Gastrointestinal disease

3.1 Gastrointestinal disease




PART I – From our food to the stomach




The nutrients in our diet


A nutrient is any substance that can be used by the body either to produce energy or to enable other vital chemical processes to take place. There are six basic nutrients: carbohydrates, fats, proteins, mineral salts, vitamins and water. A healthy diet should contain an ideal balance of these nutrients. In addition to these nutrients, a healthy diet also should provide ‘fibre’. Fibre is indigestible cellulose from plant-derived foods. Fibre enables healthy transit and elimination of waste, as it provides bulk and water-retaining properties to the faeces.


A healthy diet will consist largely of starchy foods such as bread, rice, pasta and cereals, and fruit and vegetables. Current UK guidelines for the public are that about 60% of the energy value of food (calories) should come from starchy foods and that additional energy should come from at least five portions of fruit or vegetables a day. In addition, there should be some food containing protein, either from the meat/eggs/pulses food group or from the milk/cheese food group. Foods containing fats and sugars should be kept to a minimum. The UK Food Standards Agency ‘eat well plate’ summarises this advice in pictorial form as shown in Figure 3.1a-I.




Carbohydrates


Starchy foods and fruit and vegetables together provide the carbohydrates that the body needs. Carbohydrates contain the elements carbon, hydrogen and oxygen. These are the foods that, once broken down, provide the basic fuel for the energy-producing process of internal respiration (see Chapter 1.1b). Internal respiration takes place in the mitochondria of all living cells, where simple sugars react with oxygen to produce cellular energy. Carbon dioxide and water are the waste products. The energy produced is stored partly in the form of the ‘charged’ molecule adenosine triphosphate (ATP), and is partly released as heat.


The most simple carbohydrates are the monosaccharides, or simple sugars, such as glucose and fructose. These are in a perfect form to be utilised by the mitochondria, and so provide the most rapidly accessible form of energy. Monosaccharides taste sweet.


The molecules of the monosaccharides also occur bound in pairs in our food in the form of sweet-tasting disaccharides. Sucrose and lactose (the sugar in milk) are examples of disaccharides. The monosaccharides are also found in the form of chains known as ‘polysaccharides’, of which starch is an example. These do not immediately taste sweet, but can be broken down in the digestive tract to release the monosaccharides. Starches are, therefore, a form of slow-release energy for the body. Cellulose, which forms the fibrous parts of fruit and vegetables, is also a polysaccharide, but cannot be readily utilised by the human digestive tract. This is why it can perform its role as fibre. Grass-eating animals, however, do have the capability of breaking down cellulose and extracting its valuable food energy.


If carbohydrates are in excess in the diet, superfluous monosaccharides can be converted within the liver to a polysaccharide called ‘glycogen’. Glycogen is held in the liver so that when blood sugar levels are low it can readily be converted back to accessible glucose. Any excess carbohydrate after this process has taken place is converted to fat for long-term energy storage.



Fats


Fats are non-soluble oily substances found in diverse foods in our diet, including meat, nuts, eggs, milk and some vegetables. Most fats consist of two components joined together: a fatty acid and glycerol. When broken down by the body, the fatty acids and glycerol are released to provide energy for the bodily processes.


Saturated fat is so called because of the nature of the chemical bonds in the fat molecules. It consists of molecules containing a saturated fatty acid and a glycerol. Saturated fat tends to form into a solid more readily than unsaturated fat. Lard from meat and butter are both largely saturated fats. Saturated fat is a good source of energy for the body, but an excess in the diet will cause cholesterol to be carried in the blood in the more unhealthy form of low-density lipoprotein and triglycerides (LDL and TGs).


Unsaturated fat is generally derived from vegetable matter, and tends to form a clear oil rather than a solid fat. It consists of molecules containing an unsaturated fatty acid and a glycerol. The omega-3, omega-6 and omega-9 fatty acids are all unsaturated fatty acids derived from unsaturated fats. These polyunsaturated fatty acids are essential components for cellular and intercellular communication processes and the building of cellular structures.


Vegetable, nut and olive oils contain unsaturated fat that provides omega-6 and omega-9 fatty acids. Fish oils contain unsaturated fat that provides omega-3 fatty acids. Most vegetable oils are made of polyunsaturated fats, but olive oil, canola oil and avocados contain a particular form of unsaturated fat known as a ‘monounsaturated fat’ (this contains omega-9 fatty acids).


Unsaturated fats and monosaturated fats in particular, seem to have the property of reducing the amount of cholesterol that is carried in the blood in the more unhealthy LDL form. For this reason, it is now considered important for a healthy diet that these forms of fats predominate over the saturated fats, and that monounsaturated fats predominate over polyunsaturated fats (as is found in the ‘Mediterranean diet’). Unsaturated fats may protect against cardiovascular disease by providing more membrane fluidity than the more solid saturated fats.


Cholesterol is another oily substance that is particularly important for making hormones, including the steroids. Cholesterol is found in dairy products, meat and eggs. It can also be synthesised in the body, particularly in the liver, from more simple molecules. Cholesterol is carried in the blood in the form of complex molecules called LDL, very low-density lipoprotein (VLDL) and high-density lipoprotein (HDL). These structures package the cholesterol so that it is readily accessible to the cells. As mentioned, LDL (and VLDL) is associated with vascular ill-health, but HDL appears to be protective against vascular damage. The balance of these structures in the blood seems to be less affected by the amount of cholesterol in the diet than by the relative amounts of saturated and unsaturated fats (see above).


Trans fatty acids are only found in traces in a natural diet. However, they make up a significant proportion of many western diets because they are found in vegetable oils that have been processed (hydrogenated) to preserve their longevity for foods such as margarines, cakes and biscuits. The American Food and Drugs Administration (US FDA) has estimated that the average American eats 5.8 g of trans fatty acids a day. It is known that trans fatty acids alter the balance of cholesterol in the blood to an unhealthy state (they increase levels of LDL at the expense of the more healthy HDL). In some European states (e.g. Denmark and Switzerland) the use of trans fatty acids in food manufacturing has been banned. Many other countries now have policies whereby the proportion of trans fatty acids has to be described in food labelling.



Proteins


Proteins are complex chain-like structures that are made up of simple molecules called ‘amino acids’. All amino acids contain the element nitrogen as well as carbon, hydrogen and oxygen. Some also contain trace minerals such as zinc, iron and copper. There are about 20 different amino acids, which can be combined in potentially infinite permutations to form protein chains. Proteins are made in animal and plant cells at the ribosomes as a result of decoding instructions held on the cellular DNA (see Chapter 1.1b). The ribosome is the site at which amino acids are linked together to form a unique and characteristic protein chain, after which the particular makeup of the protein chain encourages the structure to fold in a characteristic way. This means that proteins are large molecules that have a unique shape. The shape and form of a particular protein might give it special structural properties (e.g. the collagen in skin and hair) or make it soluble in water (e.g. the albumen found in blood and in egg white). In other proteins the shape is essential for communication, and this is the basis of how cell-membrane proteins ‘recognise’ the external stimulants, such as hormones, that bring about internal change in the cell itself. Antibody–antigen recognition also depends on the antibody having a unique shape that ‘fits’ the shape of the antigen.


Protein in food is found in meat, eggs, fish, cereals, nuts and pulses. All the essential amino acids can be derived from the complete proteins in meat, fish, eggs, milk and soya. Without soya products, a vegetarian will need to eat combinations of nuts, cereals and pulses to ensure that all amino acids are obtained from the diet.


Protein is converted to amino acids in the body, and these circulate dissolved in the blood so that they reach all the tissues. The ribosomes of the cells utilise amino acids to produce their own proteins so that they can reproduce and continue performing their unique functions. Proteins are used to make cellular and extracellular structures (such as the contractile fibres in muscle cells and the connective tissue fibres in cartilage), plasma proteins (such as the clotting factors and albumen), antibodies, enzymes and also some hormones.


In a state of starvation, proteins are broken down by the cellular mitochondria to produce energy. The by-products of this process include chemicals called ‘ketones’. When excess ketones are produced, the body is said to be in a state of ‘ketosis’.




Vitamins


Vitamins are more complex compounds than minerals, and are also essential for bodily processes. They are essential dietary components because either they cannot be made by the body at all or they cannot be made in sufficient quantities to sustain health. Vitamins are now broadly grouped into the four fat-soluble vitamins A, D, E and K, and the nine water-soluble vitamins B1–B8 and C. The lettering system approximately relates to the order in which the vitamins were discovered (beginning with vitamin A in 1909). Those substances initially called F–J were either reclassified as B vitamins or were subsequently deemed not to qualify as vitamins at all. The B vitamins are now recognised to be linked because they are all vital in the production of energy from nutrients by the mitochondria. The food sources and the functions of the 13 vitamins are summarised in Table 3.1a-I.


Table 3.1a-I The 13 vitamins, their main food sources and their functions in the body



























































Vitamin Food sources Use in the body
A (retinol) Green vegetables, milk, liver Pigments in eye and health of skin
D (calciferol) Milk, eggs, cod liver oil; ultraviolet light Calcium absorption and bone formation
E (tocopherol) Margarine, seeds, green leafy vegetables Antioxidant: protects fatty acids and cell membranes from damaging oxidation
K (phylloquinone) Green leafy vegetables Formation of certain clotting factors
B1 (thiamine) Meats (pork), grains, legumes Carbohydrate metabolism; also nerve and heart function
B2 (riboflavin) Milk, liver, eggs, grains, legumes Energy metabolism
B3 (niacin or nicotinic acid) Liver, lean meats, grains, legumes Energy metabolism
B5 (pantothenic acid) Milk, liver, eggs, grains, legumes Energy metabolism
B6 (pyridoxine) Wholegrain cereals, vegetables, meats Amino acid metabolism
B7 (biotin) Meats, vegetables, legumes Fat synthesis and amino acid metabolism
B9 (folic acid) Wholewheat foods, green vegetables, legumes Nucleic acid metabolism
B12 (cobalamin) Red meats, eggs, dairy products Nucleic acid production
C (ascorbic acid) Citrus fruits, green leafy vegetables, tomatoes Collagen formation in teeth, bone, and connective tissue of blood vessels; may help in resisting infection


Water


Water is an essential part of the diet because the body is continually losing water through the urine, faeces, sweat and in exhaled air. About 60% of the adult body mass is water, and all the essential bodily processes take place in a watery milieu. Water has to be lost as it is the vehicle through which waste chemicals (in urine and sweat) and also waste food materials (in the faeces) are carried for expulsion from the body. It is also lost through the breath and sweat to aid with cooling of the body.


On average, about 2.5 litres of water need to be replaced by the diet every day. Much of this is contained in food, and so a human being can survive on about 1.5 litres of water in drinks



per day. Any water excess to requirements is passed out of the body in the form of dilute urine. If insufficient water is drunk, the kidneys make dark concentrated urine from the fluid in the plasma, and the water required for excretion of wastes is drawn from the tissues, which then become dehydrated. A significant state of dehydration will be reflected in a loss of body weight of more than 2–3%. Because the sensitive tissues of the body are not able to withstand the state of dehydration for more than a few days, water is essential for life. Loss of more than 10% of the body weight through dehydration is usually not compatible with life image(see Q3.1a-2-Q3.1a-6).



The structure of the digestive tract


The digestive tract is a tube that begins at the mouth and ends at the anus. At both these orifices there is a junction between the tough and dry keratinised epithelium of the skin and the soft and moist mucous epithelium that lines the whole of the digestive tract. This junction can be easily examined in the mouth where the two lips meet. At the junction, the dry, slightly ridged keratinised skin of the external lip becomes moist and smooth mucous epithelium on the inside of the lip.


The tube of the digestive tract has a basic structure that can be found in slightly different forms along its length. The tube has four distinct layers (Figure 3.1a-II):




The mouth is the only section of the digestive tract that does not have this general structure.


The tube of the digestive tract has ‘accessory organs’, which open out or project into the hollow of the tube. These organs are the tongue, salivary glands, liver, gallbladder, pancreas and appendix.


The structure of the tube itself changes throughout its length according to the function required. The mouth, oesophagus, stomach, duodenum, small intestine, large intestine (colon), rectum and anus are described in more detail below.


The salivary glands open via tubes (ducts) into the mouth, the pancreas, liver and gallbladder all open via ducts into the duodenum, and the appendix opens directly into the beginning of the colon. Figure 3.1a-III illustrates the position of the organs associated with the digestive tract, and how, with the exception of the mouth and the oesophagus, the main part of the digestive tract is situated below the diaphragm.




The mouth


The mouth is where the process of digestion begins. The teeth, tongue and the muscles of chewing are adapted to grind up food into a paste with saliva.


Saliva is produced by six exocrine salivary glands that open into the mouth. The size and extent of these important glands is illustrated in Figure 3.1a-IV.



Saliva is produced is response to the action of eating, and also in response to the anticipation of food. Certain flavours, such as the sourness of lemons, are particularly powerful in inducing a good flow of saliva. About 1.5 litres of saliva is produced a day, and the moisture is very important to help maintain the health of the mouth and to assist with chewing. The moisture is also essential for enjoyment of food, as it enables food to be tasted. Saliva also contains protective substances such as mucus and antibodies, together with the protein lyzozyme, all of which protect the digestive tract from damage by microorganisms and toxins.


The salivary glands also produce the first digestive enzyme that the eaten food will encounter, and thus begins the breakdown of the nutrients into the building blocks that are absorbed into the blood stream. An enzyme is a biological substance that encourages a chemical reaction. In this case the enzyme is called ‘salivary amylase’, and in its presence the chains of complex polysaccharides in carbohydrate come apart to form disaccharides. This reaction only occurs in the mouth, as the acid contents of the stomach stop the amylase from working. This is why it is important to chew thoroughly (see Q3.1a-7).image


The tongue is a muscular structure adapted for two distinct functions: eating (taste, chewing and swallowing) and speech. It is covered with little bumps called ‘papillae’, which are sensitive to the four main tastes: salt, sweet, sour and bitter. The subtleties of taste are also dependent on a healthy sense of smell, as anyone who has a heavy cold will recognise. Figure 3.1a-V illustrates the position of the different sorts of papillae.





The stomach


The stomach is a stretchy expansion of the tube of the digestive tract, but still retains the four layers. Figure 3.1a-VI illustrates that the stomach is bounded by the cardiac sphincter above and the pyloric sphincter below. These muscle rings keep food contents within the stomach for up to 6 hours to enable the beginning of a thorough digestion process. The stomach muscles enable the muscle to churn the food contents stored within it to aid digestion.



Gastric (the term coming from the Greek for ‘stomach’) juices are secreted by specialised glands that open into the stomach. These juices consist of water, acid and an enzyme called ‘pepsin’, which enables the breakdown of protein into amino acids. The acid is produced by specialised proteins in the cell walls of the gastric glandular cells known as ‘proton pumps’. The stomach lining also secretes copious mucus to protect its own cells from the acid produced by the proton-pump cells.


In the stomach, the food is churned with the fluid of the gastric juice to form a liquid soup known as ‘chyme’. The pepsin and the acid work together to break down the protein in the food into amino acids. The smell of this process is the familiar smell of vomit. Very little of the diet is absorbed through the lining of the stomach, but water and alcohol are two exceptions. This explains why drinking alcohol on an empty stomach can have such a rapid effect.


The stomach is also the source of a protein called ‘intrinsic factor’, which has an attraction for vitamin B12 (cobalamin). This attraction is important, as each molecule of this essential vitamin can only be later absorbed if it is bound to a molecule of intrinsic factor (see Q3.1a-8).image



PART II – From the duodenum to the outside world




The pancreas


The pancreas is a gland with two distinct roles, one is endocrine and the other is exocrine. (For a reminder of the difference between these two categories of epithelial structure, see Chapter 1.1d.)


The endocrine role of the pancreas is to secrete the hormones insulin and glucagon directly into the blood stream. Both these hormones are important for ensuring that the concentration of glucose in the blood remains at the optimum level for the function of the cells of the body.



The exocrine role of the pancreas is to secrete a diverse array of digestive enzymes into the duodenum via the pancreatic duct. The enzymes can digest all three of the complex food components (carbohydrates, proteins and fats), and therefore will complete the work started by the salivary glands and the gastric juices.


Figure 3.1a-VII illustrates how the C-shaped loop of the duodenum hugs the pancreas. The spleen, kidneys, liver and transverse colon are all situated at this level of the abdomen




The gallbladder


This hollow organ is a store for the fluid called ‘bile’, which is manufactured in the liver. Bile is dark green and very bitter tasting. It contains substances called ‘bile salts’, which aid the digestion of fats.


Bile also contains some of the body’s waste products that have been processed by the liver. These will pass eventually into the faeces. These by-products of the liver’s detoxification .



include a deeply hued chemical called ‘stercobilin’ (derived from the breakdown of haemoglobin), which gives the faeces their characteristic brown colour.


When food enters the duodenum, the cells of its lining respond to the change by releasing hormones, including a substance called cholecystokin (CCK), into the bloodstream. These ‘messengers’ travel to the gallbladder and stimulate it to contract and release bile when it is most needed. Similarly, other duodenal hormones stimulate the pancreas to release pancreatic juices.



The small intestine


The small intestine is simply a continuation of the duodenum. It receives the fluid mixture of partly digested food and digestive enzymes from the duodenum, powered by the wave-like muscular contractions of peristalsis.


The small intestine is about 5 metres long, and its lining is thrown into folds. Microscopic peaks of mucosa project from these folds, and appear, when greatly magnified, like a vast mountain range. These peaks are called ‘villi’. Furthermore, each cell of the mucosa has tiny projections called ‘microvilli’. This unique structure greatly increases the area of the mucosa that is in contact with the fluid contents of the digestive tract, an adaptation that maximises absorption. Figure 3.1a-VIII illustrates the microscopic structure of a villus, including the tiny microvilli on each cell, and also the way the blood and lymph supply of the digestive-tract lining project into the centre of the villus.



As the digestive process continues along the length of the small intestine, the saccharides, amino acids, glycerol, water-soluble vitamins, and salts resulting from digestion are taken up (usually by facilitated diffusion) into the mucosal cells. From here they pass into the bloodstream. Numerous collections of tiny lymph nodes in the submucosal tissues protect the bloodstream from any infectious agents that may have been present in the diet.


Fatty acids and the vitamin B12–intrinsic factor complex are absorbed by the very end segment of the small intestine (the ‘terminal ileum’). The bile acids, which aid the digestion of fats, are also reabsorbed here and circulate in the bloodstream back to the liver, from where they can be used again in the bile. Vitamins A, D, E and K are soluble in fats, and so are also absorbed at this end of the small intestine. Fatty acids, glycerol and these vitamins pass directly into the lymphatic system rather than the bloodstream. The small intestine also reabsorbs over 8 litres of water a day from the fluid contents that initially enter the duodenum. This leaves a semi-solid residue to enter the large intestine. This residue consists of fibre, waste from the bile, and many thousands of dead mucosal cells and intestinal bacteria, which have been shed along the digestive journey (see Q3.1a-9 and Q3.1a-10).image



The large intestine


The large intestine, or colon, receives the residue of digestion from the small intestine. The first few centimetres of the colon are called the ‘caecum’, which literally means ‘blind ending’. This is because it is above the caecum that the end of the small intestine opens into the colon, with the result that the caecum is like a cul-de-sac opening out from the passage. At the end of this cul-de-sac is the narrow tube of the appendix. The parts of the large intestine are illustrated in Figure 3.1a-IX. Note how the horizontal stretch of the transverse colon overlies the duodenum and pancreas at the level of the T12 thoracic vertebra.



The large intestine is the home for most of the ‘healthy’ bacteria and yeasts which were first described in Chapter 2.4b. The food residue that enters the large intestine is digested further by these ‘healthy’ organisms. The by-product of this digestion is gas, which is eventually passed out of the anus. Some necessary vitamins are made as by-products of this process, which can then be absorbed into the bloodstream.


In animals that live on a diet of grass, such as sheep, the caecum and appendix are much longer than those in humans and contain many bacteria. Here, the bacteria can digest further the cellulose fibre in grass to release more saccharides, which can be used by the sheep. It is believed that the appendix in humans is simply a vestige of this larger organ found in vegetarian animals. Cellulose cannot be digested by humans, and instead provides an important role as the bulking agent known as ‘dietary fibre’.


The muscular contractions of the colon are slow and infrequent. The contractions cause the food residue to move gradually along the length of the colon before entering a storage region called the ‘rectum’. The rectum is closed at its bottom end by the muscular sphincter of the anus. When the rectum is filled, there is the sensation of needing to open the bowels. However, the act of emptying the rectum is voluntary, and usually can be delayed to a convenient time. About two-thirds of the fluid that enters the large intestine is reabsorbed, so that the substance that enters the rectum has the familiar consistency of faeces. Mucus secreted along the length of the colon lubricates the passage of the semi-solid faeces (see Q3.1a-11).image



The liver


The structure and function of this important organ have been left to last because many of the functions of the liver are not directly related to the process of breakdown of food into basic nutrients. Instead, most of the important functions of the liver are about the processing of these nutrients to make them useful to the cells of the body.


The liver is the largest organ in the body and sits under the diaphragm on the right-hand side. If the palm of the right hand is rested on the lower section of the front of the right-hand half of the rib cage so that the little finger runs along the bottom edge of the rib cage, then the hand will be resting over the liver.


The liver receives all the blood that has passed through the digestive tract, so that it is the first ‘stop’ for all the nutrients, and also toxins, that have been absorbed during the process of digestion. This nutrient-rich blood passes through tiny channels in the liver called ‘sinusoids’, so that all the liver cells can come into close contact with it. This means that, at any one time, the liver is holding a large volume of blood within its tissue. This link between the blood leaving the digestive tract and the tissue of the liver is the physical basis for the liver’s two distinct roles in the digestive process.


The first role is to act as a filter for toxins and other harmful substances such as drugs and alcohol. The liver cells are able to first absorb and then destroy or change some of these substances which have entered the bloodstream from the diet before they can affect other tissues of the body. This is the reason why many drugs and toxins, if in excess, may damage the liver (e.g. paracetamol and alcohol). There are also many phagocytic white cells (macrophages) lining the sinusoids. One of their functions is to clear away any microbes that may have entered the bloodstream from the diet.


The second role is to begin processing some of the nutrients into a useful form for the cells, or into a form in which they can be stored for later use. Glucose, for example, is stored in the stable form of glycogen within the liver, from which it can be obtained at a later time if sugar supplies are needed quickly. Amino acids are processed so that they can be used by the cells to build new proteins. A similar process occurs for fats. Many vitamins and iron are also stored for later use in the liver. This is why liver is considered to be so nutritious as a food.


Other roles of the liver include:



The last role to be described here is that of the secretion of bile. In addition to the diverse functions already listed, all the liver cells are able to produce bile and secrete it into tiny tubules in the liver. From here, the bile drains into a duct that leaves the liver and enters the duodenum. The gallbladder also opens into this duct, so that the bile collects here rather than passing directly into the duodenum (Figure 3.1a-X).





image Information Box 3.1a-V The liver: comments from a Chinese medicine perspective


The vascular spaces formed by the liver sinusoids are receptacles for all the blood that drains from the digestive tract. Here, the blood is cleansed and refreshed before travelling on to nourish other tissues. This is in keeping with the Chinese medicine observation that the Liver ‘stores Blood’ and that this function is necessary for replenishing the Qi.


The liver is also responsible for ensuring that a steady clean supply of useful nutrients is available to the cells. This would very much be in accord with the Chinese medicine function of the Liver of ensuring the smooth flow of Qi. It would also suggest that the liver plays a part in the processes described in Chinese medicine as the Transformation and Transportation of Gu (food) Qi.


However, there is no obvious conventional link between the function of the liver and the function of tendons and the sinews, or indeed in the ability to plan, which are other functions of the Liver Organ in Chinese medicine. The concept of the Hun, or the ethereal soul, has no counterpart in conventional medicine.


Interestingly, however, chronic liver disease can be conventionally recognised to cause changes in the nails, as the deficiency of plasma protein that results leads to characteristically white nails. Similarly, although there is no conventional link between the liver and the eyes in conventional medicine, in chronic liver disease the white of the eyes is the first place in which jaundice becomes apparent.


For more detail on the correspondences between the functions of the liver and gallbladder as described in conventional medicine and the Liver and Gallbladder Organs in Chinese medicine, see Appendix I.


Figure 3.1a-X helps to illustrate how the gallbladder can be surgically removed without disturbing the free flow of bile from the liver. The function of the gallbladder is simply to delay the entry of bile into the duodenum until the best time for digestion of fats. Removal of the gallbladder results in a constant trickle of bile into the duodenum. This is not ideal for perfect digestion of fats, but is not conventionally considered to be a problem for overnourished western people.



The metabolism


This last section of this chapter touches on the metabolism, which can be seen as the end result of the digestive process. ‘Metabolism’ simply means all the chemical processes that take place in the body. These processes require basic nutrients, oxygen and water to occur.


Metabolism can be broadly considered in two categories:



In health, the anabolic and catabolic processes generally balance each other. This leads to a constant process of turnover of the old substances in the body for replacement with the new. It is this balance that allows for adaptation to change. In times of growth and development the anabolic processes are more prominent, and in times of illness and ageing the catabolic processes are more prominent.


Healthy metabolism is dependent on an adequate supply of ‘fuel’ – the basic nutrients and oxygen. If either of these is lacking, fuel has to be obtained from within the body. Initially, the glucose store in the liver is drawn upon, but very soon after this body fat and muscle protein is broken down. This is a state in which catabolism is in excess, and is not a healthy state if prolonged. Nevertheless, it is the state that people who diet ‘successfully’ put themselves into by choice. Conversely, if there is excess fuel, or if the metabolism is sluggish, then a state in which anabolism is in excess results. If there are no demands for the body to grow or develop, then the excess nutrients are laid down as fat.




image Self-test 3.1a The physiology of the gastrointestinal system





Answers




1. Carbohydrates, proteins, fats, vitamins, mineral salts and water.


2. The essential nutrients that are transported to the cells after digestion are:






3. Carbohydrates are broken down to saccharides by the enzymes in saliva, and proteins are broken down to amino acids in the stomach. The chewing of food and the churning action of the stomach turn the solid diet into a fluid ready for further digestion in the small intestine.


4. Pancreatic juice contains enzymes, which further break down carbohydrates into saccharides and proteins into amino acids. These enzymes also digest some fats (not including cholesterol, which is absorbed unchanged) into fatty acids, and glycerol. Bile salts in the bile aid the digestion of fatty acids.


5. The small intestine is adapted to maximise absorption by being very long and in the structure of its mucosa, which has folds, villi and microvilli to increase the surface area further. The blood and lymphatic supply of the small intestine is very rich and is arranged so that a blood vessel and a lymphatic vessel project into each of the thousands of villi on the mucosa.


6. The colon absorbs about two-thirds of the water that enters it, and also some essential vitamins that are the by-products of digestion by colonic microorganisms.


7. The functions of the liver include:










Investigation of the gastrointestinal system


Once referred to any hospital specialist, patients may be offered a series of tests chosen to exclude a wide range of possible diagnoses that may affect the gastrointestinal system. This may mean that the patient may undergo some tests that are not strictly necessary in their particular case, but it is considered good practice to be thorough in the investigation. Some tests might involve the patient in considerable inconvenience or discomfort, but are performed because it is believed that it is best to be as informed as possible about the health of the system before treatment is chosen.


The investigations that are most likely to reveal information about the digestive tract include:



These tests are considered briefly below in turn.



Physical examination of the gastrointestinal system


The physical examination of the gastrointestinal involves the stages listed in Table 3.1b-I. For the purposes of physical examination of a supine patient, the accessible region of abdomen is considered to occupy the approximately hexagonal region that is bounded by the ribs above and the inguinal ligaments and pubic bone below.


Table 3.1b-I The stages of physical examination of the gastrointestinal system







As Figure 3.1b-I illustrates, many important organs are situated underneath the nine named regions of the abdomen. A lump felt in the suprapubic area, for example, might suggest a problem of the bladder or the uterus, whereas pain in the left iliac fossa would suggest a problem of the colon or left ureter. The names for these nine regions of the abdomen are frequently used in medical texts for the description of abdominal conditions, so it is useful to be familiar with them.






Visualisation of the digestive tract


The most efficient way of visualising the oesophagus, stomach and duodenum is by means of a slim, flexible tubular telescope called an ‘endoscope’. In upper gastrointestinal endoscopy a heavily sedated patient is encouraged to swallow the tube. As the fibre-optic end of the endoscope descends, images of the lining of the upper digestive tract can be seen by the examining doctor on a screen. This procedure does not use X-rays.


X-ray studies are also used in the investigation of digestive disease. Because the soft tissue of the bowel is not clearly exposed by X-ray imaging, a liquid mixture containing the salt barium sulphate is used to provide ‘contrast’ between the hollow space within the bowel and the surrounding soft tissues (as the metal of barium shows up as white on X-ray images). In the procedure called ‘barium swallow’, the patient is requested to drink a liquid containing barium sulphate. As the liquid lines the upper digestive tract, X-ray images will reveal its outline and show up areas of muscle spasm, ulcers or tumours. Figure 3.1b-II is a clear barium-swallow X-ray image, in this case depicting an oesophageal cancer. The white area shows the internal shape of the oesophagus, and the arrows indicate the narrowing caused by the tumour.



The endoscope can also be used to pass a fine tube into the pancreatic duct and bile ducts. Barium can be injected up this tube so that X-ray images can show up the delicate internal structure of the pancreas and the gallbladder. This procedure is known as ‘endoscopic retrograde cholangiopancreatography’ (ERCP). Figure 3.1b-III illustrates an image taken during an ERCP. The thick white curved tube in this image is the end of the endoscope.



To investigate the lower digestive tract, a form of endoscope called a ‘colonoscope’ is directed into the anal canal and thence into the rectum and colon. To investigate the lower part of the colon (sigmoid colon) and the rectum, a rigid telescope-like instrument called a ‘sigmoidoscope’ may be used. This is slightly less invasive than a colonoscopy.


A ‘barium enema’ is a procedure for visualising the lining of the bowel. In this investigation, barium sulphate liquid is injected into the colon via the anus. This is an uncomfortable procedure and may require a night in hospital to ‘prepare the bowel’ by means of the administration of a strong laxative.


Ultrasound scans, magnetic resonance imaging (MRI) scans and computerised tomography (CT) scans are all useful investigations for diseases of the digestive tract, as these all can reveal the presence of soft-tissue masses, fluid and stones. Ultrasound is the least invasive of these investigations. MRI exposes the patient to strong magnetic and



image Self-test 3.1b The investigation of the gastrointestinal system





radiofrequency fields, but these currently are considered to carry little risk. However, an abdominal CT scan exposes the patient to over 50 times the amount of radiation associated with a chest X-ray, and so its use has to be guided on the basis that the potential benefits of the information outweigh the risks of carcinogenesis (cancer formation) from radiation exposure.





Important diseases of the mouth and salivary glands



Mouth ulcers


The term ‘ulcer’ describes ‘a break in the epithelium’. This term is used for conditions of the gastrointestinal system in which the protective mucosal layer has become damaged for some reason.


Mouth ulcers are usually isolated, small, painful, whitened breaches in the mouth lining, and often have no obvious precipitating cause. They tend to be more common in some people than others. In most cases the sufferer is otherwise well, although occasionally a vitamin deficiency might be found. False or sharp teeth occasionally trigger ulcers. A small mouth ulcer will usually heal within 1–3 days.


A crop of very painful, reddened ulcers points to a viral infection. The very first encounter with the cold sore virus (herpes simplex) can cause such a condition. This is most common in young children, and can be so severe that hospital admission is necessary to give fluids by intravenous drip, as severe inflammation of the mouth prevents eating and drinking for a few days.


Less commonly, mouth ulcers may be part of a more severe digestive condition. The lower gastrointestinal diseases of Crohn’s disease, ulcerative colitis and coeliac disease are all associated with mouth ulceration. These conditions are studied in more detail in Chapter 3.1e.








Salivary gland infections (sialadenitis)


There are three pairs of major salivary glands (see Chapter 3.1a). The parotid glands hug the posterior border of the masseter muscle on the face, the submandibular glands sit under the inferior edge of the lower jaw bone (mandible), and the sublingual glands sit under the tongue. All are exocrine glands and release their secretions via ducts into the mouth cavity.


These glands can become inflamed as a result of infection. The mumps virus is probably the most common cause of this in otherwise healthy people, although this disease is much less common since the introduction of widespread vaccination of children. The ‘hamster face’ seen in children with mumps is due to inflammation and swelling of the parotid glands.


Bacteria can cause infections in the salivary glands, although this should be seen, like thrush, as a sign of immune depletion. Underlying causes can include dehydration, alcoholism and diabetes. The symptoms include tender painful swollen salivary glands and fever. Eating, which causes salivation, is painful. The cause is an overgrowth of ‘healthy’ oral bacteria.






The red flags of diseases of the mouth


Some patients with diseases of the mouth will benefit from referral to a conventional doctor for assessment and/or treatment. Red flags are those symptoms and signs that indicate that referral is to be considered. The red flags of the diseases of the mouth are described in Table 3.1c-I. This table forms part of the summary on red flags given in Appendix III, which also gives advice on the degree of urgency of referral for each of the red flag conditions listed.


Table 3.1c-I Red Flags 4 – diseases of the mouth































Red Flag Description Reasoning
4.1 Persistent oral thrush (candidiasis) (appearing as a thick, white coating on the tongue or palate) Although common in the newborn, oral thrush in children and adults is not a normal finding, and merits referral to exclude an underlying cause. Common causes include corticosteroid use (including asthma inhalers), diabetes, immunodeficiency (including HIV/AIDS) and cancer. Dentures in elderly people can also predispose to oral thrush
4.2 Persistent painless white plaque (leukoplakia) (appearing as a coat that appears to sit on the surface of the sides of the tongue)
4.3 Painless enlargement of a salivary gland over weeks to months This needs referral to exclude salivary gland cancer, which is most common in people over the age of 60 years
4.4 Painful or painless enlargement of a salivary gland immediately after eating This suggests a salivary gland stone or obstruction from dried secretions. Early treatment is to maximise hydration by encouraging drinking, and to encourage salivation (e.g. with lemon juice). If the problem is persistent, referral is recommended, as surgical removal of the stone may be necessary
4.5 Tender or inflamed gums or salivary glands which do not respond within days to your treatment May be accompanied by fever or malaise. These symptoms suggest dental abscess or infection of a salivary gland, and if they persist indicate a need for referral for antibiotic treatment to prevent inflammatory damage to the dental roots or salivary glands
4.6 Ulceration of the mouth if persistent (for more than one week) or if preventing proper hydration

Oct 3, 2016 | Posted by in MANUAL THERAPIST | Comments Off on Gastrointestinal disease
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