digestive system - anatomy and function ppt
- 1. DIGESTIVE SYSTEM AND COMMON DISORDERS DR ABHINAV SENGAR SURGICAL GASTROENTEROLOGIST (MBBS, MS, FIAGES, DrNB –SS) TULIP HOSPITAL
- 2. • Digestion is defined as the process by which food is broken down into simple chemical substances that can be absorbed and used as nutrients by the body. • A normal young adult consumes 1 kg of solid diet and 2–3 Liter of fluid per day.
- 5. Digestive Organs • Major Organs : • Mouth • Esophagus • Stomach • Small intestine • Large intestine • Rectum • Accessory digestive system : • Liver • Gallbladder • Pancreas • Salivary gland
- 6. Functions of Digestive (GI) Tract • Ingestion – Occurs when material enters via the mouth • Mechanical Processing – Crushing / Shearing – makes material easier to move through the tract • Digestion – Chemical breakdown of food into small organic compounds for absorption • Secretion – Release of water acids, buffers, enzymes & salts by epithelium of GI tract and glandular organs • Absorption – Movement of organic substrates, electrolytes, vitamins & water across digestive epithelium • Excretion – Removal of waste products from body fluids
- 8. Saliva is a very essential digestive juice, since it has many functions •Preparation of food for swallowing •Appreciation of taste •Digestive function •Cleansing and protective functions •Role in speech •Excretory function •Regulation of body temperature •Regulation of water balance
- 9. Movement of Digestive Materials • By muscular layers of digestive tract – Consist of visceral smooth muscle – Along digestive tract: • Has rhythmic cycles of activities (PERISTALSIS) – Consists of waves of muscular contractions – Move a bolus along the length of the tract • Controlled by pacesetter cells – Surrounding the lumen of the tract • Cells undergo spontaneous depolarization – Triggering wave of contraction through entire muscular sheet
- 10. Peristalsis
- 11. Functions of Oral Cavity • Sensory analysis – Of material before swallowing • Mechanical processing – Through actions of teeth, tongue, and palatal surfaces • Lubrication – Mixing with mucus and salivary gland secretions • Limited digestion – Of carbohydrates and lipids
- 12. Esophagus • A hollow muscular tube • About 25 cm (10 in.) long and 2 cm (0.80 in.) wide • Conveys solid food and liquids to the stomach • Begins posterior to cricoid cartilage • Is innervated by fibers from the esophageal plexus
- 13. Stomach Anatomy
- 14. Stomach Function • Major Functions of the Stomach – Storage of ingested food – Mechanical breakdown of ingested food – Disruption of chemical bonds in food material by acid and enzymes – Production of intrinsic factor, a glycoprotein required for absorption of vitamin B12 in small intestine
- 15. Digestion in the Stomach • Stomach performs preliminary digestion of proteins by pepsin – Some digestion of carbohydrates (by salivary amylase) – Lipids (by lingual lipase) • Stomach contents – Become more fluid – pH approaches 2.0 – Pepsin activity increases – Protein disassembly begins • Although digestion occurs in the stomach, nutrients are not absorbed there
- 16. Small Intestine • 90% of absorption occurs in the small intestine
- 17. Small Intestine • The Duodenum – The segment of small intestine closest to stomach – 25 cm (10 in.) long – “Mixing bowl” that receives chyme from stomach and digestive secretions from pancreas and liver – Functions of the duodenum • To receive chyme from stomach • To neutralize acids before they can damage the absorptive surfaces of the small intestine
- 18. Small Intestine • The Jejunum – Is the middle segment of small intestine – 2.5 meters (8.2 ft) long – Is the location of most • Chemical digestion • Nutrient absorption – Has few plicae circulares – Small villi
- 19. Small Intestine • The Ileum – The final segment of small intestine – 3.5 meters (11.48 ft) long – Ends at the ileocecal valve, a sphincter that controls flow of material from the ileum into the large intestine
- 20. Small Intestine • Intestinal Secretions – Watery intestinal juice – 1.8 liters per day enter intestinal lumen – Moisten chyme – Assist in buffering acids – Keep digestive enzymes and products of digestion in solution • Intestinal Movements – Chyme arrives in duodenum – Weak peristaltic contractions move it slowly toward jejunum • Myenteric reflexes • Not under CNS control • Parasympathetic stimulation accelerates local peristalsis and segmentation
- 21. Pancreas • Lies posterior to stomach – From duodenum toward spleen • Is bound to posterior wall of abdominal cavity • Is wrapped in thin, connective tissue capsule Functions of the Pancreas 1. Endocrine cells of the pancreatic islets: • Secrete insulin and glucagon into bloodstream 2. Exocrine cells: • Acinar cells and epithelial cells of duct system secrete pancreatic juice
- 22. Pancreas • Pancreatic Enzymes – Pancreatic alpha-amylase • A carbohydrase • Breaks down starches • Similar to salivary amylase – Pancreatic lipase • Breaks down complex lipids • Releases products (e.g., fatty acids) that are easily absorbed • Pancreatic Enzymes – Nucleases • Break down nucleic acids – Proteolytic enzymes • Break certain proteins apart • Proteases break large protein complexes • Peptidases break small peptides into amino acids • 70% of all pancreatic enzyme production • Secreted as inactive proenzymes • Activated after reaching small intestine
- 23. Liver
- 24. Liver • Hepatocytes – Are liver cells – Adjust circulating levels of nutrients • Through selective absorption and secretion – In a liver lobule form a series of irregular plates arranged like wheel spokes – Many Kupffer cells (stellate reticuloendothelial cells) are located in sinusoidal lining – As blood flows through sinusoids • Hepatocytes absorb solutes from plasma • And secrete materials such as plasma proteins
- 25. Liver Function The Physiology of the Liver 1. Metabolic regulation 2. Hematological regulation 3. Bile production
- 26. Liver Function • Metabolic Regulation – The liver regulates: 1. Composition of circulating blood 2. Nutrient metabolism (carbohydrate, lipid & amino acid) 3. Waste product removal 4. Vitamin Storage (A, D, E & K) 5. Nutrient storage (iron) 6. Drug inactivation
- 27. Liver Function • Composition of Circulating Blood – All blood leaving absorptive surfaces of digestive tract • Enters hepatic portal system • Flows into the liver – Liver cells extract nutrients or toxins from blood • Before they reach systemic circulation through hepatic veins – Liver removes and stores excess nutrients • Corrects nutrient deficiencies by mobilizing stored reserves or performing synthetic activities
- 28. Liver Function • Hematological Regulation – Largest blood reservoir in the body • Receives 25% of cardiac output • Functions of Hematological Regulation 1. Phagocytosis and antigen presentation 2. Synthesis of plasma proteins 3. Removal of circulating hormones 4. Removal of antibodies 5. Removal or storage of toxins 6. Synthesis and secretion of bile
- 29. Liver Function • The Functions of Bile – Dietary lipids are not water soluble – Mechanical processing in stomach creates large drops containing lipids – Pancreatic lipase is not lipid soluble • Interacts only at surface of lipid droplet – Bile salts break droplets apart (emulsification) • Increases surface area exposed to enzymatic attack • Creates tiny emulsion droplets coated with bile salts
- 30. Gallbladder • Is a pear-shaped, muscular sac • Stores and concentrates bile prior to excretion into small intestine • Is located in the fossa on the posterior surface of the liver’s right lobe • The Cystic Duct – Extends from gallbladder – Union with common hepatic duct forms common bile duct
- 31. Gallbladder • Functions of the Gallbladder – Stores bile – Releases bile into duodenum, but only under stimulation of hormone cholecystokinin (CCK) – CCK • Hepatopancreatic sphincter remains closed • Bile exiting liver in common hepatic duct cannot flow through common bile duct into duodenum • Bile enters cystic duct and is stored in gallbladder
- 32. Large Intestine • Is horseshoe shaped • Extends from end of ileum to anus • Lies inferior to stomach and liver • Frames the small intestine • Also called large bowel • Is about 1.5 meters (4.9 ft) long and 7.5 cm (3 in.) wide
- 33. Large Intestine
- 34. Parts of Large Intestine • The Cecum – Is an expanded pouch – Receives material arriving from the ileum – Stores materials and begins compaction • Appendix – Also called vermiform appendix – Is a slender, hollow appendage about 9 cm (3.6 in.) long – Is dominated by lymphoid nodules (a lymphoid organ)
- 35. Parts of Large Intestine • The Colon – Has a larger diameter and thinner wall than small intestine – The wall of the colon • Forms a series of pouches (haustra) – Haustra permit expansion and elongation of colon
- 36. Parts of Colon • Ascending Colon – Begins at superior border of cecum – Ascends along right lateral and posterior wall of peritoneal cavity to inferior surface of the liver and bends at right colic flexure (hepatic flexure) • Transverse Colon – Crosses abdomen from right to left; turns at left colic flexure (splenic flexure) – Is supported by transverse mesocolon – Is separated from anterior abdominal wall by greater omentum
- 37. Parts of Colon • The Descending Colon – Proceeds inferiorly along left side to the iliac fossa (inner surface of left ilium) – Is retroperitoneal, firmly attached to abdominal wall • The Sigmoid Colon – Is an S-shaped segment, about 15 cm (6 in.) long – Starts at sigmoid flexure – Lies posterior to urinary bladder – Is suspended from sigmoid mesocolon – Empties into rectum
- 38. Parts of Large Intestine • The Rectum – Forms last 15 cm (6 in.) of digestive tract – Is an expandable organ for temporary storage of feces – Movement of fecal material into rectum triggers urge to defecate • The anal canal is the last portion of the rectum – Contains small longitudinal folds called anal columns • Anus – Also called anal orifice – Is exit of the anal canal – Has keratinized epidermis like skin
- 39. Large Intestine Functions – Reabsorption of water – Compaction of intestinal contents into feces – Absorption of important vitamins produced by bacteria – Storage of fecal material prior to defecation
- 40. Common Digestive Disorders • Gastroesophageal Reflux Disease • Gastric Ulcer • Gall Stone Disease • Hepatitis • Appendicitis • Irritable Bowel Syndrome • Haemorrhoids • Anal Fissures
- 41. “Health is a state of complete physical, mental and social well being and not merely the absence of disease or infirmity” THANK YOU
- 42. Dr Abhinav Sengar Surgical Gastroenterologist and Advanced Laparoscopic Surgeon Director - Tulip Hospital • MBBS (GSVM Kanpur) - 2004 • MS (Surgery), GSVM Kanpur 2010 • DrNB SS – Medanta The Medicity, 2015 – 2018 in GI Surgery, GI Oncology, Bariatric Surgery and Liver Transplantation • Member of: ASI, IASG and IAGES • Fellowship of Association of Gastrointestinal Endosurgeons (FIAGES) – 2020 • Ex Assistant Professor – GSVM Surgery Dept 2018 – 2020
Editor's Notes
- #10: Peristaltic Motion Circular muscles contract behind bolus: While circular muscles ahead of bolus relax Longitudinal muscles ahead of bolus contract: Shortening adjacent segments Wave of contraction in circular muscles: Forces bolus forward
- #11: Salivary Glands Three pairs secrete into oral cavity Each pair has distinctive cellular organization And produces saliva with different properties Salivary Glands Produce 1.0–1.5 liters of saliva each day Saliva 99.4% water 0.6% includes Electrolytes (Na+, Cl-, and HCO3-) Buffers Glycoproteins (mucins) Antibodies Enzymes Waste products Muscles of Mastication Close the jaws Slide or rock lower jaw from side to side Chewing involves mandibular Elevation and depression Protraction and retraction Medial and lateral movement
- #12: Swallowing Also called deglutition Can be initiated voluntarily Proceeds automatically Is divided into three phases Buccal phase Pharyngeal phase Esophageal phase
- #13: Regions of the Stomach Cardia Fundus Body Pylorus Constantly being replaced, covered thick mucus, same simple columnar epithelium Pyloric Sphincter – regulates gastric emptying Gastric Glands In fundus and body of stomach Extend deep into underlying lamina propria Each gastric pit communicates with several gastric glands Parietal cells Chief cells Parietal Cells Secrete intrinsic factor and hydrochloric acid (HCl) Chief Cells Secrete hydrochloric acid (HCl) Are most abundant near base of gastric gland Secrete pepsinogen (inactive proenzyme) Pepsinogen Is converted by HCl in the gastric lumen To pepsin (active proteolytic enzyme)
- #21: Pancreatic Acini Blind pockets Are lined with simple cuboidal epithelium Contain scattered pancreatic islets Pancreatic Islets Endocrine tissues of pancreas Scattered (1% of pancreatic cells)
- #23: Is the largest visceral organ (1.5 kg; 3.3 lb) Lies in right hypochondriac and epigastric regions Extends to left hypochondriac and umbilical regions Performs essential metabolic and synthetic functions Anatomy of the Liver Is wrapped in tough fibrous capsule Is covered by visceral peritoneum Is divided into lobes
- #26: Metabolic Activities of the Liver Carbohydrate metabolism Lipid metabolism Amino acid metabolism Waste product removal Vitamin storage Mineral storage Drug inactivation
- #28: Removes damaged / old red blood cells Plasma proteins: albumin – contrbutes to osmotic concentration Reabsorped Epinephrine, norepinephrine, insulin, thyroid & steroid hormones Removes antibodies and converts to amino acids Traps some lipid-soluble toxins (DDT) or breaks down and removes from blood Bile production
- #31: Physiology of the Gallbladder Full gallbladder contains 40–70 mL bile Bile composition gradually changes in gallbladder Water is absorbed Bile salts and solutes become concentrated
- #32: Functions of the Large Intestine Reabsorption of water Compaction of intestinal contents into feces Absorption of important vitamins produced by bacteria Storage of fecal material prior to defecation