The Digestive System - Biomedical Science PDF

The Digestive System Biomedical Science Coralie Frances GDC Learning Outcomes 1.1.5 Describe relevant and appropriate dental, oral, craniofacial and general anatomy and explain their application to patient management 1.1.6 Describe relevant and appropriate physiology and explain its appli...

The Digestive System Biomedical Science Coralie Frances GDC Learning Outcomes 1.1.5 Describe relevant and appropriate dental, oral, craniofacial and general anatomy and explain their application to patient management 1.1.6 Describe relevant and appropriate physiology and explain its application to patient management Intended Learning Outcomes By the end of the session you should be able to: Describe the organs of the digestive system Explain the functions of the major organs of digestion Describe the types of tissue and linings associated with the digestive organs List the functions of gastric juice Summaries the chemical digestion of food Why is digestion part of the curriculum? As student Dental hygienists and therapists why do you need to learn about the structure and function of the digestive system? Why do you think it is important to understand the learning outcomes in this lecture? Assess your knowledge pre lecture What are the five main activities that take place in the digestive system? Look at the next slide Can you name the component parts of the alimentary canal labelled 1-10? Answers The processes are: 1. Ingestion 2. Propulsion 3. Digestion 4. Absorption 5. Elimination (defaecation) Name the component parts of the alimentary tract labelled 1 – 10 1. Mouth 2. Salivary glands 3. Gall bladder 4. Liver 5. Pancreas 6. Small intestine 7. Oesophagus 8. Stomach 9. Large intestine 10. Rectum How did you do? Rate your knowledge on a score of 1-5 (1 least knowledge; 5 greatest knowledge) Continue with the PPT to refresh your knowledge then answer the same questions again What are your scores now? Useful References Waugh, A. and Grant, A. (2018) Ross & Wilson Anatomy And Physiology In Health And Illness. 13th ed. Elsevier. Ward, J. and Linden, R. (2017) Physiology At A Glance. 4th ed. Wiley-Blackwell. What happens to the food you eat? Order of lecture The structure & function of each organ will be described chronologically at each stage as the food reaches it www.visitgreenwich.org.uk/food-and-drink Alimentary Tract Alimentary tract – a tube that extends from mouth to rectum As food moves through the canal, it is ground and mixed with various digestive juices Alimentary tract function Converts food into small, nutritional molecules for absorption and distribution by circulation to all tissues of the body, and excretes the unused residue The active processes are: Ingestion Propulsion Digestion Absorption Elimination (defaecation) Alimentary Tract Function It is also part of immune system: Mucus (IgA), Low pH lysozyme Enzymes (saliva, bile) (Saliva poisonous in some animals to quieten down living prey!) Components of digestive system Composed of the following parts: The gut – The small and The mouth oesophagus The stomach The rectum Large intestines Accessory organs The The liver The The gall pancreas bladder salivary glands General structure of the alimentary tract Walls of the digestive tract consist of four layers throughout its length Adventitia/Serosa - outer covering of connective tissue Muscularis - smooth muscle that provides contractions (peristalsis) to move food consists of two layers, out layer longitudinal, inner-circular Submucous - loose connective tissue contains blood vessels, lymphatic vessels, nerves and glands Mucosa - lining epithelial layer coated with mucous Revision question? What are the 5 activities which take place in the alimentary canal? Can you describe them? Take a break https://www.publicdomainpictures.net/en/view-image.php?image=220901&picture=coffee-amp-biscuit In the Mouth - Mechanical Teeth - To tear, rip and chew food to physically break it into smaller pieces and produce a bolus Uvula- Stops food or liquid entering nasal cavity Tongue - Voluntary muscular structure important in mastication and deglutition In the mouth - Chemical Salivary amylase (ptyalin) breaks down polysaccharides, starch in the bolus to maltose, a less complex sugar (start of digestion) Large particles like starch cannot be absorbed into small intestine Taste buds allow appreciation, also sample potential hazards Bolus A round or oval shaped mass of food formed in the mouth after thorough chewing, in preparation for swallowing Food is crushed, ground by teeth – mastication Salivary glands secrete saliva which makes food moist and easy to swallow (stuck together with mucin) as well as containing enzymes that commence digestion Salivary Glands (3 pairs) Submandibular A at the angle of the jaw opens into the floor of the mouth, source of 70% of saliva Sublingual B in front of the submandibular pair and opens into the floor of the mouth, source of 5% of saliva Parotid C below the external acoustic meatus the duct opens into the mouth opposite the buccal of second upper molar, source of 25% of saliva Saliva D 99.5% is water and only 0.5% other substances (mucus a and digestive enzyme called salivary amylase which begins the digestion of carbohydrates)  Swallowing Involves co-ordinated activity of tongue, soft palate, 1 pharynx and oesophagus 2 First phase is voluntary as food is forced into the pharynx by the tongue 3 After this, swallowing is a reflex process Tongue blocks the mouth, soft palate closes nose and 4 larynx rises so that epiglottis closes off trachea Food moves into pharynx and 5 onwards by peristalsis Video of swallowing https://www.bing.com/videos/search?q=video+of+swallow+anatomy&ru=%2fvideo s%2fsearch%3fq%3dvideo%2520of%2520swallow%2520anatomy%26qs%3dMM%2 6form%3dQBVR%26sp%3d2%26ghc%3d1%26pq%3dvideo%2520of%2520swallowin g%26sk%3dMM1%26sc%3d2-19%26cvid%3d7492F7227E984C7C9811A7634E7F469 9&view=detail&mid=81EC2DB5BDE9964A8EC081EC2DB5BDE9964A8EC0&rvsmid= BDAFC53EBDE8FEE9E496BDAFC53EBDE8FEE9E496&FORM=VDQVAP  Oesophagus Swallowed bolus travels from mouth to stomach via a muscular tube, the oesophagus About 25cm long, it is the first part of the digestive tract proper Oesophagus: - Lined with mucus membrane - Secretes fluid to lubricate downward movement of food - Smooth muscle wall contracts to squeeze food towards stomach Peristalsis Rhythmic contraction of smooth muscles propels contents through digestive tract Waves – circular contraction occurs behind bolus to prevent backwards movement, followed by contraction of longitudinal smooth muscles to push bolus forwards Bolus enters stomach to become chyme More digestive tract movements Segmentation: A muscular movement in the small intestine Periodic constriction of segments of intestine without movement backwards or forwards A mixing rather than a propulsive movement Vomiting: Propulsion comes from contraction of abdominal muscles- peristalsis does not reverse in the oesophagus Questions? What is formed during mastication, ready for swallowing? What assists this to be formed? What needs to be closed off before swallowing takes place? Question? What is the function of the smooth muscle found in the wall of the oesophagus?  Stomach Hollow muscular organ, J-shaped, left Fundus, body and side of the abdominal pylorus recognised as cavity (liver is on the distinct regions right) Pyloric sphincter - separates stomach from small intestine Highly acidic Oesophageal sphincter environment - separates stomach from oesophagus Structures of the Stomach The lining of the stomach has numerous folds when empty called rugae; they allow for expansion when we eat Has numerous gastric glands that secrete “gastric juice” into the stomach The most common cells found in the glands are: Parietal cells – produce HCL acid that denatures proteins. Chief cells – produce pepsin that begins protein digestion Mucus cells – produce mucus that protects from Hydrochloric action Stomach lining Epithelium forms deep pits which can contain glands Hormones – e.g. gastrin which increases Hall secretion and stomach motility Glands secrete enzymes, hormones and mucus Stomach absorbs some water, lipids, caffeine, alcohol Enzymes – e.g. pepsinogen → pepsin, necessary for protein digestion Section through stomach lining Functions of the Stomach Temporary storage area for food (3-4 hours) which is also churned by muscular layers to form chyme, a creamy substance voided via pyloric sphincter to duodenum Muscles relax and contract to aid mechanical breakdown Surface area increased by rugae Pyloric sphincter holds food in stomach allows for emptying of chyme into small intestine Questions What is the food called within the stomach? What is the name of sphincter A? A B What is the name of sphincter B? What is the pH environment of the stomach? Small intestine Comprises: 1. Duodenum 2. Jejunum 3. Ileum Site of majority of digestion Jkjfg Longest part of system Usually sterile Duodenum First part of small intestine, 25 cms long Curves around head of pancreas and entry of common bile duct Chemical degradation of small amounts of food controlled by pyloric sphincter begins here Enzymes secreted by pancreas and duodenum itself aid digestion of fats by emulsifying fats 2 Ducts enter Duodenum Bile duct draining gall bladder from liver Pancreatic duct draining pancreas Jejunum & Ileum Jejunum (2metres) and ileum (3 metres) continue the absorption process of carbohydrates, proteins & fats Surface area increased by being covered in wrinkles/folds with microscopic projections called villi Lined with simple columnar epithelium, the cells of the villi carry projections called microvilli Large surface area available for nutrient absorption Villi Each villus has a capillary and a lacteal: Lacteal Capillaries absorb fat into absorb lymphatic system everything else Video of role & structure of small intestine Questions? What are the parts of the small intestine? What 2 ducts enter the small intestine? What is the major function of the small intestine apart from digestion? Accessory Organs Liver Largest solid organ and largest gland in the body Multifunctional Secretes bile, which accumulates in gall bladder between meals Capillaries of small intestine drain fat and other nutrient- rich lymph into it via hepatic portal system Gall Bladder Small pear-shaped organ on underside of liver Stores and concentrates bile during the fasting state When fat enters duodenum, mucosal cells release the peptide hormone cholecystokinin on its release this stimulates the gall bladder to contract and discharge bile Bile is alkaline and makes the food alkaline so pancreatic enzymes can act on it Gallstones are usually cholesterol-based; may block the hepatic or common bile ducts causing pain and jaundice Bile A watery greenish fluid produced by liver and secreted via hepatic duct and cystic duct to gall bladder for storage Released on demand via common bile duct to an opening near the pancreatic duct in duodenum Contains bile salts/acids, bile pigments (mainly bilirubin, the non-iron part of haemoglobin), cholesterol and phospholipids Bile salts and phospholipids emulsify fats, the rest are for excretion Large amounts of bile (acids) secreted every day, but only relatively small quantities lost as 95% are reabsorbed in the ileum, returned to the liver and reused Pancreas Endocrine and exocrine gland The exocrine part produces many enzymes which enter the duodenum via the pancreatic duct The endocrine part produces (insulin and glucagon) The exocrine pancreas has two main digestive functions: 1. Secretes digestive enzymes in response to cholecystokinin to help with digestion of fats, starches, proteins 2. Secretes aqueous bicarbonate solution to help neutralise stomach acid entering small intestine Pancreatic Fluid Contains: Sodium bicarbonate to neutralise acidity of contents arriving from stomach (brings pH back up to 8) Pancreatic amylase – carbohydrates → simple sugars (together with maltase, sucrase, lactase) Pancreatic lipase – lipids → fatty acids & glycerol Trypsin & chymotrypsin – protein → amino acids Nucleases – hydrolyse ingested nucleic acids (RNA/DNA) into component nucleotides Functions of the liver including the role the liver plays in digestion Https://www.youtube.com/watch ?v=s2JwoqcnyS8 Time 5.39 minutes Questions Name the accessory organs of the digestive system GI What hormone stimulates the release of bile from the gall bladder? What is the function of the bile salts and phospholipids in the bile? The GI tract continued –the large intestine Large Intestine (colon) Food not broken down any more Absorption of remaining water from indigestible food matter Some electrolytes and indigestible food left Stores and eliminates waste Absorbs vitamins produced by gut bacteria, especially vitamin K and certain B vitamins  Less muscular More goblet cells which secrete mucus for lubrication No villi Takes about 16 hours to complete remaining processes Gas – due to bacterial fermentation of undigested material Chyme mixed with mucus and bacteria (mostly commensals) → Faeces (given colour by bile pigments) Gut bacteria: - synthesise vitamins - digest polysaccharides for which we have no enzymes (10% of our calories) Rectum Last 13 cms of large intestine Stores solid waste until it leaves the body through the anus – external opening Peristaltic waves Sphincter relaxation (voluntary and involuntary) Questions What is absorbed in the large intestine? What is the reason for gas production in the large intestine? Digestion Digestion Involves the mixing of food, the movement of food and the chemical breakdown of larger food molecules into smaller ones(catabolism) Gut modifies food physically and chemically and disposes of unusable waste Modification depends on exocrine and endocrine secretions and controlled movement of food through digestive tract Digestive juices Stomach and small intestine each produce a digestive juice Other digestive juices empty into the alimentary canal from salivary glands, gall bladder and pancreas Most juices contain digestive enzymes which speed up the reactions involved in the breakdown of food Digestive Enzymes AMYLASE: 3 main starch → types: maltose → glucose LIPASE: PROTEASE: lipids → protein → fatty acids amino and acids glycerol Digestion of Carbohydrates Digestion begins in the mouth (salivary amylase) Salivary and pancreatic amylase converts disaccharides (double sugars) Intestinal enzymes (sucrase, maltase, lactase) break down into disaccharides and monosaccharides Polysaccharide + salivary amylase -> maltose & small polysaccharides Undigested polysaccharides + pancreatic amylase -> maltose, disaccharides + maltase, sucrase & lactase -> monosaccharides Digestion of Proteins Starts in the stomach and ends in the small intestine Pepsin in stomach, trypsin and chymotrypsin in pancreatic juice digest protein. Aminopeptidase present in intestinal secretion finally digest protein into amino acids. Protein + pepsin -> short polypeptides Short polypeptides + trypsin, chymotrypsin -> small polypeptides & peptides + carboxypeptidase, peptidases, dipeptidases -> amino acids Digestion of Lipids Bile produced by the liver is poured into the duodenum and brings about emulsification Pancreatic lipase splits the lipid molecules into fatty acids and glycerol Fats + bile salts -> emulsified fat droplets + pancreatic lipase -> fatty acids & glycerol Absorption Stomach absorbs only a few substances Main absorption occurs in small intestine Occurs by combination of simple diffusion, facilitated diffusion and active transport Amino acids and glucose are directly transported to the liver via the hepatic portal vein Absorption Majority occurs in the jejunum Fatty acids and glycerol are absorbed by intestinal cells Iron absorbed in duodenum Vitamin B12 / bile salts absorbed in terminal ileum Water and lipids absorbed throughout Please complete the following table with the aid of Ross & Wilson P.342 Table 12.2 Summary of the sites of digestion and absorption of nutrients Small Intestine Nutrient Mouth Stomach Digestion Absorption Large Intestine Questions What type of enzyme helps digestion of starch? What type of enzyme helps digest protein? What type of enzyme helps digest lipids? Revision Exercise Review and revise the exercises on pages 366 & 367 in Waugh, A. and Grant, A. (2018) Ross & Wilson Anatomy And Physiology In Health And Illness. 13th ed. Elsevier. Links to youtube video https://www.youtube.com/watch/Og5xAdC8EUI TEDex digestion 5 mins long summarises digestion throughout the alimentary canal The End