1. THE DIGESTIVE SYSTEM Digestive Tract Accessory Organs

2. The Functions of the system To ingest food and transform it into a state where by the body can digest and absorb the nutrients within it for the purposes of energy, growth and repair. To do this by both chemical and mechanical means and to excrete the waste once the above has been achieved. To work in relation to the cardio vascular, endocrine and lymphatic systems to facilitate the above.

3. The System

4. The Digestive Tract The tract or alimentary canal begins with the mouth and ends at the anus. The teeth and tongue, hard and soft palate, 3 pairs of salivary glands The Pharynx The Epiglottis The Oesophagus The Stomach The Small intestine The Large intestine or colon The Rectum The Anus

5. The upper digestive tract The mouth forms the start of the digestive tract The tongue and the teeth are both vital for chemical and mechanical digestion as are the salivary glands which are located around the oral cavity. The 3 pairs of salivary glands : 1. Submandibular 2. Sublingual 3. Parotid ( largest)

6. The tongue is a voluntary muscle structure, it is attached at its base to the hyoid bone and by a fold of its membrane to the floor of the mouth. Its surface is covered in compound epithelial tissue with many little projections which are called papillae. In amongst the papillae are found nerve endings or taste buds. The papillae are of different shapes and are located in different areas of the tongue as indicated on this picture. 1.Filliform 2. Fungiform 3. Vallate ( largest)

7. The taste buds which are situated amongst the papillae are our taste organs ; there are considered to be 4 basic different taste sensations, sweet, sour, bitter and salt, located at different sites on the tongue. However this is a generalisation and many variations exist. The sense of taste triggers the production of saliva and also the release of gastric juices. The sensory information about taste travels in the cranial nerves 1.Glosso pharyngeal 2.Facial 3.Vagus To the thalamus and eventually the cerebrum of the brain where perception of taste is realised.

8. THE TEETH There are 32 teeth in the adult mouth. They include : 12 molars,8 premolars,4 canine,8 incisors. Permanent teeth are located in the alveoli of the mandible and maxilla forming fixed joints. The shapes of the teeth vary but the Structure is basically the same. 1.The crown ( above the gum) 2.The root ( embedded in the gum) 3.The neck ( narrow area where the crown emerges). Inside the tooth there is pulp which is supplied by blood and lymphatic vessels and nerves. Surrounding this is a layer of hard dentine and above the gum is found the hardest substance in the body enamel

9. The Pharynx and oesophagus. The oro pharynx and naso pharynx form a common passageway for air and food. By the time food reaches here swallowing is no longer under voluntary control and the outer layer consisting of sphincter type muscles are engaged in swallowing. The oesophagus is about 25 cm long and 2 cm wide continuing from the pharynx and extending through the diaphragm to enter the stomach at the cardiac sphincter

10. THE STOMACH The stomach may be seen as a dilation of the digestive tract. It is a muscular organ with a sphincter at the top and another at the bottom. It has a greater and lesser curvature and is divided up into 3 areas : The Cardia The Fundus The pylorus It has three layers of smooth muscle which travel in different directions as follows: The outer : longitudinal The middle :circular The inner : oblique These muscles provide the mechanical churning of food necessary for breaking it down The stomach is also a reservoir for food which can stay there for up to 4 hours.Inside the stomach. are found ruggae or folds in the lining of the stomach when it is empty.

11. THE SMALL INTESTINE The small intestine continues from the pyloric sphincter of the stomach till it reaches the iliocaecal valve of the colon and is around 5 meters long. It has 3 parts as follows : 1.The duodenum 2.The jejunum 3.The ilium The duodenum is about 25cms long with ducts passing into it from both the gall bladder and the pancreas. The jejunum is around 2meters long. The ileum is around 3 meters long and is the final section in which absorption of nutrients takes place before the remains of food pass into the colon.

12. The ileum and jejunum are characterised by thousands of finger like projections known as villi and micro villi. These increase the surface area for maximum absorption of nutrients. Inside some of the villi are located lymphatic vessels called lacteals which assist in the digestion of fats. The mucosal tissue of these villi contains mucus goblet glands and at their base gastric glands. The internal epithelium is rubbed away and replaced every 3 to 5 days. The internal environment of the intestines

13. The Large Intestine also known as the colon Starting at the ilio caecal valve the colon has 5 sections : 1. The caecum or blind ended gut from which the vermiform appendix protrudes. 2. The ascending colon turning at the hepatic flexure. 3. The transverse colon which travels across the body and turns at the splenic flexure. 4. The descending colon. 5. The sigmoid colon which extends on from the descending. This then becomes the rectum and finally the anus. Internally it contains three layers of smooth muscle and sac like shapes known as haustrae. The very muscular walls provide strong peristaltic movements.

14. The Accessory organs These organs assist the tract and include : The Liver The Gall bladder The Pancreas

15. The Liver The liver is called the largest gland in the body It sits just below the diaphragm at the top of the abdomen. It is shaped like a wedge, its fat end is positioned to the right and the point towards the left of the body. It is divided up into two main lobes and two smaller lobes : Right lobe Left lobe Caudate lobe Quadrate lobe The two main lobes are divided by the Falciform ligament. Internally, the liver is divided up into hexagonal units in which the specific tasks of the liver take place. Each unit is supplied by veins and arteries.

16. The Pancreas The pancreas is a gland which is situated behind the stomach and between the duodenum and the spleen. It is both an endocrine and an exocrine gland which means that it secretes pancreatic gastric juices from its acinar cells and hormones from its Islets of langerhan cells. There is a central duct which carries juices directly to the duodenum to help digest all 3 food groups.

17. The Gall Bladder The gall bladder is a pear shaped sac which is located underneath the liver and attached to it by a system of ducts. This is known as the biliary system. Bile produced by the liver surplus to immediate use is condensed and stored by this organ. It releases it into the duodenum when required for the digestion of fats.

18. Digestion and Absorption The 3 food groups Protein Carbohydrate Fat Are digested and absorbed in different areas of the tract.

19. Digestion takes place through both mechanical and chemical means. Muscular movements and gastric juices are employed in breaking down large food molecules into their smallest units so that they can be absorbed through the walls of the intestines. This begins by both means in the mouth. Food is broken down through mastication, moistened by saliva and propelled into the pharynx by the tongue, this moistened food is called the bolus. Carbohydrates begin to be broken down here by an enzyme called salivary amylase or ptyalin released in the saliva. Gastric juices begin to be produced further down in the tract even before food enters the mouth when we smell, see or anticipate food.

20. Digestive process Once the bolus is in the oesophagus it takes hardly any time to reach the stomach. It has to pass through a circular muscle called the cardiac sphincter to get there. The stomach acts as a reservoir but is also heavily engaged in both mechanical and chemical breakdown of food. The internal environment of the stomach is full of undulations called gastric pits which secrete a large number of substances including enzymes, hormones, hydrochloric acid and large amounts of mucous which helps to protect the lining. Proteins begin to be processed here by both the gastric juices, hydrochloric acid and a special enzyme called pepsinogen which requires the acid to become the active Pepsin. Pepsin breaks large proteins into peptides which are further broken into polypeptides and amino acids in the intestines.

21. The digestive process continues Food can stay in the stomach for 3 to 4 hours depending on what it is, red meat can take longer to leave the area. Once it is ready it leaves via another circular muscle called the Pyloric sphincter and enters the small intestine. The first part,the duodenum is a very busy section and is heavily engaged in the chemical breakdown of food receiving juices from the pancreas and bile from the gall bladder. Together these provide alkalise to neutralise acid and to begin the process of breaking triglyceride fat units into smaller units of fatty acids and glycerides. The pancreatic juices are Lipase for fats Trypsin and Chymo trypsin for proteins ( also known as protease) Amylase for carbohydrates Bile contains salts and pigments which help to emulsify large fat droplets into small droplets.

22. The digestive process continued Food is moved through the intestine by muscular movements called Peristalsis, this is also aided by the movements of the villi and microvilli. The main task of the intestines is to complete the final digestion of nutrients and then to absorb them through its walls. The bile and the pancreatric enzymes will go on working, however the intestines release few enzymes into their lumen, rather they release them to be active within the wall and amongst the epitheliel cells of the micro villi.

23. The enzymes which are active in the intestinal walls will complete the task with all three food groups Carbohydrates will have been broken down into disaccharide or double unit sugars in the stomach and duodenum so in the jejunum and ilium these double units of sucrose, lactose and maltose will be broken down by enzymes lactase, maltase and sucrase t o make glucose and galactose. Proteins which are now in the form of peptides are further broken down by the enzyme peptidase into amino acids. Digestion and Absorption

24. Channels are opened up in the walls of the intestines and the small nutrients pass through with the help of special proteins. This process works rather like a lock and key system so that molecules are received by the correct enzymes and pass into the blood stream or into the lymphatic vessels as with fats.

25. THE FINAL STAGES OF ABSORPTION By the time the food or chyme finds its way through the ilio caecal valve of the colon, the vast majority of absorption has taken place and the main task of the colon is to form faeces, however the colon absorbs water and certain minerals, salts and some vitamins. The bacteria of the colon will produce further vitamins from the substances within it, things like B vitamins and vitamin K. The bulk of the faeces will be made up from such things as cellulose and pectin from cell walls and then will also include waste from metabolism, dead cells including erythrocytes and phagocytes.

26. THE LIVER Blood from the major absorption sites of the intestines will carry nutrients in the hepatic portal vein to the liver itself It is said to have over 400 functions. amongst these are : Heat production Removal of toxins from drugs, alcohol and medications. Storage of fat soluble vitamins, iron and glucose Production of cholesterol and bile. Conversion of fats, glucose, protein. Aids in the control of growth hormone

28. Some more diseases and disorders Cirrhosis: the most common form is of the liver. Chronic damage of the tissue causing necrosis and formation of scar tissue which eventually renders the gland incapable of functioning. In this case normally caused by alcohol. Jaundice : Caused by excessive levels of bile pigments in the blood which make the skin look yellow. This is caused by a malfunction or a blockage in the gall bladder. Gall stones :Stones formed from bile pigments, calcium salts and cholesterol. Peptic ulcers :Often caused by bacteria ( helicobactor pylori),they disrupt the normal protection of the mucosal lining and cause burning and pain. They can be located in the duodenum, stomach, and pyloric areas. Ulcers are worsened by negative lifestyle choices such as smoking and drinking alcohol. Peptic ulcers are often assisted by eating. With gastric ulcers this can be the reverse.