The Major Anatomical regions, landmarks, directions and cavities of the liver
The liver is considered as the heart of the digestive system. In humans, the liver is present in the upper right quadrant pf the abdominal cavity. The liver lies below the diaphragm. The gallbladder is covered by the liver to some extent. It is a vital organ that plays an important role in the production of chemicals for digestion in humans. The liver is divided in to two lobes, the left and the right lobe respectively. The two lobes are separated by the imaginary plan called the Cantlie's line. The liver is connected by two large blood vessels, the portal vein and the hepatic artery. The portal vein is associated with the transport of digested nutrients from the spleen, pancreas, and the entire gastrointestinal tract. On the other hand, the hepatic artery is associated with the transport of blood from the aorta. Each of the blood vessels subdivide in to capillaries that form a lobule. Lobules are the functional unit of the liver and play an important role in metabolism. (Skandalakis JE, et al, 2004)
The liver is also associated with protein synthesis and detoxification. The liver is a brown-reddish organ with four lobes of unequal shape and size. A human liver is triangular, soft, and pinkish-brown in color. The human liver weighs approximately 1.44–1.66 kg. The liver is the largest gland in the human body. The human liver is also the largest internal organ (skin is the largest external organ). (Abdel-Misih SR & Bloomston M. 2010)
The cells present in the liver (Organ Syatems)
There are two main cell types in the human liver that have important roles in metabolism, digestion, and detoxification. The parenchymal cells constitute 80% of the liver volume and the non-parenchymal cells constitute around 20% of the human liver. The parenchymal cells in the human liver are also called as hepatocytes. Some of the non-parenchymal cells are hepatic stellate cells, Sinusoidal hepatic endothelial cells, and Kupffer cells. Most of the non-parenchymal cells line the liver sinusoid. However, non-parenchymal cells constitute 40% of the liver cells but only take up 6.5% of the total volume. (Bismuth H. 2013).
The chemical basis of physiologic processes in the liver
The liver is involved in many chemical physiological processes of the human body. The liver produces bile that is responsible for the digestion process. Bile is a mixture of bile salts, pigment bilirubin, water, and cholesterol. The parenchyma (hepatocytes) in the liver produce bile. Bile is stored in the gallbladder that is stimulated by the hormone cholecystokinin when the food reaches the duodenum. The fat present in the food triggers cholecystokinin that stimulates the gallbladder to release bile, Bile engulfs large masses of fat. The liver is also responsible in the digestion of worn out red blood cells. Hence, bile contains some amounts of bilirubin. The Kupffer cells breakdown red blood cells. Similarly, the liver has different physiological processes in the body that have been mentioned in the next section.
Functions of the liver: The liver is associated with different roles in the human body. Most of the functions are carried out by the parenchymal (hepatocytes) cells in the liver. Currently, there is no artificial mechanism or organ that could carry out the functions of the human liver. The liver is known to carry out more than five hundred functions in combination with other systems and organs in the human body. The liver is associated with protein synthesis. The liver also plays an important role in carbohydrate metabolism. The human liver is involved in the synthesis (Gluconeogenesis), breakdown (Glycogenolysis), and formation of glucose (Glycogenesis) in the human body. Similar to carbohydrate metabolism, the liver is responsible in lipid metabolism. Some of the important roles of the liver in lipid metabolism are cholesterol synthesis, synthesis of lipoproteins, and lipogenesis (production of triglycerides). Other than metabolism, the human liver plays important role as a storehouse and producer of chemicals, nutrients, and minerals essential for the normal functioning of the body. The liver is known to store vitamin B12, Vitamin D, Vitamin K, and Vitamin A. The liver is also associated with the production of albumin, the major component of blood serum.
The integration of the liver in maintaining homeostasis: The lungs, liver, and the kidneys are responsible in maintaining homeostasis in the human body. The liver plays an important role in the maintenance of homeostasis by regulating blood sugar levels and conversion of toxic nitrogenous waste. As mentioned earlier, the liver is responsible for digestion and aids in the regulation of sugar in the human body. The storage and release of sugar is the primary function of the liver. The excess sugar transported from the intestine by the hepatic portal vein is stored as glycogen in the liver. The excess sugar is mainly formed just after a meal. In the event that body requires sugar (during stress), the stored glycogen in the liver is converted to glucose to maintain homeostasis. The liver is also associated with the breakdown of proteins. However, the breakdown of proteins is associated with ammonia that is highly toxic to the human body. The liver converts the ammonia to urea and sent to the kidneys for filtration. Excess of ammonia in the body can lead to serious health complications. The liver maintains the toxicity levels in the body to a significant extent. Thus, the liver is responsible in maintaining homeostasis in the body by regulating blood sugar and nitrogenous wastes.
The functional relationships between the liver and the body system: The liver co-ordinates with different organs and systems of the body. The liver sends in excess of ammonia to the kidneys to help in homeostasis. Thus, both the liver and the kidney help in maintaining homeostasis in the human body. The liver co-ordinates with the immune system. As mentioned earlier, Kupffer cells in the liver breakdown worn out red blood cells. Kuppfer cells also act like phagocytic cells and engulf fungi, bacteria, parasites, and cellular debris. The liver is also known as the storehouse of many vitamins, proteins and minerals. For example, stores minerals such as copper and iron. The liver is also responsible in the production of vital protein components of the blood. For example, fibrinogen, prothrombin, and albumins. Thus, the liver is the largest internal organ with numerous functions. Cirrhosis of the liver can affect any of the functions of the liver. (Fasel, H., D., J & Schenk, A. 2013).
Abdel-Misih SR & Bloomston M. (2010). Liver anatomy. Surg Clin North Am. 2010 Aug; 90 (4):643-53.
Skandalakis JE, Skandalakis LJ, Skandalakis PN, & Mirilas P. (2004). Hepatic surgical anatomy. Surg Clin North Am. 2004 Apr; 84(2):413-35, viii.
Bismuth H. (2013). Revisiting liver anatomy and terminology of hepatectomies. Ann Surg. 2013 Mar; 257(3):383-6.
Fasel, H., D., J & Schenk, A. (2013). Concepts for Liver Segment Classification: Neither Old Ones nor New Ones, but a Comprehensive One. J Clin Imaging Sci. 2013; 3: 48.