The presentation on the Digestive system simplified.pptx

Presentation

1. Digestive System

2. The digestive system is the collective name used to describe the alimentary canal , its accessory organs and a variety of digestive processes that take place at different levels in the canal. Function : Break down food into simpler molecules High-energy adenosine triphosphate

3. Activities in the digestive system Ingestion Propulsion Digestion Absorption Elimination

4. Organs of the digestive system Alimentary canal Accessory organs Mouth Pharynx Esophagus Stomach Small intestine Large intestine Rectum and anal canal Three pairs of salivary glands The pancreas The liver and biliary tract

5. FIG. THE DIGESTIVE SYSTEM

6. Basic structure of alimentary canal The walls of the alimentary tract are formed by four layers of tissue: Adventitia or serosa – outer covering Muscle layer (tunica muscularis ) Submucosa (tunica submucosa ) Mucosa – lining (tunica mucosa)

7. Tongue Voluntary muscle Extrinsic muscles – for movement Intrinsic muscle – for changing size and shape. Papillae – containing sensory receptors.

8. Teeth They are embedded in the alveoli or sockets of the alveolar ridges of the mandible and the maxilla. Used for mastication of food. 8 incisors, 4 canines ( cuspids ), 8 premolars (bicuspids) and 12 molars (tricuspids) = 32 teeth A. Deciduous teeth, B. Permanent teeth

9. Salivary glands There are three pairs of salivary glands: Parotid glands Submandibular glands Sublingual glands

10. Composition of saliva: Water Mineral salts Salivary amylase Mucus Lysozyme Immunoglobulins Blood-clothing factors

11. Pharynx Divided into three parts, the nasopharynx , oropharynx and the laryngopharynx . Walls of pharynx has three layers: Lining membrane (mucosa) Middle layer consists of connective tissue and contains blood and lymph vessels and nerves. Outer muscle layer of involuntary muscles.

12. Oesophagus 25 cm long, 2 cm diameter and lies in median plane in the thorax. Present anterior to vertebral column and posterior to the trachea and heart. Oesophagus curves upwards before opening to stomach.

13. Swallowing (deglutition) Initiated voluntarily but completed by a reflex (involuntary) action. The mouth is closed, muscles of tongue and cheeks push the food into the pharynx. Muscles of pharynx are stimulated which contracts and propels the bolus down into oesophagus . This is coordinated by the medulla and lower pons in brain stem.

14. The soft palate rises up and closes off the nasopharynx ; tongue and pharyngeal folds block the way back into the mouth.

15. Sequence of swallowing (Deglutition)

16. Stomach It is a J-shaped dilated portion of the alimentary tract epigastric , umbilical and left hypochondriac regions of the abdominal cavity.

17. Structure of the stomach Two curvatures: lesser and greater curvature. It divided into three regions: The fundus The body The pylorus ( Antrum )

18. Muscle layer Longitudinal fibres Circular fibres Oblique fibres Mucosa: consists of specialized cells that secrete gastric juice.

19. Secretions of the stomach Gastric acid ( HCl ) from parietal cells Pepsin from chief cells Mucus and bicarbonate from mucus neck cells

20. Small intestine Comprised of three continuous parts: Duodenum 25cm Secretions from gall bladder and pancreas – through duodenal papilla Jejunum 2m Ileum 3m

21. Structure of small intestine Mucosa – greater surface area Permanent circular folds – villi and microvilli Goblet cells secrete mucus Cells replaced from time to time (replaced every 3-5 days)

22. A highly magnified diagram of a villus in the small intestine Scanning electron micrograph showing many villi

23. Intestinal juice 1500 ml secreted daily Consists of: water, mucus and mineral salts pH 7.8 and 8.0

24. Large intestine, rectum and anus Large intestine: 1.5 m long, 6.5 cm diameter, begins at caecum and terminates at the rectum. Caecum The colon – The ascending colon The transverse colon The descending colon The sigmoid colon Rectum (13 cm long) Anal canal (3.8 cm long)

25. Functions of large intestine Absorption Microbial activity : Synthesis of vitamin K & folic acid, bacteria – Escherichia coli, Enterobacter aerogenes , Streptococcus faecalis and Clostridium perfringens . Mass movement – gastrocolic reflex Defaecation

26. Digestive enzymes and their functions Oral cavity (pH 6.8) secretes Amylase : Digests carbohydrates - Converts polysaccharides to disaccharide maltose. Stomach (pH 1.5 -3.5) secretes Pepsin: Digests of proteins - Converts polypeptides to tripeptides , dipeptides and amino acid.

27. Small intestine (pH 8) secretes Trypsin and Chymotrypsin for digestion of proteins - Converts polypeptides to tripeptides , dipeptides and amino acid. Pacreatic amylase for digestion of carbohydrates - Converts polysaccharides to disaccharide. Lipase for digestion of fats - Converts fats into fatty acids and glycerol. Sucrase , maltase, lactase for complete digestion of carbohydrates: converts disaccharides such as sucrose, maltose and lactose to monosaccharides .

28. Location Enzyme Function Oral cavity (pH 6.8) Salivary Amylase Digestion of carbohydrates: Converts polysaccharides to disaccharide maltose Stomach (pH 1.5 -3.5) Pepsin Digestion of proteins: Converts polypeptides to tripeptides , dipeptides and amino acid Small intestine (pH 8) Activated by enterokinase Trypsin Digestion of proteins: Converts polypeptides to tripeptides , dipeptides and amino acid Chymotrypsin Pacreatic amylase Digestion of carbohydrates: Converts polysaccharides to disaccharide Lipase Digestion of fats: Converts fats into fatty acids and glycerol Sucrase , maltase, lactase Complete digestion of carbohydrates: converts disaccharides such as sucrose, maltose and lactose to monosaccharides Digestive enzymes and their functions

29. Bile Secreted by the liver stored in gall bladder Consists of: water, mineral salts, mucus, bile salts, bile pigments ( bilirubin ), cholesterol. Enters the duodenum through the hepatopancreatic sphincter – when sphincter is closed goes to the gall bladder through cystic duct. Emulsification of fats.

30. Gall Bladder The gall bladder is a pear-shaped sac attached to the posterior surface of the liver by connective tissue. It has a fundus or expanded end, a body or main part and a neck, which is continuous with the cystic duct. Function: reservoir for bile concentration of the bile by up to 10- or 15-fold, by absorption of water through the walls of the gall bladder release of stored bile.

31. Pancreas Pale grey gland weighing about 60 gm, it is 12 to 15 cm long. Situated in the epigastric and left hypochondriac region. Consists of a broad head, a body and a narrow tail. It is both an exocrine as well as an endocrine gland.

32. Liver Largest gland in the body, weighing between 1 to 2.3 kg. Occupies right hypochondriac region and part of epigastric region. Liver has four lobes: Right and left lobe, and other two the caudate and quadrate lobe.

33. Anatomy of liver

34. Functions of the Liver The functions of the liver are so numerous and important that we cannot survive without it. The liver has six major functions: The liver manufactures the anticoagulant heparin and most of the other plasma proteins, such as prothrombin and thrombin, that are involved in the blood clotting mechanism. Kupffer’s cells of the liver phagocytose (eat) certain bacteria and old, worn-out white and red blood cells.

35. Liver cells contain various enzymes that either break down poisons or transform them into less harmful substances. If the body cannot break down and excrete certain poisons, it stores those poisons. When we digest proteins into amino acids, the amino acids go to the mitochondria to be converted into ATP. This process produces ammonia as a waste product, which is toxic to cells. The liver cells convert ammonia to urea (harmless) that is then excreted by the kidneys or the sweat glands.

36. Excess glucose and other monosaccharides can be stored as glycogen (animal starch) or converted to fat. When needed, the liver can then transform glycogen and fat into glucose. The liver stores glycogen, copper and iron, as well as vitamins A, D, E, and K. The liver produces bile salts that break down fats. These bile salts are sent to the duodenum of the small intestine for the emulsification (break-up) and absorption of fats.