Art & science
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The synthesis of art and science is lived by the nurse in the nursing act
Josephine G Paterson
The digestive system: part 2 Hendry C et al (2014) The digestive system: part 2. Nursing Standard. 28, 25, 37-44. Date of submission: December 18 2012; date of acceptance: March 18 2013.
Abstract This article, which forms part of the life sciences series and is the second of two articles on the digestive system, explores the structure and function of the liver, gall bladder and pancreas. It is important that nurses understand how the digestive system works and identify its role in maintaining health. The gross structures of the liver, gall bladder and pancreas associated with the gastrointestinal tract are described, along with relevant physiology and pathologies.
Authors Charles Hendry Retired. Former senior lecturer, School of Nursing and Midwifery, University of Dundee. Alistair Farley Retired. Former lecturer in nursing, School of Nursing and Midwifery, University of Dundee. Ella McLafferty Retired. Former senior lecturer, School of Nursing and Midwifery, University of Dundee. Carolyn Johnstone Lecturer in nursing, School of Nursing and Midwifery, University of Dundee. Correspondence to: [email protected]
Keywords Absorption, cirrhosis, digestion, digestive system and disorders, enzymes, gall bladder, liver, metabolism, pancreas, pancreatitis
Review All articles are subject to external double-blind peer review and checked for plagiarism using automated software.
Online Guidelines on writing for publication are available at www.nursing-standard.co.uk. For related articles, visit the archive and search using the keywords above.
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THE LIVER, GALL BLADDER and pancreas are accessory organs of the digestive system. They have many important functions, including providing enzymes for the digestion of food in preparation for absorption of nutrients from the digestive system.
Liver Most of the liver is situated in the right upper quadrant of the abdominal cavity (Thibodeau and Patton 2008) (Figure 1). It is tucked under the diaphragm and is in contact with the ribs on the right side of the body (Seeley et al 2007). It is the second largest organ of the body after the skin, weighing 1.4kg (Seeley et al 2007, Tortora and Derrickson 2009). The liver has two main lobes, the right and left lobes, and two smaller lobes, the caudate and quadrate lobes, which are found under the main lobes (Seeley et al 2007). Since the liver produces bile, it has also been described as an exocrine gland. Blood supply to the liver is important and reaches the liver from two sources. Oxygenated blood travels to the liver via the hepatic artery, oxygenating the liver. Venous blood is carried from the organs of the gastrointestinal tract and the spleen via the hepatic portal vein. This venous blood is rich in nutrients and other substances that have been absorbed from the digestive system. Consequently, the products are carried directly to the liver for processing, storage or detoxification, before products needed by other cells are secreted back into the circulation (Sherwood 2013). Blood leaves the liver through the hepatic vein, which then empties into the inferior vena cava. The liver has many functions, including (Tortora and Derrickson 2009, Sherwood 2013): Metabolism of carbohydrate, lipid and protein nutrients absorbed from the digestive system. february 19 :: vol 28 no 25 :: 2014 37
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Art & science life sciences: 17 Secretion of bile salts, which are important in the digestion and absorption of fat. Detoxification of body waste, hormones, drugs and other foreign compounds. Synthesis of plasma proteins, including globulins, albumin, prothrombin and fibrinogen. Storage of glycogen, fats, iron, copper and many vitamins. Activation of vitamin D in conjunction with the kidneys and skin. Removal of bacteria and aged red blood cells. Excretion of cholesterol and bilirubin. Bilirubin is a breakdown product of red blood cells. The liver is made up of lobules, hepatocytes, bile canaliculi and hepatic sinusoids. The lobules are hexagonal in shape and surround a central vein. At the outer edge of each lobule, there is a branch of the hepatic artery, a branch of the portal vein and a bile duct (Sherwood 2013). Between the centre and margins of each lobule are hepatocytes forming hepatic rows (Seeley et al 2007), and it is these hepatocytes that carry out the metabolic and secretory functions of the liver. Between the rows of hepatocytes, there are small ducts called bile canaliculi that collect bile produced by the hepatocytes and carry bile to the bile ducts (Tortora and Derrickson 2009). The bile ducts eventually come together to form the right and left hepatic ducts that converge and leave the liver as the common hepatic duct. The common hepatic duct then joins the cystic duct from the gall bladder to become the common bile duct. Bile enters the small intestine at the duodenum through the common bile duct. When the hepato-pancreatic sphincter, which is also called the sphincter of Oddi, is closed, bile is unable to enter the duodenum and is stored in the gall bladder until the sphincter is relaxed (Waugh and Grant 2010). Between the rows of hepatocytes, blood channels known as hepatic sinusoids are found. The sinusoids receive oxygenated blood from branches of the hepatic artery and nutrient-rich blood from branches of the hepatic portal vein. The sinusoids come together and deliver blood into a central vein, which flows into the hepatic vein and into the inferior vena cava (Tortora and Derrickson 2009). Phagocytes called stellate reticuloendothelial cells or Kupffer cells are found in the sinusoids and these destroy damaged red and white blood cells, bacteria and other foreign substances in the venous blood received from the digestive system (Tortora and Derrickson 2009). 38 february 19 :: vol 28 no 25 :: 2014
Gall bladder The gall bladder is a pear-shaped organ lying under the right lobe of the liver (Figure 1). Its main function is to store and concentrate bile until it is required for digestion and it can hold 30-60mL of bile (Watson 2005). When the sphincter of Oddi is closed, bile does not directly enter the duodenum, but is diverted into the gall bladder from the common bile duct (Sherwood 2013). Between 250mL and 1L of bile is secreted every day, depending on the level of stimulation, with such stimulants being the presence of acid and/or lipids or fats in the duodenum (Sherwood 2013). Secretin is released from the duodenal mucosa in response to the presence of acid in the duodenum, stimulating the liver to secrete bile. When chyme containing lipids or fat enters the duodenum, the gall bladder contracts and forces bile into the small intestine. The fats in chyme stimulate the secretion of the hormone cholecystokinin from the duodenal mucosa. This then stimulates the contraction of the gall bladder, causing bile to flow into the duodenum (Seeley et al 2007, Thibodeau and Patton 2008).
Bile
Although there are no enzymes in bile, it is important in digestion because it dilutes and neutralises acid from the stomach (Seeley et al 2007). It is also important in the digestion and absorption of fats (Sherwood 2013). Bile has an approximate pH of 8 and contains water, mineral salts, mucus, bile salts, bile pigments (mainly bilirubin), cholesterol and lecithin (Waugh and Grant 2010, Sherwood 2013). The liver secretes bile in response to the hormones secretin and cholecystokinin. As mentioned previously, cholecystokinin causes the gall bladder to contract and release bile into the duodenum (Seeley et al 2007, Thibodeau and Patton 2008)). Bile salts, derived from cholesterol, are found in substantial amounts in bile and are important in the mechanical breakdown of fats through the process of emulsification (Seeley et al 2007). Most bile salts are reabsorbed in the ileum and returned to the liver (Seeley et al 2007). Cholesterol is excreted in bile (Thibodeau and Patton 2008) and if there is too much cholesterol in bile, then gallstones can form (Sherwood 2013). Bilirubin is not involved in digestion; however, it is important because it is mainly obtained from the breakdown of red blood cells. Red blood cells have a useful life of approximately 120 days before they are broken down and bilirubin is the product of the haem component of haemoglobin.
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Pancreas The pancreas lies behind the stomach and fits into the area where the duodenum curves (Figure 1). It is both an exocrine and endocrine gland. It is an endocrine gland because it secretes hormones directly into the bloodstream. The endocrine portion accounts for 1% of the cells throughout the pancreas, which form clusters called pancreatic islets or islets of Langerhans (Tortora and Derrickson 2009). The islets manufacture the hormones insulin and glucagon, which are essential for the regulation of blood glucose levels (Seeley et al 2007). The exocrine portion of the pancreas is organised into grape-like sacs called acini, which connect into small ducts, then larger ducts and finally form the pancreatic duct, which joins the common bile duct and terminates in the duodenum at the sphincter of Oddi (Tortora and Derrickson 2009). The acini secrete pancreatic juice, which is colourless and comprises digestive enzymes, some salts, and water (Tortora and Derrickson 2009). Pancreatic juice is slightly alkaline as a result of the presence of bicarbonate ions and has a pH of 7.1-8.2 (Tortora and Derrickson 2009). This is important because it helps to deactivate pepsin from the stomach and to create an environment in the small intestine where the enzymes can function effectively. The alkalinity of the pancreatic juice also neutralises the potential effects of acidic chyme on the surface of the duodenum (Seeley et al 2007). The presence of chyme in the duodenum during the intestinal phase of digestion, stimulates the release of pancreatic enzymes. The acini secrete three main types of digestive enzymes: Proteolytic enzymes for digestion of proteins. Pancreatic amylase for digestion of carbohydrates. Pancreatic lipase for digestion of fats. The pancreas secretes three main proteolytic enzymes in an inactive form: trypsinogen, chymotrypsinogen and procarboxypeptidase. When trypsinogen is secreted into the duodenum, enterokinase, an enzyme found in the duodenal
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mucosa, activates trypsinogen to form trypsin. Trypsin is activated outside the pancreas because if it formed inside the pancreas, digestion of the pancreatic cells would occur. In the duodenum, trypsin converts chymotrypsinogen to chymotrypsin and procarboxypeptidase to carboxypeptidase. These enzymes break down proteins with different peptide linkages into amino acids and peptide chains. Pancreatic amylase converts polysaccharides into disaccharides, and pancreatic lipase breaks down triglycerides into monoglycerides and free fatty acids that can be readily absorbed (Sherwood 2013). Exocrine secretion from the pancreas is mainly regulated by the hormones secretin and cholecystokinin, which are released when chyme enters the duodenum (Seeley et al 2007). Secretin is carried in the bloodstream to the pancreas where it triggers the release of the alkaline pancreatic juice, with the amount of juice released being directly proportional to the amount of acid present in the duodenum. The role of cholecystokinin is to control the amount of pancreatic enzyme secretions and the trigger for its release from the duodenal mucosa is the presence of fat and protein (Seeley et al 2007). Cholecystokinin also travels to the pancreas via the bloodstream, where it triggers the acinar cells to secrete digestive enzymes (Sherwood 2013).
FIGURE 1 Anterior view of the liver, gall bladder and pancreas Right lobe of liver
Diaphragm
Left lobe of liver
Right hepatic duct Left hepatic Leftduct lobe
Common hepatic duct
of liver Common bile duct Pancreatic duct
Gall bladder Duodenum
Sphincter of Oddi
Pancreas
Jejunum
PETER LAMB
The hepatocytes remove bilirubin from red blood cells and excrete it in bile, and it is this process that gives bile its yellow colour. In the large intestine, bacteria break down bilirubin and the by-product is stercobilin, and it is this which gives faeces their characteristic brown colour. A small amount of bilirubin is reabsorbed by the intestine into the bloodstream and excreted by the kidneys, giving urine its yellow colour (Sherwood 2013).
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Art & science life sciences: 17 Digestion The digestive system transports nutrients, water and electrolytes from food into the body’s inner environment. Food provides a source of energy for the production of adenosine triphosphate (ATP) by cells so that the functions of active transport, contraction, synthesis and secretion, which are energy-dependent activities, can be carried out (Sherwood 2013). Food is also required so that body tissues can be repaired and renewed and for this to occur, food needs to be processed into a form that the body can use readily. There are four fundamental digestive processes: motility, secretion, digestion and absorption.
Motility, secretion and digestion
Motility is the process by which the contents of the gastrointestinal tract are mixed and moved forward by muscular contractions. Smooth muscle in the walls of the gastrointestinal tract maintains a steady low level of contraction called tone. This tone keeps a constant pressure on the contents of the gastrointestinal tract and also allows it to return to its normal size once food has passed through the system (Sherwood 2013). In addition to this tonic activity, there are propulsive movements in the gastrointestinal tract that ensure food contents can be pushed through the system (Tortora and Derrickson 2009), and these movements occur at different speeds depending on the functions of the organs of the gastrointestinal tract. For example, food moves quickly through the oesophagus (five to nine seconds), whereas food remains for longer in the small intestine to permit the breakdown and absorption of nutrients and products of digestion (Sherwood 2013). There are also mixing movements in which the food contents are mixed with digestive juices to aid digestion, and these movements also aid absorption of food by exposing the contents to the surfaces of the gastrointestinal tract where absorption occurs (Sherwood 2013). In addition, exocrine glands secrete digestive juices along the gastrointestinal tract, aiding digestion. Mechanical digestion occurs where food is broken down into its smaller constituent parts, mixed with digestive juices, moved along the gastrointestinal tract and removed from the body as faeces. It consists of chewing, swallowing, peristalsis and defecation. Chemical digestion occurs when food is broken down into absorbable units so that they can pass through the intestinal mucosa into the circulatory system (Thibodeau and Patton 2008). The aim of digestion is to hydrolyse (break down) food using enzymes from the different organs and 40 february 19 :: vol 28 no 25 :: 2014
these enzymes achieve this by breaking covalent chemical bonds in organic molecules (Seeley et al 2007). Carbohydrate digestion starts in the mouth with the action of salivary amylase, but the food does not spend enough time in the mouth to be fully digested. Therefore, most carbohydrate digestion takes place in the small intestine through the action of pancreatic amylase. Pancreatic amylase breaks down polysaccharides into disaccharides (Waugh and Grant 2010). Disaccharides are broken down into monosaccharides by the enzymes maltase, sucrase and lactase, acting on maltose, sucrose and lactose respectively in the microvilli of the intestinal mucosa (Thibodeau and Patton 2008). The end products of these enzymatic activities are glucose, fructose and galactose, and it is these monosaccharides that are absorbed by cells (Sherwood 2013). Protein digestion commences in the stomach. Pepsinogen is secreted in gastric juice and activated by hydrochloric acid, becoming pepsin and causing large protein molecules to be broken down into smaller peptide fragments. In the small intestine, digestion of polypeptide proteins continues through the action of pancreatic trypsin and intestinal juice peptidases (Thibodeau and Patton 2008). The peptide bonds are broken down, resulting in amino acids, which are absorbed by cells. Fat or lipid molecules are insoluble or only slightly insoluble in water, and they include triglycerides, phospholipids, steroids, and fat-soluble vitamins A, D, E and K. The most common types of fat are triglycerides. Fats provide a concentrated source of energy for the body. During digestion, lipids are emulsified in the small intestine, and bile salts from the liver are important in this process. Emulsification increases the surface area of the lipid droplets for the action of the enzyme pancreatic lipase, resulting in fatty acids and monoglycerides (Tortora and Derrickson 2009). Bile salts in the small intestine surround the small droplets of digested lipids to form structures known as micelles (Seeley et al 2007).
Absorption
Digestion is completed in the small intestine, with most absorption occurring here, although a small amount of absorption of digestion products also occurs in the large intestine. The components of carbohydrates, proteins and fats, as well as water, vitamins and electrolytes are transported from the mucosal lining of the small intestine into the blood or lymph systems. Minerals are actively transported through the intestinal mucosa, while water moves through by osmosis – approximately 9L of water is absorbed
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daily from the gastrointestinal tract (Tortora and Derrickson 2009). Monosaccharides enter the epithelial cells of a villus, enter a blood capillary within the villus and are transported to the liver via the hepatic portal vein. Amino acids, dipeptides and tripeptides are absorbed mainly in the duodenum and jejunum, where they are absorbed into the cells of the villi and enter blood capillaries. Amino acids are carried into the hepatic portal system and into the general circulation if they are not removed by the liver cells, whereby the body cells take up amino acids for protein synthesis and the production of ATP (Tortora and Derrickson 2009). When a micelle comes into contact with the epithelial cells of the small intestine, the fatty acids and monoglycerides diffuse through the epithelial walls and the micelles remain in the chyme. Once inside the epithelial cells, the fatty acids and monoglycerides reform to make triglycerides. The triglycerides combine with cholesterol and are re-packaged inside a protein coat and are now known as chylomicrons. The chylomicrons leave the epithelial cells and enter the lacteals of the villus and are then transported in the lymphatic vessels as chyle. Chyle is transported to the thoracic duct and enters the bloodstream at the left subclavian vein and the fats eventually enter the liver via the hepatic artery. Water-soluble vitamins C and B are dissolved in water and are absorbed mostly from the small intestine. Vitamin B12 must be combined with intrinsic factor, secreted in the stomach, for absorption via active transport in the ileum. The fat-soluble vitamins A, D, E and K are absorbed along with the end products of fat digestion and pass into the lacteals (Thibodeau and Patton 2008).
Metabolism Once food is digested and absorbed, it needs to be metabolised to provide energy for renewal and replacement of cells in the body. Metabolism encompasses all the chemical reactions that occur in the body (Waugh and Grant 2010). Catabolism is the breakdown of large molecules into small molecules, releasing chemical energy which is stored as ATP and heat. The heat produced keeps the core temperature of the body at 36.8°C, which is the optimum level for chemical function (Waugh and Grant 2010). Any excess heat is dispersed through the skin. Anabolism is the building up or synthesis of smaller molecules into larger molecules, and ATP usually provides the energy source for these processes (Waugh and Grant 2010). Catabolism and anabolism usually entail a series of chemical
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reactions known as metabolic pathways and these pathways contain a number of small steps that allow a controlled release of energy from ATP. The pathways are regulated by hormones so that they meet the individual’s varying requirements (Waugh and Grant 2010). The metabolic rate is the rate at which energy is released within cells, and this release of energy requires oxygen and produces carbon dioxide, water and heat as by-products.
Chronic liver disease There are several causes of chronic liver disease (Table 1), with the commonest in western countries being hepatitis C virus (HCV) and excessive alcohol consumption (Ballinger 2012). Chronic liver disease may be asymptomatic until the disease has progressed significantly or it is discovered by accident when routine blood tests are carried out for other disorders. Hepatitis is inflammation of the liver that can be a mild self-limited condition, serious chronic illness or fatal condition, depending on the cause (Poole 2009). There are several different viruses from hepatitis A to hepatitis G that can cause illness, but only the types identified in Table 1 result in chronic liver disease (Poole 2009). Hepatitis B virus (HBV) is commonly found in areas of Africa, and the Middle and Far East (Ballinger 2012). Transmission may occur between mother and baby during childbirth, through blood and blood products, through sexual intercourse and through minor abrasions and close contact (Ballinger 2012). HBV enters the hepatocyte causing a cellular response to the presence of foreign HBV proteins. This response can clear the infection in
TABLE 1 Causes of chronic liver disease Causes
Examples
Viral
Hepatitis B Hepatitis D Hepatitis C
Autoimmune
Associated with pernicious anaemia and thyroiditis
Drugs
Methotrexate Nitrofurantoin Isoniazid Ketoconazole
Hereditary
Wilson’s disease
Other
Inflammatory bowel disease Excessive alcohol consumption
(Ballinger 2012)
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Art & science life sciences: 17 99% of infected adults (Ballinger 2012). However, the infection can be asymptomatic, and if the infected proteins are not cleared then the patient may develop chronic hepatitis. Treatment of chronic HBV involves antiviral therapy and monitoring for liver damage (Poole 2009). Advice should be given to patients limiting alcohol consumption, smoking cessation and preventing transmission of the virus to others. This should include informing partners of their hepatitis status and avoiding sharing personal items, including toothbrushes and razors. Pregnant women should be given information on the risk of transfer of infection to their baby during childbirth (Lee et al 2010). Hepatitis D virus (HDV) is only present in people infected with HBV, and it can affect all risk groups for HBV, but is particularly prevalent in intravenous drug users and is also transmitted through close personal contact such as during sexual intercourse (Poole 2009, Ballinger 2012). It can either occur as a co-infection or a superinfection in the patient who has proteins for HBV. HDV progresses to severe liver damage and more commonly results in death than HBV alone (Tortora and Derrickson 2009). HCV can be found in populations worldwide, but is more common in southern Europe, Africa and Egypt (Ballinger 2012). In the UK, the main mode of transmission is via intravenous drug use. It can be spread through the use of drug-injecting paraphernalia, including needles and spoons, but it can also be transferred through the use of equipment for intranasal administration of drugs (Pears 2010). In developing countries, it is commonly transmitted through blood products and exposure to poorly sterilised instruments. An estimated 80% of people with HCV will progress to chronic hepatitis C (National Institute for Health and Care Excellence 2010).
Cirrhosis of the liver
Cirrhosis occurs when liver cells become necrosed and hepatocytes are replaced with thickened and scarred tissue (fibrosis) (Tortora and Derrickson 2009). These changes result in impaired liver function and alterations in the gross structure of the liver (Ballinger 2012). Portal hypertension is a common complication of cirrhosis where the pressure in the portal vein is raised, resulting in oesophageal and gastric varices. If the varices rupture, bleeding will occur (Fullwood 2012), which can be fatal. Cirrhosis of the liver is commonly linked to excessive alcohol consumption. Investigations to confirm cirrhosis include (Ballinger 2012): Liver biochemistry may be normal or serum alkaline phosphatase may be slightly raised. Full blood count indicates thrombocytopenia. Altered liver function is demonstrated by 42 february 19 :: vol 28 no 25 :: 2014
changes in prothrombin time and serum albumin. Serum electrolytes demonstrate a decrease in sodium levels indicative of severe liver disease. Elevated serum creatinine. Presence of raised levels of alpha-fetoproteins, which are not normally present after the fetal stage of life has ended. Signs and symptoms of cirrhosis include: Haematemesis (vomiting blood) and melaena (blood in faeces) related to gastrointestinal bleeding. Pyrexia related to sepsis and spontaneous bacterial peritonitis. Ascites (fluid accumulation within the abdominal cavity). Renal failure. Confusion and drowsiness related to hepatic encephalopathy. Low oxygen saturation related to pulmonary oedema (Kumar Bhamidimarri 2009). Other signs of chronic liver disease including spider naevi, spider telangiectases and reddening of palms (Ballinger 2012). Pruritis (itchy skin) related to jaundice caused by raised levels of bilirubin deposited under subcutaneous tissue, including the skin, sclera in the eyes and mucous membranes (Sargent and Clayton 2011). Symptoms of cirrhosis should be managed to make the patient comfortable; however, the disease is irreversible and commonly progresses with a five-year survival rate of 50% (Ballinger 2012).
Pancreatitis The most common cause of pancreatitis is the presence of gallstones, accounting for 45% of cases, and excessive alcohol intake, accounting for 35% of cases (Callaghan et al 2007). However, 10-20% of cases are idiopathic (Andris 2010) (Box 1). Pancreatitis can be classified as acute, when an attack occurs in a previously healthy person
BOX 1 Other causes of pancreatitis Hypertriglyceridaemia. Complication of endoscopic retrograde cholangiopancreatography. Drug reactions. Autoimmune disorders. Genetic mutations. Abdominal trauma. Infection. Hypercalcaemia. Hyperparathyroidism.
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with resolution of the problem, or chronic, where there are repeated attacks and the continuation of symptoms lead to a decrease in endocrine and exocrine function of the pancreas (Andris 2010). Acute pancreatitis is a serious medical condition. It can range from being fairly mild, where recovery occurs without complications, to severe pancreatitis causing necrotising pancreatitis with multisystem organ failure. The overall mortality rate for acute pancreatitis is 10-15%, and 40-50% for severe acute pancreatitis (Burroughs and Westaby 2009). In acute pancreatitis there is inflammation of the pancreas, which is followed by oedema and necrosis of pancreatic tissue. If the pancreatic duct is obstructed there will be hypertension in the duct, leading to a risk of rupture. If this happens, digestive enzymes are released into the pancreas leading to auto-digestion of the pancreas. If the disease progresses, the patient experiences severe fluid shifts, haemorrhage, sepsis and multiple system organ failure (Andris 2010). Fluid shifts occur when leaked enzymes result in autolysis of tissues causing oedema, and fluid may collect in spaces such as the peritoneal cavity. Acute pancreatitis may present with epigastric pain that may radiate to the back or chest and is eased by lying in the fetal position. Fatty foods and/or alcohol may exacerbate the pain. Nausea and vomiting are not uncommon, and bowel sounds are decreased or absent. Fluid loss contributes to hypotension and a subsequent rise in pulse rate in an attempt to maintain cardiac output. Hypotension may result in reduced peripheral perfusion. Pyrexia may be present (Huether 2006). Diagnosis of the condition will be made based on a history of the symptoms, physical examination and blood tests. A diagnosis of pancreatitis can be confirmed by (Burroughs and Westaby 2009): Raised serum amylase and serum lipase levels. Signs of paralytic ileus on abdominal X-ray. Gallstones or pancreatic enlargement on pancreatic and gall bladder ultrasound. Extent and severity of acute pancreatitis and complications identified on a computed tomography scan. Deformities in the pancreatic duct or impacted gallstones identified on endoscopic retrograde cholangiopancreatography. Management of patients with mild pancreatitis may include being nil-by-mouth to rest the pancreas and bowel, intravenous hydration, central venous pressure measurement, hourly measurement of urinary output, pain management, oxygen therapy, and management of nausea and vomiting, which may require insertion of a nasogastric tube
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to keep the stomach empty. In addition, hourly measurement of blood glucose in the acute phase is required because the endocrine function of the pancreas can be affected (Ballinger 2012). Regular recordings of temperature, pulse, blood pressure, respiration and pulse oximetry should also be done. Nutritional support using a naso-jejunal tube that bypasses the stomach and duodenum should be commenced so that the risk of stimulating the pancreas is bypassed. Feeding can be commenced after 48 hours if the patient is unable to begin oral feeding (Andris 2010). However, Talukdar and Swaroop Vege (2011) suggested that enteral nutrition should be started as early as possible in severe acute pancreatitis because the pancreas is in a state of unresponsiveness during an acute episode and the secretion of trypsin is reduced. If the patient shows signs or symptoms of alcohol withdrawal, it is important to treat this with benzodiazepines (Andris 2010). Late complications of pancreatitis include multiple system organ failure and necrotising pancreatitis (Burroughs and Westaby 2009).
Gall bladder disease The gall bladder, bile ducts and sphincter of Oddi work together to adapt, store and control the flow of bile. The main function of the gall bladder is to store bile, and gallstones can form when the gall bladder cannot maintain the soluble state of some of the components of bile. Gallstones are formed from either cholesterol or pigment, with cholesterol gallstones accounting for 80% of all gallstones (Burroughs and Westaby 2009). Pigment gallstones are made up of polymers of bilirubin and calcium bilirubinate (Ballinger 2012). Most gallstones do not cause symptoms, but biliary pain or colic can be exacerbated when there is a temporary obstruction of the cystic or common bile duct by a gallstone. Risk factors associated with the development of gallstones are listed in Box 2 (Ballinger 2012).
BOX 2 Risk factors for the development of gallstones Cirrhosis. Diabetes mellitus. Diet high in animal fat and low in fibre. Family history of gallstones. Female gender. Ileal disease leading to bile salt loss. Increasing age. Multiparity. Obesity. Rapid weight loss. (Ballinger 2012)
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Art & science life sciences: 17 Other signs and symptoms of acute cholecystitis, inflammation of the gall bladder that is usually related to gallstones, include (Baltimore and Davidson 2007): Sudden onset of severe pain in the right upper quadrant of the abdomen. Pain becomes worse on deep breathing and radiates to the right shoulder. Pain may recur for some hours after meals. Nausea and vomiting. Mild pyrexia. Stomach becomes distended. Investigations include history and abdominal ultrasound. Management includes analgesia and elective cholecystectomy, which is usually carried out laparascopically.
GLOSSARY
Conclusion
POINTS FOR PRACTICE
It is essential that nurses have a sound knowledge of the digestive system, including its components and accessory organs, so that they can identify any changes and select the appropriate nursing strategies to manage disorders of the digestive system NS
Hepatic sinusoids Blood vessels with incomplete walls containing a mixture of blood from the tiny branches of the hepatic artery and hepatic portal vein. This arrangement allows the arterial blood and the venous blood to come into close contact with the liver cells. Oxidation A chemical reaction in which oxygen is added to an element or compound. Spider naevi A form of telangiectasia, typified by a central elevated red dot the size of a pinhead from which small vessels radiate. Telangiectasis A branched group of dilated capillary vessels forming a spider-like image on the skin.
A diet high in saturated fats is associated with gallstone formation. Identify foods that contain saturated fats and those that contain unsaturated fats. Identify and describe the protocols in your clinical area for the nursing management of a patient who requires a liver biopsy. Describe the signs and symptoms that might be observed in a patient with alcohol withdrawal. Outline the management of such a patient.
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Appraisal Guidance 75 and 106. NICE, London Pears E (2010) Hepatitis C virus infection: risk factors, diagnosis and management. Nursing Standard. 25, 15-17, 49-56. Poole S (2009) Update on the treatment and management of patients with hepatitis. Journal of Infusion Nursing. 32, 5, 269-275. Sargent S, Clayton M (2011) Adult jaundice – the pathophysiology, classification and causes. Gastroenterology Nursing. 9, 4, 34-40. Seeley RR, Stephens TD, Tate P (2007) Essentials of Anatomy and Physiology. Sixth edition. McGraw Hill, Boston MA. Sherwood L (2013) Human Physiology: From Cells to Systems. Eighth edition. Brooks/Cole Cengage Learning, Belmont CA.
Talukdar R, Swaroop Vege S (2011) Early management of severe acute pancreatitis. Current Gastronenterology Reports. 13, 2, 123-130. Thibodeau GA, Patton KT (2008) Structure & Function of the Body. 13th edition. Elsevier Mosby, St. Louis MO. Tortora GJ, Derrickson BH (2009) Essentials of Anatomy and Physiology. Eighth edition International Student version. John Wiley and Sons, Hoboken NJ. Watson R (2005) Anatomy and Physiology for Nurses. 12th edition. Elsevier, Edinburgh. Waugh A, Grant A (2010) Ross and Wilson Anatomy and Physiology in Health and Illness. 11th edition. Churchill Livingstone Elsevier, Edinburgh.
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If you would like to contribute to the Art & science section, email [email protected]
The synthesis of art and science is lived by the nurse in the nursing act
Josephine G Paterson
The digestive system: part 2 Hendry C et al (2014) The digestive system: part 2. Nursing Standard. 28, 25, 37-44. Date of submission: December 18 2012; date of acceptance: March 18 2013.
Abstract This article, which forms part of the life sciences series and is the second of two articles on the digestive system, explores the structure and function of the liver, gall bladder and pancreas. It is important that nurses understand how the digestive system works and identify its role in maintaining health. The gross structures of the liver, gall bladder and pancreas associated with the gastrointestinal tract are described, along with relevant physiology and pathologies.
Authors Charles Hendry Retired. Former senior lecturer, School of Nursing and Midwifery, University of Dundee. Alistair Farley Retired. Former lecturer in nursing, School of Nursing and Midwifery, University of Dundee. Ella McLafferty Retired. Former senior lecturer, School of Nursing and Midwifery, University of Dundee. Carolyn Johnstone Lecturer in nursing, School of Nursing and Midwifery, University of Dundee. Correspondence to: [email protected]
Keywords Absorption, cirrhosis, digestion, digestive system and disorders, enzymes, gall bladder, liver, metabolism, pancreas, pancreatitis
Review All articles are subject to external double-blind peer review and checked for plagiarism using automated software.
Online Guidelines on writing for publication are available at www.nursing-standard.co.uk. For related articles, visit the archive and search using the keywords above.
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THE LIVER, GALL BLADDER and pancreas are accessory organs of the digestive system. They have many important functions, including providing enzymes for the digestion of food in preparation for absorption of nutrients from the digestive system.
Liver Most of the liver is situated in the right upper quadrant of the abdominal cavity (Thibodeau and Patton 2008) (Figure 1). It is tucked under the diaphragm and is in contact with the ribs on the right side of the body (Seeley et al 2007). It is the second largest organ of the body after the skin, weighing 1.4kg (Seeley et al 2007, Tortora and Derrickson 2009). The liver has two main lobes, the right and left lobes, and two smaller lobes, the caudate and quadrate lobes, which are found under the main lobes (Seeley et al 2007). Since the liver produces bile, it has also been described as an exocrine gland. Blood supply to the liver is important and reaches the liver from two sources. Oxygenated blood travels to the liver via the hepatic artery, oxygenating the liver. Venous blood is carried from the organs of the gastrointestinal tract and the spleen via the hepatic portal vein. This venous blood is rich in nutrients and other substances that have been absorbed from the digestive system. Consequently, the products are carried directly to the liver for processing, storage or detoxification, before products needed by other cells are secreted back into the circulation (Sherwood 2013). Blood leaves the liver through the hepatic vein, which then empties into the inferior vena cava. The liver has many functions, including (Tortora and Derrickson 2009, Sherwood 2013): Metabolism of carbohydrate, lipid and protein nutrients absorbed from the digestive system. february 19 :: vol 28 no 25 :: 2014 37
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Art & science life sciences: 17 Secretion of bile salts, which are important in the digestion and absorption of fat. Detoxification of body waste, hormones, drugs and other foreign compounds. Synthesis of plasma proteins, including globulins, albumin, prothrombin and fibrinogen. Storage of glycogen, fats, iron, copper and many vitamins. Activation of vitamin D in conjunction with the kidneys and skin. Removal of bacteria and aged red blood cells. Excretion of cholesterol and bilirubin. Bilirubin is a breakdown product of red blood cells. The liver is made up of lobules, hepatocytes, bile canaliculi and hepatic sinusoids. The lobules are hexagonal in shape and surround a central vein. At the outer edge of each lobule, there is a branch of the hepatic artery, a branch of the portal vein and a bile duct (Sherwood 2013). Between the centre and margins of each lobule are hepatocytes forming hepatic rows (Seeley et al 2007), and it is these hepatocytes that carry out the metabolic and secretory functions of the liver. Between the rows of hepatocytes, there are small ducts called bile canaliculi that collect bile produced by the hepatocytes and carry bile to the bile ducts (Tortora and Derrickson 2009). The bile ducts eventually come together to form the right and left hepatic ducts that converge and leave the liver as the common hepatic duct. The common hepatic duct then joins the cystic duct from the gall bladder to become the common bile duct. Bile enters the small intestine at the duodenum through the common bile duct. When the hepato-pancreatic sphincter, which is also called the sphincter of Oddi, is closed, bile is unable to enter the duodenum and is stored in the gall bladder until the sphincter is relaxed (Waugh and Grant 2010). Between the rows of hepatocytes, blood channels known as hepatic sinusoids are found. The sinusoids receive oxygenated blood from branches of the hepatic artery and nutrient-rich blood from branches of the hepatic portal vein. The sinusoids come together and deliver blood into a central vein, which flows into the hepatic vein and into the inferior vena cava (Tortora and Derrickson 2009). Phagocytes called stellate reticuloendothelial cells or Kupffer cells are found in the sinusoids and these destroy damaged red and white blood cells, bacteria and other foreign substances in the venous blood received from the digestive system (Tortora and Derrickson 2009). 38 february 19 :: vol 28 no 25 :: 2014
Gall bladder The gall bladder is a pear-shaped organ lying under the right lobe of the liver (Figure 1). Its main function is to store and concentrate bile until it is required for digestion and it can hold 30-60mL of bile (Watson 2005). When the sphincter of Oddi is closed, bile does not directly enter the duodenum, but is diverted into the gall bladder from the common bile duct (Sherwood 2013). Between 250mL and 1L of bile is secreted every day, depending on the level of stimulation, with such stimulants being the presence of acid and/or lipids or fats in the duodenum (Sherwood 2013). Secretin is released from the duodenal mucosa in response to the presence of acid in the duodenum, stimulating the liver to secrete bile. When chyme containing lipids or fat enters the duodenum, the gall bladder contracts and forces bile into the small intestine. The fats in chyme stimulate the secretion of the hormone cholecystokinin from the duodenal mucosa. This then stimulates the contraction of the gall bladder, causing bile to flow into the duodenum (Seeley et al 2007, Thibodeau and Patton 2008).
Bile
Although there are no enzymes in bile, it is important in digestion because it dilutes and neutralises acid from the stomach (Seeley et al 2007). It is also important in the digestion and absorption of fats (Sherwood 2013). Bile has an approximate pH of 8 and contains water, mineral salts, mucus, bile salts, bile pigments (mainly bilirubin), cholesterol and lecithin (Waugh and Grant 2010, Sherwood 2013). The liver secretes bile in response to the hormones secretin and cholecystokinin. As mentioned previously, cholecystokinin causes the gall bladder to contract and release bile into the duodenum (Seeley et al 2007, Thibodeau and Patton 2008)). Bile salts, derived from cholesterol, are found in substantial amounts in bile and are important in the mechanical breakdown of fats through the process of emulsification (Seeley et al 2007). Most bile salts are reabsorbed in the ileum and returned to the liver (Seeley et al 2007). Cholesterol is excreted in bile (Thibodeau and Patton 2008) and if there is too much cholesterol in bile, then gallstones can form (Sherwood 2013). Bilirubin is not involved in digestion; however, it is important because it is mainly obtained from the breakdown of red blood cells. Red blood cells have a useful life of approximately 120 days before they are broken down and bilirubin is the product of the haem component of haemoglobin.
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Pancreas The pancreas lies behind the stomach and fits into the area where the duodenum curves (Figure 1). It is both an exocrine and endocrine gland. It is an endocrine gland because it secretes hormones directly into the bloodstream. The endocrine portion accounts for 1% of the cells throughout the pancreas, which form clusters called pancreatic islets or islets of Langerhans (Tortora and Derrickson 2009). The islets manufacture the hormones insulin and glucagon, which are essential for the regulation of blood glucose levels (Seeley et al 2007). The exocrine portion of the pancreas is organised into grape-like sacs called acini, which connect into small ducts, then larger ducts and finally form the pancreatic duct, which joins the common bile duct and terminates in the duodenum at the sphincter of Oddi (Tortora and Derrickson 2009). The acini secrete pancreatic juice, which is colourless and comprises digestive enzymes, some salts, and water (Tortora and Derrickson 2009). Pancreatic juice is slightly alkaline as a result of the presence of bicarbonate ions and has a pH of 7.1-8.2 (Tortora and Derrickson 2009). This is important because it helps to deactivate pepsin from the stomach and to create an environment in the small intestine where the enzymes can function effectively. The alkalinity of the pancreatic juice also neutralises the potential effects of acidic chyme on the surface of the duodenum (Seeley et al 2007). The presence of chyme in the duodenum during the intestinal phase of digestion, stimulates the release of pancreatic enzymes. The acini secrete three main types of digestive enzymes: Proteolytic enzymes for digestion of proteins. Pancreatic amylase for digestion of carbohydrates. Pancreatic lipase for digestion of fats. The pancreas secretes three main proteolytic enzymes in an inactive form: trypsinogen, chymotrypsinogen and procarboxypeptidase. When trypsinogen is secreted into the duodenum, enterokinase, an enzyme found in the duodenal
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mucosa, activates trypsinogen to form trypsin. Trypsin is activated outside the pancreas because if it formed inside the pancreas, digestion of the pancreatic cells would occur. In the duodenum, trypsin converts chymotrypsinogen to chymotrypsin and procarboxypeptidase to carboxypeptidase. These enzymes break down proteins with different peptide linkages into amino acids and peptide chains. Pancreatic amylase converts polysaccharides into disaccharides, and pancreatic lipase breaks down triglycerides into monoglycerides and free fatty acids that can be readily absorbed (Sherwood 2013). Exocrine secretion from the pancreas is mainly regulated by the hormones secretin and cholecystokinin, which are released when chyme enters the duodenum (Seeley et al 2007). Secretin is carried in the bloodstream to the pancreas where it triggers the release of the alkaline pancreatic juice, with the amount of juice released being directly proportional to the amount of acid present in the duodenum. The role of cholecystokinin is to control the amount of pancreatic enzyme secretions and the trigger for its release from the duodenal mucosa is the presence of fat and protein (Seeley et al 2007). Cholecystokinin also travels to the pancreas via the bloodstream, where it triggers the acinar cells to secrete digestive enzymes (Sherwood 2013).
FIGURE 1 Anterior view of the liver, gall bladder and pancreas Right lobe of liver
Diaphragm
Left lobe of liver
Right hepatic duct Left hepatic Leftduct lobe
Common hepatic duct
of liver Common bile duct Pancreatic duct
Gall bladder Duodenum
Sphincter of Oddi
Pancreas
Jejunum
PETER LAMB
The hepatocytes remove bilirubin from red blood cells and excrete it in bile, and it is this process that gives bile its yellow colour. In the large intestine, bacteria break down bilirubin and the by-product is stercobilin, and it is this which gives faeces their characteristic brown colour. A small amount of bilirubin is reabsorbed by the intestine into the bloodstream and excreted by the kidneys, giving urine its yellow colour (Sherwood 2013).
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Art & science life sciences: 17 Digestion The digestive system transports nutrients, water and electrolytes from food into the body’s inner environment. Food provides a source of energy for the production of adenosine triphosphate (ATP) by cells so that the functions of active transport, contraction, synthesis and secretion, which are energy-dependent activities, can be carried out (Sherwood 2013). Food is also required so that body tissues can be repaired and renewed and for this to occur, food needs to be processed into a form that the body can use readily. There are four fundamental digestive processes: motility, secretion, digestion and absorption.
Motility, secretion and digestion
Motility is the process by which the contents of the gastrointestinal tract are mixed and moved forward by muscular contractions. Smooth muscle in the walls of the gastrointestinal tract maintains a steady low level of contraction called tone. This tone keeps a constant pressure on the contents of the gastrointestinal tract and also allows it to return to its normal size once food has passed through the system (Sherwood 2013). In addition to this tonic activity, there are propulsive movements in the gastrointestinal tract that ensure food contents can be pushed through the system (Tortora and Derrickson 2009), and these movements occur at different speeds depending on the functions of the organs of the gastrointestinal tract. For example, food moves quickly through the oesophagus (five to nine seconds), whereas food remains for longer in the small intestine to permit the breakdown and absorption of nutrients and products of digestion (Sherwood 2013). There are also mixing movements in which the food contents are mixed with digestive juices to aid digestion, and these movements also aid absorption of food by exposing the contents to the surfaces of the gastrointestinal tract where absorption occurs (Sherwood 2013). In addition, exocrine glands secrete digestive juices along the gastrointestinal tract, aiding digestion. Mechanical digestion occurs where food is broken down into its smaller constituent parts, mixed with digestive juices, moved along the gastrointestinal tract and removed from the body as faeces. It consists of chewing, swallowing, peristalsis and defecation. Chemical digestion occurs when food is broken down into absorbable units so that they can pass through the intestinal mucosa into the circulatory system (Thibodeau and Patton 2008). The aim of digestion is to hydrolyse (break down) food using enzymes from the different organs and 40 february 19 :: vol 28 no 25 :: 2014
these enzymes achieve this by breaking covalent chemical bonds in organic molecules (Seeley et al 2007). Carbohydrate digestion starts in the mouth with the action of salivary amylase, but the food does not spend enough time in the mouth to be fully digested. Therefore, most carbohydrate digestion takes place in the small intestine through the action of pancreatic amylase. Pancreatic amylase breaks down polysaccharides into disaccharides (Waugh and Grant 2010). Disaccharides are broken down into monosaccharides by the enzymes maltase, sucrase and lactase, acting on maltose, sucrose and lactose respectively in the microvilli of the intestinal mucosa (Thibodeau and Patton 2008). The end products of these enzymatic activities are glucose, fructose and galactose, and it is these monosaccharides that are absorbed by cells (Sherwood 2013). Protein digestion commences in the stomach. Pepsinogen is secreted in gastric juice and activated by hydrochloric acid, becoming pepsin and causing large protein molecules to be broken down into smaller peptide fragments. In the small intestine, digestion of polypeptide proteins continues through the action of pancreatic trypsin and intestinal juice peptidases (Thibodeau and Patton 2008). The peptide bonds are broken down, resulting in amino acids, which are absorbed by cells. Fat or lipid molecules are insoluble or only slightly insoluble in water, and they include triglycerides, phospholipids, steroids, and fat-soluble vitamins A, D, E and K. The most common types of fat are triglycerides. Fats provide a concentrated source of energy for the body. During digestion, lipids are emulsified in the small intestine, and bile salts from the liver are important in this process. Emulsification increases the surface area of the lipid droplets for the action of the enzyme pancreatic lipase, resulting in fatty acids and monoglycerides (Tortora and Derrickson 2009). Bile salts in the small intestine surround the small droplets of digested lipids to form structures known as micelles (Seeley et al 2007).
Absorption
Digestion is completed in the small intestine, with most absorption occurring here, although a small amount of absorption of digestion products also occurs in the large intestine. The components of carbohydrates, proteins and fats, as well as water, vitamins and electrolytes are transported from the mucosal lining of the small intestine into the blood or lymph systems. Minerals are actively transported through the intestinal mucosa, while water moves through by osmosis – approximately 9L of water is absorbed
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daily from the gastrointestinal tract (Tortora and Derrickson 2009). Monosaccharides enter the epithelial cells of a villus, enter a blood capillary within the villus and are transported to the liver via the hepatic portal vein. Amino acids, dipeptides and tripeptides are absorbed mainly in the duodenum and jejunum, where they are absorbed into the cells of the villi and enter blood capillaries. Amino acids are carried into the hepatic portal system and into the general circulation if they are not removed by the liver cells, whereby the body cells take up amino acids for protein synthesis and the production of ATP (Tortora and Derrickson 2009). When a micelle comes into contact with the epithelial cells of the small intestine, the fatty acids and monoglycerides diffuse through the epithelial walls and the micelles remain in the chyme. Once inside the epithelial cells, the fatty acids and monoglycerides reform to make triglycerides. The triglycerides combine with cholesterol and are re-packaged inside a protein coat and are now known as chylomicrons. The chylomicrons leave the epithelial cells and enter the lacteals of the villus and are then transported in the lymphatic vessels as chyle. Chyle is transported to the thoracic duct and enters the bloodstream at the left subclavian vein and the fats eventually enter the liver via the hepatic artery. Water-soluble vitamins C and B are dissolved in water and are absorbed mostly from the small intestine. Vitamin B12 must be combined with intrinsic factor, secreted in the stomach, for absorption via active transport in the ileum. The fat-soluble vitamins A, D, E and K are absorbed along with the end products of fat digestion and pass into the lacteals (Thibodeau and Patton 2008).
Metabolism Once food is digested and absorbed, it needs to be metabolised to provide energy for renewal and replacement of cells in the body. Metabolism encompasses all the chemical reactions that occur in the body (Waugh and Grant 2010). Catabolism is the breakdown of large molecules into small molecules, releasing chemical energy which is stored as ATP and heat. The heat produced keeps the core temperature of the body at 36.8°C, which is the optimum level for chemical function (Waugh and Grant 2010). Any excess heat is dispersed through the skin. Anabolism is the building up or synthesis of smaller molecules into larger molecules, and ATP usually provides the energy source for these processes (Waugh and Grant 2010). Catabolism and anabolism usually entail a series of chemical
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reactions known as metabolic pathways and these pathways contain a number of small steps that allow a controlled release of energy from ATP. The pathways are regulated by hormones so that they meet the individual’s varying requirements (Waugh and Grant 2010). The metabolic rate is the rate at which energy is released within cells, and this release of energy requires oxygen and produces carbon dioxide, water and heat as by-products.
Chronic liver disease There are several causes of chronic liver disease (Table 1), with the commonest in western countries being hepatitis C virus (HCV) and excessive alcohol consumption (Ballinger 2012). Chronic liver disease may be asymptomatic until the disease has progressed significantly or it is discovered by accident when routine blood tests are carried out for other disorders. Hepatitis is inflammation of the liver that can be a mild self-limited condition, serious chronic illness or fatal condition, depending on the cause (Poole 2009). There are several different viruses from hepatitis A to hepatitis G that can cause illness, but only the types identified in Table 1 result in chronic liver disease (Poole 2009). Hepatitis B virus (HBV) is commonly found in areas of Africa, and the Middle and Far East (Ballinger 2012). Transmission may occur between mother and baby during childbirth, through blood and blood products, through sexual intercourse and through minor abrasions and close contact (Ballinger 2012). HBV enters the hepatocyte causing a cellular response to the presence of foreign HBV proteins. This response can clear the infection in
TABLE 1 Causes of chronic liver disease Causes
Examples
Viral
Hepatitis B Hepatitis D Hepatitis C
Autoimmune
Associated with pernicious anaemia and thyroiditis
Drugs
Methotrexate Nitrofurantoin Isoniazid Ketoconazole
Hereditary
Wilson’s disease
Other
Inflammatory bowel disease Excessive alcohol consumption
(Ballinger 2012)
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Art & science life sciences: 17 99% of infected adults (Ballinger 2012). However, the infection can be asymptomatic, and if the infected proteins are not cleared then the patient may develop chronic hepatitis. Treatment of chronic HBV involves antiviral therapy and monitoring for liver damage (Poole 2009). Advice should be given to patients limiting alcohol consumption, smoking cessation and preventing transmission of the virus to others. This should include informing partners of their hepatitis status and avoiding sharing personal items, including toothbrushes and razors. Pregnant women should be given information on the risk of transfer of infection to their baby during childbirth (Lee et al 2010). Hepatitis D virus (HDV) is only present in people infected with HBV, and it can affect all risk groups for HBV, but is particularly prevalent in intravenous drug users and is also transmitted through close personal contact such as during sexual intercourse (Poole 2009, Ballinger 2012). It can either occur as a co-infection or a superinfection in the patient who has proteins for HBV. HDV progresses to severe liver damage and more commonly results in death than HBV alone (Tortora and Derrickson 2009). HCV can be found in populations worldwide, but is more common in southern Europe, Africa and Egypt (Ballinger 2012). In the UK, the main mode of transmission is via intravenous drug use. It can be spread through the use of drug-injecting paraphernalia, including needles and spoons, but it can also be transferred through the use of equipment for intranasal administration of drugs (Pears 2010). In developing countries, it is commonly transmitted through blood products and exposure to poorly sterilised instruments. An estimated 80% of people with HCV will progress to chronic hepatitis C (National Institute for Health and Care Excellence 2010).
Cirrhosis of the liver
Cirrhosis occurs when liver cells become necrosed and hepatocytes are replaced with thickened and scarred tissue (fibrosis) (Tortora and Derrickson 2009). These changes result in impaired liver function and alterations in the gross structure of the liver (Ballinger 2012). Portal hypertension is a common complication of cirrhosis where the pressure in the portal vein is raised, resulting in oesophageal and gastric varices. If the varices rupture, bleeding will occur (Fullwood 2012), which can be fatal. Cirrhosis of the liver is commonly linked to excessive alcohol consumption. Investigations to confirm cirrhosis include (Ballinger 2012): Liver biochemistry may be normal or serum alkaline phosphatase may be slightly raised. Full blood count indicates thrombocytopenia. Altered liver function is demonstrated by 42 february 19 :: vol 28 no 25 :: 2014
changes in prothrombin time and serum albumin. Serum electrolytes demonstrate a decrease in sodium levels indicative of severe liver disease. Elevated serum creatinine. Presence of raised levels of alpha-fetoproteins, which are not normally present after the fetal stage of life has ended. Signs and symptoms of cirrhosis include: Haematemesis (vomiting blood) and melaena (blood in faeces) related to gastrointestinal bleeding. Pyrexia related to sepsis and spontaneous bacterial peritonitis. Ascites (fluid accumulation within the abdominal cavity). Renal failure. Confusion and drowsiness related to hepatic encephalopathy. Low oxygen saturation related to pulmonary oedema (Kumar Bhamidimarri 2009). Other signs of chronic liver disease including spider naevi, spider telangiectases and reddening of palms (Ballinger 2012). Pruritis (itchy skin) related to jaundice caused by raised levels of bilirubin deposited under subcutaneous tissue, including the skin, sclera in the eyes and mucous membranes (Sargent and Clayton 2011). Symptoms of cirrhosis should be managed to make the patient comfortable; however, the disease is irreversible and commonly progresses with a five-year survival rate of 50% (Ballinger 2012).
Pancreatitis The most common cause of pancreatitis is the presence of gallstones, accounting for 45% of cases, and excessive alcohol intake, accounting for 35% of cases (Callaghan et al 2007). However, 10-20% of cases are idiopathic (Andris 2010) (Box 1). Pancreatitis can be classified as acute, when an attack occurs in a previously healthy person
BOX 1 Other causes of pancreatitis Hypertriglyceridaemia. Complication of endoscopic retrograde cholangiopancreatography. Drug reactions. Autoimmune disorders. Genetic mutations. Abdominal trauma. Infection. Hypercalcaemia. Hyperparathyroidism.
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with resolution of the problem, or chronic, where there are repeated attacks and the continuation of symptoms lead to a decrease in endocrine and exocrine function of the pancreas (Andris 2010). Acute pancreatitis is a serious medical condition. It can range from being fairly mild, where recovery occurs without complications, to severe pancreatitis causing necrotising pancreatitis with multisystem organ failure. The overall mortality rate for acute pancreatitis is 10-15%, and 40-50% for severe acute pancreatitis (Burroughs and Westaby 2009). In acute pancreatitis there is inflammation of the pancreas, which is followed by oedema and necrosis of pancreatic tissue. If the pancreatic duct is obstructed there will be hypertension in the duct, leading to a risk of rupture. If this happens, digestive enzymes are released into the pancreas leading to auto-digestion of the pancreas. If the disease progresses, the patient experiences severe fluid shifts, haemorrhage, sepsis and multiple system organ failure (Andris 2010). Fluid shifts occur when leaked enzymes result in autolysis of tissues causing oedema, and fluid may collect in spaces such as the peritoneal cavity. Acute pancreatitis may present with epigastric pain that may radiate to the back or chest and is eased by lying in the fetal position. Fatty foods and/or alcohol may exacerbate the pain. Nausea and vomiting are not uncommon, and bowel sounds are decreased or absent. Fluid loss contributes to hypotension and a subsequent rise in pulse rate in an attempt to maintain cardiac output. Hypotension may result in reduced peripheral perfusion. Pyrexia may be present (Huether 2006). Diagnosis of the condition will be made based on a history of the symptoms, physical examination and blood tests. A diagnosis of pancreatitis can be confirmed by (Burroughs and Westaby 2009): Raised serum amylase and serum lipase levels. Signs of paralytic ileus on abdominal X-ray. Gallstones or pancreatic enlargement on pancreatic and gall bladder ultrasound. Extent and severity of acute pancreatitis and complications identified on a computed tomography scan. Deformities in the pancreatic duct or impacted gallstones identified on endoscopic retrograde cholangiopancreatography. Management of patients with mild pancreatitis may include being nil-by-mouth to rest the pancreas and bowel, intravenous hydration, central venous pressure measurement, hourly measurement of urinary output, pain management, oxygen therapy, and management of nausea and vomiting, which may require insertion of a nasogastric tube
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to keep the stomach empty. In addition, hourly measurement of blood glucose in the acute phase is required because the endocrine function of the pancreas can be affected (Ballinger 2012). Regular recordings of temperature, pulse, blood pressure, respiration and pulse oximetry should also be done. Nutritional support using a naso-jejunal tube that bypasses the stomach and duodenum should be commenced so that the risk of stimulating the pancreas is bypassed. Feeding can be commenced after 48 hours if the patient is unable to begin oral feeding (Andris 2010). However, Talukdar and Swaroop Vege (2011) suggested that enteral nutrition should be started as early as possible in severe acute pancreatitis because the pancreas is in a state of unresponsiveness during an acute episode and the secretion of trypsin is reduced. If the patient shows signs or symptoms of alcohol withdrawal, it is important to treat this with benzodiazepines (Andris 2010). Late complications of pancreatitis include multiple system organ failure and necrotising pancreatitis (Burroughs and Westaby 2009).
Gall bladder disease The gall bladder, bile ducts and sphincter of Oddi work together to adapt, store and control the flow of bile. The main function of the gall bladder is to store bile, and gallstones can form when the gall bladder cannot maintain the soluble state of some of the components of bile. Gallstones are formed from either cholesterol or pigment, with cholesterol gallstones accounting for 80% of all gallstones (Burroughs and Westaby 2009). Pigment gallstones are made up of polymers of bilirubin and calcium bilirubinate (Ballinger 2012). Most gallstones do not cause symptoms, but biliary pain or colic can be exacerbated when there is a temporary obstruction of the cystic or common bile duct by a gallstone. Risk factors associated with the development of gallstones are listed in Box 2 (Ballinger 2012).
BOX 2 Risk factors for the development of gallstones Cirrhosis. Diabetes mellitus. Diet high in animal fat and low in fibre. Family history of gallstones. Female gender. Ileal disease leading to bile salt loss. Increasing age. Multiparity. Obesity. Rapid weight loss. (Ballinger 2012)
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Art & science life sciences: 17 Other signs and symptoms of acute cholecystitis, inflammation of the gall bladder that is usually related to gallstones, include (Baltimore and Davidson 2007): Sudden onset of severe pain in the right upper quadrant of the abdomen. Pain becomes worse on deep breathing and radiates to the right shoulder. Pain may recur for some hours after meals. Nausea and vomiting. Mild pyrexia. Stomach becomes distended. Investigations include history and abdominal ultrasound. Management includes analgesia and elective cholecystectomy, which is usually carried out laparascopically.
GLOSSARY
Conclusion
POINTS FOR PRACTICE
It is essential that nurses have a sound knowledge of the digestive system, including its components and accessory organs, so that they can identify any changes and select the appropriate nursing strategies to manage disorders of the digestive system NS
Hepatic sinusoids Blood vessels with incomplete walls containing a mixture of blood from the tiny branches of the hepatic artery and hepatic portal vein. This arrangement allows the arterial blood and the venous blood to come into close contact with the liver cells. Oxidation A chemical reaction in which oxygen is added to an element or compound. Spider naevi A form of telangiectasia, typified by a central elevated red dot the size of a pinhead from which small vessels radiate. Telangiectasis A branched group of dilated capillary vessels forming a spider-like image on the skin.
A diet high in saturated fats is associated with gallstone formation. Identify foods that contain saturated fats and those that contain unsaturated fats. Identify and describe the protocols in your clinical area for the nursing management of a patient who requires a liver biopsy. Describe the signs and symptoms that might be observed in a patient with alcohol withdrawal. Outline the management of such a patient.
References Andris A (2010) Pancreatitis: understanding the disease and implications for care. AACN Advanced Critical Care. 21, 2, 195-204.
Fullwood D (2012) Portal hypertension and varices in patients with liver cirrhosis. Nursing Standard. 26, 48, 52-57.
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