The Digestive System 2024-2025 PDF

The Digestive System Physiology department 2024-2025 Outlines Functions of digestive system Regulation of digestive functions Functions of mastication, swallowing and chewing Gastric mixing and emptying Digestion and absorption in stomach Digestive System Anatomy ...

The Digestive System Physiology department 2024-2025 Outlines Functions of digestive system Regulation of digestive functions Functions of mastication, swallowing and chewing Gastric mixing and emptying Digestion and absorption in stomach Digestive System Anatomy  Food Chewing Mixing with saliva Mouth Boluses Mincing Mixing with gastric juice Stomach Chyme Stomach Digestion Small intestine absorption Large intestine! Large intestine Feces Mouth Esophagus STOMACH GENERAL REVIEW OF DIGESTIVE SYSTEM Primary function of digestive system = transfer of nutrients, water and electrolytes from the food into the body’s internal environment. Ingested food is essential as energy source from which cells can produce ATP. Organic molecules + O2……........... Energy + CO2 + H2O Basic digestive processes Motility Secretion Digestion Absorption Excretion Basic digestive processes 1. Motility: (MIXING MOVEMENTS) Muscular contractions that mix the food. (PROPULSIVE MOVEMENTS) move the digestive the contents of the digestive tract forward. Digestive Motility GIT PART MIXING MOVEMENT PROPUSTIVE MOVEMENT Mouth Chewing & Mixing Beginning of Swallowing Esophagus - Peristalsis Stomach Gastric Mixing Gastric Mixing Gastric emptying Small intestine Segmentation Migrating Motor Complex Large intestine Haustrations Mass movement  Exocrine glands secrete digestive juices into the Secretion GIT lumen. Digestion Endocrine glands secrete hormones into the blood. Biochemical breakdown process whereby complex food Absorption stuffs are converted to smaller absorbable units. Mostly occurs in the small intestine. The absorbable units are transferred from GI tract lumen into the blood or lymph Excretion Secretions  Regulation of Digestive Function Digestive motility and secretion are carefully regulated to maximize digestion and absorption of food. 2 factors are involved in regulation of digestive system function  Neural Intrinsic nerve plexuses ( interconnecting network of nerve cells. They are located entirely within the GIT tract. Extrinsic nerves Nerve fibers that originate outside the GI tract. These fibers are: Sympathetic: inhibit or decreases digestive contraction and secretion. Parasympathetic ( vagus nerve ): increase motility and Cartoon of Santa Wearing Ho Ho Ho Boxers and Sunglasses, Relaxing In the Sun - Royalty Free Clipart Picture secretion (rest and digest)  Hormonal GI tract hormones Endocrine gland cells that release hormones into the blood. These hormones are carried to other areas of the GI tract to cause smooth muscle contraction and exocrine gland secretion.  Local changes in GI tract ( chemical, mechanical, osmolarity of contents ) Intrinsic nerve plexuses Extrinsic autonomic nerves GIT hormones Smooth muscle of wall ( motility ) Exocrine gland cells ( secretion of digestive juices ) Endocrine gland cells ( secretion of GI and pancreatic hormones ) Mouth  Mastication ( Chewing ) First step in the digestive process Motility of the mouth that involves slicing, tearing, grinding and mixing of food by teeth. The purposes of chewing are: to grind and break food into smaller pieces to facilitate swallowing to mix food with saliva to stimulate the taste buds SALIVA Secretion associated with the mouth Produced by three major salivary glands: sublingual submandibular parotid Daily secretion: 1 – 2 liters  Functions of Saliva Begins digestion of carbohydrates in the mouth by salivary amylase Facilitates swallowing by moistening food particles lubrication by the mucus which aids in speech and prevents dryness of mouth epithelium. Oral hygiene: Salivary flow washes away bacteria from the mouth Lysozyme; an enzyme which destroys ingested bacteria. Esophagus SWALLOWING ( Deglutition ) Process of moving food from the mouth through the esophagus into the stomach. Initiated when a bolus is voluntarily forced by the tongue to the rear of the mouth into the pharynx. The following peristalsis to and through the esophagus is involuntary.  Stages of Swallowing: Buccal Stage: Voluntary stage Pharyngeal Stage Involuntary reflex Esophageal Stage Involuntary Bolus of food is pushed down by peristaltic waves of contractions induced by impulses from swallowing center. Bolus goes into stomach  Peristalsis in the Esophagus Bolus Peristalsis: ring like contractions of the smooth muscle that move forward, pushing the bolus ahead of contraction Ring like Peristaltic Contraction Sweeping Down the Esophagus  When a bolus enters Pharynx + Pressure receptors + Medulla oblongata Swallowing Center Highly Coordinated Motility of Pharynx & Esophagus Oropharyngeal Esophageal Stage Stage  GERD (Gastroesophageal reflux disease) GERD occurs when stomach acid continuously refluxes into the esophagus. It may be caused by: Elevated intraabdominal pressure (e.g obesity, big meals, tight clothing, pregnancy) Reduced LES tone. Symptoms include pain, heartburn and inflammation in esophagus (as unlike stomach esophagus does not have protection from acid). Treatment is with antacids, Histamine H2 receptor antagonists or proton pump inhibitors. If medical treatment fails then surgery to tighten LES can be performed. Stomach  FUNCTIONS OF THE STOMACH 1. GASTRIC MOTILITY Filling ( the stomach volume is 50 ml when empty. It can expand to about 1 liter during a meal. ) Storage of large quantities of food before being processed by the intestines. Mixing of lumen contents with gastric juices Emptying slowly into the duodenum to allow time for absorption  Gastric Mixing and Emptying Strong peristaltic contractions of the stomach are responsible for the mixing of food with gastric secretions………..which results in converting the food into Chyme. Gastric secretions Secretions in the stomach are done by two types of glands: 1. Oxyntic glands: HCl (provide acidic environment) Intrinsic factor (vitamin B12 absorption). Oxyntic glands Volume: 2 L/day Pepsinogen. (enzyme for protein digestion) pH: 2 (1-3.5) Mucus secreting cells 2. Pyloric glands: Pyloric The hormone gastrin in the blood glands Secretes highly acidic gastric secretions Promotes growth of the lining of stomach and intestine.  HCL Pepsinogen is inactive Requires acidity ( HCl ) to turn into pepsin, which is the active protein digesting enzyme Breaks down connective tissue, muscle fibers and other strong organic material. Pepsin digests proteins into polypeptides Kills most of microorganisms in food.  Absorption in the stomach Stomach is a poor absorptive area because: No food and little water is absorbed from stomach 1. Carbohydrate and protein digestion is not complete. 2. Digestion of fats has not begun in stomach. 3. Only few highly lipid-soluble substances like alcohol, drugs like aspirin, electrolyte are absorbed in small quantities. Tight junctions between cells of stomach wall inhibit the absorption from the stomach. Peptic Ulcer Disease Imbalance between defensive & aggressive factors can lead to peptic ulcer disease Defensive Causative factor factors Gastric mucosal Helicobacter pylori barrier: infection. Mucosal membrane Drugs - anti- impermeable to inflammatory HCl. (NSAIDs) & Corticostroids. Tight junctions. Cigarette smoking, Mucous coat Alcohol, Bicarbonate Stress Blood supply Decrease blood flow Complications of Ulcer http://4.bp.blogspot.com/-fsHQuW1MQpY/TlzEJ_qJo1I/AAAAAAAAAc0/ptVUIummWog/s1600/Gastric+Ulcer.jpg Pancreas and Biliary system The Gallbladder Small and Large Intestine Outlines Functions of pancreas Functions of bile salts Composition and functions of small and large intestine Composition And Function Of Pancreatic Juice Pancreatic Secretions Watery alkaline secretion consisting of: large amounts of HCO3- (to neutralize acidic Potent digestive chyme) enzymes Water PANCREATIC ENZYMES INACTIVE PROTEOLYTIC ENZYMES For the protein digestion ACTIVE PANCREATIC LIPASE For the digestion of fat ACTIVE PANCREATIC AMYLASE For the carbohydrates digestion Bile and Its Functions BILE SALTS EMULSIFICATION EMULSIFICATION The ability of the bile salts to convert large fat globules into a lipid emulsion consisting of many small fat droplets suspended in aqueous chyme, thus increasing the surface area available for the action of pancreatic lipase is called as emulsification or detergent action.  Case of Gall stones Cholelethiasis Fatima is a 45-year old married woman having eight kids, presented to emergency room with persistent severe pain in the right hypochondrium, with vomiting. She said that she had recurrent attacks of pain at the same quadrant with vomiting and diarrhea for the last 10 months. Fatima noticed that this pain appears after eating fatty meals like fried food, pastries etc. She also noticed that her stools float in lavoratory…Steatorrhea. Ultrasound abdomen showed multiple small stones in the gallbladder. Risk factors of Gallstones Small Intestine Functions Of Small Intestine Completion of digestion Absorption of nutrients (has large absorptive area and special transport mechanisms)  Brush border enzymes Enterokinase Disacharidases Aminopeptidases Maltase Sucrase Complete protein Activates Lactase digestion pancreatic enzymes Maltose Sucrose Small Intestinal Motility Propulsive Movements : Short peristaltic contractions travelling 10- 15 cms pushing the chyme forward slowly. Mixing contractions (Segmentation contractions): alternate contraction & relaxation of complete segments of small intestine. MIGRATING MOTOR COMPLEX These movements occur between the meals. These waves take 100 to 150 minutes to gradually migrate from the stomach to the end of small intestine, with each contraction sweeping the remnants of preceding meal plus mucous and bacteria forward to the colon. The migrating motor complex is regulated between meals by the hormone motilin which is secreted by the endocrine cells of small intestine during unfed state. Large Intestine Secretions and Absorption in Large Intestine Absorption Secretions Active absorption of Na+ Mostly mucus and and Cl- creates an large amounts of osmotic gradient across HCO3- the large intestinal lining, which in turn causes absorption of water. Motility of Large Intestine Absorption and storage do not require intense movements Haustral contractions: Mass movements: Infoldings of the large intestine Intense contractions wall from distinct pouches called Occur infrequently ( 2 -3 times Haustra. Distention in haustra-- daily , after meals generally ). walls contract and squeeze the Initiated by the presence of contents into next haustrum. food in stomach. These movements shuffle Drive colonic contents into contents back and forth. rectum until defecation. Defecation ( Emptying of the rectum ) Mass movements -initiated by the presence of food in stomach- of the colon move feces into rectum. **Distention of the rectum** stimulates stretch receptors in the rectal wall ---- this initiates the defecation reflex.  DIARRHEA Diarrhea is defined by the World Health Organization as having 3 or more loose or liquid stools per day, or as having more stools than is normal for that person. The most common cause of diarrhea is an infection of the intestines, such as gastroenteritis or food poisoning. The intestinal lining becomes irritated and inflamed, which prevent the absorption of water from food waste. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and electrolyte imbalances. Constipation Constipation is where you have dry and hard stools that are infrequent or hard to pass. It is usually caused by a low fiber diet, low liquid intake or not enough exercise. DIGESTION AND ABSORPTION IN SMALL AND LARGE INTESTINE Chemical Digestion Of Food Review Carbohydrates: In mouth by salivary amylase, CHO →→→→→→→→→ disaccharides Salivary amylase In small intestine CHO →→→→→→→→→ disaccharides pancreatic amylase Disaccharides→→→→→→ monosaccharides (mostly glucose) Brush border disaccharidases  Review Proteins In stomach by pepsin →→→→ proteoses, peptones, large polypeptides. In small intestine Polypeptides →→→→→→→→→ →dipeptides pancreatic proteolytic enzymes Dipeptides →→→→→→ amino acids Brush border peptidases  Review Protein Digestion (Pancreas)  Review Fats: Digestion of fats starts in small intestine. Bile salts Fat →→→→→→→ Emulsified fats Pancreatic lipase Emulsified fats →→→→→→→→ free fatty acids , monoglyceride  Absorption In Small Intestine Passage of nutrients across enterocytes. Through the basement membrane of enterocyte Finally, into blood capillaries or into lymph. 90 % of absorption occurs in small intestine because of : The great absorptive surface area ( villi + microvilli ) Presence of special transport mechanisms ( Active Transport, Diffusion, Osmosis ( water ) ) Thank You