Liver

The liver is a vital organ of the digestive system. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion. The liver is necessary for survival. 

The liver is a soft, pinkish-brown, triangular organ. It is both the largest internal organ (the skin being the largest organ overall) and the largest gland in the human body. It is located in the right upper quadrant of the abdominal cavity, resting just below the diaphragm. The liver lies to the right of the stomach and overlies the gallbladder. It is connected to two large blood vessels, one called the hepatic artery and one called the portal vein. The hepatic artery carries blood from the aorta, whereas the portal vein carries blood containing digested nutrients from the entire gastrointestinal tract and also from the spleen and pancreas. These blood vessels subdivide into capillaries, which then lead to a lobule. Each lobule is made up of millions of hepatic cells which are the basic metabolic cells. Lobules are the functional units of the liver.

The diaphragmatic surface of the liver is the smooth, superior part of the organ that is in contact with the diaphragm. The potential space between the diaphragmatic surface of the liver and the inferior surface of the diaphragm is the subphrenic space. The inferior surface of the liver (opposite the diaphragmatic surface) is the visceral surface.

The liver is normally divided into two lobes (left and right lobes), if viewed from the parietal surface; but if observed on the visceral surface it is divided into four lobes with the addition of the caudate and quadrate lobes. Other anatomical landmarks exist, such as the ligamentum venosum and the round ligament (ligamentum teres) that further divide the left side of the liver in two sections. The falciform ligament is visible on the front (anterior side) of the liver. This divides the liver into a left anatomical lobe, and a right anatomical lobe.

The liver gets a dual blood supply from the hepatic portal vein and hepatic arteries. Supplying approximately 75% of the liver's blood supply, the hepatic portal vein carries venous blood drained from the spleen, gastrointestinal tract, and its associated organs. The hepatic arteries supply arterial blood to the liver, accounting for the remainder of its blood flow. Oxygen is provided from both sources; approximately half of the liver's oxygen demand is met by the hepatic portal vein, and half is met by the hepatic arteries. Blood flows through the liver sinusoids and empties into the central vein of each lobule. The central veins coalesce into hepatic veins, which leave the liver.