Just below the diaphragm in the epigastric and hypochondriac regions of the abdomen, is the largest internal organ of the adult human body; the liver. Weighing in between 3 ½ and 4 pounds, the liver is reddish brown in appearance due to its high level of vascular consumption. It is segregated into four distinct lobes and is held in position by two supporting ligaments. Along the anterior portion, the right lobe is noticeably segregated by the falciform from the smaller left lobe. Along the inferior section, the inferior vena cava creates the boundary between the caudate lobe and the quadrate lobe, which is adjacent to the gall bladder. The liver is held to the wall of the abdomen by the falciform ligament. This ligament also holds the liver to the diaphragm. Reaching from the falciform ligament, the round ligament (or the ligamentum teres) holds the falciform to the umbilicus. This ligament was once the umbilical cord that fed the human as an embryo.


Despite its claim as the largest internal organ the liver is in all reality only about two cells thick. Liver cells, known alternatively as hepatocytes, create one or two cell thick plates known as hepatic plates. These hepatic plates are kept segregated from each other by hepatic sinusoids. These sinusoids form significant capillary spaces between the plates. The sinusoids are also more permeable than other capillaries found in the body due to the phagocytic Kupffer cells which line the sinusoids. The combination of the structure of the plates and the level of permeation of the sinusoids permits contact with the blood by every hepatocyte in the liver. The plates are designed to create structural necessity, and they do as they form the liver lobules. A central vein can be found within each lobule. The peripheral edge of each lobule also houses a branch of the hepatic portal vein and the hepatic artery. The result is a wider space between each hepatic plate. Portal venous blood, which hosts molecules from the absorption in the GI tract mixes with arterial blood as the blood travels through the liver sinusoids, which originated in the periphery of the lobule to the central vein. The hepatic vein is actually created by the various central veins of the liver lobules. The hepatic vein is responsible for transporting blood to the vena cava.


Image: Liver


The liver lobules are multi-functional. They are responsible for the synthesis of vitamins, along with their storage and their eventual release into the bloodstream as well as the release of glycogen. The liver lobules are additionally responsible for the creation of blood proteins. The liver lobules are able to remove toxic substances from the body as well as accomplish the phagocytosis of certain bacteria and all old red blood cells, and of course, bile production.

The gall bladder is the storage unit for the bile that the liver produces, where it is eventually emptied into the duodenum where it can continue the digestion process by breaking food down into its molecular structure. Hepatocytes are the liver cells which create the bile, which is then drained into the gall bladder for storage via the tiny ducts known as bile canaliculi. These tiny ducts are found within every hepatic plate. The bile ducts ultimately drain into the hepatic ducts, and the hepatic ducts take the bile from the liver. Within the hepatic plates, blood flows in one direction and bile flows in the other. It is of vital importance that the blood and the bile remain segregated from each other.

The vagus nerves deliver parasympathetic innervation to the liver, while the liver in sympathetically innervated by the thoracolumnar nerves via celiac ganglia.
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