The liver is an organ found in all vertebrates. The liver functions as an interface between the digestive tract and the blood. In humans the liver is a large organ that rests below the diaphragm in the abdominal cavity. The liver’s right lobe dominates the right anterior hypochondriac region, and the left lobe takes a fair dividend of the anterior epigastric region.
An organ is a group of tissues that work together to perform a specific function. The liver is a vital organ performing a great variety of different functions. The liver hosts a multitude of biochemical reaction pathways required for metabolisms- including carbohydrate and fat metabolisms. The liver also contributes to the breakdown of erythrocytes and the detoxification of drugs and toxicants in the blood. The liver functions on the deactivation of hormones which are substances secreted by an endocrine gland into the circulatory system. In the liver, enzymes remove the nitrogenous section of unanabolized proteins, catabolising them in a structured reaction pathway yielding urea destined for the kidneys, this process is called deaminiation.
Embryonicly the liver is a gland derived from an outgrowth of the gut epithelium and performs both endocrine and exocrine functions. Structurally the liver is made up of countless lobules. Around the circumference of the lobules are arteries, veins and bile ducts - centripetal to their structure is their central vein. A complex of blood filled sinuids radiate from the central vein within the lobule. The fractal structure of the sinuids gives the liver a large surface area to maximize membrane transport and diffusion.
The liver undergoes three phases of depreciation of oxygen content in the blood as oxygen diffuses into the sinuid tissues; this is called the liver acinus. As blood channels from the hepatic artery into the central vein, the blood travels through three phases: preiportal- high oxygen content, intermediate and central venous drainage; the lowest oxygen content – plays a role in detoxification.
The size of the liver is controlled by metabolic requirements; mature differentiated hepatocytes may proliferate at any stage of their life. In rats transplanted or mutilated livers may grow to accommodate the specific organism very quickly potentially tripling in size within two weeks. Korkut Uygun has stripped the cells off the liver of a rat to its bear collagen structure and reconstituted cells over the old structure. The reformed liver was successfully transplanted into a genetically similar rat.
Hepatic macrophages float within the sinuids and are used for breaking down erythrocytes; this also occurs in the spleen and bone marrow. Heme, derived from heamaglobin, is broken down in the liver by enzymes. Heme oxygenase removes the iron from the heme to produce biliverdin, releasing an iron atom. Ferritin binds the iron atom in a cyclopentadienide anion complex on the catalase tetramer; these proteins are stored in the peroxisome. Preoxisomes are bountiful in the liver hepatocytes. Catalase tetramer has its role in the breakdown of methanol. The enzyme biliverdinase reduces biliverdin into bilirubin. Bilirubin is non-miscible however when conjugated with glucuronic acid - forming sterobilin - it is soluble enough to travel though the bile ducts into the intestines for defecation. Some bilirubin is also absorbed into the neighbouring kidney and synthesized into urobilinogen to be relieved in the urine.
A thin layer of squamous endothelial cells lines the sinuids, however hexagonal-cuboidal hepatocytes form the majority of dense matter in the liver. Between the endothelial cells and the hepatocityes is the space of disse formed from collagen. The hepatocytes apical domain forms a thin extracellular canal called the bile canaliculus. The bile canaliculus leads into the bile ducts. Bile is the waste product of the hepatocytes metabolism; concentrated by the gall bladder. Bile facilitates the emulsification of lipids in the small intestine. The liver is associative with many other organs including the right kidney, oesophagus, gall bladder and adrenal gland. The falciform ligament separates the liver’s right and left lobes as can be seen in figure (1). The anterior superior right lateral region consists of three impressions: the colic, the duodenal and the right renal. Inferior to this is the right adrenal gland impression. The superior medial anterior of the liver is where the bile ducts, the portal vein and the hepatic artery affix illustrated in figure (1). The inferior medal region of the anterior liver appends the inferior vena cava; to the left is the caudate lobe. The liver is our largest and most metabolically active organ and thus produces the majority of our body heat. At the medial superior anterior is the quadrate lobe. At the inferior anterior of the left lobe is the gastric impression.
The liver receives nutrient rich blood originated from the small intestine from the portal vein leading though the left lobe; unmetabolized glucose carried up from the small intestine may be stockpiled as glycogen. The synthesis of glycogen from glucose monomers is a condensation reaction; this process is regulated by pancreatic hormonal signals received in the blood. Glycogen is a helical branched polymer stored in dense granules associated to the smooth endoplasmic reticulum of the hepatocytes. Glycogen is stored for when the body needs additional energy for catabolism. Glyocogen-debranching enzymes are encrusted in the plasma-cellular membrane of the hepatocytes. Glucose, also known as blood sugar, has a hydroxyl and an aldehyde functional group. Glycolysis is a stratified reaction pathway dictated by enzymes that produces ATP and occurs in the mitochondrion. In the liver, oxygenated blood is received through the right lobe’s hepatic artery to enable the preferable aerobic pathway Krebs cycle; each individual glucose molecule yields six carbon monoxide and thirty-four adenosine 5’-triphosphate molecules.
In hunter-gatherer communities, offal is valued over the animal’s meat. The liver is an extremely nutritious organ especially when eaten raw. The liver contains all the essential vitamins. As well as glycogen and iron, the liver stores fat-soluble vitamins: A, D, E and K, copper and some miscible vitamins, including vitamin B12. However the liver must be eaten quickly and cleaned thoroughly because bile taints the flesh.
Figure 1 posterior and anterior veiws of their liver by Caspar Zialor
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