Hemorrhoid

Hemorrhoid Hemorrhoids Classification and external resources Schematic demonstrating the anatomy of hemorrhoids. ICD-10 I84. ICD-9 455 DiseasesDB 10036 MedlinePlus 000292 eMedicine med/2821 emerg/242 MeSH D006484 Hemorrhoids (US English) or haemorrhoids (Commonwealth English), also known as piles and "Tum-Bum" are part of the normal human anatomy of the anal canal. They become pathological when swollen or inflamed. In their physiological state they act as cushions composed of arterio-venous channels and connective tissue that aid the passage of stool. The symptoms of pathological hemorrhoids depend on the type present. Internal hemorrhoids usually present with painless rectal bleeding while external hemorrhoids present with pain in the area of the anus. Recommended treatment consists of increasing fiber intake, oral fluids to maintain hydration, NSAID analgesics, sitz baths, and rest. Surgery is reserved for those who fail to improve following these measures. Contents • 1 Signs and symptoms • 2 Causes • 3 Pathophysiology • 4 Prevention • 5 Diagnosis o 5.1 Differential • 6 Treatments o 6.1 Procedures • 7 Epidemiology • 8 Notable cases • 9 References Signs and symptoms Classical appearance of an external hemorrhoid. Hemorrhoids are usually benign. In most cases, symptoms will resolve within a few days. External hemorrhoids are painful while internal hemorrhoids usually are not. The most common symptom of internal hemorrhoids is bright red blood covering the stool, a condition known as hematochezia, on toilet paper, or in the toilet bowl. They may protrude through the anus. Symptoms of external hemorrhoids include painful swelling or lump around the anus. Causes A number of factors may lead to the formations of hemorrhoids including irregular bowel habits (constipation or diarrhea), exercise, gravity, nutrition (low-fiber diet), increased intra-abdominal pressure (prolonged straining), pregnancy, genetics, absence of valves within the hemorrhoidal veins, and aging. Other factors that can increase the rectal vein pressure resulting in hemorrhoids include obesity, and sitting for long periods of time. During pregnancy, pressure from the fetus on the abdomen and hormonal changes cause the hemorrhoidal vessels to enlarge. Delivery also leads to increase intra abdominal pressures. Surgical treatment is rarely needed as symptoms usually resolve post delivery. Pathophysiology This section requires expansion. Hemorrhoid cushions are a part of normal human anatomy and only become a pathological disease when they experience abnormal changes. There are three cushions present in the normal anal canal. Prevention The best way to prevent hemorrhoids is to keep stools soft so they pass easily, thus decreasing pressure and straining, and to empty bowels as soon as possible after the urge occurs. Exercise, including walking, and increased fiber in the diet help reduce constipation and straining by producing stools that are softer and easier to pass. Spending less time attempting to defecate and avoiding reading while on the toilet have been recommended. Diagnosis Endoscopic image of internal hemorrhoids seen on retroflexion of the flexible sigmoidoscope at the ano-rectal junction A visual examination of the anus and surrounding area may be able to diagnose external or prolapsed hemorrhoids. A rectal exam may be performed to detect possible rectal tumors, polyps, an enlarged prostate, or abscesses. This examination may not be possible without appropriate sedation due to pain. Visual confirmation of internal hemorrhoids is via anoscopy. This device is basically a hollow tube with a light attached at one end that allows one to see the internal hemorrhoids, as well possible polyps in the rectum. Differential Many anorectal problems, including fissures, fistulae, abscesses, colorectal cancer, rectal varices and itching,diverticulosis,polyps have similar symptoms and may be incorrectly referred to as hemorrhoids. Treatments Conservative treatment typically consists of increasing dietary fiber, oral fluids to maintain hydration, non-steroidal anti-inflammatory drugs (NSAID)s, sitz baths, and rest. Increased fiber intake has been shown to improve outcomes and may be achieved by dietary alterations or the consumption of fibre supplements . While many topical agents and suppositories are available for the treatment of hemorrhoids there is little evidence to support their use. Preparation H may improve local symptoms but does not improve the underlying disorder and long term use is discouraged due to local irritation of the skin. Procedures • Rubber band ligation is a procedure in which elastic bands are applied onto an internal hemorrhoid at least 1 cm above the dentate line to cut off its blood supply. Within 5–7 days, the withered hemorrhoid falls off. If the band is placed too close to the dentate line intense pain results immediately afterwards.Cure rate has been found to be about 87%. • Sclerotherapy involves the injection of a sclerosing agent (such as phenol) into the hemorrhoid. This causes the vein walls to collapse and the hemorrhoids to shrivel up. The success rate at four years is 70%. • A number of cautery methods have been shown to be effective for hemorrhoids. This can be done using electrocautery, infrared radiation, or cryosurgery. A number of surgical techniques may be used if conservative medical management fails. All are associated with some degree of complications including urinary retention, due to the close proximity to the rectum of the nerves that supply the bladder, bleeding, infection, and anal strictures. • Hemorrhoidectomy is a surgical excision of the hemorrhoid used primary only in severe cases. It is associated with significant post operative pain and usually requires 2–4 weeks for recovery. • Doppler guided transanal hemorrhoidal dearterialization is a minimally invasive treatment. Consiosts in ligation of the six branches of the superior rectal artery, the cause of arterial hyperinflux and therefore of swelling and bleeding of the haemorrhoidal plexus, which are localised and ligated high in the rectal canal. It is not at all invasive as no tissue is cut or removed in the anal-rectal canal. Given its non-invasiveness, no significant complications can occur. The method can be repeated and does not prevent other operations on the anal-rectal channel from being carried out as full restitutio ad integrum occurs within three months from the operation, that is, the anal-rectal canal regains its normal anatomy as though it had never been operated on at all. • Stapled hemorrhoidectomy is a procedure that involves resection of soft tissue proximal to the dentate line, disrupting the blood flow to the hemorrhoids. It is generally less painful than complete removal of hemorrhoids and was associated with faster healing compare to a hemorrhoidectomy. Epidemiology Symptomatic hemorrhoids affect at least 50% of the American population at some time during their lives, with around 5% of the population suffering at any given time, and both sexes experiencing the same incidence of the condition. They are more common in Caucasians

Heart

Heart Vertebrate heart The heart is a found in all with a (including all that is responsible for pumping throughout the by repeated, rhythmic contractions. The term cardiac (as in means "related to the heart" and comes from the "heart." The vertebrate heart is composed of which is an involuntary striated muscle tissue found only within this organ, and The average human heart, beating at 72 beats per minute, will beat approximately 2.5 billion times during an average 66 year lifespan, and weighs approximately 250 to 300 grams (9 to 11 oz) in females and 300 to 350 grams (11 to 12 oz) in males. In that possess a circulatory system, the heart is typically a tube or small sac and pumps fluid that contains water and nutrients such as and In the "heart" is often called the dorsal tube and insect "blood" is almost always not oxygenated since they usually (breathe) directly from their body surfaces (internal and external) to air. However, the hearts of some other (including and such as and ) and some other animals pump which contains the -based protein as an oxygen transporter similar to the -based in red found Early development Main article: The heart is derived from embryonic germ-layer cells that differentiate after into and. Mesothelial forms the outer lining of the heart. The inner lining of the heart, lymphatic and blood vessels, develop from endothelium. Heart muscle is termed myocardium.From tissue, the carcinogenic plate develops cranially and laterally to In the carcinogenic plate, two separate antigenic cell clusters form on either side of the embryo. Each cell cluster coalesces to form an endocrinal tube continuous with a dorsal aorta and a vitteloumbilical vein. As embryonic tissue continues to fold, the two endocrinal tubes are pushed into the thoracic cavity, begin to fuse together, and complete the fusing process at approximately 21 days. At 21 days after, the human heart begins beating at 70 to 80 beats per minute and accelerates linearly for the first month of beating. The human heart begins beating at around 21 days after conception, or five weeks after the last normal (LMP). The first day of the LMP is normally used to date the start of the gestation (pregnancy). It is unknown how blood in the human embryo circulates for the first 21 days in the absence of a functioning heart. The human heart begins beating at a rate near the mother’s, about 75-80 beats per minute (BPM). The embryonic heart rate (EHR) then accelerates approximately 100 BPM during the first month of beating, peaking at 165-185 BPM during the early 7th week, (early 9th week after the LMP). This acceleration is approximately 3.3 BPM per day, or about 10 BPM every three days, which is an increase of 100 BPM in the first month. After 9.1 weeks after the LMP, it decelerates to about 152 BPM (+/-25 BPM) during the 15th week post LMP. After the 15th week, the deceleration slows to an average rate of about 145 (+/-25 BPM) BPM, at term. The regression formula, which describes this acceleration before the embryo reaches 25 mm in crown-rump length, or 9.2 LMP weeks, is: Age in days = EHR(0.3)+6. There is no difference in female and male heart rates before birtStructure The structure of the heart varies among the different branches of See have two "gill hearts" and one "systemic heart". In vertebrates, the heart lies in the anterior part of the body cavity, dorsal to the gut. It is always surrounded by which is usually a distinct structure, but may be continuous with the in jawless and cartilaginous fish. Uniquely among vertebrates, also possess a second heart-like structure in the tail. In humans Structure diagram of the human heart. Blue components indicate de-oxygenated blood pathways and red components indicate oxygenated pathways. The human heart is about the size of a fist and has a mass of between 250 and 350 grams. It is located anterior to the vertebral column and posterior to the sternum. It is enclosed in a double-walled sac called The superficial part of this sac is called the fibrous pericardium. This sac protects the heart, anchors its surrounding structures, and prevents overfilling of the heart with blood. The outer wall of the human heart is composed of three layers. The outer layer is called the epicedium, or visceral pericardium since it is also the inner wall of the pericardium. The middle layer is called the and is composed of muscle which contracts. The inner layer is called the and is in contact with the blood that the heart pumps. Also, it merges with the inner lining of blood vessels and covers heart valves. The human heart has four chambers, two superior atria and two inferior ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers. The right ventricle discharges into the lungs to oxygenate the blood. The left ventricle discharges its blood toward the rest of the body via the aorta. ventricles, and out of the great The pathway of blood through the human heart consists of a pulmonary circuit and a systemic circuit. Blood flows through the heart in one direction, from the atria to the arteries, or the aorta for example. This is done by four valves which are the and In fish Schematic of simplified fish heart Primitive fish have a four-chambered heart; however, the chambers are arranged sequentially so that this primitive heart is quite unlike the four-chambered hearts of mammals and birds. The first chamber is the which collects de-oxygenated blood, from the body, through the and From here, blood flows into the and then to the powerful muscular where the main pumping action will take place. The fourth and final chamber is the which contains several valves and sends blood to the ventral aorta. The ventral aorta delivers blood to the gills where it is oxygenated and flows, through the into the rest of the body. (In the ventral aorta has divided in two; one half forms the while the other forms the In the adult fish, the four chambers are not arranged in a straight row but, instead, form an S-shape with the latter two chambers lying above the former two. This relatively simpler pattern is found in and in the more primitive In the cones asterisks is very small and can more accurately be described as part of the aorta rather than of the heart proper. The cones atrocious is not present in any presumably having been absorbed into the ventricles over the course of evolution. Similarly, while the sinus venous is present as a vestigial structure in some reptiles and birds, it is otherwise absorbed into the right atrium and is no longer distinguishable. In double circulatory systems In and most a is used but the heart is not completely separated into two pumps. The development of the double system is necessitated by the presence of which deliver oxygenated blood directly to the heart. In living amphibians, the atrium is divided into two separate chambers by the presence of a muscular even though there is only a single ventricle. The sinus venous, which remains large in amphibians but connects only to the right atrium, receives blood from the with the by-passing it entirely to enter the left atrium. In the heart of the septum extends part-way into the ventricle. This allows for some degree of separation between the de-oxygenated bloodstream destined for the lungs and the oxygenated stream that is delivered to the rest of the body. The absence of such a division in living amphibian species may be at least partly due to the amount of respiration that occurs through the skin in such species; thus, the blood returned to the heart through the vena caves is, in fact, already partially oxygenated. As a result, there may be less need for a finer division between the two bloodstreams than in lungfish or other Nonetheless, in at least some species of amphibian, the spongy nature of the ventricle seems to maintain more of a separation between the bloodstreams than appears the case at first glance. Furthermore, the conus arteriosus has lost its original valves and contains a spiral valve, instead, that divides it into two parallel parts, thus helping to keep the two bloodstreams separate. The heart of most reptiles (except for crocodilians; see below) has a similar structure to that of lungfish but, here, the septum is generally much larger. This divides the ventricle into two halves but, because the septum does not reach the whole length of the heart, there is a considerable gap near the openings to the pulmonary artery and the aorta. In practice, however, in the majority of reptilian species, there appears to be little, if any, mixing between the bloodstreams, so the aorta receives, essentially, only oxygenated blood. The fully divided heart Human heart removed from a 64-year-old male. Surface of The heart is demarcated by: -A point 9 cm to the left of the midstream (apex of the heart) -The seventh right stern costal -The upper border of the third right costal cartilage 1 cm from the right eternal -The lower border of the second left costal cartilage 2.5 cm from the left lateral sternal line. show complete separation of the heart into two pumps for a total of four it is thought that the four-chambered heart of archosaurs evolved independently from that of mammals. In crocodilians, there is a small opening, the at the base of the arterial trunks and there is some degree of mixing between the blood in each side of the heart; thus, only in birds and mammals are the two streams of blood - those to the pulmonary and systemic circulations - kept entirely separate by a physical barrier. In the human body, the heart is usually situated in the middle of the with the largest part of the heart slightly offset to the left, although sometimes it is on the right see underneath The heart is usually felt to be on the left side because the (left ventricle) is stronger (it pumps to all body parts). The left is smaller than the right lung because the heart occupies more of the left The heart is fed by the and is enclosed by a sac known as the ; it is also surrounded by The pericardium comprises two parts: the fibrous pericardium, made of and a double membrane structure (parietal and visceral pericardium) containing a fluid to reduce friction during heart contractions. The heart is located in the which is the central sub-division of the thoracic cavity. The mediastinum also contains other structures, such as the esophagus and trachea, and is flanked on either side by the right and left pulmonary cavities; these cavities house The apex is the blunt point situated in an inferior (pointing down and left) direction. A can be placed directly over the apex so that the beats can be counted. It is located posterior to the 5th intercostal space just medial of the left mid-clavicular line. In normal adults, the mass of the heart is 250-350 g (9-12 oz), or about twice the size of a clenched fist (it is about the size of a clenched fist in children), but an extremely diseased heart can be up to 1000 g (2 lb) in mass due to It consists of four chambers, the two upper atria and the two lower ventricles. Functioning ood flow diagram of the human heart. Blue components indicate de-oxygenated blood pathways and red components indicate oxygenated pathways. Image showing the Conduction System of the Heart In mammals, the function of the right side of the heart (see right ) is to collect de-oxygenated blood, in the from the body (via superior and inferior vena cave) and pump it, through the tricuspid valve, via the, into the lungs (pulmonary ) so that carbon dioxide can be dropped off and oxygen picked up . This happens through the passive process of The left side (see left heart) collects oxygenated blood from the lungs into the left atrium From the left atrium the blood moves to the through the bicuspid valve, which pumps it out to the body (via the aorta). On both sides, the lower ventricles are thicker and stronger than the upper atria. The muscle wall surrounding the left ventricle is thicker than the wall surrounding the right ventricle due to the higher force needed to pump the blood through the systemic circulation Starting in the right atrium, the blood flows through the tricuspid valve to the right ventricle. Here, it is pumped out the pulmonary semilunar valve and travels through the pulmonary artery to the lungs. From there, oxygenated blood flows back through the pulmonary vein to the left atrium. It then travels through the mitral valve to the left ventricle, from where it is pumped through the aortic semilunar valve to the aorta The aorta forks and the blood is divided between major arteries which supply the upper and lower body. The blood travels in the arteries to the smaller arterioles and then, finally, to the tiny capillaries which feed each cell. The (relatively) deoxygenated blood then travels to the venues, which coalesce into veins, then to the inferior and superior venue caveat and finally back to the right atrium where the process began. The heart is effectively a syncytium a meshwork of cardiac muscle cells interconnected by contiguous cytoplasmic bridges. This relates to electrical stimulation of one cell spreading to neighboring cells. Some cardiac cells are self-excitable, contracting without any signal from the nervous system, even if removed from the heart and placed in culture. Each of these cells have their own intrinsic contraction rhythm. A region of the human heart called the sinoatrial node, or pacemaker, sets the rate and timing at which all cardiac muscle cells contract. The SA node generates electrical impulses, much like those produced by nerve cells. Because cardiac muscle cells are electrically coupled by inter-calated disks between adjacent cells, impulses from the SA node spread rapidly through the walls of the artria, causing both artria to contract in unison. The impulses also pass to another region of specialized cardiac muscle tissue, a relay point called the atrioventricular node, located in the wall between the right atrium and the right ventricle. Here, the impulses are delayed for about 0.1s before spreading to the walls of the ventricle. The delay ensures that the atria empty completely before the ventricles contract. Specialized muscle fibers called Purkinje fibers then conduct the signals to the apex of the heart along and throughout the ventricular walls. The Purkinje fibers form conducting pathways called bundle branches. This entire cycle, a single heart beat, lasts about 0.8 seconds. The impulses generated during the heart cycle produce electrical currents, which are conducted through body fluids to the skin, where they can be detected by electrodes and recorded as an electrocardiogram (ECG or EKG). The events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next can be referred to a cardiac cycle. The SA node is found in all amniotes but not in more primitive vertebrates. In these animals, the muscles of the heart are relatively continuous and the sinus venosus coordinates the beat which passes in a wave through the remaining chambers. Indeed, since the sinus venosus is incorporated into the right atrium in amniotes, it is likely homologous with the SA node. In teleosts, with their vestigial sinus venosus, the main centre of coordination is, instead, in the atrium. The rate of heartbeat varies enormously between different species, ranging from around 20 beats per minute in codfish to around 600 in hummingbirds. Cardiac arrest is the sudden cessation of normal heart rhythm which can include a number of pathologies such as tachycardia, an extremely rapid heart beat which prevents the heart from effectively pumping blood, fibrillation, which is an irregular and ineffective heart rhythm, and asystole, which is the cessation of heart rhythm entirely. Cardiac tamponade is a condition in which the fibrous sac surrounding the heart fills with excess fluid or blood, suppressing the heart's ability to beat properly. Tamponade is treated by pericardiocentesis, the gentle insertion of the needle of a syringe into the pericardial sac (avoiding the heart itself) on an angle, usually from just below the sternum, and gently withdrawing the tamponading fluids. History of discoveries A preserved human heart with a visible gunshot wound The valves of the heart were discovered by a physician of the Hippocrates School around the 4th century BC. However, their function was not properly understood then. Because blood pools in the veins after death, arteries look empty. Ancient anatomists assumed they were filled with air and that they were for transport of air. Philosophers distinguished veins from arteries but thought that the pulse was a property of arteries themselves. Erasistratos observed the arteries that were cut during life bleed. He described the fact to the phenomenon that air escaping from an artery is replaced with blood which entered by very small vessels between veins and arteries. Thus he apparently postulated capillaries but with reversed flow of blood. The 2nd century AD, Greek physician Galenos (Galen) knew that blood vessels carried blood and identified venous (dark red) and arterial (brighter and thinner) blood, each with distinct and separate functions. Growth and energy were derived from venous blood created in the liver from chyle, while arterial blood gave vitality by containing pneuma (air) and originated in the heart. Blood flowed from both creating organs to all parts of the body where it was consumed and there was no return of blood to the heart or liver. The heart did not pump blood around, the heart's motion sucked blood in during diastole and the blood moved by the pulsation of the arteries themselves. Galen believed that the arterial blood was created by venous blood passing from the left ventricle to the right through 'pores' in the inter ventricular septum while air passed from the lungs via the pulmonary artery to the left side of the heart. As the arterial blood was created, 'sooty' vapors were created and passed to the lungs, also via the pulmonary artery, to be exhaled. For more recent technological developments, see Cardiac surgery, Healthy heart Obesity, high blood pressure, and high cholesterol can increase the risk of developing heart disease. However, half the amount of heart attacks occur in people with normal cholesterol levels. Heart disease is a major cause of death (and the number one cause of death in the Western World). Of course one must also consider other factors such as lifestyle, for instance the amount of exercise one undertakes and their diet, as well as their overall health (mental and social as well as physical).

No Mercy

Liver Function

Liver function

The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion. The liver is necessary for survival; there is currently no way to compensate for the absence of liver function.


This organ plays a major role in metabolism and has a number of functions in the body, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, hormone production, and detoxification. It lies below the diaphragm in the thoracic region of the abdomen. It produces bile, an alkaline compound which aids in digestion, via the emulsification of lipids. The liver's highly specialized tissues regulate a wide variety of high-volume biochemical reactions, including the synthesis and breakdown of small and complex molecules, many of which are necessary for normal vital functions.


Medical terms related to the liver often start in hepato- or hepatic from the Greek word for liver, hēpar (ἡπαρ )


Anatom
The liver is a reddish brown organ with four lobes of unequal size and shape. A human liver normally weighs between 1.4–1.6 kg (3.1–3.5 lb),and 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 small intestine and the descending colon. 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.


Blood flow
The liver receives 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 sinusoids and empties into the central vein of each lobule. The central veins coalesce into hepatic veins, which leave the liver and empty into the inferior vena cava.


Billiard flow
The term billiard tree is derived from the arboreal branches of the bile ducts. The bile produced in the liver is collected in bile canaliculi, which merge to form bile ducts. Within the liver, these ducts are called intrahepatic (within the liver) bile ducts, and once they exit the liver they are considered extra hepatic (outside the liver). The intrahepatic ducts eventually drain into the right and left hepatic ducts, which merge to form the common hepatic duct. The cystic duct from the gallbladder joins with the common hepatic duct to form the common bile duct.


Bile can either drain directly into the duodenum via the common bile duct or be temporarily stored in the gallbladder via the cystic duct. The common bile duct and the pancreatic duct enter the second part of the duodenum together at the ampullae’s of Vaster


Apart from a patch where it connects to the diaphragm (the so-called "bare area"), the liver is covered entirely by visceral peritoneum, a thin, double-layered membrane that reduces friction against other organs. The peritoneum folds back on itself to form the aciform ligament and the right and left triangular ligaments.
These "lets" are in no way related to the true anatomic ligaments in joints, and have essentially no functional importance, but they are easily recognizable surface landmarks. An exception to this is the aciform ligament, which attaches the liver to the posterior portion of the anterior body wall.


Lobes
Traditional gross anatomy divided the liver into four lobes based on surface features. The aciform 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.


If the liver is flipped over, to look at it from behind (the visceral surface), there are two additional lobes between the right and left. These are the caudate lobe (the more superior), and below this the quadrate lobe.


From behind, the lobes are divided up by the ligament venous and ligament tares (anything left of these is the left lobe), the transverse fissure (or portal hepatics) divides the caudate from the quadrate lobe, and the right societal fossil, which the inferior vena cava runs over, separates these two lobes from the right lobe.


Each of the lobes is made up of lobules; a vein goes from the centre of each lobule which then joins to the hepatic vein to carry blood out from the liver.


On the surface of the lobules there are ducts, veins and arteries that carry fluids to and from them.


Functional anatomy
* or lobe in the case of the caudate lobe.


Each number in the list corresponds to one in the table.


The central area where the common bile duct, hepatic portal vein, and hepatic artery proper enter is the haulm or "portal hepatics". The duct, vein, and artery divide into left and right branches, and the portions of the liver supplied by these branches constitute the functional left and right lobes.

The functional lobes are separated by an imaginary plane joining the gallbladder fosses to the inferior vena cava. The plane separates the liver into the true right and left lobes. The middle hepatic vein also demarcates the true right and left lobes. The right lobe is further divided into an anterior and posterior segment by the right hepatic vein. The left lobe is divided into the medial and lateral segments by the left hepatic vein. The fissure for the ligament terse also separates the medial and lateral segments. The medial segment is also called the quadrate lobe. In the widely used Coquina (or "French") system, the functional lobes are further divided into a total of eight sub segments based on a transverse plane through the bifurcation of the main portal vein. The caudate lobe is a separate structure which receives blood flow from both the right- and left-sided vascular branches.


In other animals
The liver is found in all vertebrates, and is typically the largest visceral organ. Its form varies considerably in different species, and is largely determined by the shape and arrangement of the surrounding organs. Nonetheless, in most species it is divided into right and left lobes; exceptions to this general rule include snakes, where the shape of the body necessitates a simple cigar-like form. The internal structure of the liver is broadly similar in all vertebrates.


An organ sometimes referred to as a liver is found associated with the digestive tract of the primitive chordate Amphioxus. However, this is an enzyme secreting gland, not a metabolic organ, and it is unclear how truly homologous it is to the vertebrate liver.


Physiology
The various functions of the liver are carried out by the liver cells or hepatocytes. Currently, there is no artificial organ or device capable of emulating all the functions of the liver. Some functions can be emulated by liver dialysis, an experimental treatment for liver failure.


Synthesis
Further information: Proteins produced and secreted by the liver


* A large part of amino acid synthesis


* The liver performs several roles in carbohydrate metabolism:


o Gluconeogenesis (the synthesis of glucose from certain amino acids, lactate or glycerol). Note that humans and some other mammals cannot synthesize glucose from glycerol.


o Glycogenolysis (the breakdown of glycogen into glucose)


o Glycogen sis (the formation of glycogen from glucose)(muscle tissues can also do this)


* The liver is responsible for the mainstay of protein metabolism, synthesis as well as degradation


* The liver also performs several roles in lipid metabolism: Cholesterol synthesis


Lip genesis, the production of triglycerides (fats).


* The liver produces coagulation factors I (fibrinogen), II (prothrombin), V, VII, IX, X and XI, as well as protein C, protein S and ant thrombin.


* In the first trimester fetus, the liver is the main site of red blood cell production. By the 32nd week of gestation, the bone marrow has almost completely taken over that task.


* The liver produces and excretes bile (a yellowish liquid) required for emulsifying fats. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder.


* The liver also produces insulin-like growth factor 1 (IGF-1), a polypeptide protein hormone that plays an important role in childhood growth and continues to have anabolic effects in adults.


* The liver is a major site of thrombopoietin production. Thrombopoietin is a glycoprotein hormone that regulates the production of platelets by the bone marrow.


* The breakdown of insulin and other hormones


* The liver breaks down hemoglobin, creating metabolites that are added to bile as pigment (bilirubin and biliverdin).


* The liver breaks down or modifies toxic substances (e.g., methylamine) and most medicinal products in a process called drug metabolism. This sometimes results in oxidations, when the metabolite is more toxic than its precursor. Preferably, the toxins are conjugated to avail excretion in bile or urine.