on the lining of the sinusoids, proliferate then enable the release of interleukin 6 and hepatocyte growth factor. The release of these growth factors then triggers the hepatocytes to multiply exponentially, replacing the dead and dying liver tissues.