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132-491: The liver is also an accessory digestive organ that produces bile , an alkaline fluid containing cholesterol and bile acids , which emulsifies and aids the breakdown of dietary fat . The gallbladder , a small hollow pouch that sits just under the right lobe of liver, stores and concentrates the bile produced by the liver, which is later excreted to the duodenum to help with digestion . The liver's highly specialized tissue , consisting mostly of hepatocytes , regulates

264-426: A benign tumour the most common type of liver tumour, thought to be congenital. A genetic disorder causing multiple cysts to form in the liver tissue, usually in later life, and usually asymptomatic, is polycystic liver disease . Diseases that interfere with liver function will lead to derangement of these processes. However, the liver has a great capacity to regenerate and has a large reserve capacity. In most cases,

396-406: A common bile duct with the gallbladder. Bile is stored in the gallbladder for release when food is discharged into the duodenum and also after a few hours. The gallbladder is a hollow part of the biliary tract that sits just beneath the liver, with the gallbladder body resting in a small depression. It is a small organ where the bile produced by the liver is stored, before being released into

528-407: A monoglyceride . These are then absorbed by villi on the intestinal wall. If fats are not absorbed in this way in the small intestine problems can arise later in the large intestine which is not equipped to absorb fats. Bile also helps in the absorption of vitamin K from the diet. Bile is collected and delivered through the common hepatic duct . This duct joins with the cystic duct to connect in

660-584: A bone-like material called dentin , which is covered by the hardest tissue in the body— enamel . Teeth have different shapes to deal with different aspects of mastication employed in tearing and chewing pieces of food into smaller and smaller pieces. This results in a much larger surface area for the action of digestive enzymes. The teeth are named after their particular roles in the process of mastication— incisors are used for cutting or biting off pieces of food; canines , are used for tearing, premolars and molars are used for chewing and grinding. Mastication of

792-478: A branch of the facial nerve the chorda tympani , and the glossopharyngeal nerve . Taste messages are sent via these cranial nerves to the brain . The brain can distinguish between the chemical qualities of the food. The five basic tastes are referred to as those of saltiness , sourness , bitterness , sweetness , and umami . The detection of saltiness and sourness enables the control of salt and acid balance. The detection of bitterness warns of poisons—many of

924-410: A dual blood supply from the hepatic portal vein and hepatic arteries. The hepatic portal vein delivers around 75% of the liver's blood supply and 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 remaining quarter of its blood flow. Oxygen is provided from both sources; about half of

1056-405: A key role in this phenomenon. At birth, the liver comprises roughly 4% of body weight and weighs on average about 120 g (4 oz). Over the course of further development, it will increase to 1.4–1.6 kg (3.1–3.5 lb) but will only take up 2.5–3.5% of body weight. Hepatosomatic index (HSI) is the ratio of liver weight to body weight. In the growing fetus, a major source of blood to

1188-408: A more horizontal position, with its upper side functioning as part of the pharynx. In this manner it prevents food from going into the trachea and instead directs it to the esophagus, which is behind. During swallowing, the backward motion of the tongue forces the epiglottis over the glottis' opening to prevent any food that is being swallowed from entering the larynx which leads to the lungs; the larynx

1320-406: A natural, semi-liquid form at all times. Hydrogen ions secreted from the inner lining of the gallbladder keep the bile acidic enough to prevent hardening. To dilute the bile, water and electrolytes from the digestion system are added. Also, salts attach themselves to cholesterol molecules in the bile to keep them from crystallising . If there is too much cholesterol or bilirubin in the bile, or if

1452-430: A plant's defences are of poisonous compounds that are bitter. Sweetness guides to those foods that will supply energy; the initial breakdown of the energy-giving carbohydrates by salivary amylase creates the taste of sweetness since simple sugars are the first result. The taste of umami is thought to signal protein-rich food. Sour tastes are acidic which is often found in bad food. The brain has to decide very quickly whether

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1584-408: A population of the bipotential hepatoblasts. Hepatic stellate cells are derived from mesenchyme. After migration of hepatoblasts into the septum transversum mesenchyme, the hepatic architecture begins to be established, with liver sinusoids and bile canaliculi appearing. The liver bud separates into the lobes. The left umbilical vein becomes the ductus venosus and the right vitelline vein becomes

1716-448: A protective benefit against liver cancer for moderate coffee drinkers. A 2017 study revealed that the positive effects of caffeine on the liver were evident regardless of the coffee preparation method. Accessory digestive organ The human digestive system consists of the gastrointestinal tract plus the accessory organs of digestion (the tongue , salivary glands , pancreas , liver , and gallbladder ). Digestion involves

1848-416: A right and a left lobe – and four parts when viewed from below (left, right, caudate , and quadrate lobes ). The falciform ligament makes a superficial division of the liver into a left and right lobe. From below, the two additional lobes are located between the right and left lobes, one in front of the other. A line can be imagined running from the left of the vena cava and all the way forward to divide

1980-409: A role in the production of clotting factors, as well as red blood cell production. Some of the proteins synthesized by the liver include coagulation factors I (fibrinogen), II (prothrombin), V , VII , VIII , IX , X , XI , XII , XIII , as well as protein C , protein S and antithrombin . The liver is a major site of production for thrombopoietin , a glycoprotein hormone that regulates

2112-424: A wide variety of high-volume biochemical reactions, including the synthesis and breakdown of small and complex organic molecules, many of which are necessary for normal vital functions. Estimates regarding the organ's total number of functions vary, but is generally cited as being around 500. For this reason, the liver has sometimes been described as the body's chemical factory . It is not known how to compensate for

2244-409: A width of about 15 centimetres (6 inches). There is considerable size variation between individuals, with the standard reference range for men being 970–1,860 grams (2.14–4.10 lb) and for women 600–1,770 g (1.32–3.90 lb). It is both the heaviest internal organ and the largest gland in the human body. It is located in the right upper quadrant of the abdominal cavity , resting just below

2376-400: Is a "satellite" of hepatitis B virus (it can only infect in the presence of hepatitis B), and co-infects nearly 20 million people with hepatitis B, globally. Hepatic encephalopathy is caused by an accumulation of toxins in the bloodstream that are normally removed by the liver. This condition can result in coma and can prove fatal. Budd–Chiari syndrome is a condition caused by blockage of

2508-426: Is a form of chemoreception that takes place in the specialised taste receptors , contained in structures called taste buds in the mouth. Taste buds are mainly on the upper surface (dorsum) of the tongue. The function of taste perception is vital to help prevent harmful or rotten foods from being consumed. There are also taste buds on the epiglottis and upper part of the esophagus . The taste buds are innervated by

2640-417: Is also pulled upwards to assist this process. Stimulation of the larynx by ingested matter produces a strong cough reflex in order to protect the lungs. The pharynx is a part of the conducting zone of the respiratory system and also a part of the digestive system. It is the part of the throat immediately behind the nasal cavity at the back of the mouth and above the esophagus and larynx . The pharynx

2772-484: Is an important part of the body's digestive system. The muscular diaphragm separates the thoracic cavity from the abdominal cavity where most of the digestive organs are located. The suspensory muscle attaches the ascending duodenum to the diaphragm. This muscle is thought to be of help in the digestive system in that its attachment offers a wider angle to the duodenojejunal flexure for the easier passage of digesting material. The diaphragm also attaches to, and anchors

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2904-420: Is closed at both ends, by the upper and lower esophageal sphincters . The opening of the upper sphincter is triggered by the swallowing reflex so that food is allowed through. The sphincter also serves to prevent back flow from the esophagus into the pharynx. The esophagus has a mucous membrane and the epithelium which has a protective function is continuously replaced due to the volume of food that passes inside

3036-413: Is covered with a mucous membrane and there are taste buds on its lingual surface which faces into the mouth. Its laryngeal surface faces into the larynx. The epiglottis functions to guard the entrance of the glottis , the opening between the vocal folds . It is normally pointed upward during breathing with its underside functioning as part of the pharynx, but during swallowing, the epiglottis folds down to

3168-402: Is eaten. The stomach is half empty after an average of 1.2 hours. After four or five hours the stomach has emptied. In the small intestine, the pH becomes crucial; it needs to be finely balanced in order to activate digestive enzymes. The chyme is very acidic, with a low pH, having been released from the stomach and needs to be made much more alkaline. This is achieved in the duodenum by

3300-512: Is further helped by the lubrication provided by the saliva in its passage from the mouth into the esophagus. Also of importance is the presence in saliva of the digestive enzymes amylase and lipase. Amylase starts to work on the starch in carbohydrates , breaking it down into the simple sugars of maltose and dextrose that can be further broken down in the small intestine. Saliva in the mouth can account for 30% of this initial starch digestion. Lipase starts to work on breaking down fats . Lipase

3432-432: Is further produced in the pancreas where it is released to continue this digestion of fats. The presence of salivary lipase is of prime importance in young babies whose pancreatic lipase has yet to be developed. As well as its role in supplying digestive enzymes, saliva has a cleansing action for the teeth and mouth. It also has an immunological role in supplying antibodies to the system, such as immunoglobulin A . This

3564-407: Is hard at the front of the mouth since the overlying mucosa is covering a plate of bone ; it is softer and more pliable at the back being made of muscle and connective tissue, and it can move to swallow food and liquids. The soft palate ends at the uvula . The surface of the hard palate allows for the pressure needed in eating food, to leave the nasal passage clear. The opening between the lips

3696-466: Is its major pigment. Bile acts partly as a surfactant which lowers the surface tension between either two liquids or a solid and a liquid and helps to emulsify the fats in the chyme. Food fat is dispersed by the action of bile into smaller units called micelles . The breaking down into micelles creates a much larger surface area for the pancreatic enzyme, lipase to work on. Lipase digests the triglycerides which are broken down into two fatty acids and

3828-448: Is known as the duodenal impression. The inferior surface of the left lobe of the liver presents behind and to the left of the gastric impression. This is moulded over the upper front surface of the stomach, and to the right of this is a rounded eminence, the tuber omentale , which fits into the concavity of the lesser curvature of the stomach and lies in front of the anterior layer of the lesser omentum . Microscopically, each liver lobe

3960-427: Is made up of three parts. The lower two parts—the oropharynx and the laryngopharynx are involved in the digestive system. The laryngopharynx connects to the esophagus and it serves as a passageway for both air and food. Air enters the larynx anteriorly but anything swallowed has priority and the passage of air is temporarily blocked. The pharynx is innervated by the pharyngeal plexus of the vagus nerve . Muscles in

4092-449: Is responsible for the breakdown and excretion of many waste products. It plays a key role in breaking down or modifying toxic substances (e.g., methylation ) and most medicinal products in a process called drug metabolism . This sometimes results in toxication , when the metabolite is more toxic than its precursor. Preferably, the toxins are conjugated to avail excretion in bile or urine. The liver converts ammonia into urea as part of

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4224-459: Is seen to be key in preventing infections of the salivary glands, importantly that of parotitis . Saliva also contains a glycoprotein called haptocorrin which is a binding protein to vitamin B 12 . It binds with the vitamin in order to carry it safely through the acidic content of the stomach. When it reaches the duodenum, pancreatic enzymes break down the glycoprotein and free the vitamin which then binds with intrinsic factor . Food enters

4356-404: Is seen to be made up of hepatic lobules . The lobules are roughly hexagonal, and consist of plates of hepatocytes , and sinusoids radiating from a central vein towards an imaginary perimeter of interlobular portal triads. The central vein joins to the hepatic vein to carry blood out from the liver. A distinctive component of a lobule is the portal triad , which can be found running along each of

4488-402: Is termed the oral fissure, and the opening into the throat is called the fauces . At either side of the soft palate are the palatoglossus muscles which also reach into regions of the tongue. These muscles raise the back of the tongue and also close both sides of the fauces to enable food to be swallowed. Mucus helps in the mastication of food in its ability to soften and collect the food in

4620-455: Is the jejunum and the third is the ileum ). The duodenum is the first and shortest section of the small intestine. It is a hollow, jointed C-shaped tube connecting the stomach to the jejunum. It starts at the duodenal bulb and ends at the suspensory muscle of duodenum . The attachment of the suspensory muscle to the diaphragm is thought to help the passage of food by making a wider angle at its attachment. Most food digestion takes place in

4752-498: Is the stomach . Within its mucosa are millions of embedded gastric glands . Their secretions are vital to the functioning of the organ. Most of the digestion of food takes place in the small intestine which is the longest part of the GI tract. The largest part of the GI tract is the colon or large intestine . Water is absorbed here and the remaining waste matter is stored prior to defecation . There are many specialised cells of

4884-402: Is the largest lymphoid organ in the body but has other functions. It breaks down both red and white blood cells that are spent . This is why it is sometimes known as the 'graveyard of red blood cells'. A product of this digestion is the pigment bilirubin , which is sent to the liver and secreted in the bile . Another product is iron , which is used in the formation of new blood cells in

5016-405: Is the tube of endoderm that extends out from the foregut into the surrounding mesenchyme. The mesenchyme of septum transversum induces this endoderm to proliferate, to branch, and to form the glandular epithelium of the liver. A portion of the hepatic diverticulum (that region closest to the digestive tube) continues to function as the drainage duct of the liver, and a branch from this duct produces

5148-412: Is uneven and concave. It is covered in peritoneum apart from where it attaches the gallbladder and the porta hepatis. The fossa of gallbladder lies to the right of the quadrate lobe, occupied by the gallbladder with its cystic duct close to the right end of porta hepatis. Several impressions on the surface of the liver accommodate the various adjacent structures and organs. Underneath the right lobe and to

5280-440: The ampulla of Vater . The liver plays a major role in carbohydrate, protein, amino acid, and lipid metabolism. The liver performs several roles in carbohydrate metabolism. The liver is responsible for the mainstay of protein metabolism , synthesis as well as degradation. All plasma proteins except Gamma-globulins are synthesised in the liver. It is also responsible for a large part of amino acid synthesis . The liver plays

5412-536: The bone marrow . Medicine treats the spleen solely as belonging to the lymphatic system , though it is acknowledged that the full range of its important functions is not yet understood. The liver is the second largest organ (after the skin ) and is an accessory digestive gland which plays a role in the body's metabolism . The liver has many functions some of which are important to digestion. The liver can detoxify various metabolites ; synthesise proteins and produce biochemicals needed for digestion. It regulates

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5544-421: The duodenum via the pyloric canal , contains countless glands which secrete digestive enzymes including gastrin. After an hour or two, a thick semi-liquid called chyme is produced. When the pyloric sphincter , or valve opens, chyme enters the duodenum where it mixes further with digestive enzymes from the pancreas, and then passes through the small intestine, where digestion continues. The parietal cells in

5676-430: The falciform ligament and the right and left triangular ligaments . These peritoneal ligaments are not related to the anatomic ligaments in joints, and the right and left triangular ligaments have no known functional importance, though they serve as surface landmarks. The falciform ligament functions to attach the liver to the posterior portion of the anterior body wall. The visceral surface or inferior surface

5808-420: The fibrinogen beta chain protein. Organogenesis , the development of the organs, takes place from the third to the eighth week during embryogenesis . The origins of the liver lie in both the ventral portion of the foregut endoderm (endoderm being one of the three embryonic germ layers ) and the constituents of the adjacent septum transversum mesenchyme . In the human embryo , the hepatic diverticulum

5940-638: The hepatic veins (including thrombosis ) that drain the liver. It presents with the classical triad of abdominal pain, ascites and liver enlargement . Many diseases of the liver are accompanied by jaundice caused by increased levels of bilirubin in the system. The bilirubin results from the breakup of the hemoglobin of dead red blood cells; normally, the liver removes bilirubin from the blood and excretes it through bile. Other disorders caused by excessive alcohol consumption are grouped under alcoholic liver diseases and these include alcoholic hepatitis , fatty liver , and cirrhosis . Factors contributing to

6072-434: The muscles of mastication , the tongue, and the teeth , and also by the contractions of peristalsis , and segmentation . Gastric acid, and the production of mucus in the stomach, are essential for the continuation of digestion. Peristalsis is the rhythmic contraction of muscles that begins in the esophagus and continues along the wall of the stomach and the rest of the gastrointestinal tract. This initially results in

6204-427: The ornithine cycle or the urea cycle, and the urea is excreted in the urine. Because the liver is an expandable organ, large quantities of blood can be stored in its blood vessels. Its normal blood volume, including both that in the hepatic veins and that in the hepatic sinuses, is about 450 milliliters, or almost 10 percent of the body's total blood volume. When high pressure in the right atrium causes backpressure in

6336-411: The thorax and enters the stomach through a hole in the thoracic diaphragm —the esophageal hiatus , at the level of the tenth thoracic vertebra (T10). Its length averages 25 cm, varying with an individual's height. It is divided into cervical, thoracic and abdominal parts. The pharynx joins the esophagus at the esophageal inlet which is behind the cricoid cartilage . At rest the esophagus

6468-452: The GI tract. These include the various cells of the gastric glands, taste cells , pancreatic duct cells , enterocytes and microfold cells . Some parts of the digestive system are also part of the excretory system , including the large intestine. The mouth is the first part of the upper gastrointestinal tract and is equipped with several structures that begin the first processes of digestion. These include salivary glands, teeth and

6600-487: The absence of liver function in the long term, although liver dialysis techniques can be used in the short term. Artificial livers have not been developed to promote long-term replacement in the absence of the liver. As of 2018, liver transplantation is the only option for complete liver failure . The liver is a dark reddish brown, wedge-shaped organ with two lobes of unequal size and shape. A human liver normally weighs approximately 1.5 kilograms (3.3 pounds) and has

6732-504: The absorption of vitamin K from the diet. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder. The liver produces insulin-like growth factor 1 , a polypeptide protein hormone that plays an important role in childhood growth and continues to have anabolic effects in adults. The liver is responsible for the breakdown of insulin and other hormones . The liver breaks down bilirubin via glucuronidation , facilitating its excretion into bile. The liver

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6864-414: The addition of bile from the gall bladder combined with the bicarbonate secretions from the pancreatic duct and also from secretions of bicarbonate-rich mucus from duodenal glands known as Brunner's glands . The chyme arrives in the intestines having been released from the stomach through the opening of the pyloric sphincter . The resulting alkaline fluid mix neutralises the gastric acid which would damage

6996-430: The bile and pancreatic juice can act on the chyme that is released from the stomach into the duodenum. Aqueous pancreatic secretions from pancreatic duct cells contain bicarbonate ions which are alkaline and help with the bile to neutralise the acidic chyme that is churned out by the stomach. The pancreas is also the main source of enzymes for the digestion of fats and proteins. Some of these are released in response to

7128-402: The biliary tract via the cystic duct , which then joins the common hepatic duct to form the common bile duct. At this junction is a mucosal fold called Hartmann's pouch , where gallstones commonly get stuck. The muscular layer of the body is of smooth muscle tissue that helps the gallbladder contract, so that it can discharge its bile into the bile duct. The gallbladder needs to store bile in

7260-455: The blood and constitute plasma proteins and hepatokines . Other liver-specific proteins are certain liver enzymes such as HAO1 and RDH16 , proteins involved in bile synthesis such as BAAT and SLC27A5 , and transporter proteins involved in the metabolism of drugs, such as ABCB11 and SLC2A2 . Examples of highly liver-specific proteins include apolipoprotein A II , coagulation factors F2 and F9 , complement factor related proteins , and

7392-432: The blood sugar is low; glucagon allows stored sugar to be broken down into glucose by the liver in order to re-balance the sugar levels. The pancreas produces and releases important digestive enzymes in the pancreatic juice that it delivers to the duodenum. The pancreas lies below and at the back of the stomach. It connects to the duodenum via the pancreatic duct which it joins near to the bile duct's connection where both

7524-405: The body but they all produce a lubricating mucus, which is either secreted by surface cells or more usually by underlying glands. The mucous membrane in the mouth continues as the thin mucosa which lines the bases of the teeth. The main component of mucus is a glycoprotein called mucin and the type secreted varies according to the region involved. Mucin is viscous, clear, and clinging. Underlying

7656-408: The body into the heart . In humans they are the superior vena cava and the inferior vena cava , and both empty into the right atrium . They are located slightly off-center, toward the right side of the body. The right atrium receives deoxygenated blood through coronary sinus and two large veins called venae cavae. The inferior vena cava (or caudal vena cava in some animals) travels up alongside

7788-430: The bowel or the gut. The lower GI starts at the pyloric sphincter of the stomach and finishes at the anus. The small intestine is subdivided into the duodenum , the jejunum and the ileum . The cecum marks the division between the small and large intestine. The large intestine includes the rectum and anal canal . Partially digested food starts to arrive in the small intestine as semi-liquid chyme , one hour after it

7920-442: The breakdown of food into smaller and smaller components, until they can be absorbed and assimilated into the body. The process of digestion has three stages: the cephalic phase , the gastric phase , and the intestinal phase . The first stage, the cephalic phase of digestion, begins with secretions from gastric glands in response to the sight and smell of food. This stage includes the mechanical breakdown of food by chewing , and

8052-467: The bulk of lipoproteins. The liver is located in the upper right quadrant of the abdomen and below the diaphragm to which it is attached at one part, the bare area of the liver. This is to the right of the stomach and it overlies the gall bladder. The liver synthesises bile acids and lecithin to promote the digestion of fat. Bile produced by the liver is made up of water (97%), bile salts , mucus and pigments , 1% fats and inorganic salts. Bilirubin

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8184-466: The centre of each segment are branches of the portal vein, hepatic artery, and bile duct. In the periphery of each segment is vascular outflow through the hepatic veins. The classification system uses the vascular supply in the liver to separate the functional units (numbered I to VIII) with unit 1, the caudate lobe, receiving its supply from both the right and the left branches of the portal vein. It contains one or more hepatic veins which drain directly into

8316-413: The chemical breakdown by digestive enzymes , that takes place in the mouth . Saliva contains the digestive enzymes amylase , and lingual lipase , secreted by the salivary and serous glands on the tongue. Chewing, in which the food is mixed with saliva, begins the mechanical process of digestion. This produces a bolus which is swallowed down the esophagus to enter the stomach . The second stage,

8448-413: The common hepatic duct to form the common bile duct. The biliary system and connective tissue is supplied by the hepatic artery alone. Bile either drains directly into the duodenum via the common bile duct, or is 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 hepatopancreatic ampulla, also known as

8580-407: The development of alcoholic liver diseases are not only the quantity and frequency of alcohol consumption, but can also include gender, genetics, and liver insult. Liver damage can also be caused by drugs , particularly paracetamol and drugs used to treat cancer. A rupture of the liver can be caused by a liver shot used in combat sports. Primary biliary cholangitis is an autoimmune disease of

8712-550: The diaphragm, to the right of the stomach, and overlying the gallbladder . The liver is connected to two large blood vessels : the hepatic artery and the portal vein . The hepatic artery carries oxygen-rich blood from the aorta via the celiac trunk , whereas the portal vein carries blood rich in digested nutrients from the entire gastrointestinal tract and also from the spleen and pancreas . These blood vessels subdivide into small capillaries known as liver sinusoids , which then lead to hepatic lobules . Hepatic lobules are

8844-424: The digestion of proteins . As these two chemicals would damage the stomach wall, mucus is secreted by innumerable gastric glands in the stomach, to provide a slimy protective layer against the damaging effects of the chemicals on the inner layers of the stomach. At the same time that protein is being digested, mechanical churning occurs through the action of peristalsis, waves of muscular contractions that move along

8976-441: The digestion of food. The organs known as the accessory digestive organs are the liver , gall bladder and pancreas . Other components include the mouth , salivary glands , tongue , teeth and epiglottis . The largest structure of the digestive system is the gastrointestinal tract (GI tract). This starts at the mouth and ends at the anus , covering a distance of about nine metres (30 ft). A major digestive organ

9108-401: The digestive process, and mainly contains hydrochloric acid and sodium chloride . A peptide hormone , gastrin , produced by G cells in the gastric glands , stimulates the production of gastric juice which activates the digestive enzymes. Pepsinogen is a precursor enzyme ( zymogen ) produced by the gastric chief cells , and gastric acid activates this to the enzyme pepsin which begins

9240-418: The edge of the liver lobule, where they merge to form bile ducts. Within the liver, these ducts are termed intrahepatic bile ducts, and once they exit the liver, they are considered extrahepatic. The intrahepatic ducts eventually drain into the right and left hepatic ducts, which exit the liver at the transverse fissure , and merge to form the common hepatic duct. The cystic duct from the gallbladder joins with

9372-435: The eighth segment is only visible in the visceral view. On the diaphragmatic surface, apart from a triangular bare area where it connects to the diaphragm, the liver is covered by a thin, double-layered membrane, the peritoneum , that helps to reduce friction against other organs. This surface covers the convex shape of the two lobes where it accommodates the shape of the diaphragm. The peritoneum folds back on itself to form

9504-590: The enterocyte villi and into their lymph capillaries called lacteals . A milky fluid called chyle , consisting mainly of the emulsified fats of the chylomicrons, results from the absorbed mix with the lymph in the lacteals. Chyle is then transported through the lymphatic system to the rest of the body. Vena cava In anatomy , the venae cavae ( / ˈ v iː n i ˈ k eɪ v i / ; sg. : vena cava / ˈ v iː n ə ˈ k eɪ v ə / ; from Latin  'hollow veins') are two large veins ( great vessels ) that return deoxygenated blood from

9636-406: The enzymes; which avoids the onset of pancreatitis caused by autodegradation. Once released in the intestine, the enzyme enteropeptidase present in the intestinal mucosa activates trypsinogen by cleaving it to form trypsin; further cleavage results in chymotripsin. The lower gastrointestinal tract (GI), includes the small intestine and all of the large intestine . The intestine is also called

9768-429: The esophagus. During swallowing, food passes from the mouth through the pharynx into the esophagus. The epiglottis folds down to a more horizontal position to direct the food into the esophagus, and away from the trachea . Once in the esophagus, the bolus travels down to the stomach via rhythmic contraction and relaxation of muscles known as peristalsis . The lower esophageal sphincter is a muscular sphincter surrounding

9900-558: The family Herpesviridae such as the herpes simplex virus . Chronic (rather than acute) infection with hepatitis B virus or hepatitis C virus is the main cause of liver cancer . Globally, about 248 million individuals are chronically infected with hepatitis B (with 843,724 in the U.S.), and 142 million are chronically infected with hepatitis C (with 2.7 million in the U.S.). Globally there are about 114 million and 20 million cases of hepatitis A and hepatitis E respectively, but these generally resolve and do not become chronic. Hepatitis D virus

10032-462: The fat is absorbed, the bile is also absorbed and transported back to the liver for reuse. The pancreas is a major organ functioning as an accessory digestive gland in the digestive system. It is both an endocrine gland and an exocrine gland . The endocrine part secretes insulin when the blood sugar becomes high; insulin moves glucose from the blood into the muscles and other tissues for use as energy. The endocrine part releases glucagon when

10164-493: The food should be eaten or not. It was the findings in 1991, describing the first olfactory receptors that helped to prompt the research into taste. The olfactory receptors are located on cell surfaces in the nose which bind to chemicals enabling the detection of smells. It is assumed that signals from taste receptors work together with those from the nose, to form an idea of complex food flavours. Teeth are complex structures made of materials specific to them. They are made of

10296-399: The food with the help of saliva and mucus results in the formation of a soft bolus which can then be swallowed to make its way down the upper gastrointestinal tract to the stomach. The digestive enzymes in saliva also help in keeping the teeth clean by breaking down any lodged food particles. The epiglottis is a flap of elastic cartilage attached to the entrance of the larynx . It

10428-414: The formation of the bolus. There are three pairs of main salivary glands and between 800 and 1,000 minor salivary glands, all of which mainly serve the digestive process, and also play an important role in the maintenance of dental health and general mouth lubrication, without which speech would be impossible. The main glands are all exocrine glands , secreting via ducts. All of these glands terminate in

10560-445: The functional lobes are further divided into a total of eight subsegments based on a transverse plane through the bifurcation of the main portal vein. The caudate lobe is a separate structure that receives blood flow from both the right- and left-sided vascular branches. The Couinaud classification divides the liver into eight functionally independent liver segments. Each segment has its own vascular inflow, outflow and biliary drainage. In

10692-410: The functional units of the liver. Each lobule is made up of millions of hepatic cells (hepatocytes), which are the basic metabolic cells. The lobules are held together by a fine, dense, irregular, fibroelastic connective tissue layer extending from the fibrous capsule covering the entire liver known as Glisson's capsule after British doctor Francis Glisson . This tissue extends into the structure of

10824-485: The functions of a mature hepatocyte, and eventually mature hepatocytes appear as highly polarized epithelial cells with abundant glycogen accumulation. In the adult liver, hepatocytes are not equivalent, with position along the portocentrovenular axis within a liver lobule dictating expression of metabolic genes involved in drug metabolism, carbohydrate metabolism , ammonia detoxification, and bile production and secretion. WNT/β-catenin has now been identified to be playing

10956-486: The fundus of the stomach, produce a glycoprotein called intrinsic factor which is essential for the absorption of vitamin B12 . Vitamin B12 (cobalamin), is carried to, and through the stomach, bound to a glycoprotein secreted by the salivary glands – transcobalamin I also called haptocorrin, which protects the acid-sensitive vitamin from the acidic stomach contents. Once in the more neutral duodenum, pancreatic enzymes break down

11088-437: The gallbladder does not empty properly the systems can fail. This is how gallstones form when a small piece of calcium gets coated with either cholesterol or bilirubin and the bile crystallises and forms a gallstone. The main purpose of the gallbladder is to store and release bile, or gall . Bile is released into the small intestine in order to help in the digestion of fats by breaking down larger molecules into smaller ones. After

11220-411: The gallbladder. Besides signals from the septum transversum mesenchyme, fibroblast growth factor from the developing heart also contributes to hepatic competence, along with retinoic acid emanating from the lateral plate mesoderm . The hepatic endodermal cells undergo a morphological transition from columnar to pseudostratified resulting in thickening into the early liver bud . Their expansion forms

11352-409: The gastric phase, happens in the stomach. Here, the food is further broken down by mixing with gastric acid until it passes into the duodenum , the first part of the small intestine . The third stage, the intestinal phase, begins in the duodenum. Here, the partially digested food is mixed with a number of enzymes produced by the pancreas. Digestion is helped by the chewing of food carried out by

11484-405: The imaginary plane, Cantlie's line, joining the gallbladder fossa 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

11616-404: The immune system) against microbes in food, when it makes contact with these glands on the tongue tissue. Sensory information can stimulate the secretion of saliva providing the necessary fluid for the tongue to work with and also to ease swallowing of the food. Saliva moistens and softens food, and along with the chewing action of the teeth, transforms the food into a smooth bolus . The bolus

11748-437: The inferior vena cava, allowing placental blood to bypass the liver. In the fetus, the liver does not perform the normal digestive processes and filtration of the infant liver because nutrients are received directly from the mother via the placenta . The fetal liver releases some blood stem cells that migrate to the fetal thymus , creating the T cells (or T lymphocytes). After birth, the formation of blood stem cells shifts to

11880-459: The inferior vena cava. The remainder of the units (II to VIII) are numbered in a clockwise fashion: About 20,000 protein coding genes are expressed in human cells and 60% of these genes are expressed in a normal, adult liver. Over 400 genes are more specifically expressed in the liver, with some 150 genes highly specific for liver tissue. A large fraction of the corresponding liver-specific proteins are mainly expressed in hepatocytes and secreted into

12012-425: The intestines (the majority being in the small intestine). They are unusual cells in that they have villi on their surface which in turn have innumerable microvilli on their surface. All these villi make for a greater surface area, not only for the absorption of chyme but also for its further digestion by large numbers of digestive enzymes present on the microvilli. The chylomicrons are small enough to pass through

12144-421: The left hepatic vein. The hilum of the liver is described in terms of three plates that contain the bile ducts and blood vessels. The contents of the whole plate system are surrounded by a sheath. The three plates are the hilar plate , the cystic plate and the umbilical plate and the plate system is the site of the many anatomical variations to be found in the liver. In the widely used Couinaud system,

12276-414: The lining of the intestine. The mucus component lubricates the walls of the intestine. When the digested food particles are reduced enough in size and composition, they can be absorbed by the intestinal wall and carried to the bloodstream. The first receptacle for this chyme is the duodenal bulb . From here it passes into the first of the three sections of the small intestine, the duodenum (the next section

12408-444: The liver and drain into the inferior vena cava. The biliary tract is derived from the branches of the bile ducts. The biliary tract, also known as the biliary tree, is the path by which bile is secreted by the liver then transported to the first part of the small intestine, the duodenum . The bile produced in the liver is collected in bile canaliculi , small grooves between the faces of adjacent hepatocytes. The canaliculi radiate to

12540-492: The liver and gallbladder into two halves. This line is called Cantlie's line . Other anatomical landmarks include the ligamentum venosum and the round ligament of the liver , which further divide the left side of the liver in two sections. An important anatomical landmark, the porta hepatis , divides this left portion into four segments, which can be numbered starting at the caudate lobe as I in an anticlockwise manner. From this parietal view, seven segments can be seen, because

12672-492: The liver are carried out by the liver cells or hepatocytes. The liver is thought to be responsible for up to 500 separate functions, usually in combination with other systems and organs. Currently, no artificial organ or device is capable of reproducing all the functions of the liver. Some functions can be carried out by liver dialysis , an experimental treatment for liver failure . The liver also accounts for about 20% of resting total body oxygen consumption. The liver receives

12804-410: The liver at its bare area . The esophagus enters the abdomen through a hole in the diaphragm at the level of T10 . The stomach is a major organ of the gastrointestinal tract and digestive system. It is a consistently J-shaped organ joined to the esophagus at its upper end and to the duodenum at its lower end. Gastric acid (informally gastric juice ), produced in the stomach plays a vital role in

12936-493: The liver by accompanying the blood vessels, ducts, and nerves at the hepatic hilum. The whole surface of the liver, except for the bare area , is covered in a serous coat derived from the peritoneum , and this firmly adheres to the inner Glisson's capsule. Terminology related to the liver often starts in hepat- from ἡπατο-, from the Greek word for liver. The liver is grossly divided into two parts when viewed from above –

13068-489: The liver in response to injury or inflammation. The most common chronic liver disease is nonalcoholic fatty liver disease , which affects an estimated one-third of the world population. Hepatitis is a common condition of inflammation of the liver. The most usual cause of this is viral , and the most common of these infections are hepatitis A , B , C , D , and E . Some of these infections are sexually transmitted . Inflammation can also be caused by other viruses in

13200-404: The liver is the umbilical vein, which supplies nutrients to the growing fetus. The umbilical vein enters the abdomen at the umbilicus and passes upward along the free margin of the falciform ligament of the liver to the inferior surface of the liver. There, it joins with the left branch of the portal vein. The ductus venosus carries blood from the left portal vein to the left hepatic vein and then to

13332-418: The liver only produces symptoms after extensive damage. Hepatomegaly refers to an enlarged liver and can be due to many causes. It can be palpated in a liver span measurement. Consuming caffeine regularly may help safeguard individuals from liver cirrhosis . Additionally, it has been shown to slow the advancement of liver disease in those already affected, lower the risk of liver fibrosis, and provide

13464-464: The liver volume is occupied by parenchymal hepatocytes. Nonparenchymal cells constitute 40% of the total number of liver cells but only 6.5% of its volume. The liver sinusoids are lined with two types of cell, sinusoidal endothelial cells , and phagocytic Kupffer cells . Hepatic stellate cells are nonparenchymal cells found in the perisinusoidal space , between a sinusoid and a hepatocyte. Additionally, intrahepatic lymphocytes are often present in

13596-443: The liver's oxygen demand is met by the hepatic portal vein, and half is met by the hepatic arteries. The hepatic artery also has both alpha- and beta-adrenergic receptors; therefore, flow through the artery is controlled, in part, by the splanchnic nerves of the autonomic nervous system. Blood flows through the liver sinusoids and empties into the central vein of each lobule. The central veins coalesce into hepatic veins, which leave

13728-420: The liver, the liver expands, and 0.5 to 1 liter of extra blood is occasionally stored in the hepatic veins and sinuses. This occurs especially in cardiac failure with peripheral congestion. Thus, in effect, the liver is a large, expandable, venous organ capable of acting as a valuable blood reservoir in times of excess blood volume and capable of supplying extra blood in times of diminished blood volume. Because

13860-431: The liver. It is marked by slow progressive destruction of the small bile ducts of the liver, with the intralobular ducts ( Canals of Hering ) affected early in the disease. When these ducts are damaged, bile and other toxins build up in the liver ( cholestasis ) and over time damages the liver tissue in combination with ongoing immune related damage. This can lead to scarring ( fibrosis ) and cirrhosis . Cirrhosis increases

13992-427: The lobule's corners. The portal triad consists of the hepatic artery, the portal vein, and the common bile duct. The triad may be seen on a liver ultrasound, as a Mickey Mouse sign with the portal vein as the head, and the hepatic artery, and the common bile duct as the ears. Histology , the study of microscopic anatomy, shows two major types of liver cell: parenchymal cells and nonparenchymal cells. About 70–85% of

14124-447: The lower part of the esophagus. The gastroesophageal junction between the esophagus and the stomach is controlled by the lower esophageal sphincter, which remains constricted at all times other than during swallowing and vomiting to prevent the contents of the stomach from entering the esophagus. As the esophagus does not have the same protection from acid as the stomach, any failure of this sphincter can lead to heartburn. The diaphragm

14256-551: The lymph formed in the body under resting conditions arises in the liver. The liver is a vital organ and supports almost every other organ in the body. Because of its strategic location and multidimensional functions, the liver is prone to many diseases. The bare area of the liver is a site that is vulnerable to the passing of infection from the abdominal cavity to the thoracic cavity . Liver diseases may be diagnosed by liver function tests –blood tests that can identify various markers. For example, acute-phase reactants are produced by

14388-409: The manipulation of food (and speech ); the range of manipulation is optimally controlled by the action of several muscles and limited in its external range by the stretch of the frenum. The tongue's two sets of muscles, are four intrinsic muscles that originate in the tongue and are involved with its shaping, and four extrinsic muscles originating in bone that are involved with its movement. Taste

14520-424: The mouth where the first stage in the digestive process takes place, with the action of the tongue and the secretion of saliva. The tongue is a fleshy and muscular sensory organ , and the first sensory information is received via the taste buds in the papillae on its surface. If the taste is agreeable, the tongue will go into action, manipulating the food in the mouth which stimulates the secretion of saliva from

14652-423: The mouth. The largest of these are the parotid glands —their secretion is mainly serous . The next pair are underneath the jaw, the submandibular glands , these produce both serous fluid and mucus. The serous fluid is produced by serous glands in these salivary glands which also produce lingual lipase . They produce about 70% of the oral cavity saliva. The third pair are the sublingual glands located underneath

14784-405: The mucous membrane in the mouth is a thin layer of smooth muscle tissue and the loose connection to the membrane gives it its great elasticity. It covers the cheeks, inner surfaces of the lips , and floor of the mouth, and the mucin produced is highly protective against tooth decay . The roof of the mouth is termed the palate and it separates the oral cavity from the nasal cavity. The palate

14916-402: The pharynx push the food into the esophagus. The pharynx joins the esophagus at the oesophageal inlet which is located behind the cricoid cartilage . The esophagus , commonly known as the foodpipe or gullet, consists of a muscular tube through which food passes from the pharynx to the stomach. The esophagus is continuous with the laryngopharynx. It passes through the posterior mediastinum in

15048-429: The pores in the hepatic sinusoids are very permeable and allow ready passage of both fluid and proteins into the perisinusoidal space , the lymph draining from the liver usually has a protein concentration of about 6 g/dl, which is only slightly less than the protein concentration of plasma. Also, the high permeability of the liver sinusoid epithelium allows large quantities of lymph to form. Therefore, about half of all

15180-753: The portal vein. The expanding liver bud is colonized by hematopoietic cells . The bipotential hepatoblasts begin differentiating into biliary epithelial cells and hepatocytes. The biliary epithelial cells differentiate from hepatoblasts around portal veins, first producing a monolayer, and then a bilayer of cuboidal cells. In ductal plate, focal dilations emerge at points in the bilayer, become surrounded by portal mesenchyme, and undergo tubulogenesis into intrahepatic bile ducts. Hepatoblasts not adjacent to portal veins instead differentiate into hepatocytes and arrange into cords lined by sinusoidal epithelial cells and bile canaliculi. Once hepatoblasts are specified into hepatocytes and undergo further expansion, they begin acquiring

15312-447: The production of chyme which when fully broken down in the small intestine is absorbed as chyle into the lymphatic system . Most of the digestion of food takes place in the small intestine. Water and some minerals are reabsorbed back into the blood in the colon of the large intestine . The waste products of digestion ( feces ) are defecated from the rectum via the anus . There are several organs and other components involved in

15444-399: The production of platelets by the bone marrow. The liver plays several roles in lipid metabolism: it performs cholesterol synthesis, lipogenesis , and the production of triglycerides , and a bulk of the body's lipoproteins are synthesized in the liver. The liver plays a key role in digestion, as it produces and excretes bile (a yellowish liquid) required for emulsifying fats and help

15576-590: The production of cholecystokinin in the duodenum. (The enzymes that digest polysaccharides, by contrast, are primarily produced by the walls of the intestines.) The cells are filled with secretory granules containing the precursor digestive enzymes. The major proteases , the pancreatic enzymes which work on proteins, are trypsinogen and chymotrypsinogen . Elastase is also produced. Smaller amounts of lipase and amylase are secreted. The pancreas also secretes phospholipase A2 , lysophospholipase , and cholesterol esterase . The precursor zymogens , are inactive variants of

15708-419: The protective glycoprotein. The freed vitamin B12 then binds to intrinsic factor which is then absorbed by the enterocytes in the ileum. The stomach is a distensible organ and can normally expand to hold about one litre of food. This expansion is enabled by a series of gastric folds in the inner walls of the stomach. The stomach of a newborn baby will only be able to expand to retain about 30 ml. The spleen

15840-408: The red bone marrow . After 2–5 days, the umbilical vein and ductus venosus are obliterated; the former becomes the round ligament of liver and the latter becomes the ligamentum venosum. In the disorders of cirrhosis and portal hypertension , the umbilical vein can open up again. Unlike eutherian mammals, in marsupials the liver remains haematopoietic well after birth. The various functions of

15972-440: The resistance to blood flow in the liver, and can result in portal hypertension . Congested anastomoses between the portal venous system and the systemic circulation, can be a subsequent condition. There are also many pediatric liver diseases, including biliary atresia , alpha-1 antitrypsin deficiency , alagille syndrome , progressive familial intrahepatic cholestasis , Langerhans cell histiocytosis and hepatic hemangioma

16104-414: The right of the fossa , between the bare area and the caudate lobe, and immediately above the renal impression. The greater part of the suprarenal impression is devoid of peritoneum and it lodges the right suprarenal gland. Medial to the renal impression is a third and slightly marked impression, lying between it and the neck of the gall bladder. This is caused by the descending portion of the duodenum, and

16236-409: The right of the gallbladder fossa are two impressions, one behind the other and separated by a ridge. The one in front is a shallow colic impression, formed by the hepatic flexure and the one behind is a deeper renal impression accommodating part of the right kidney and part of the suprarenal gland . The suprarenal impression is a small, triangular, depressed area on the liver. It is located close to

16368-428: The salivary glands. The liquid quality of the saliva will help in the softening of the food and its enzyme content will start to break down the food whilst it is still in the mouth. The first part of the food to be broken down is the starch of carbohydrates (by the enzyme amylase in the saliva). The tongue is attached to the floor of the mouth by a ligamentous band called the frenum and this gives it great mobility for

16500-415: The sinusoidal lumen. The central area or hepatic hilum , includes the opening known as the porta hepatis which carries the common bile duct and common hepatic artery , and the opening for the portal vein. The duct, vein, and artery divide into left and right branches, and the areas of the liver supplied by these branches constitute the functional left and right lobes. The functional lobes are separated by

16632-480: The small intestine. Segmentation contractions act to mix and move the chyme more slowly in the small intestine allowing more time for absorption (and these continue in the large intestine). In the duodenum, pancreatic lipase is secreted together with a co-enzyme , colipase to further digest the fat content of the chyme. From this breakdown, smaller particles of emulsified fats called chylomicrons are produced. There are also digestive cells called enterocytes lining

16764-425: The small intestine. Bile flows from the liver through the bile ducts and into the gall bladder for storage. The bile is released in response to cholecystokinin (CCK), a peptide hormone released from the duodenum. The production of CCK (by endocrine cells of the duodenum) is stimulated by the presence of fat in the duodenum. It is divided into three sections, a fundus, body and neck. The neck tapers and connects to

16896-443: The starch content into maltose. There are other serous glands on the surface of the tongue that encircle taste buds on the back part of the tongue and these also produce lingual lipase . Lipase is a digestive enzyme that catalyses the hydrolysis of lipids (fats). These glands are termed Von Ebner's glands which have also been shown to have another function in the secretion of histatins which offer an early defense (outside of

17028-422: The stomach wall. This allows the mass of food to further mix with the digestive enzymes. Gastric lipase secreted by the chief cells in the fundic glands in the gastric mucosa of the stomach, is an acidic lipase, in contrast with the alkaline pancreatic lipase. This breaks down fats to some degree though is not as efficient as the pancreatic lipase. The pylorus , the lowest section of the stomach which attaches to

17160-427: The storage of glycogen which it can form from glucose ( glycogenesis ). The liver can also synthesise glucose from certain amino acids . Its digestive functions are largely involved with the breaking down of carbohydrates. It also maintains protein metabolism in its synthesis and degradation. In lipid metabolism it synthesises cholesterol . Fats are also produced in the process of lipogenesis . The liver synthesises

17292-412: The tongue and their secretion is mainly mucous with a small percentage of saliva. Within the oral mucosa, and also on the tongue, palates, and floor of the mouth, are the minor salivary glands; their secretions are mainly mucous and they are innervated by the facial nerve ( CN7 ). The glands also secrete amylase a first stage in the breakdown of food acting on the carbohydrate in the food to transform

17424-404: The tongue. The mouth consists of two regions; the vestibule and the oral cavity proper. The vestibule is the area between the teeth, lips and cheeks, and the rest is the oral cavity proper. Most of the oral cavity is lined with oral mucosa , a mucous membrane that produces a lubricating mucus , of which only a small amount is needed. Mucous membranes vary in structure in the different regions of

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