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Gastric Mucosal Barrier (GMB)
[1] Luminal membrane impermeable to HCL.
[2] Tight junctions between cells.
Ulcer
Peptic ulcer in oesophagus, stomach or duodenum
Weakness in GMB.
Increased acidity leads to increased histamine leading
to increased acidity and a vicious cycle
Helicobacter Pylori 90% of peptic ulcers](https://image.slidesharecdn.com/ramadan-gitphysiology-220330083538/75/Ramadan-GIT-physiology-pdf-31-2048.jpg)
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Ramadan- GIT physiology.pdf
The document provides an overview of gastrointestinal physiology. It describes the main components and layers of the gastrointestinal tract, from the mouth to the anus. It then discusses the four main functions of the digestive system: motility, secretion, digestion, and absorption. Specific sections cover the salivary glands, swallowing process, stomach functions and secretions, pancreatic secretions, liver and biliary system, gastrointestinal hormones, and the histology and innervation of the gastrointestinal tract.
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Ramadan- GIT physiology.pdf
- 1. Gastrointestinal Physiology Dr. RamadanMohamed Ahmed
- 2. Gastrointestinal tract isa continuous tube that consists of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus. The lumen of this tube is continuous with the external environment. The accessory organs are the salivary glands, exocrine glands, and biliary system (liver and gallbladder). pharynx Upper esophygeal sphincter Lower esophygeal sphincter stomach Descending colon duodenum cecum anus rectum liver Salivary gland larynx esophagus
- 3. Functions of thedigestive system This system has four functions: 1. Motility is the muscular contractions that mix and move the contents forward of the digestive tract. 2. Secretion is the transfer of digestive juices by exocrine glands into the digestive tract. 3. Digestion is the hydrolysis of large molecules (e.g., carbohydrates, proteins, and fats) into their smaller subunits. 4. Absorption is the passage of the products of digestion from gastrointestinal lumen into the blood.
- 4. The wall ofthe digestive tract consists of four layers; • The mucosa lines the luminal surface. Its inner epithelial layer has exocrine and endocrine cells. • The submucosa is under the mucosa This connective tissue has large blood and lymph vessels. It contains a submucous plexus. • The muscularis externa is the main smooth layer of the digestive tube. The muscularis externa has an inner circular layer and an outer longitudinal layer. A myenteric plexus is between the two smooth muscle layers. • Serosa: outer protective layer.
- 5.
- 6. 6 Innervation of theGIT 1- Intrinsic innervation A- The Myenteric plexus: It controls mainly the motor function (motility) of the GIT. B- The Submucosal plexus: It controls mainly the secretory function of the GIT and the blood flow. 2- Extrinsic innervation: A- Parasympathetic nervous system: It is usually excitatory on the functions of the GIT. B- Sympathetic nervous system: It is usually inhibitory on the functions of the GIT.
- 7. Fig. 15-3, p.471 External influence Local changes in digestive tract Receptors in digestive tract Intrinsic nerve plexuses Extrinsic automatic nerves Gastrointestinal hormones Smooth muscle (contraction for motility) Exocrine gland cells (secretion of digestive juices) Endocrine gland cells (secretion of gastrointestinal and pancreatic hormones) Self- excitable = Short reflex = Long reflex = Hormonal pathway Regulation of GIT function.
- 8. Chewing ** is thefirst step in digestive process ** is can be voluntary or reflex (involuntary) action. It’s functions 1. Breaks food up into smaller pieces to facilitates swallowing 2. Mixes food with saliva 3. Stimulates taste buds by exposing them to food
- 9.
- 10.
- 11. Basic saliva components •Water 99.5% • Ions: Na+, K+, Ca2+, Cl–, HCO3 – • Enzymes: salivary amylase • Immunoglobolins: IgA • Mucus: lubrication of food and protection of oral mucosa • Lysozyme. (bacterial killing enzyme) • pH of saliva is about 7.
- 12. Innervation of salivaryglands Excitation of parasympathetic nerve fibers causes: - Increased watery secretion rich in enzymes Excitation of sympathetic nerve fibers causes: - Slight increase in viscid saliva (rich in mucus)
- 13. Cerebral cortex Otherinputs Salivary center in medulla Conditioned reflex Pressure receptors and chemoreceptors in mouth Unconditioned reflex Autonomic nerves Salivary glands Salivary secretions Control of salivary secretion.
- 14. Function of Saliva 1.Moistens oral mucosa .It facilitates speaking and chewing. 2. Moistens dry food, lubricates food to facilitate swallowing and cools hot food. 3. Provides a medium for dissolved foods to stimulate the taste buds. 4. Buffers oral cavity contents. Saliva has a high concentration of bicarbonate ions. 5. Digestion. Alpha-amylase, contained in saliva, breaks down polysaccharides into disaccharides, while lingual lipase helps break down fats. 6. Neutralizes any gastric acid that refluxes from stomach into the lower esophagus. 7. Mineralization of new teeth and repair of precarious enamel lesions. Saliva is high in calcium and phosphate. 8. Contains antibacterial compounds. Thus, problems with the salivary glands generally result in dental caries .
- 15. The process offood coming into the stomach from oral cavity . Swallowing 1.Voluntary stage Oral cavity Pharynx 2.Pharyngeal stage Pharynx Esophagus 3.Esophageal stage Stomach Esophagus
- 16.
- 17. 1.Voluntary stage Oralcavity Pharynx The pressure of the tongue upward and backward against the palate.
- 18. 2.Pharyngeal stage PharynxEsophagus Receptors (pharynx) Brain stem Series of automatic pharyngeal muscle contractions
- 19. Pharyngeal stage Impulses comingfrom swallowing center to pharynx and esophagus to finish stage 2 and 3 of the swallowing act. In pharyngeal stage, the following events occur: 1. pushing the soft palate upward to prevent reflux of food to nasal cavity. 2. to prevent passage of food into trachea. This done by a. The vocal cords are tightly closed b. larynx is elevated c. Epiglottis swing back over the opening of larynx. 3. Relaxation of upper esophageal sphincter 4. Pharyngeal muscle contraction starts (peristalsis) from upper parts and spreading down ward
- 20. trachea (windpipe) glottis During breathing, the larynxis lowered and the glottis is open. pharynx oesophagus larynx (voice-box) air What Happens During Breathing and Swallowing? Normally, air passes into the trachea (windpipe) while food passes into the oesophagus.
- 21. 21 During swallowing, the larynxis raised and the glottis is covered by the epiglottis. This prevents food particles from entering the trachea. pharynx trachea (windpipe) oesophagus glottis epiglottis food particles larynx (voice-box) What Happens During Breathing and Swallowing?
- 22. (3) Esophageal stage •Movement of bolus through esophagus is through peristalsists: • Primary peristalsis is continuation of pharyngeal peristalsis which takes 5-9 second to travel along the esophagus. This peristalsis is capable to push the bolus down ward. • Secondary peristalsis starts if primary peristalsis fails to push the bolus downward and will continue until the esophagus is empty. This peristalsis is initiated by distention of the esophagus by retained food. It is due to stimulation of the myentric plexus in the wall of esophagus.
- 23. VOMITING The sudden andforceful expulsion of gastric and upper intestinal contents * It is controlled by neurons in medulla (the ‘vomiting centre’) *It is triggered by one or more of the following stimuli: - excessive gastric or duodenal distension - noxious substances in stomach - certain smells or sights - emotional factors - touch receptors at back of throat - reflexes involving semi-circular canals (‘motion sickness’) - stimulation of the ‘chemoreceptor trigger zone’ by circulating ‘emetics’
- 24. THE VOMITING REFLEX SEQUENCEOF EVENTS • It starts by salivation and sensation of nausea • Deep inspiration • Closure of glottis (to prevent passage of vomit into airways) • Elevation of uvula (to prevent passage of vomit into nasal cavity). • Relaxation of lower esophageal sphincter • Contraction of diaphragm and abdominal muscles causes increased intra-abdominal pressure. • Rapid rise in intra-gastric pressure causes reverse expulsion of gastric and upper parts of small intestine contents *** Vomiting of gastric content alone for prolonged time leads to metabolic alkalosis
- 25.
- 26. Functions of thestomach 1- Storage of food: stomach can store large amount of food to be stored during the day. 2- Evacuation: evacuation of food into the intestine occur slowly over a long time to allow intestinal digestion and absorption. 3- Digestion: partial digestion of proteins and fats. 4- Antibacterial action: by the high acidity to kill most of microorganisms 5- Secretion of intrinsic factor: which is essential for vit. B12 absorption. 6- Absorption: of small amount of water and alcohol. 7- Iron absorption: is facilitated by HCl.
- 27.
- 28. 28 Functions of HCl •Kills many bacteria. • Helps protein digestion by conversion of pepsinogen to pepsin. • Helps absorption of Ca++and iron.
- 30. Pepsinogen: It is inactiveenzyme, activated by HCl in gastric lumen into active form Pepsin. It initiate protein digestion. Mucous: It serves as a protective barrier. 1- Lubricating properties: it protects the gastric mucosa against mechanical injury 2- It protects the stomach wall from self-digestion because pepsin is inhibited when it comes in contact with the mucous layer coating the stomach. 3- Being alkaline, protecting against acid in injury by neutralizing HCI in the vicinity of gastric lining.
- 31. 31 Gastric Mucosal Barrier(GMB) [1] Luminal membrane impermeable to HCL. [2] Tight junctions between cells. Ulcer Peptic ulcer in oesophagus, stomach or duodenum Weakness in GMB. Increased acidity leads to increased histamine leading to increased acidity and a vicious cycle Helicobacter Pylori 90% of peptic ulcers
- 32. 32 Control of gastricsecretion • Gastric secretions in response to a meal are divided into 3 phases: 1-Cephalic phase: Represent 30% of the response. • Conditioned: Sight, smell, sound and even thinking of food lead to secretions of HCL, pepsin and mucous. • Unconditioned: Stimulation of taste, touch & thermal receptors in the mouth. 2- Gastric phase: 60% of acid secretions: • The presence of food in the stomach increases gastric secretions. it is through gastrin hormone and stimulation of intrinsic nerve plexuses. 3- Intestinal phase: • Accounts only for 10% of secretions, protein digestion products stimulate acid secretion.
- 33. 33 The Pancreatic Secretion ▪The pancreatic secretion is about 1200- 1500ml/day. Its PH is alkaline (7.6-8.2). Composition of pancreatic juice: The pancreatic juice is composed of pancreatic enzymes secreted by the acinar cells and bicarbonate solution secreted by the duct cells. 1- Pancreatic enzymes: Pancreatic juice contains enzymes for digestion of all types of food. These enzymes are secreted by the acini of the pancreatic glands.
- 34. 34 1- Pancreatic Enzymes Thepancreatic enzymes include: A- Enzymes for protein digestion: 1- Trypsin and chymotrypsin 2- Carboxypeptidases: 3- Ribonuclease and deoxyribonuclease: These enzymes digest RNA and DNA. B- Enzymes for fat digestion: 1- Pancreatic lipase which digest fats. 2- Cholesterol esterase and Phospholipase. C- Enzymes for carbohydrate digestion: Pancreatic amylase
- 35. 35 2- Bicarbonate Secretion Thepancreatic juice contains high bicarbonate content that neutralizes the acidic chyme that reaches the duodenum thus regulates the PH of the upper small intestine. Bicarbonate is secreted by the epithelial cells of pancreatic ducts.
- 36.
- 37. Regulation of PancreaticSecretion The pancreatic secretion is regulated by hormonal and nervous regulation. A- Hormonal regulation: 1- Cholecystokinin hormone (CCK): It stimulates pancreatic secretion rich in enzymes. 2- Secretin hormone: It stimulates pancreatic secretion rich in bicarbonates. B- Nervous regulation: Vagal stimulation stimulates enzyme secretion by cells and increases the action of secretin on bicarbonate secretion.
- 38. 38 Regulation Of PancreaticSecretions Pancreatic enzymes released Acinar cells stimulated Cholecystokinin secreted Protein/Fat/Carb Sodium bicarbonate released Duct cells in pancreas stimulated Secretin secreted Acid Chyme Enters Duodenum
- 39. 39 Gastrointestinal hormones Hormone Secretedby: Actions 1- Gastrin 2.Cholecystokinin (CCK) 3- Secretin G-cells of the gastric antrum and duodenum the upper part of the small intestine the upper part of the small intestine. 1- Stimulates HCL secretion. 2- Stimulates gastric motility. 3- Tropic to gastric mucosa. 1- stimulate pancreatic enzymatic secretion 2- Stimulates the contraction of gall bladder. 1-Stimulates pancreatic secretion rich in alkalie 2- stimulate bile secretion from the liver
- 40.
- 41. Bile Secretion andRecycling
- 42. 42 Functions of theLiver 1. Regulation of blood glucose concentration – 70-90mg of glucose / 100cm3 of blood (normal conditions) 2. Production of bile – Liver produces bile which is stored in the gall bladder
- 43. Functions of theliver 3. Iron storage – Red blood cells are destroyed in the spleen and their haemoglobin is sent to the liver to be broken down. The iron released is then stored in the liver. 4. Protein synthesis – Liver synthesizes proteins found in blood plasma, e.g. albumins, globulins, fibrinogen
- 44. Functions of theliver 5. Detoxification – Liver cells contain alcohol dehydrogenase to break down alcohol. – Prolonged alcohol abuse may lead to liver cirrhosis. 6- Protective role: removal of bacteria, due to the presence of Kupffer cells or macrophages. 7- Excretion of cholesterol and bilirubin. 8- Activation of vitamin D.
- 45. 45 Bile Salts Functions ofbile salts: 1- Emulsification of fats: Bile salts reduce surface tension and emulsify fats into small droplets preparatory to their digestion by pancreatic lipase. 2- Absorption of fats: Bile salts are amphipathic i.e. one surface is hydrophilic and the other is hydrophobic. Thus bile salts tend to form cylindrical discs called micelles, with the hydrophilic surface facing out and a hydrophobic center containing fats. Thus, micelles keep fats in solution and transport them to the brush border of small intestine (?) where they are absorbed. 3- Help absorption of fat soluble vitamins: Vitamin A, D, E and K. 4- Stimulate intestinal motility.
- 46. 46 The Bile Pigments • Bilirubinis a greenish yellow pigment formed as an end product of hemoglobin metabolism. • In the plasma bilirubin combines with albumin to form free bilirubin (?). • Free bilirubin is not excreted in urine (why?). • Free bilirubin enters the liver cells where it is conjugated with glucuronic acid forming conjugated bilirubin. • Conjugated bilirubin is excreted by the liver cells in bile to reach the intestine. • In the intestine conjugated bilirubin is converted by bacterial action to urobilinogen which is changed to stercobilinogen and excreted in feces where it is oxidized to stercobilin.
- 47.
- 48. Jaundice: It is theyellowish tint of the skin and mucous membrane as a result of increased levels of free or conjugated bilirubin (normal level?). Types of Jaundice: 1- Hemolytic jaundice: It is due to excessive hemolysis of RBCs and increased production of free bilirubin. Thus plasma levels of free bilirubin increase. 2- Hepatocellular jaundice: It is due to inability of the liver cells to conjugate all free bilirubin and to excrete all the conjugated bilirulin. Thus free and conjugated bilirubin increase in plasma. 3- Obstructive jaundice: It is due to obstruction of bile flow. Thus the level of conjugated bilirubin increases in plasma.
- 49. The Gall Bladder Functions: 1-Storage of bile. 2- Concentration of bile 3- Acidification of bile. Control of gall bladder evacuation: 1- CCK: The most important stimulus for gall bladder evacuation. 2- Vagal stimulation.
- 50.
- 51. Small Intestinal Motility Typesof small intestinal motility: A- Segmentation movement: 1- They are ring like contractions that appear at regular intervals along the gut and then disappear and are replaced by another set of ring contractions in the segments between the previous contractions. 2- They move the food to and fro and increase its exposure to mucosal surface. 3- These to an fro movements cause mixing of food without any net forward movements. B- Peristalsis: 1- circular contraction behind the bolus of food and an area of relaxation in front of it. 2- The wave of contraction then moves in a forward direction propelling the contents of the lumen forward through the small intestine toward the large intestine.
- 52.
- 53. 53 Small Intestinal secretion 1-Mucus: • a- secreted by bruners glands and goblet cells. • b- Functions: • - Protection of duodenal mucosa against acidic gastric juice . • - Lubrication and facilitation of passage of food along intestine . 2- Alkaline fluid: • - An isotonic alkaline fluid (ph 7.5) containing mainaly NaHCO3 but no digestive enzymes . • - After secretion it is rapidly reabsorbed by the villi, thus it dissolves the chime and act as a watery vehicle for absorption of various substances from the small intestine. 3- Sloughed mucosa containing digestive enzymes (cellular enzymes): • Large number of mucosal cells (cotaining digestive enzymes) is continuously sloughed (sheded) into the intestinal lumen and gets mixed with intestinal secretion.
- 54. Absorption Adaptations of thesmall intestine • Small intestine is very long (~5 m) • Internal surface of the small intestine has many folds. • On these folds, there are many finger-like projections called villi • These 3 adaptations increase surface area for absorption
- 55.
- 56. 56 Lacteal – fattyacids and glycerol recombine in the epithelium to form fat which then enters the lacteal as fine fat droplets Blood capillaries – transport sugars and amino acids away from the small intestine One cell thick epithelium – for efficient absorption of food particles This continual transport of digested food substances maintains the concentration gradient for the absorption of digested food substances.
- 57. What happens toamino acids and glucose after absorption? Products released from liver into general blood circulation Molecules pass into the epithelial cells Through walls of capillaries in the villus and into bloodstream The capillaries join up to form veins Veins unite to form 1 large vein: Hepatic Portal Vein Hepatic portal vein carries blood to liver Liver stores or alters products of digestion
- 58. What happens tofatty acids and glycerol after absorption? Molecules pass into the epithelial cells Recombine into fats again in the epithelial cells Fats enter the lacteals Lymph (fluid in lacteals) + fat = chyle Lymphatic vessels discharge chyle into bloodstream
- 59.
- 60. Function of largeintestine • Absorption of H2O and electrolytes from chime by proximal colon (absorbing colon). • The large intestine can absorb a maximum of 5 to 8 liters of fluid and electrolytes each day. • Storage of feces by distal colon (storage colon) • Defection by rectum and anal canal: Defection is the act of emptying the colon contents through the anal canal. • Secretion (Mucus Secretion). • Bicarbonate neutralizes acids: produced by local bacteria fermentation.
- 61.
- 62. Defecation Haustral contractions =slow =allow bacteria to brow in large intestine Ascending and transverse colon contract simultaneously to drive faeces to descending colon. Once faeces reaches the rectum, it stretches and sphincters relax External sphincter is skeletal voluntary muscle Abdominal muscles contract and the individual breaths a sigh of relief.
- 63.